transducers and sensors

TRANSDUCERS

Transducers

Transducer is a device that converts energy in one form of energy in another.

In electrical and electronics, transducer converts:First: Electrical energy to non-electrical energy; orSecond: Non-electrical energy to electrical energy

Transducers The second conversion pertains to

device called sensor Non electrical energy is sometimes

called stimulus, and usually in the form of heat, light, sound, displacement etc.

Main functions of transducer is to:SENSE the presence of measurand

Humidity level, Force and load, Color, Amplitude, etc

PROVIDE output for the electrical/ electronic read out.

Classification of Transduceraccording to their electrical operating principle

PASSIVE This transducer requires an

external power, and their output is measure of some variation, such as resistance or capacitance.

SELF-GENERATINGThese transducers do not

require an external power, and they produce electrical output (such as voltage) when triggered by some form of non-electrical energy.

Proximity/Position Sensors Passive type of transducer Usually used to determine when an object has

moved within some particular critical distance of the sensor.

Application: Collision detection Detection of the

presence/absent of an object Metal and Non metal

detection Industrial manufacturing

applications: packaging, parts sorting, etc.

Proximity/Position Sensors Categorized as:

Contact Type*Limit Switch Non-Contact Type*Capacitive Type - ex. Sense the non-metal and metal object* Inductive Type – ex. Metal detection*Optical Type – ex. Collision Avoidance mobile robot

Inductive TransducerAs self-generating type

Utilizes the basic electrical generator principle , that when there is relative motion between a conductor and magnetic field, a voltage is induced in the conductor (generator action)

Example: TACHOMETER A tachometer is an inductive transducer that directly converts speed or velocity into an electrical signal

Piezolectric Transducer A Self generating type transducer Converts Vibration to electrical signal and

vice versa. This device can produce an voltage across

the crystal proportional to the magnitude of the applied pressure (Vibration)

The output is typically on order of 1 to 30mV per gram of acceleration.

The principal disadvantage of this transducer is that voltage will generated only as long the pressure applied to piezoelectric element is changing.

Temperature Transducer Some types are passive and

some are self generating Four Main Categories:

Resistance Temperature Detector (RTD)- Passive type

Thermocouples –Self-generating type Thermistor – passive type Ultrasonic Transducer – passive type

Resistance Temperature Detectors (RTD) It is also called Resistance

Thermometer Used to determine the temperature

by measuring the resistance of pure electrical wire. This wire is referred to as a temperature sensor. If we want to measure temperature with high accuracy, RTD is the only one solution in industries. It has good linear characteristics over a wide range of temperature.

Resistance Temperature Detectors (RTD)

In RTD devices; Copper, Nickel and Platinum are widely used metals. These three metals are having different resistance variations with respective to the temperature variations. That is called resistance-temperature characteristics. Platinum has the temperature range of 650°C, and then the Copper and Nickel have 120°C and 300°C respectively

Thermocouples One of the most commonly used methods of measuring

temperature in science and industry depends on the thermocouple effect.

Usually constructed from two different metals (Thermoelements) that are joined together at the one end, a temperature difference between this end and the other end of the wires produce a voltage between the wires.

Joint junction of the two wires of the thermocouple is called the sensing junction

Thermocouples are made from a number of difference metals or metal alloys covering wide range of temperatures from as low as 270 °C as high as 2700 °C.

SEEbeck effect

Thermocouples The Seebeck effect is a phenomenon in which a

temperature difference between two dissimilar electrical conductors  produces a voltage difference between the two substances. The German physicist Thomas Johann Seebeck discovered (1821) this effect.

Applications:Engineering – to monitor the operating

temperature of electrical and mechanical equipment.

Industrial Process – to monitor the temperatures of liquids and gases in the storage flowing in the pipes and ducts

Medical Works – to measure internal body temperatures.

Thermistors A semiconductor device made by

sintering mixtures metallic oxide such as oxides of manganese, nickel, cobalt, copper, and aluminium.

The device is negative temperature coefficient The resistance decreases as the

temperature rises. The typical sensitivity of thermistor is

approximately 3mV/°C at 200 °C

Photoelectric Transducer Some are passive and some are self generating Three main Categories

Photoemissive – passive typeRadiation Falling on the cathode causes electrons

to be emitted from the cathode surface (i.e LED and LASER).

Photoconductive – passive typeResistance of material is changed when it is

illuminated.

Photovoltaic– self generatingCan generate an output voltage proportional to

the radiation intensity. The photovoltaic cell or solar cell as its

sometimes called, will produce an electrical current when connected to a load. Both silicon (Si) and Selenium (Se) types are known.

Displacement Transducer

Passive type transducer Convert certain movement into some

electrical signal variation. It is concerned with the

measurement of the amount by which some object has been moved

Example: Rotating the control knob of potentiometer, varies equivalent resistance.

Classification ofDisplacement Transducer Reluctance Transducers

Used in AC measuring circuitsSome examples: reluctance

bridge, differential transformer Potentiometric

Used in DC systems Digital Output Transducer

Used when very close accuracy of measurements is required.

Factors in Selecting Transducer Operating Range Sensitivity Frequency Response and Resonant

Frequency Environmental Compatibility Accuracy Usage and Ruggedness Electrical

REVIEW QUESTION:

What do you call the thermocuple junction where the two wires joined ?

Sensing Junction

REVIEW QUESTION:Which of the following sensor has negative temperature coefficient?

(a) Thermistor(b) Photodiode(c) RTD(d) Thermocouple

Thermistor

REVIEW QUESTION:Which of the following is not a

factor in selecting a transducer(a) Operating Range(b) Selectivity(c) Frequency Response and

Resonant frequency(d) Durability Durability

REVIEW QUESTION:These transducers do not require

an external power, and they produce electrical output (such as voltage) when triggered by some form of non-electrical energy.

Self-generating

REVIEW QUESTION:This transducer requires an

external power, and their output is measure of some variation, such as resistance or capacitance

Passive

REVIEW QUESTION:The output voltage of

piezoelectric transducer is typically on the order of ___mV to ___ mV per gram of acceleration.

1mV to 30mV

REVIEW QUESTION:Which of the following

temperature transducer is classified as self generating?

(a) RTD(b) Thermocouples(c) Thermistor(d) Ultrasonic Transducers

Thermocouples

REVIEW QUESTION:A device that responds to a

stimulus such as heat, light, or pressure and generates a signal that can be measured and interpreted

Sensors

REVIEW QUESTION:It is a device that used to

determine the temperature by measuring the resistance of the wire

Resistance Temperature Detector(RTD)

REVIEW QUESTION:An electrical temperature

sensing device which is composed of a pair of different kind of metal wires joined together at the end and the other end produces voltage between the wires.Thermocouple

REVIEW QUESTION:In ____ devices, radiation falling

on a cathode causes the electrons to be emitted from the cathode surface.

Photoemissive

REVIEW QUESTION:In ___ devices, the resistance of

material is changed when it is illuminated.

Photoconductive

REVIEW QUESTION:A ____ is a device, usually

electrical, electronic or electro-mechanical that coverts one type of energy to another for various purposes including measurement or information transfer. Transducer

REVIEW QUESTION:Device that converts changes in

electrical signals into acoustic form.

Loudspeaker or Speaker