Properties of Transducers: Range, Accuracy, Resolution, and Repeatability

Electrical Transducer converts value of controlled variable into an electrical signal. Examples: Hydrophone, Loudspeaker, Earphone,

Microphone, Piezoelectrical Crystal,

Photoelectric Transducer Laser Diode, LED, Photodiode, Phototransistor, and Photomultiplier tube, Solar Cell, Photocell or LDR.

Electromagnetic Transducer- converts EM into an electrical signal. Examples: Antenna, Magnetic Cartridge, Tape Head, Hall Effect Sensor,

CRT, Fluorescent lamp, Light bulb, Reed switch

Electrostatic transducer LCD

Temperature Transducer Thermocouples, RTD, Thermistor, Semiconductor(Diode, Transistor, IC) temperature sensors

Mechanical Transducer voltage/torque into mechanical/electrical signal. Examples are Gear

Pressure Transducer fluid pressure to electrical signal

IC transducer variation in temperature to current (mA or A)

Industrial Sensors: Potentiometer, LVDT (Linear Variable Differential Transformers), Strain Gauges, Piezoelectric

Potentiometer- a resistor made of thin film of resistive material. Inexpensive but subject to wear. It can measured the angular position of a

shaft.

A Sensor is a device that measures or detects real-world condition, such as motion, heat or light and converts the condition into an analog

or digital representation. It also converts physical processes such as temperature, pressure, liquid level or the presence/absence of an

object into discrete or continuous voltage or current values that may be interpreted by a computer or PLC to control a process or process

sequence in a desired manner.

Sensor Limitations

Accuracy- This is the maximum difference between the indicated and actual reading.

Resolution- Used for systems that step through readings. This is the smallest increment that the sensor can detect, this may also

be incorporated into the accuracy value.

A sensor provides: Feedback on task completion, Information on the status of the process, Inspection and measurement data, Collect

Product or process data for quality monitoring.

Sensor Types:

1. Contact Sensor: There is a physical contact between the sensor and the parameter it measures.

2. Non-contact Sensor: Are also called Proximity Sensors. Proximity indicates that the object is near, but contact is not required. Do

not operate mechanically and are more reliable. Less likely to fail than the mechanical ones. Much faster than Mechanical

Devices.

3. Digital Sensors: Have two states: on or off, Presence/absence of an object, Counting such as used in a rotary encoder. Examples

are Switches, Optical (photoelectric) sensors, Encoders, Ultrasonic Sensors, Inductive Sensors, Capacitive sensors

4. Analog Sensor: It senses continuous variables such as temperature and pressure. It also provides a continuous (usually linear)

voltage or current according to an input/output transfer function. More complex than digital and can provide more information.

Solenoid Valve:

solen meaning pipe

eidos meaning shape

a type of electromagnet

Electromechanically operated valve, Frequently used as control elements in fluidics, Shut off,

release, dose, distribute, mix fluids

Components of Solenoid Valve

Advantages of Solenoid Valves: Fast and safe switching, High reliability, Long service life, Good medium compatibility, Low control power.

Types of Valves

Direct-Acting: In a direct-acting solenoid valve, a coil magnetically opens the valve in a direct action, lifting the shaft and the seat

of the valve without depending on outside pressure.

Pilot-Operated: In pilot-operated valves, the plunger opens up the pilot opening while built-up pressure causes the valve to open

and close.

Multi-way valves

1. 2-way valve: Can be normally open or normally close. Each of the two ports on a two way valve are alternately used to

permit flow as well as close it off.

2. 3way valve: Has 3 pipe connections and 2 orifices, When one orifice is open, the other is closed, and vice versa.

Uses of Solenoid Valves: Pneumatic actuators, Hydraulic actuators, Electric actuators

Pneumatic System: Converts energy from pressurized gas into motion, A pneumatic actuator converts energy formed by vacuum or

compressed air at high pressure into either linear or rotary motion.

Advantages of Pneumatics: Pneumatic are a clean system (suitable for food manufacturing. Pneumatics offer rapid movement of

cylinders. Pneumatic have great availability in small sizes. Pneumatic can safely release compressed air.

Hydraulic System: Liquid version of pneumatic system, A hydraulic actuator consists of a cylinder or fluid motor that uses hydraulic power

(usually using pressurized oil) to facilitate mechanical operation.

Advantages of Hydraulics: Hydraulics has more force to offer than pneumatics. Hydraulics can smoothly lift and move loads.

Cheaper than pneumatics.

Electric Systems: The electric actuator uses an electric motor to provide torque to operate a valve. They are quiet, non-toxic and energy

efficient. However, electricity must be available, which is not always the case.

Advantages of Electric: simpler and smaller installation, easier control, lower energy costs, higher accuracy, less maintenance, less

noise, and a cleaner, healthier environment.

SWITCH is a device for making and breaking the connection in an electric circuit. Switch

symbols, like the ones shown in the following illustration, are also used to indicate an open

or closed path of current flow. Variations of these symbols are used to represent a number

of different switch types.

RELAY is usually an electromechanical device that is actuated by an electrical current. The current flowing in one circuit causes the opening

or closing of another circuit. Relays are like remote control switches and are used in many applications because of their relative simplicity,

long life, and proven high reliability. It is used to protect electric power systems against trouble and power blackouts and to regulate and

control the generation and distribution of power.

SWITCH IN A RELAY: Each switch in a relay is referred to as pole. Relays may have one or more poles. The number of poles in a relay

indicates the number of switches contained within the relay. Each pole may be configured as SINGLE or DOUBLE throw, indicating the

number of circuits that can be controlled per pole.

BREAK is the number of separate place or contacts that a switch uses to open or close a single electrical circuit. There are two basic

classifications of relays: Electromechanical and Solid State. Electromechanical relays have moving parts, whereas solid state relays have no

moving parts.

Advantages of Electromechanical relays include lower cost, no heat sink is required, multiple poles are available, and they can switch AC or

DC with equal ease.

General Purpose Relay: The general-purpose relay is rated by the amount of current its switch contacts can handle. Most versions of the

general-purpose relay have one to eight poles and can be single or double throw. These are found in computers, copy machines, and other

consumer electronic equipment and appliances.

Power Relay: The power relay is capable of handling larger power loads 10-50 amperes or more. They are usually single-pole or double

pole unit.

Contactor: A special type of high power relay, its used mainly to control high voltages and currents in industrial electrical applications.

Because of these high power requirements, contactors always have double-make contactable-pole units.

Time-Delay Relay: The contacts might not open or close until some time interval after the coil has been energized. This is called delay-on-

operate. Delay-on-release means that the contacts will remain in their actuated position until some interval after the power has been

removed from the coil

SOLID STATE RELAY: These active semiconductor devices use light instead of magnetism to actuate a switch. The light comes from an LED, or

light emitting diode. When control power is applied to the devices output, the light is turned on and shines across an open space. On the

load side of this space, a part of the device senses the presence of the light, and triggers a solid state switch that either opens or closes the

circuit under control.

OVERLOAD RELAY: A motor overload relay is an electro-mechanical relay that is operated by heat developed in the relay. When the level of

current in a circuit reaches a preset value, the increased temperature opens a set of contacts.

Overload relay should install in our motor starter application for extra protection. Why? Overload relay can avoid serious damage

for electric motor when overload happen to our system with proper setting. The increased temperature opens the contact through a

bimetallic strip or by melting an alloy which activates a mechanism that opens the contact depending on our setting for overload relay. The

details about common types of overload relay for motor control.

Types of Overload relay:

1. Thermal Overload Relay:

Melting alloy: These are probably the most popular type of overload protection. The motor current passes through a small heater

winding and under overload conditions. The heat causes a special solder to melt allowing a ratchet wheel to spin thus opening

the control circuit contacts.

Bi-metallic strip: This design uses a bimetal strip associated with a current-carrying heater coil.

When an overload occurs, the heat causes the bimetal to deflect and actuate a tripping mechanism which opens a set of contacts

in the control circuit interrupting power to the coil and opening the power contacts.

2. Magnetic Overload Relay:

A magnetic overload relay is an electro-mechanical relay operated by the current flow in a circuit. When the level of current in

the circuit reaches a preset value, the increased magnetic field opens a set of contacts. Electromagnetic overload relays operate

on the magnetic action of the load current flowing through a coil. When the load current becomes too high, a plunger is pulled up

into the coil interrupting the circuit. The tripping current is adjusted by altering the initial position of the plunger with respect to

the coil.

CHEMICAL TRANSDUCER

A salinometer is a device designed to measure the salinity, or

dissolved salt content, of a solution.

A pH meter is an electronic device used for measuring the pH. The pH

will indicate if the solution is acidic or basic.

A Oxygen Analyzer used to measure exhaust gas concentration for

internal combustion engines, for divers to measure partial

pressure of O2 in breathing gas and to measure respiration or

production of oxygen.

A Hydrometer is an instrument used to measure the specific gravity

or the relative density of liquids. A certain liquid density is

commonly compared with the density of pure water.

Oil in Water analyzers provide accurate and reliable Oil in Water

measurements, and are used for water discharge monitoring as well as produced water treatment process monitoring and management

which includes wastewater, groundwater, produced water, process water, and natural run-off.

PHOTOELECTRIC TRANSDUCERS

Solar (or photovoltaic) cells convert the suns energy into electricity. Silicon is its key material.

Sunlight -> Photons + Silicon Atoms -> Electrical Imbalance (N-type & P-Type) > Insulator (Silicon) -> Electricity

USES: Power Calculators and Satellites

Photocells: A component that has a variable resistance that changes with the light intensity that falls upon it. This allows them to be used in

light sensing circuits. Light Intensity inversely proportional to Resistance: Daylight= 5000 and Dark = 20000000

Photocells are sensors that detects light AND produces voltage and current when exposed to light.

Photoelectric Effect: Occurs when light is used to push electrons freeing them from the surface of a solid.

USES: Camera Shutter Control

Photovoltaic cells- made from two layers of semiconductor placed on top of one another.

Photo emissive- oldest and most elaborate way of turning light to electricity.

A rotary encoder, also called a shaft encoder, is an electro-mechanical device that converts the angular position or motion of a shaft or axle

to an analog or digital code. It is a sensor that generate digital signals in response to movement.

Optical. This uses a light shining onto a photodiode through slits in a metal or glass disc.

A liquid-crystal display (LCD) is a flat panel display, electronic visual display, or video display that uses the light modulating properties of

liquid crystals. Like LEDs and gas-plasma technologies, LCDs allow displays to be much thinner than cathode ray tube (CRT) technology.

LED is a semiconductor that produces light through the process ELECTROLUMINESCENCE.

Advantages: Energy efficient, Long Lifetime, No warm-up period

Disadvantage: LEDs must be supplied with the correct voltage and current at a constant

flow.

Light Bulb: A device that converts electricity to light.

Advantages: Easy to operate, Convenient

Disadvantage: Poor energy efficiency

Incandescent Light Bulbs: Commonly Used Light bulbs, It can last about 700 to 1000 hours operation

Halogen Light Bulbs: It contains a halogen gas, Has a longer life than an Incandescent light bulb

Flourescent Light Bulbs: Light up large areas, Can last up to 10,000

20,000 hours

CFL or Compacted Flourescent Lamps: Low power consumption than

Incandescent lamps, Has a smaller packaging than flourescent lamps,

Usually last up to 10,000 hours

Vapor Lamps: Another type of lamps/bulbs that is used to light up very

large areas.

LED/ Light Emitting Diode

LDR change from high resistance in bright light to low resistance in the dark.

ELECTROMAGNETIC TRANSDUCERS:

Antenna: Converts radio frequencies (electromagnetic waves) into electrical currents (alternating currents) and vice versa. Types of

Antenna:

Applications: Radio and television broadcasting, telephone communication, Wireless LAN

Advantages: Can operate in outer space, under water or through soil

Disadvantages: Obstructions, Limited frequencies, Large size at low frequencies (dipole, slot and microstrip)

Magnetic Cartridge: A mechanical device that converts vibration energy into an electrical signal.

Advantages: high output, Removable and replaceable stylus

Disadvantages: Heavy, Cant move quickly in the record groove

Tape Head is used in tape recorders which convert electrical signal to

magnetic fluctuations. Its application is Videocassette recorders.

Advantages: Separated from the media

Disadvantages: Simple sequential access to read the data or the

information

Hall Effect Sensor: Transducer that varies its output voltage in response to a

magnetic field.

Application: Position Sensing, DC current transformers, Automotive fuel

level indicator

Advantage: Can measure wide range of magnetic fields

Disadvantage: Provide much lower measuring accuracy

CRT (Cathode Ray Tube): Converts electrical signals into visual signals. CRT:

Technology used in the traditional TV and Computer Systems. a vacuum

tube containing one or more electron guns, and a fluorescent screen used to view

images. Consumes a lot of power

Applications: Televisions, Cathode Ray Oscilloscope

Advantages: High contrast ratio, Excellent color, Can be used or stored in both

extreme hot and cold temperature conditions without harm to the system capable

of true multisyncing.

Disadvantages: Large size and weight, High power consumption, A lot of heat can be emitted during operation, Sensitive to

magnetic interference, which can cause the image to shimmer.

Gears are generally used for one of four different reasons: To reverse the direction of rotation, To increase or decrease the speed of

rotation, To move rotational motion to a different axis, To keep the rotation of two axis synchronized

A tachometer (revolution-counter, tach, rev-counter, RPM gauge) is an instrument measuring the rotation speed of a shaft or disk, as in a

motor or other machine. The device usually displays the revolutions per minute (RPM) on a calibrated analogue dial, but digital displays are

increasingly common.

REED SWITCH: Basically switches that are operated using magnetic fields. Applications: Proximity Sensor and security alarm.

Advantages: Requires no physical contact in switching it on and off, Very small gap between the two contacts

Disadvantages: Requires a magnetic material to operate, Dangerous if not shielded from other sources of magnetic fields in the

environment

Light Dependent Resistor: Photocell, photoresistor, CdS device and photoconductor, Converts light into electrical resistance,

Photoconductivity

Advantages: Cheap, Availability, Popular, Small power and voltage, Long-life, Low Noise

Disadvantages: Slow response time, Range, Low sensitivity, Latent effect

Applications: Camera light meters, Street Lights, Clock radios, Alarm devices, Outdoor Clock, Mobile phones

TEMPERATURE TRANSDUCERS

Bimetallic Strip: The essential element in a bimetallic thermometer is a bimetallic strip consisting of two layers of

different metals fused together having different coefficients of linear expansion. There are two types of Bimetallic strip: Cantilever strip

and Spiral strip.

Spiral Strip: Bimetallic strip is coiled into a spiral attached to a dial that indicates temperature.

Cantilever Strip: Bimetallic strip is attached as a cantilever. The deflection is used to indicate temperature.

Advantages: Power source not required. Simple, sturdy, easy to use and cheap.

Disadvantage: Not suitable for very low

temperatures

Liquid in Glass Thermometer:

Thermocouple: Temperature

Measuri

ng

Device,

Seebeck Effect

Thermistor: Constructed from semiconductive material, Responds to changes in temperature, Resistance decreases when temperature rises, Different from normal resistors.

RTD (Resistance Temperature Detector)

Temperature is the measure of hotness or coldness of a body or an object. It is a measure of the amount of heat energy possessed by an

object. Inferred measurement means temperature cannot be measured directly. To measure temperature is to observe changes in other

objects or materials.

Kelvin Celsius Rankine Fahrenheit

Absolute Zero 0 K -273 C 0 R - 460 F

Freezing Point 273.15 K 0 C 492 R 32 F

Boiling Point 373.15 K 100 C 672 R 212 F

LIQUID IN GLASS THERMOMETER

Mercury is from - 38 C (its freezing point) to 360 C but if pressurized would go up to 600 C. It is used for measuring

MODERATE temperature. If Quartz Mercury is used and the space above the mercury is filled with nitrogen or CO2 under

pressure, boiling point can be suppressed and goes up to 600 C. Alcohol is from - 80 C to 70 C (or toluene) & Pentane used

from -196 C to 100 C. It is used for measuring lower Temperature.

Advantages: comparatively cheaper, handy and convenient to use, do not necessitate power supply or batteries for charging,

can be frequently applied in areas where there is problem of electricity, provide very good repeatability and their calibration

remains unaffected.

Disadvantages: considered inapt for applications involving extremely high or low temperatures, very weak and delicate,

handled with extra care because they are likely to break, cannot provide digital and automated results, their use is limited to

areas where only manual reading is adequate, for example, a household thermometer, Temperature readings should be

noted immediately after removal, can be affected by the environmental temperature, heat produced by the hand holding it,

cleaning, etc., should be recorded because a glass thermometer does not offer a recall of the measured temperature, Reading

temperature call for brilliant eyesight, Liquid element used may be risky to health owing to their potential chemical spills,

display temperature either in Celsius or Fahrenheit scales.

FILLED SYSTEM THERMOMETER - utilized a bulb sensor, connecting capillary and bourdon tube measure element. It has 3

types of Filled System: LIQUID FILLED/EXPANSION THERMOMETERS, VAPOUR PRESSURE THERMOMETERS, GAS FILLED

THERMOMETER

Advantages: Do not require electric power, Do not pose explosion hazards, Stable even after repeated cycling, Do not

generate data that are easily recorded or transmitted, Cannot make spot or point measurements.

BI-METALLIC THERMOMETER - It is a differential expansion of two different materials rigidly joined together, one on the

other. It is employed between 40 C and 320 C. INVAR (36% Ni, 64% Fe) has low coefficient of expansion and when welded

to a Ni-Mo alloy gives a good bi-metallic strip. Take advantage of the difference in rate of thermal expansion between

different metals. Strips of two metals are bonded together. When heated, one side will expand more than the other, and the

resulting bending is translated into a temperature reading by mechanical linkage to a pointer. These devices are portable and

they do not require a power supply, but they are usually not as accurate as thermocouples or RTDs and they do not readily

lend themselves to temperature recording.

Electrical thermometry: RESISTANCE THERMOMETER 2. THERMISTOR 3. THERMOCOUPLE

RESISTANCE THERMOMETER - resistance type of temperature measuring unit using the well known Wheatstone bridge

principle. Capitalizes on the fact that the electrical resistance of a material changes as its temperature changes. It is commonly

referred to as (Resistance Temperature Detectors) RTDs. RTDs rely on resistance change in a metal, with the resistance rising

more or less linearly with temperature.

Constantan - made of a metal whose resistance does not vary with temperature especially for the measurement of ambient

temperature conditions.

COPPER and NICKEL used in the range of -100 C to 200 C TUNGSTEN, MOLYBDENUM, and TANTALUM is used to 1200 C

in protective atmospheres.

PLATINUM - the most suitable sensing wire element. It has a resistance of 100 ohms at 0 C in which case resistance of wires

is limited to 3 ohms. It is used up to 600 C with twin wires is often acceptable with the three wire method used for higher

accuracy.

Advantages The response time compared to thermocouples is very fast (in the order of fractions of a second). Within its

range it is more accurate and has higher sensitivity than a thermocouple. In an installation where long leads are required, the

RTD does not require special extension cable.

Disadvantages Because the metal used for a RTD must be in its purest form, they are much more expensive than

thermocouples. In general, an RTD is not capable of measuring as wide as temperature range as a thermocouple. Small

changes in resistance are being measured, thus all connections must be tight and free of corrosion, which will create errors.

THERMISTOR (or Thermally Sensitive Resistor) - a second class of resistance thermometer utilizing elements made of semi-

conducting material all of which have a characteristic of a resistance decrease with temperature increase.

Sintering is a process of heating under pressure. It is a method used to create objects from powders. It is used powder

mixtures of metallic oxides such as manganese, nickel, cobalt, copper, or uranium. Size and configuration can be controlled so

that rods, beads, discs, and washer shapes can be produced as desired. The range from -100 C to 300 C but it can go as high

as 1600 C.

Advantages of thermistors : Relatively small and compact. It can have a diameter of up to 2.5mm with a resistance up to

about 100 megaohms. Low specific heat. It does not take very much heat away. Physically strong and rugged. Relatively high

temperature coefficient of resistance. It could be as high as ten times that of some metals. They could be used for extremely

low temperature measurement with greater accuracy.

Thermocouple

What is seebeck effect? It is a phenomenon in which a DIFFERENCE TEMPERATURE between two dissimilar electrical

conductors or semiconductors produces a voltage difference between the two substances. When heat is applied to one of the

two conductors or semiconductors, heated electrons flow toward the cooler one. If the pair is connected through an electrical

circuit, direct current (DC) flows through that circuit. The voltages produced by Seebeck effect are small, usually only a few

microvolts (millionths of a volt) per kelvin of temperature difference at the junction. The Seebeck effect is responsible for the

behavior of thermocouples, which are used to approximately measure temperature differences or to actuate electronic

switches that can turn large systems on and off.

What is peltier effect? If a current flows across the junction of two dissimilar metal conductors that have the SAME

TEMPERATURE, the heat is either released or absorbed, depending on the direction of current flow. If the current flow is in the

same direction as that produced by the Seebeck effect, heat is released at the hot junction and absorbed at the cold junction.

Thermocouple It consists of two dissimilar metals, joined together at one end. When the junction of the two metals is heated

or cooled a voltage is produced that can be correlated back to the temperature. Commonly used thermocouple metal

combinations include constantan/copper, constantan/iron, constantan/chromel and constantan/alumel.

A copper (+) and constantan (-) couple is used up to about 350 C, constantan being a 40% Ni and 60% Cu alloy. Up to 850 C

an iron-constantan couple is used with a chromel (90% Ni 10% Cr) and alumel (94% Ni 2% Al) couple up to 1200 C. Average

emf is 0.05mV/ C which compares with about 18mV/ C for a thermistor. Platinum-platinum plus 10% rhodium couples have

been used to 1400 C.

Advantages: Thermocouples are used exclusively around the main engine exhaust gas system because of their rugged

construction and low cost. It is capable of measuring a wider temperature than RTD.

Disadvantages: If the thermocouple is located some distance away from the measuring device, expensive extension grade

thermocouple wires or compensating cables have to be used. Thermocouples are slower in response than RTDs.

PYROMETER is also known as Radiation Thermometer or Infrared radiation thermometers. Pyro means

Fire and thermo means hot. It measures thermal radiations and surface temperatures. It is made up of an optical system and

a detector. The optical system (a lens) is used to focus the infrared (IR) energy naturally emitted by an object onto a sensor or

detector. Sensor is responsive to the infrared radiation and hence transforms IR energy into electrical energy.

Types of radiation pyrometer 1. OPTICAL PYROMETER 2. PHOTO-ELECTRIC PYROMETER

Optical pyrometer is a device which allows contactless temperature measuring by using the incandescence color. It is a non-

contacting device that intercepts and measures thermal radiation. This device can be used to determine the temperature of

an object's surface. The range is from 500 C to 1600 C.

APPLICATIONS: It is used where the target under consideration is moving such as in rollers, moving machinery, or a conveyor

belt. It employed for monitoring products on a movable production line where temperature measurement is required. Areas

where the object is enclosed by an Electromagnetic field such as in Induction heating. Apt for areas where the object is

restricted in a vacuum or other controlled atmosphere. Applications needing quick and fast response also employ IR radiation

thermometers. It is employed in areas where non-contact measurements are desired. Example is contaminated or hazardous

areas involving high voltages. It is found suitable for applications where large distances and high temperatures are involved.

It employed in the calibration of many heating devices used for cooking purposes such as furnaces, ovens etc. It is employed

in areas where direct temperature measurement is complicated. For example, in large electrical components and arrays and

the inside of car engines where parts are blocked from contact by other mechanical and hydraulic devices. It is also used for

weather forecasting and research and can determine the temperature of clouds at high altitudes. It is employed in variety of

manufacturing processes such as metals, glass, cement, ceramics, semiconductors, plastics, paper, textiles, coatings, etc.

ADVANTAGES: Light in weight, Compact in size, Simple and convenient to use, Proficiency to measure hot, hazardous and

contaminated surfaces without causing any harm to the object, Fast response. They can give several readings per second in

contrast to conventional sensors which takes several minutes to give readings.

DISADVANTAGES: Higher cost as compared to conventional thermocouples or resistance temperature detectors. Regular

maintenance is required to keep the optical system clean. Advanced radiation thermometers involve extra complicated design

and optics. Unlike thermocouples and RTDs, no calibration standards and curves are available for radiation thermometers.

PRESSURE TRANSDUCERS

PRESSURE is the result of force acting over a given area. Pressure can be result from one object set on another

such as elevating liquids some distance above another object, expansion of gas, and the force of a fluid flow. It is

also a universal processing condition because all forms of life depend on pressure for survival. Atmospheric

Pressure enables us to breathe oxygen and to control movements. Pressure supplies us with water for various

uses.

ELEMENT TYPES : 1. Bellows Pressure Sensing Element 2. Bourdon Tube Type Detectors

Bellows Pressure Sensing Element The need for a pressure sensing element that is extremely sensitive to

low pressures and provides power for activating recording and indicating mechanisms prompted development of

the metallic BELLOWS pressure sensing element.

Bellows is a pressure sensor that converts pressure to linear displacements. It is a one

piece, collapsible, seamless, metallic unit that has deep folds formed in thin-walled

tubing.

Its diameter of the bellows ranges from 0.5 to 12 inches, and the bellows may have as

many as 24 folds. It is most accurate in measuring pressures from 0.5 to 75 psig. When

used in conjunction with a heavy range spring, some bellows can be used to measure

pressures of more than 1000 psig. Note: PSIG pound per square inch gauge; pressure referenced to ambient

atmospheric pressure.

Bourdon Tube Type Detectors

Bourdon Tube is one of the oldest pressure-sensing instruments still in use. It consists of a

thin-walled tube that is flattened diametrically on opposite sides to produce an elliptical

cross-sectional area that has two long, flat sides, and two short, round side. The tube is

bent lengthwise into an arc of 270 to 300.

Pressure instruments are sensitive to variations in the atmospheric pressure surrounding

the detector. This is especially apparent when the detector is located within an enclosed

space. Variations in the pressure surrounding the detector cause an indicated pressure

from the detector to change; this greatly reduces the accuracy of the pressure

measurement. Ambient temperature variations affect the accuracy and reliability of the pressure-detection

instrumentation. Variations in ambient temperature can directly affect the resistance of components in the

instrumentation circuitry, and they therefore affect the calibration of electrical component. The effects of

temperature variations are reduced by the design of the circuitry and by maintaining the pressure-detection

instrumentation in the proper environment. Humidity affects most electrical equipment, especially electronic

equipment. High humidity causes moisture to collect on the equipment causing short circuits, grounds, and

corrosions, which can damage components. The effects of humidity are controlled by maintaining the equipment

in the proper environment.

Functional Uses of Pressure Detectors

Functions of Pressure Detectors Remedies for Inoperative Pressure

Detectors

Environmental Concerns

Indication A spare detector element can be

used (if installed).

Atmospheric Pressure

Alarm A local mechanical pressure gauge

can be used (if available).

Ambient Temperature

Control A precision pressure gauge can be

installed in the system.

Humidity

GAUGE PRESSURE shows the actual force applied to an object such as a vessel or a line. It is a differential

pressure.

It is also equal to absolute pressure minus local atmospheric pressure. Differential Pressure is the difference in

static pressure between two identical pressure taps. As humans, we do not feel the results of atmospheric

pressure because the pressure inside our bodies equalizes to outside pressure as we climb a mountain, descend

below sea level, or experience pressure variations accompanying weather changes. This equalization applies to

gauge pressure measurement. Gauge pressure starts at 14.7 lb per square inch of absolute pressure (when

measured at sea level). In gauge pressure measurement, 14.7 psi is subtracted from the 14.7 psia (absolute

pressure) of atmospheric pressure. Thus, at sea level, a gauge pressure meter would read ZERO, or 0 psig (gauge).

ABSOLUTE PRESSURE is measured from the point of zero atmospheric pressure. It is the sum of gauge pressure

plus atmospheric pressure. Absolute pressure gauge is less common because they require a vacuum chamber.

This makes the gauge more expensive to manufacture and use.

VACUUM PRESSURE is any pressure below atmospheric pressure, and as a reference, gauge pressure is any point

above atmospheric pressure. It is a measurement of -14.7 psig represents a perfect vacuum, and could also be

described as 0 psia.

MANOMETER

2 Types of Manometer: a. Water Manometer b. Mercury Manometer

Water Manometer is used for measuring pressures of a low order such as fan

pressures, etc. Note: 1 cubic meter of fresh water has a mass of 1 Mg and weighs 9.81 x

10 3 N.

Mercury Manometer is used for measuring pressures of a higher order than that

measured by the water manometer, such as scavenge or supercharge air pressure for IC

engines. Its relative density of mercury is 13.6.

Two Types of Manometers based on Physical Construction

WELL-TYPE MANOMETER INCLINED MANOMETER

WELL-TYPE MANOMETER - Making one leg of a manometer a large chamber (reservoir) makes it easier to read.

INCLINED MANOMETER - If one leg of a manometer tube is set at an angle or incline, the instrument is made more

sensitive.

BOURDON TUBES (PRESSURE GAUGE) A pressure relay tube is the principal working component (detecting element).

This tube which is semi-elliptical in cross section is connected to the pressure

source. When the tube is subjected to a pressure increase, it tends to unwind or

straighten out and the motion is transmitted to the gauge pointer through the

linkage, quadrant, and gear (measuring element). If the tube is subjected to a

pressure decrease, it winds, or coils up and the motion is again transmitted to the

pointer. Due to their robust construction, bourdon are often used in harsh

environments and high pressures, but can also be used for very low pressures;

the response time however, is slower than the bellows or diaphragm. Bourdon

Tube is therefore suitable for measuring pressures above or below atmospheric

pressure.

Materials used: Phosphor bronze or stainless steel for the pressure relay tube. Bronze or stainless for the quadrant,

gear, and linkage. Case, brass or plastic. Frequently used in transducers and controllers to vary output signals in

pneumatic or electrical form.

Application: They are used to measure medium to very high pressures.

ADVANTAGES These Bourdon tube pressure gauges give accurate results: Low Cost. Simple in construction. Modified

to give electrical outputs. Safe even for high pressure measurement. High Accuracy especially at high pressures.

DISADVANTAGES It has slow response rate with pressure change. Hysteresis is a phenomenon wherein two (or

more) physical quantities bear a relationship which depends on prior history. It is the lagging of an effect behind its

cause. It is sensitive to shocks and vibrations. Amplification is a must as the displacement of the free end of the

bourdon tube is low. It cannot be used for precision measurement.

Diaphragms is a circular-shaped convoluted membrane that is

attached to the pressure fixture around the circumference. The

pressure medium is on one side and the indication medium is on the

other. The deflection that is created by pressure in the vessel would be

in the direction of the arrow indicated.

- provide fast acting and accurate pressure indication. However, the

movement or stroke is not as large as the bellows.

Bellows Gauge It contains an elastic element that is a convoluted unit

that expands and contracts axially with changes in pressure. The

pressure to be measured can be applied to the outside or inside of

the bellows. Most bellows measuring devices have the pressure

applied to the outside of the bellows. Like Bourdon-

tube elements, the elastic elements in bellows gauges are made of

brass, phosphor, bronze, stainless steel, beryllium-

copper, or other metal that is suitable for the intended purpose of

the gauge. Most bellows gauges are spring-loaded; that is, a spring

opposes the bellows, thus preventing full expansion of the bellows.

Limiting the expansion of the bellows in this way protects the bellows

and prolongs its life.

In a spring-loaded bellows element, the deflection is the result of

the force acting on the bellows and the opposing force of the spring.

Although some bellows instruments can be designed for

measuring pressures up to 800 psig, the primary application aboard

ship is in the measurement of LOW PRESSURES or small pressure differentials.

STRAIN GAUGE It is resistive wire of about 0.01 mm diameter subject to strain by pressure with electrical resistance

change proportional to strain.

The strain gauge is a device that can be affixed to the

surface of an object to detect the force applied to it.

One form of the strain gauge is a metal wire of very

small diameter that is attached to the surface of a

device being monitored. For a metal, the electrical

resistance will increase as the length of the metal

increases or as the cross sectional diameter decreases. When force is applied as indicated in the figure above, the

overall length of the wire tends to increase while the cross-sectional area decreases. The amount of increase in

resistance is proportional to the force that produced the change in length and area. The output of the strain gauge is

a change in resistance that can be measured by the input circuit of an amplifier.

Piezoelectric Transducer A certain crystal when subjected to deformation produces an electric potential, which

results in the flow of an electric charge for a few seconds. Piezoelectric materials (crystals) change form when an

electrical field is applied to them. Conversely, piezoelectric materials produce an electrical field when deformed.

Quartz transducers exhibit remarkable properties that justify their large scale use in research, development,

production and testing. They are extremely stable, rugged and compact. Of the large number of piezoelectric

materials available today, quartz is employed preferentially in transducer designs because of the following excellent

properties:

high material stress limit, around 100 MPa (~ 14 km water depth) temperature resistance (up to 500C) very high rigidity, high linearity and negligible hysteresis almost constant sensitivity over a wide

temperature range

ultra high insulation resistance (10+14 ohms) allowing low frequency measurements (

valve, or all three. A typical system has three probes; a low level probe, a high level probe, and a high level alarm probe.

Magnetic Bond

Developed to overcome the problems of cages and stuffing boxes. It consists of a magnetic float which rises and falls with change in level. The float travels outside of a non-magnetic tube which houses an inner magnet connected to a level indicator. When the float rises and falls, the outer magnet will attract the inner magnet, causing the inner magnet to follow the level within the vessel. The magnetic bond method offers a very safe method for measurement of process fluids that are a release hazard. The use of magnetic bond method is advisable when the accidental release of process fluid could pose a threat to personnel or the environment. The magnetic bond method offers more protection than a glass tube device.

Capacitance Level Sensor

also known as Radio Frequency or Admittance Level Sensors. It operates on low MHz radio frequency range. A capacitance level sensor probe is inserted into the tank and senses the level change by related capacitive and resistive value of the liquid resulting into accurate level measurement. A metal rod (or plate) is inserted into a tank and serves as one of the capacitance plates, and the tank wall serves as another. When the tank is empty, the dielectric is air. When the tank is filled to some level, the dielectric changes because the fluid becomes the dielectric and changes the original value. The fluid can have a better or worse dielectric rating; the change is the function calculated by the sensor. Capacitance measurement devices must be calibrated in place and only with the process fluid to be measured. Failure to do so is likely results in erroneous measurements.

RADAR

The typical frequency used is 10 GHz. A portion of the transmitted wave is reflected to the antenna, where it is collected and routed

to the receiver. A microprocessor calculates the time of flight and calculates the resulting level from the time-of-flight measurement.

Time-of-flight - is the period between the transmission of the radar pulse and the reception of the return echo, and it is determined

by the radar detector; which is simultaneously exposed to the transmitted and reflected signals.

Radar sensors consist of a transmitter, an antenna, a receiver with signal processor, and an operator interface. The transmitter is

mounted on top of the vessel. Its solid-state oscillator sends out an electromagnetic wave (using a selected carrier frequency and waveform)

aimed downward at the surface of the process fluid in the tank. The signal is radiated by a parabolic dish or horn-type antenna toward the

surface of the process liquid. A portion is reflected back to the antenna, where it is collected and routed to the receiver. Here, a microprocessor

calculates the time of flight and calculates the level. It is determined by the radar detector, which is simultaneously exposed to both the sent

and the reflected signal. The detector output is based on the difference. The frequency-modulated (FM) signal varies from 0 to 200 Hz as the

distance to the process fluid surface varies between 0 and 200 ft. Because this measurement takes place in the frequency domain, it is

reasonably free of noise interference. Radar beams can penetrate plastic and fiberglass; therefore, noncontact radar gauges can be isolated

from the process vapors by a seal. Contact radar gauges send a pulse down a wire to the vapor-liquid interface. The reflective properties of the

process material affect the returned radar signal strength. Whereas liquids have good reflectivity characteristics, solids do not. Radar can

detect the liquid level under a layer of light dust or airy foam, but if the dust particle size increases, or if the foam or dust gets thick, it will no

longer detect the liquid level. Instead, the level of the foam or dust will be measured.

ULTRASONIC

The frequency range of audible sound is 9-10 kHz, slightly below the 20-45 kHz range used by industrial level gages. The velocity of an ultrasonic

pulse varies with both the substance through which it travels and with the temperature of that substance. This means that if the speed of

sound is to be used in measuring a level (distance or position), the substance through which it travels must be well known and its temperature

variations must be measured and compensated for. Ultrasonic sensors perform better in dirty applications.

FLOW TRANSDUCERS

Fluids - defined as liquids, gases, or vapors. - materials which exist in liquid, gas, or vapor form. Volumetric Flow Rate - a given quantity moving past a given point in a specified time period.

Ex: Gallons per minute (GPM) and Gallons per hour (GPH) Solids. Normally expressed in weight rate like Tonnes/hour, Kg/minute etc. Liquids. Expressed both in weight rate and in volume rate. Ex: Tonnes/hour, Kg/minute, litres/hour, litres/minute, m3/hour etc. Gases. Expressed in volume rate at NTP or STP like Std m3/hour, Nm3/hour etc. Steam. Expressed in weight rate like Tonnes/hour, Kg/minutes etc. Steam density at different temperatures and pressures vary. Hence the measurement is converted into weight rate of water which is used to produce steam at the point of measurement. Bernoullis Principle

Moving fluid contains energy. Energy in a flow consists of the sum of the pressure energy and the velocity energy. As the velocity in a given line is decreased, the pressure must increase, and vice versa. The sum of pressure energy and velocity energy in a line is a constant throughout the system if potential energy and friction are ignored. Q = V X A where Q rate of flow, V velocity of flow (in inches per second), A cross sectional area (in sq. in) Summarized as follows: The rate of flow is equal to the cross-sectional area of the pipe (A) times the velocity of the fluid (V). The velocity (V) is equal to the square root of the differential pressure (h). The rate of flow is equal throughout a process line. A restriction in a pipe causes a permanent pressure loss and a change in pressure and velocity. Fluid friction is a force that opposes the flow of fluids ensuing from the fluids viscosity and the resulting turbulence. Viscosity the extent of friction between two adjacent layers of fluid; the greater the viscosity of a fluid, the more energy is required to cause them to slide; the inherent resistance of a substance to flow. Density mass per unit volume, with the density of water being 1000 kilograms of force per cubic meter, or 68 pounds per cubic foot. Friction energy is lost to heat dissipation when a fluid moves through a pipe. Friction results when a moving fluid comes into contact with the pipe walls. Laminar Flow and Turbulent Flow Laminar straight-line flow of a fluid. Turbulent fluid flow affected by factors causing it to deviate from a straight line. Measurement of Flow Flow meter - is a device that measures the rate of flow or quantity of a

moving fluid in an open or closed conduit. Flow measuring devices are generally classified into four groups. 1. Mechanical type flow meters - Fixed restriction variable head type flow meters using different sensors like orifice plate, venturi tube, flow nozzle, pitot tube, dall tube, quantity meters like positive displacement meters, mass flow meters etc. fall under mechanical type flow meters. 2. Inferential type flow meters. - Variable area flow meters (Rotameters), turbine flow meter, target flow meters etc. 3. Electrical type flow meters. - Electromagnetic flow meter, Ultrasonic flow meter, Laser doppler Anemometers etc. fall under electrical type flow meters. 4. Other flow meters. - Purge flow regulators, Flow meters for Solids flow measurement, Cross-correlation flow meter, Vortex shedding flow meters, flow switches etc. Mechanical Flow Meters orifice plate, venturi tube, flow nozzle, pitot tube, dall tube, quantity meters like positive displacement meters, mass flow meters DIFFERENTIAL PRESSURE METERS

The basic principle is that the pressure drop across the meter is proportional to the square of the flow rate. DP meters have primary and secondary elements. The primary element is responsible for causing a change in the kinetic energy, which causes the pressure drop across the element. An orifice plate is one common application.

The secondary element analyzes the primary elements information and provides signal or readout that is converted to the actual flow rate. This is called a differential pressure transmitter. Orifice Plates

The simplest of the flow path restrictions used in flow detection, and it is the most economical. Orifice Plates are flat plates that are 1/16 to inch thick. They are normally mounted between a pair of flanges and are installed in a straight run of smooth pipe to avoid disturbance of flow patterns from fittings and valves. Precisely sized for correct line size, flow rate, and liquid properties and allow an accurate measurement over a reasonable range. It used to create restriction for differential head flow measurement.

There are 3 kinds of orifice plates. 1. Concentric 2. Eccentric 3. segmental

Concentric type is used for clean fluids. In metering dirty fluids, slurries, and fluids containing solids, eccentric or segmental type is used in such a way that its lower edge coincides with the inside bottom of the pipe. This allows

the solids to flow through without any obstruction. Two disadvantages:

1. Causes a high, permanent pressure drop (outlet pressure is 60% to 80% of inlet pressure). 2. Subject to erosion of which eventually causes inaccuracies in the measured differential pressure.

Venturi Tube

It has a converging conical inlet, a cylindrical throat, and a diverging recovery cone. It has no projections into the fluid, no sharp corners, and no sudden changes in contour. The inlet section decreases the area of the fluid stream, causing the velocity to increase and the pressure to decrease. The low pressure is measured in the center of the cylindrical throat,

where the pressure is its lowest value, and neither the pressure nor the velocity changes. The recovery cone enables the recovery of pressure such that total pressure loss is only 10% to 25%. The highest pressure is measured upstream of the entrance cone. Major disadvantages:

1. the high initial costs for installation 2. difficulty in installation and inspection

DISPLACEMENT METERS (Nutating Disc) Operation involves separating liquids into accurately measured increments and then moving them along. Each segment is connected to a register that counts each segment as a volume amount. These units are popular with automatic batch processes and accounting applications. The meters are particularly good for applications in which the measurement of viscous liquids using a simple mechanical meter system is needed. Nutating Disc

It is otherwise known as wobble plate meter or disk meter. It is most common type of displacement flow meter. A typical nutating disc is used normally for water service, such as raw water supply and evaporator feed. Used extensively for residential water service. Velocity Meters (Dall Flow Tube, Pitot Tube) It operates with linearity with respect to the flow volume. There is no square-root relationship, and their rangeability is greater. Have minimum sensitivity to viscosity changes. Comes with flanges, making the suitable piping arrangements to allow installation directly into pipelines. Dall Flow Tube Consists of a short, straight inlet section followed by an abrupt decrease in the inside diameter of the tube. The section, called the INLET SHOULDER, is followed by the converging inlet cone and a diverging exit cone. The two cones are separated by a slot of gap

between the two cones. The low pressure is measured at the slotted throat (i.e., area between the two cones). The high pressure is measured at the upstream edge of the inlet shoulder. A higher ratio of pressure developed to pressure lost than seen in the Venturi Tube. More compact and is commonly used in large-flow applications. Dall Flow Tube is available in medium to very large sizes. The cost of the large sizes is normally less than that of a Venturi flow tube. It has a pressure loss of about 5%. Advantages of Dall Flow Tube: Low head loss, Short lying length, It is available in numerous materials of construction. Disadvantages of Dall Flow Tube: Pressure difference is sensitive to up-stream disturbances, More straight pipe required in the approach pipe length, It is not considered for measuring flow of hot feed water.

Pitot Tube Another primary flow element used to produce a differential pressure for flow detection. It consists of a tube with an opening at the end. The small hole in the end is positioned so that it faces the flowing fluid. The velocity of the fluid at the opening of the tube decreases to zero. This provides the high-pressure input to a differential pressure detector. A Pressure tap provides the low pressure input. Advantages of Pitot Tube

1. No pressure loss. 2. It is relatively simple. 3. It is readily adapted for flow measurements made in very large pipes or ducts.

Disadvantages of Pitot Tube 1. Poor accuracy. 2. Not suitable for dirty or sticky fluids and fluids containing solid particles. 3. Sensitive to upstream disturbances.

Flow Nozzle The Flow nozzle is a smooth, convergent section that discharges the flow parallel to the axis of the downstream pipe. Pressure recovery is better than that of an orifice. Flow nozzles are usually made of gun metals, stainless steel, bronze metal. They are frequently chromium plated. Advantages of Flow Nozzle

1. Permanent pressure loss lower than that for an orifice plate. 2. It is suitable for fluids containing solids that settle. 3. It is widely accepted for high pressure and temperature steam flow.

Disadvantages of Flow Nozzle 1. Cost is higher than orifice plate. 2. It is limited to moderate pipe sizes. 3. It requires more maintenance. (It is necessary to remove a section of pipe to inspect or install it).

Mass Flow Meters (Coriolis Meter) The demand for accurate flow measurements in mass-related processes (e.g. chemical, refining, heat transfer) has generated the design of mass flow meters. Coriolis meter is the most widely used designs for mass flow meters. Coriolis Meter

Coriolis Meters are true mass meters that measure the mass rate of flow directly rather than volumetric flow. Uses an obstruction-less, U-shaped tube as a sensor and applies Newtons second law of motion to deter mine the flow rate. Inside the sensor housing, the sensor tube vibrates at its natural frequency. The sensor tube is driven by an electromagnetic drive coil located at the center of the bend in the tube that vibrates like a tuning fork.

Inferrential Flow Meters (Variable area flow meters (Rotameters), turbine flow meter,

target flow meters) Variable Area Meters (Rotameters and Piston type meter). Rotameter

It is an area flow meter whose indicating element is a rotating float. It consists of a metal float and a conical glass tube, constructed such that the diameter increases with height. When

there is no fluid passing through the rotameter, the float rests at the bottom of the tube. As fluid enters the tube, the higher density of the float causes the float to remain on the bottom. The space between the float and the tube allows flow past the float. As flow increases in the tube, the pressure drop increases. When the pressure drop is sufficient, the float rises to indicate the amount of flow. The higher the flow rate, the greater the pressure dropped. Piston Type Meters

A piston is accurately fitted inside a sleeve and is lifted by fluid pressure until sufficient post area in the sleeve is uncovered to permit the passage of the flow. The flow is indicated by the position of the piston. Turbine Flow Meters

It mainly used for the purpose of measurement of liquid and gas at very low flow rates. The turbine meters are widely used for military applications. They are particularly useful in blending systems for the petroleum industry. They are effective in aerospace and air borne applications for energy-fuel and cryogenic flow measurements.

Advantages of Turbine Flow Meters

1. Better Accuracy [ 0.25% to 0.5%]. 2. It provides excellent repeatability [ 0.25% to 0.02%] and rangeability

(10 : 1 and 20 : 1). 3. It has fairly low pressure drop. 4. It is easy to install and maintain. 5. It has good temperature and pressure ratings. 6. It can be compensated for viscosity variation.

Disadvantages of Turbine Flow Meters 1. High cost. 2. It has limited use for slurry applications. 3. It is not suitable for non-lubricating fluids. 4. They cannot maintain its original calibration over a very long

period and therefore periodical recalibration is necessary. 5. They are sensitive to changes in the viscosity of the liquid passing through the meters. 6. They are sensitive to flow disturbances. 7. Due to high bearing friction is possible in small meters, they are not preferred well for low flow rates.

Electrical Flow Meters (Electromagnetic flow meter, Ultrasonic flow meter, Laser Doppler Anemoemeters) Electromagnetic Flow Meter

It is similar in principle to the generator. The rotor of the generator is replaced by a pipe between the poles of a magnet so that the flow of the fluid in the pipe is normal to the magnetic field. As the fluid flows through this magnetic field, an electromotive force is induced in it that is mutually normal (i.e. perpendicular) to the magnetic field and the motion of the fluid.

Ultrasonic Flow Meter The term ultrasonic refers to the pressure differences (usually are short bursts of sine waves) whose frequency is above the range audible to human hearing which is 20 to 20000 Hz. The ultrasonic flow

meter operates on the principle that the velocity of sound in a fluid in motion is the resultant of the velocity of sound in the fluid at rest plus or minus the velocity of the fluid itself. Two types of Ultrasonic Flow Meters

a) Transit time flow meters b) Doppler Flow meter. Transit Time Flow Meters

As the name implies; these devices measure flow by measuring the time taken for an ultrasonic energy pulse to traverse a pipe section, both with and against the flow of the liquid within the pipe.

Doppler Flow Meters This type of flow meter is based

on Doppler principle. The transmitter of a Doppler flow meter projects an ultrasonic beam at a frequency of about 0.5 MHz into the flowing stream and deflects the reflected frequency. The difference between transmitted and reflected velocities is called the beat frequency and is related to the velocity of the reflecting surfaces (solid particles and gas bubbles) in the process stream. Laser Doppler Anemometers

Anemometers are used to measure air and gas flows in a variety of applications. When sound or light is beamed into the atmosphere, the in homogeneities in the air will reflect these beams. The resulting Doppler shift in the returning frequencies can be interpreted as an indication of wind velocity. When laser-based Doppler anemometers are used, the intensity of the light scattered by the particles in the air is a function of their refractive index and the size of the reflecting particles. The Laser Doppler anemometer (LDA) is based on the Doppler effect. The Doppler shift of frequency occurs as light is dispersed on the surface of moving particles. The shift in the frequency of the light source (laser beam) is

proportional to the velocity of the particles. The frequency shift is very small (from 1 KHz up to a tenth of a MHz) in comparison with the light frequency and thus it can be directly measured. Therefore, the arrangement using the interference of the original and refracted lights is used. This is called as differential mode of LDA. The use of this non-contact measurement method is suitable for nearly all hydro dynamical and aero dynamical velocity measurement applications. Other Flow Meters

1. Purge flow regulators for low flow rate measurements 2. Cross-correlation flow meters for solids flow measurements 3. Belt type feeders for solids flow measurements 4. Vortex flow meters for moderate flow measurements and different

designs of flow switches Purge Flow Regulators

Purge flows are low flow rates of either gases or liquids. They usually serve to protect pressure taps from contacting hot or corrosive process fluids or from plugging. They can also protect electrical devices from becoming ignition sources by maintaining a positive inert gas pressure inside their housings or to protect the cleanliness of the optics of analyzers through purging.

Cross-Correlation Flow Meters The oldest and simplest methods of flow measurement are the

various tagging techniques. Here a portion of the flow stream is tagged at some upstream point and the flow rate is determined as a measurement of transmit time. Variation of this technique includes particle tracking, pulse tracking, dye or chemical tracing, including the radioactive types. Vortex Shedding Flow Meter

A vortex flow meter is typically made of 316 stainless steel or Hastelloy and includes a bluff body, a

vortex sensor assembly and the transmitter electronics, although the latter can also be mounted remotely. They are typically available in flange sizes from 1/2 in. to 12 in. The installed cost of vortex meters is competitive with that of orifice meters in sizes under six inches. Wafer body meters

(flangeless) have the lowest cost, while flanged meters are preferred if the process fluid is hazardous or is at a high temperature.

TACHOMETER Other names of TACHOMETERS: REVOLUTION COUNTERS, RPM GAUGE, TACH, REV-COUNTER, TACHOGENERATOR, RATE

GENERATOR

It comes from Greek words tachos means SPEED and metron means TO MEASURE. It is a device used to measure the rotation speed of a

shaft or disk, as in motor or other machine. Usually displays the revolutions per minute (RPM) on a calibrated analogue dial, but digital

displays are increasingly common.

2 Main Functions of TACHOMETER: Stabilization of System 2. Computation of closed loops in control system

Types of Tachometers: AC Tachometer, DC Tachometer

DC TACHOMETERS: The device is nothing but a permanent-magnet generator. The output of this device is 2 to 10 volts per 1,000

revolutions/minute. For indicating the speed, a voltmeter having a high resistant value is built into calibration in revolutions per minute. A

small DC generator. Easily modified for different voltage constants current capability, internal resistance, and all the electrical parameters of

a DC Tachometer. Self-powered. No external power or excitation is required.

AC TACHOMETERS: revolving permanent-magnet field and a stationary winding are the elements require for constructing an AC

tachometer. The voltage output and frequency that is generated here stay in proportion to the speed of rotation. It has two stator windings

90 degrees apart, and an aluminum or copper cup rotor. The rotor rotates around a stationary soft-iron, magnetic core. One stator winding

is energized by a reference AC source. The other stator winding is the output, or secondary winding the voltage applied to the primary

winding produce a magnetic field at the right angle to the secondary winding when the rotor is stationary.

Other names of TORQUE METER: TORQUE SENSOR, TORQUE TRANSDUCER, TORQUE DETECTOR

It is a device for measuring and recording the torque on a rotating system, such as an engine, crankshaft, gear box, transmission, rotor or a

bicycle crank. A device designed to determine the torque or torsion in a shaft, usually by measuring the twist in a calibrated length of

shafting.

VISCOMETER is also called VISCOSIMETER. An instrument used to measure the viscosity of a fluid under one flow condition. Either the fluid

remains stationary and an object moves through it, or the object is stationary and the fluid moves past it. The drag caused by relative

motion of the fluid and a surface is a measure of the viscosity.

RHEOMETER A laboratory device used to measure the way in which a liquid, suspension or slurry flows in response to applied forces. It is

used for those fluids which cannot be defined by a single value of viscosity and therefore require more parameters to be set and measured

than is the case for a viscometer.

PHOTOELECTRIC CELL

"Photo" means light. Means electricity produced by a light beam. It is a device that is activated by electromagnetic energy in the form of

light waves. Exists in many types, and they are used for many things. It is a type of electric cell whose operation depends upon the extent to

which it is exposed to light. Light is a form of energy. When light strikes certain chemical substances, such as selenium and silicon, its energy

causes a push on the electrons in the substances.

What is photoelectric effect? Light is a kind of electromagnetic energy: it travels in the same way (and at the same speed) as X-rays,

microwaves, radio waves, and other kinds of electromagnetism. We also know that energy can readily be transformed from one kind into

another: potential energy can be turned into kinetic energy and either can be converted into heat or sound.

OIL IN WATER SENSOR

It is a simple and effective method of detecting visible oil on water. Deployed as a floating sensor on a suitable calm surface of an oil

interceptor the monitor reacts rapidly to partial and complete films of oil on the surface of the water. Sensor used with a leak-wise

controller, is installed in sump and ground monitoring water wells to detect floating oil sheens resulting from oil leak in underground

storage tank and pipe line. Monitoring hydrocarbon and other organic solvents during site assessment and remediation. Detecting and

monitoring floating hydrocarbons in sewer system wastewater treatment system, oil/water separator, cooling water trenches and canals,

storm water runs off, retention ponds and sumps and boiler condensate tank.

OIL IN MIST DETECTOR otherwise known as OMDS (Oil Mist Detection System)

A monitoring system for the detection of oil mist in the atmosphere and is designed for severe industrial environments. Adopted in the

monitoring of oil separators & engine rooms, pump & power pack spaces and wherever the risk of an oil mist build-up might be assessed.

IN THE ATMOSPHERE OF THE ENGINE ROOM: There are number of fires that start in machine room spaces. Places most at risk are engine

and purifier rooms. However, other areas have their own problems and these include bow thruster rooms, steering gear and hydraulic

pumps. Up to 65% of machine room fires are the result of oil mist.

There are two ways oil mist can be formed. One is when oil mist is generated through minute leaks in oil lines which, under pressure, give

off a very fine atomized spray. Danger occurs when high pressure type leaks of oil mist are formed with a particle size of between 3 - 10

microns that builds up to a hazardous concentration of mist in the atmosphere. At levels of saturation conditions are truly hazardous, and if

no action is taken a fire can start. The ignition temperature for this type of oil mist can be extremely low depending on the fuel that is being

atomized. Other ways oil mist can be generated is when drops of oil hit a hot spot or surface and boils. When oil mist is produced by boiling

the particle size is then about 3-10 microns. This mist is visible and is known as blue smoke. The larger and hotter the hot area is the quicker

oil mist is produced. At this stage a temperature as low as 150C can cause ignition.

SOURCES OF MIST: leaking injectors, fractured flexible hoses, loose or incorrectly fitted pipe fittings, broken welds, poor maintenance of

machinery,

SOME CAUSES O F I G N I T I O N: exhaust pipes, Turbochargers, non-flameproof motor, electrical contacts, static electricity, faulty wiring

How to prevent oil mist fires? The ideal is to make sure no leaks occur in the first instance. The practical answer is to install an oil mist

detection system that will detect oil mist as it is being diffused into the atmosphere which will alarm long before it saturates the

atmosphere to a danger level. It should be noted that steam and smoke have approximately the same particle size, so an oil mist detector

should be able to detect these parameters if the right system is used - which is a bonus.

How does it work? The detectors are placed around the vessel in vulnerable areas where oil mist leaks are more likely to occur. The

detectors are placed in the air stream that can normally be found by using a smoke generator. The route the oil mist usually takes is

towards the turbocharger or the exit ventilation duct. Detectors have a built-in fan and continuously draw in and monitor the surrounding

atmosphere. This is because oil mist diffuses into the environment and does not generally stay in one place. The detector communicates to

the monitor through 6-core cable. The monitor can be stationed away from the danger area. The cable carries the signal and power to and

from each detector and fan.

SMOKE DENSITY DETECTOR can detect combustion product (smoke) generated by a fire, and transmit an alarm signal to the fire alarm

control panel. It can detect a fire in an earlier stage than a heat detector. It can be installed in the spaces such as basements, ordinary

floors, staircases, elevator shafts. It is composed of a light source, light sensing element, light shielding element and detecting chamber. The

light source (a light-emitting diode) emits light at intervals of about 3.5 seconds, which does not reach the light sensing element (photo

diode) under normal conditions because of the light shielding mold. If smoke enters the detecting chamber, the light from the light source

is scattered by smoke particles and reaches the light sensing element. The light reaching the light sensing element varies with smoke

density and if it exceeds the predetermined level, the detector operates and automatically holds its operation. The detector then transmits

the alarm signal to the fire alarm panel and the response lamp of the detector turns on.

Smoke detectors provide early warning in the event of a fire, and enable emergency action in the event of a fire. They are inexpensive, easy

to install, unobtrusive, and require very little maintenance, and no home should be without them.

Photoelectric Smoke Detectors look for the presence of visible by-products of combustion in the detection chamber. When sufficient

density of visible combustibles fill the detection chamber, the detector sounds an alarm condition.

Ionization smoke detectors feature a harmless radioactive source within a dual detection chamber. Ionization Smoke detectors respond to

invisible by-products of combustion. They operate by sensing for a change in the electrical conductivity across the detection chamber. The

advantage of the ionization detector is that the smoke can be invisible to the human eye, while remaining very much visible to the

ionization detector.

FLAME DETECTOR is a type of device that uses optical sensors in order to detect flames. These detectors are optical equipment for the

detection of flame phenomena of a fire. They also respond to the production of one or a combination of ultra-violet or infrared spectrums

of electromagnetic radiation.

There are several types of flame detector. The optical flame detector is a detector that uses optical sensors to detect flames. There are also

ionization flame detectors, which use current flow in the flame to detect flame presence, and thermocouple flame detectors.

Types: Ultraviolet, Near IR Array, Infrared, UV/IR, IR/IR Flame Detection, IR3 Flame Detection, Visible Sensors, Ionization Current Flame

Detection, Thermocouple Flame Detection

FIRE DETECTORS A temperature sensing device designed to sound an alarm, to turn on a sprinkler system, or to activate some others fire

preventives measure at the first sign of fire. It is a useful device that saves lives and material possessions by intimating about fire before it

gets violent. Their primary function is to detect fire and to kick off a desired action in immediate response.

HEAT DETECTORS senses the presence of fire as the temperature of surroundings exceeds a predefined value or the rate of temperature

rise shoots up.

SMOKE DETECTORS measure the concentration of solid or liquid particles in a specified area. As the concentration of these particles in air

increases beyond a certain value, it notifies about the fire.

FLAME DETECTORS sense the occurrence of fire by sensing the presence of light. It uses a light sensitive receiving element for fire detection.

Advantage is that it is capable of detecting fire within milliseconds and can activate explosion suppression system thus enabling to curb fire

while it is in initial stages.

RESPONSES OF FIRE DETECTORS: Once the fire is detected, the immediate response of the detector is to trigger a desired responsive action.

The immediate responsive action depends upon the overall design of fire prevention system. It can be activation of audible and visual

alarms. Fire detectors can transmit signals to remote monitoring stations. It can even activate fire extinguishing systems and emergency

shutdown of equipment and processes that might increase the severity of fire.

EXPLOSIVE GAS DETECTOR is a device used to detect explosive gas leaks in objects, such as propane gas. Carbon monoxide detectors will

not detect this, thus the device is often recommended to complement the CO detector. Combination explosive gas leak and carbon

monoxide detectors exist. It used to detect a gas leak and interface with a control system so a process can be automatically shut down. It

can also sound an alarm to operators in the area where the leak is occurring, giving them the opportunity to leave the area. It is important

because there are many gases that can be harmful to organic life, such as humans or animals. Gas detectors can be used to detect

combustible, flammable and toxic gases, and oxygen depletion. It is usually battery operated. It transmits warnings via series of audible and

visible signals such as alarms and flashing lights when dangerous levels of gas vapors are detected. As detectors measure a gas

concentration, the sensor responds to a calibration gas, which serves as the reference point scale. As the sensors detection exceeds a

preset alarm level, the alarm or signal will be activated. As units, gas detectors are produced to detect a single gas, but modern units may

detect several toxic or combustible gases, or even a combination or both types.

LIST OF GASES

FLAMMABLE GASES: Ammonia, Benzene, Butane, Carbon Monoxide, Ethane, Hydrogen cyanide, Hydrogen sulfide, Methane,

Propane, Vinyl Chloride, Acetylene, Ethylene

COMBUSTIBLE GASES: Propane, Methane, Anaerobic Digestor Gas, Coal Gasification Gas, Municipal Waste Pyrolysis, Gasification

Gas

LIST OF EXPLOSIVE GASES: HYDROGEN, METHANE, PROPANE, BUTANE, ACETYLENE

TWO MAIN TYPES OF GAS DETECTORS:

PORTABLE GAS DETECTOR used to monitor the atmosphere around personnel and is worn on clothing or on a belt/harness.

FIXED GAS DETECTOR is a fixed type which may be used for detection of one or more gas types. It is mounted near the process

area of a plant or control room.

Applications of EXPLOSIVE GAS DETECTOR: Boiler rooms, Plants rooms, and workshops, Laboratories, Design and Technology rooms,

Garages, Mechanical Handling Equipment battery charging systems, Car Park CO Detection System, Leak Detection Systems for Water,

Hydrocarbons, Refrigerants, and Chemicals, Multi-tenancy properties, Halls of residence, Student accommodations, Swimming pool plant

room, Pub cellars, Boat Gas Detection, Caravan and Mobile Homes, Domestic Installations e.g. gas cooker, gas fire, etc.

VIBRATION MONITOR All operating machines vibrate. Since an increase in vibration almost always accompanies deterioration in running

conditions, it is possible to gain information about a machines condition by monitoring vibration levels. The overall level of vibration

indicates the general condition of the machine. Vibration analysis can be used to determine the cause of vibration, including such factors as

unbalance, misalignment, or bearing defects. It provides an overall picture of total plant and operations equipment condition. It measures

the vibration at critical points of a motor or other type of rotating equipment when it is running. It is used primarily on rotating plant to

detect common problems such as misalignment, bearing wear, resonances, and broken or loose parts which can be key indicators of a state

of a particular machine. It gives warnings of possible failure and determines the mechanical condition of the unit under test based from the

magnitude and frequency of the vibrations.

Advantages: minimum costs, provide continuous improvement in plant operations and maintenance functions. Technician uses laser

velocity transducer to take vibration readings on rear side dryer bearings.

Application of VIBRATION MONITOR: Belt Conveyors, Vibratory Conveyors, Drag Conveyors, Fan and Blowers, Screw Conveyors, Rotary

Airlocks, Bucket Elevators, Pumps, Turbine and Generators, Centrifuges, Mixers, Motor

OXYGEN ANALYZER is a device that measures the level of oxygen in a system that determines if the level needs to be increased or not. It

uses a kind of oxygen sensor constructed of ceramic materials to measure the oxygen level. To decrease pollution in industrial, vehicular, or

rather all types of emissions.

Types of OXYGEN ANALYZER: Ambient temperature-Oxygen Analyzer, Electrochemical-Oxygen Analyzer, Paramagnetic-Oxygen Analyzer,

Polarographic- Oxygen Analyzer, Zirconium Oxide- Oxygen Analyzer.

Ambient temperature-Oxygen Analyzer is also known as a galvanic sensor. It is a small, partially sealed, cylindrical device which

contains two dissimilar electrodes immersed in an electrolyte. The oxygen molecules diffuse in the electrolyte and that results in a

chemical reaction that generates a certain amount of current that tells us the level of oxygen in the system.

Electrochemical-Oxygen Analyzer is based on electrochemical reduction of O2 at a negatively polarized electrode. It is also known as

fuel cells, measure percent or trace (ppm) levels of oxygen in a gas or gas mixture.

Paramagnetic analyzer works on a simple principle that oxygen has a very high magnetic susceptibility and shows a paramagnetic

behavior.

Polarographic analyzers work well in case of percent measurement and the main advantage is that when it is not operative, there is

no consumption of the electrode. It can be stored for longer duration of time.

Uses of Oxygen Analyzer: To measure the exhaust gas concentration of oxygen for internal combustion engines in automobiles and

other vehicles. To measure respiration or production of oxygen. Used for combustion monitoring and keeping a control over it in a

range of applications and help the industries to achieve considerably in saving energy.

Applications of Oxygen Analyzer: Vary from energy-consuming industries to various combustion facilities. Used in industries such as iron and

steel, electric power, oil and petrochemicals, ceramics, pulp and paper, food and textiles and in facilities such as incinerators and small or

medium-sized boilers. Helps in lowering the amount of carbon dioxide, Sulfur dioxide and Nitrogen oxides in the emissions by resisting the

incomplete combustion of fuel, therefore preventing the world from global warming and air pollution.

CARBON DIOXIDE ANALYZER is an instrument for the measurement of carbon dioxide gas. It used to monitor ventilation rate or indoor air

quality. As CO2 concentration increases the quality of indoor air lowers. It provides a basic spot check of atmosphere in any area, and such

spot checks are important as preinstalled monitors give average results of carbon dioxide concentration, not real data related to many

confined areas.

RELATIVE HUMIDITY If the air is at 100-percent relative humidity, sweat will not evaporate into the air. As a result, we feel much hotter than

the actual temperature when the relative humidity is high. Humidity is something we hear about daily in weather reports. Humidity is to

blame for that muggy, steam-room feeling you experience on certain summer days.

Absolute humidity is the mass of water vapor divided by the mass of dry air in a volume of air at a given temperature. The hotter the air is,

the more water it can contain.

RELATIVE HUMIDITY is the ratio of the current absolute humidity to the highest possible absolute humidity (which depends on the current

air temperature). It shows the relationship between absolute moisture (the amount really there) and the saturation state of water vapor. It

is a term used to describe the amount of water vapor in a mixture of air and water vapor. It defined as the ratio of the partial pressure of

water vapor in the air-water mixture to the saturated vapor pressure of water at those conditions. Relative humidity of air depends not only

on temperature but also on the pressure of the system of interest. It is often used instead of absolute humidity in situations where the rate

of water evaporation is important, as it takes into account the variation in saturated vapor pressure. A reading of 100 percent relative

humidity means that the air is totally saturated with water vapor and cannot hold any more, creating the possibility of rain. This doesn't

mean that the relative humidity must be 100 percent in order for it to rain -- it must be 100 percent where the clouds are forming, but the

relative humidity near the ground could be much less.

Humans are very sensitive to humidity, as the skin relies on the air to get rid of moisture. The process of sweating is your body's attempt to

keep cool and maintain its current temperature. If the air is at 100-percent relative humidity, sweat will not evaporate into the air. As a

result, we feel much hotter than the actual temperature when the relative humidity is high. If the relative humidity is low, we can feel much

cooler than the actual temperature because our sweat evaporates easily, cooling us off. For example, if the air temperature is 75 degrees

Fahrenheit (24 degrees Celsius) and the relative humidity is zero percent, the air temperature feels like 69 degrees Fahrenheit (21 C) to our

bodies. If the air temperature is 75 degrees Fahre nheit (24 C) and the relative humidity is 100 percent, we feel like it's 80 degrees (27 C)

out. People tend to feel most comfortable at a relative humidity of about 45 percent. Humidifiers and dehumidifiers help to keep indoor

humidity at a comfortable level. Relative air humidity is measured using relative humidity meters, that show on their displays from 0%

(absolutely dry air) up to 100% (air that is completely saturated, such as fog, clouds or steam baths). Some models of relative humidity

meters have an unlimited measurement range. The physical area is between 40 and 65% r.h. Given that hot air possesses the ability to

absorb more water vapour than cold air, people feel that in winter, air is too dry and in summer it is too humid.

RELATIVE HUMIDITY METER is also known as Hygrometers. It used in residential and commercial applications to measure the amount of

moisture in the air. It is important for health and safety in the home and construction, laboratories, and hospitals. It measures the amount

of moisture in the air as a percentage of the maximum amount of water vapor the air can hold at a given temperature. Since warm air can

hold moisture more than cool air, relative humidity meters include a thermometer function. Most digital humidity meters, regardless of

type, are also thermometers and measure relative humidity. Humidity meters that include data logging functions can collect up to several

thousand individual humidity readings and generate analyses of trends. A data logging hygrometer can both generate graphs on the hand-

held device and transfer data to a computer for analysis.

SALINITY MEASUREMENT

What is SALINITY? The measure of all the salts dissolved in water. Measured in parts per thousand (ppt). The average ocean salinity is 35ppt

and the average river water salinity is 0.5ppt or less. This means that in every kilogram (1000 grams) of seawater, 35 grams are salt. Because

the water in estuaries is a mix of fresh water and ocean water, the salinity in most estuaries is less than the open ocean. Bottom water

almost always contains more salt than surface waters. The salt in the ocean is mostly made up of the elements sodium (Na) and chlorine

(Cl). Together they account for 85.7% of the dissolved salt. The other major compon