Instrumentation and Control

INSTRUMENTAION& CONTROL (1/4)M.BOKAEIAN

Instrumentation & Control:The art and science of measurement and control of process variables within a production or manufacturing area.Process Variables

PressureTemperatureFlowLevelDensityHumidityForcePHSpeed

PRESSURE

Pressure:Is the ratio of force to the area over which that force is distributed.Type of Pressure Measurement

Absolute Pressure Measurement Gauge Pressure Measurement Differential Pressure Measurement Perfect VacuumAtmospheric PressureGauge PressureAbsolute PressureGauge

Pressure:Sensors of Pressure Measurement

ManometerBourdon TubeBellowsPiezoelectricPiezoresistive (Strain Gauge)CapacitiveUnit Conversion:

Diaphragm

Pressure/Manometric Measurement:Is based on pressure ability to displace a column of a liquid in a manometer (Pressure head calculations)

Pressure/Manometric Measurement:

ManometersFluid

Mercury (Hg)Water (H2O)Application

Higher Density Small ManometersToxic

AvailabilityNon-ToxicLow Density-Accuracy

Blood PressureLung PressureFluid Pressure in PipelineDisadvantages

Low RangeCapillary RiseSlow Response to Pressure FluctuationsMin 15mm diameter

Pressure/Inclined Manometer:For low pressure measurement or high accuracy applications.

Pressure/Bourdon Tube Measurement: Is based on the principle that a flattened tube tends to straighten or regain its circular form in cross-section when pressurized

C-ShapeHelicalSpiralTwistedBourdon Tube Types

Pressure/Bellows: Are elastic vessels that can be compressed when pressure is applied to the outside of the vessel, or extended under vacuum. When the pressure or vacuum is released, the bellows will return to its original shape.

Pressure/Diaphragm:Pressure exerted by the fluid causes elastic deflection of the diaphragm.

Pressure/Piezoelectric:Piezoelectric materials produce electricity charge when exposing to mechanical stress.

Pressure/Piezoelectric:Piezoelectric materials produce electricity charge when exposing to mechanical stress.Advantages

-Very high frequency response and sensitivity.-Self generating, so no need of external source.-Simple to use, small dimensions, large measuring range, low cost.Disadvantages

-It is not suitable for measurement in static condition.-Affected by temperature variation.- Exceptional linearity and repeatability.

Pressure/Piezoelectric:Piezoelectric materials produce electricity charge when exposing to mechanical stress.Applications

- Ultrasonic transmitters and receivers.- Frequency references.(Crystal Oscillators)- Temperature sensors (resonant frequency changes with temperature)- Accelerometers- Microphones and loudspeakers (small loudspeakers with poor audio characteristics =beepers)- Pressure sensor- Force sensor

Pressure/Piezoresistive (Strain Gauge):The resistance of Piezoresistive sensors (either metal or semiconductors types) changes when pressure is applied.

Pressure/Piezoresistive (Strain Gauge):

Pressure/Piezoresistive (Strain Gauge):Advantages

-Bond excellently to most surfaces, Rugged, Small size-High frequency response-High linearity, Low impedanceDisadvantages

-Strain gauge grid expands and contracts at a different rate than the surface it is attached to-Compared to piezoresistive sensors strain gauges have much lower sensitivity- Can be wrapped around curved surfaces unlike the piezoresistorApplications

- Mechanical Engineering- Load cell- Tactile sensors in robots

Pressure/Capacitive:Uses a diaphragm and pressure cavity to create a variable capacitor to detect strain due to applied pressure.

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TEMPERATURE

Temperature:Is a comparative objective measurement of hot and cold.Sensors of Temperature Measurement

Thermocouple (TC)Resistance Temperature Detector (RTD) (TE) Bimetal

Filled Thermal SystemsOpticalUnit From CelsiusTo CelsiusFahrenheit[F]=[C]95+32[C]=([F]32)59Kelvin[K]=[C]+273.15[C]=[K]273.15

ThermistorIC Sensors

Temperature/Thermocouple:Consists of two dissimilar conductors (or semiconductors) that contact each other at one or more spots, where a temperature is experienced. It produces a voltage when the temperature of one of the spots differs from the reference temperature at other parts of the circuit.Thomas Johan SeebeckSeebeck effect:The temperature difference between hot and cold junctions produces an electric potential (voltage) which can drive an electric current in a closed circuit.

Temperature/Thermocouple:

Temperature/Thermocouple:

Temperature/Thermocouple:Advantages

Temperature-Voltage Curve

Self PoweredSimple, RuggedInexpensiveDisadvantagesWide VarietyWide Range

Non LinearLow VoltageReference RequiredLeast StableLeast Sensitive vs. Temperature Change

Temperature/RTD:Are sensors, used to measure temperature by correlating the resistance of the RTD element with temperature. They are typically platinum, copper or nickel.RTD Main Categories

Thin FilmWire-woundCoil Elements

Temperature/RTD:RTD Configurations

Two-wire configurationThree-wire configurationFour-wire configuration

Temperature/RTD:Advantages

High AccuracyHigh LinearityWide Operating Range

Disadvantages

Self HeatingSlow Response Time

Power Source Required

Temperature/Thermistor:A thermistor`s output is based on the resistance change in a metal-oxide semiconductor material as its temperature changes. ThermistorsType

NTC (Negative Temperature Coefficient) PTC (Positive Temperature Coefficient)

Advantages

High output Fast response time Low cost Accurate over small ranges Disadvantages

Non LinearLimited Temperature RangePower Source requiredSelf Heating

Temperature/IC Sensors:The newest type of temperature sensor to be developed is the integrated circuit (IC) temperature transducer. Advantages

Most LinearHigh OutputInexpensive Disadvantages

Temperatures limited to 200 degrees C Power supply required Slow response time Self Heating

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Temperature/Bimetal (Thermostat):Refers to an object that is composed of two separate metals joined together, which converts a temperature change into mechanical displacement.

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Temperature/Bimetal:Refers to an object that is composed of two separate metals joined together, which converts a temperature change into mechanical displacement.

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Temperature/Filled Thermal Systems:Consists of a liquid enclosed in a tube. The volume of the fluid changes as a function of temperature.Advantages

PowerlessNot Hazardous for Explosive AtmosphereStable, High Repeatability Disadvantages

Only VisualLow AccuracySlow response time

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Temperature/Optical Systems:These sensors measure electro magnetic radiations related to temperature.Optical Sensors

Optical pyrometer IR Thermometer

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FLOW

Flow:Is volume/mass of fluid which passes through cross section per unit time.Methods of FlowMeasurement

DP Flowmeters Velocity Flowmeters Mass Flowmeters Positive Displacement Flowmeters

Flow:DP Flowmeters

Orifice Plate Flowmeters Venturi Tube Flowmeters

Flow Nozzle Flowmeters Pitot Tube Flowmeters

Annubar Flowmeters Elbow Flowmeters Bernoulli's Principle: For an inviscid flow of a nonconducting fluid, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid`s potential energy .

Daniel Bernoulli

Flow/Orifice Plate Flowmeters :This sensors measure differential pressure caused by orifice plates. The differential pressure is related directly to flow.Characteristics:- Turn down ratio less than 5:1- Poor accuracy at low flow rates- Accuracy depend on orifice plate shape- Plugging with slurries- High pressure drop- Low cost

Flow/Venturi Tube Flowmeters :This sensors measure differential pressure caused by Venturi Tube. The differential pressure is related directly to flow.Characteristics:Lower pressure drops Higher turn down ratio 10:1 High cost No slurry plugging

Flow/Flow Nozzle Flowmeters :This sensors measure differential pressure caused by flow nozzle. The differential pressure is related directly to flow.Characteristics:- Mostly air and gas flow measurement - Turn down ratio and accuracy like orifice- Intermediate pressure loss- Higher cost than orifice plate - Good for slurry services

Flow/Pitot Tube Flowmeters :This sensors measure differential pressure between stagnation pressure and static pressureCharacteristics:- Low pressure low- Poor performance with slurry services

Flow/Flow Annubar Flowmeters :This sensors measure differential pressure between stagnation pressure and static pressure

Characteristics:-Less pressure drop than orifice plate (1/25)-Less clogging due to fluid flow direction around meterFlow/Elbow Flowmeters :Base on Fluid centrifugal force that is related directly with its speed.

Characteristics:- Low cost- Very poor accuracy- Low pressure loss

Flow:Velocity Flowmeters

Vortex Flowmeters Turbine Flowmeters

Ultrasonic Flowmeters Magnetic Flowmeters Variable Area Flowmeters (Rotameter, Vane-Style)

Flow/Vortex Flowmeters :This measurement involves placing a bluff body (called a shedder bar) in the path of the fluid. As the fluid passes this bar, disturbances in the flow called vortices are created. The frequency at which these vortices alternate sides is essentially proportional to the flow rate of the fluid. a sensor measures the frequency of the vortex shedding. This sensor is often a piezoelectric crystal, which produces a small, but measurable, voltage pulse every time a vortex is created. Since the frequency of such a voltage pulse is also proportional to the fluid velocity, a volumetric flow rate is calculated using the cross sectional area of the flow meter.

Characteristics:- Not affected by pipe vibration, pressure surge, temperature shocks-Low pressure lossHigh accuracy and repeatability

Flow/Vortex Flowmeters :

Flow/Turbine Flowmeters :Turbine flowmeters use the mechanical energy of the fluid to rotate a pinwheel (rotor) in the flow stream. The rotor shaft spins on bearings. When the fluid moves faster, the rotor spins proportionally faster. Shaft rotation can be sensed mechanically or by detecting the movement of the blades. Blade movement is often detected magnetically, with each blade or embedded piece of metal generating a pulse.

Characteristics:Less accurate at low flow rates Not suitable for dirty fluids High repeatability and accuracy Fast response Expensive

Flow/Ultrasonic Flowmeters :Measures the velocity of a fluid with ultrasound to calculate volumetric flow.Using ultrasonic transducer, the flow meter can measure the average velocity along the path of an emitted beam of ultrasound, by averaging the difference in measured transit time between the pulses of ultrasound propagating into and against the direction of the flow or by measuring the frequency shift from the Doppler.

1- Transit time (1~2MHz): Measures the upstream and down stream time Linear, accurate, wide measuring span, high repeatability No pressure drop Low cost

Flow/Ultrasonic Flowmeters :Measures the velocity of a fluid with ultrasound to calculate volumetric flow.Using ultrasonic transducer, the flow meter can measure the average velocity along the path of an emitted beam of ultrasound, by averaging the difference in measured transit time between the pulses of ultrasound propagating into and against the direction of the flow or by measuring the frequency shift from the Doppler.

2- Doppler effect (640kHz~1MHz):Is the change in frequency of a wave for an observer moving relative to its source.

Characteristics:Needs 100 PPM or more particles in fluidParticles must be large enough (>/4) Particle velocity often differs noticeably from the velocity of the liquid.The velocity needs to be far higher than the critical velocity at which particles settle.

Flow/Magnetic Flowmeters : Magnetic flowmeters use Faradays Law of Electromagnetic Induction to determine the flow of liquid in a pipe. In a magnetic flow meter, a magnetic field is generated and channeled into the liquid flowing through the pipe. Following Faradays Law, flow of a conductive liquid through the magnetic field will cause a voltage signal to be sensed by electrodes located on the flow tube walls. When the fluid moves faster, more voltage is generated. Faradays Law states that the voltage generated is proportional to the movement of the flowing liquid. Characteristics:- No Moving Parts- Very Wide Rangeability- Ideal For SlurriesUnobstructed Flow PathLiquid Must Be Conductive

Flow/Variable Area Flowmeters (Rotameter) :Variable area flowmeters measure flow by allowing the flow stream to change the opening within the flow meter by moving an internal part. When the flow increases, the fluid generates more force and moves the internal part farther. Spring-opposed float designs allow this type of flow meter to be installed in horizontal pipes, because the functioning of the float is not dependent upon gravity.

Characteristics: No external power source Not suitable for slurry fluids Not expensive Approximately linear Must always be vertically oriented unless it be a Vane-Style or Piston type

Vane-Style

Flow/Variable Area Flowmeters (Rotameter) :Variable area flowmeters measure flow by allowing the flow stream to change the opening within the flow meter by moving an internal part. When the flow increases, the fluid generates more force and moves the internal part farther. Spring-opposed float designs allow this type of flow meter to be installed in horizontal pipes, because the functioning of the float is not dependent upon gravity. Bypass Design: Rotameters are not generally manufactured in sizes greater than 6 inches /150mm, but bypass designs are sometimes used on very large pipes.

Flow:MassFlowmeters

Coriolis Flowmeters Thermal Flowmeters

Mass Flow Rate (m) : In physics and engineering, mass flow rate is the mass of a substance which passes per unit of time. (Kg/h)

Mass Flow Meters/ Coriolis:

The Coriolis mass flow meter uses a tube that is designed to vibrate up and down due to angular momentom of fluid at its natural frequency while all of the fluid flows through it. A strong magnet is used to make the tube vibrate.

Characteristics: High accuracy and repeatability No obstructions in the fluid path Suitable for applications where temperature and pressures fluctuateSuitable for Custody transfer

Mass Flow Meters/ Coriolis:

The Coriolis mass flow meter uses a tube that is designed to vibrate up and down due to angular momentom of fluid at its natural frequency while all of the fluid flows through it. A strong magnet is used to make the tube vibrate.

Mass Flow Meters/ Coriolis:Coriolis FlowmeterComponents

Drive CoilPick off Sensor

TubeRTDProcessorFlow SplitterCaseProcess Connection

Mass Flow Meters/ Thermal:

Thermal flowmeters use the thermal properties of the fluid to measure the flow of the fluid in a pipe or duct. In a typical thermal flow meter, a measured amount of heat is applied to the heater of the sensor. Some of this heat is lost to the flowing fluid. As flow increases, more heat is lost. The amount of heat lost is sensed using temperature measurements in the sensor.

Characteristics: High accuracy and repeatability No flow rate limitations Excellent turn down ratio, typically 50:1 No moving parts Relatively high initial cost Suitable for applications where temperature and pressures fluctuate

Flow / Positive Displacement Flow Meters:PositiveDisplacement FlowmetersPositive Displacement (PD) Flow meters are volumetric flow measurement instruments that measure flow by passing a precise volume of fluid with each revolution.Characteristics: High accuracy and repeatability No flow rate limitations Not affected by flow viscosity, density and turbulence

Gear Flowmeters Piston Flowmeters

Helical Flowmeters

LEVEL

Level:Refers to instrumentation techniques designed to measure the height of a fluid or solid within a containing vessel.Methods of LevelMeasurement

Manual / MechanicalElectro Mechanical Contacting

Electronic Non-Contacting

Level / Manual or Mechanical Level Measurement:Methods

Float SystemsRod Gauging / Dip Probe / Dip StickSight / Gauge GlassTape Systems

Level / Manual or Mechanical Level Measurement:

LevelGauges

TransparentReflexBi-ColourMagnetic

Level / Electro Mechanical Contacting Level Measurement:Methods

DisplacerMagnetostricitiveServo Operated DisplacerResistance Tape (Metritape)

Archimedes' principle :Archimedes' principle indicates that the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially submerged, is equal to the weight of the fluid that the body displaces.

ConductivityCapacitanceHydrostatic Pressure Level MeterOpticalVibration Fork Level Switch

Level / Displacer Level Meter:

Level / Magnetostricitive Level Meter:

Principle :A low-current interrogation pulse is generated in the transmitter electronics and transmitted down the waveguide creating an electromagnetic field along the length of the waveguide. When this magnetic field interacts with the permanent magnetic field of a magnet mounted inside the float, a torsional strain pulse, or waveguide twist, results. This waveguide twist is detected as a return pulse. The time between the initiation of the interrogation pulse and the detection of the return pulse is used to determine the level measurement with a high degree of accuracy and reliability.

Level / Metritape Level Meter:The outer envelope jacket (1) is compressed by the hydrostatic pressure of the liquid (2). This causes the gold wire winding to contact the gold plated base strip. The resulting change in the resistance of the gold wire (3) indicates the length of active helix and the distance from sensor top to liquid surface.

Level / Servo Operated Displacer Level Meter:

The displacer is suspended from a strong and flexible measuring wire wound on ameasuring drum. A transducer measures the apparent weight of the displacer partlyimmersed in liquid. When the level starts moving downwards, the transducer willsense the change in weight. The servo motor drives the measuring drum to unwindthe measuring wire until the displacer is partly immersed in liquid. When thelevel rises, the servo motor drives the measuring drum to wind up the measuringwire until the displacer is again partly immersed in liquid.

Level / Conductivity Level Meter:

Level / Capacitance Level Meter:

Level / Optical Level Meter:The sensor contains an infrared light emitter or LED, and a photocell receiver. Light is transmitted across a gap to the receiver. As the sensor is lowered into the clarifier sludge blanket, the instrument will indicate a gradual decrease in opacity.

Level / Hydrostatic Pressure Level Meter:

Methods

Differential Pressure MeasurementBubbler Systems

Level / Vibration Fork Level Switch:When the service material covers the tines, they cause damping of the vibrations. This stoppage of vibrations is sensed by the electronic circuitry and the signal after processing is used to operate a relay.

Level / Electronic Non-Contacting Level Measurement:Methods

RadarUltrasonicLoad CellLaser

Radiometric

Level / Radar Level Measurement:

Characteristics: Needs high dielectric constant High accuracy Not affected by ambient conditions Very expensive Restricted pressure rating

Level / Guided Wave Radar Level Measurement:Characteristics: 20 times more efficient than Radar level transmitter due to more focused energy path Can measure level for liquids with dielectric constant less than 1.4

TDR (Time Domain Reflectometry)

Level / Ultrasonic Level Measurement:When ultrasonic pulse signal is targeted towards an object, it is reflected by the object and echo returns to the sender. The time travelled by the ultrasonic pulse is calculated, and the distance of the object is found.

Characteristics: No mechanical movement and no contact High accuracy Affected by air quality and temperature

Level / Laser Level Measurement:Operates on a principle very similar to that of ultrasonic level sensors. Instead of using the speed of sound to find the level, however, they use the speed of light.

Characteristics: No beam spread, can be targeted on a point Good for bulk, slurry and opaque fluidsAccurate even in vapor and foam environments Very Expensive

Level / Load Cell Level Measurement:Is a transducer that is used to create an electrical signal whose magnitude is directly proportional to the force being measured.

Characteristics: Requires support structure Poor turn down ratio Very Expensive

Level / Radiometric Level Measurement:It employs a radioactive source(usually Cesium-137 or Cobalt-60 isotopes) which emits gamma radiation that passes through the walls of the pipe or vessel containing the medium being monitored. A detector is mounted on the opposite side of the container which senses the radiation that is not absorbed by the medium and is directly related to the parameter being measured.Characteristics: No vessel penetration is needed suitable for hazardous and corrosive materials Very Expensive