Definition and General Concept of Transducer

Definition

The transducer is a device which converts one form of energy into another form. Examples: Mechanical transducer and Electrical transducer

Electrical Transducer: A device which converts a physical quantity into the proportional electrical signal is called electrical transducer.

Advantages of Electrical Transducer:

• Electrical output can be amplified to any desired level
• Low power requirement
• Easy transmission
• Suitable with digital control
• Low cost
• Small size
• Reduced friction effect
• The output can be modified as per requirements of the indicating or controlling equipments

Characteristics of Transducer: 

• High accuracy
• Rugged
• High output
• High stability and reliability
• High sensitivity 
• Small size
• Fast speed of response
• Dynamic range
• Possess repeatability

Selection factor of Transducers: 

• Nature of measurement
• Range
• Loading effect
• Environmental considerations
• Measuring system compatibility
• Cost and availability
• Errors
• Calibration

Classification of Transducers

The following is the basic classification of the transducers. The figure 5.1 shows the

classification of transducers.

Active Transducer

• The transducers, which develop their output in form of electrical voltage or current without any auxiliary source are known as active transducers.

• They draw energy from the system under measurement.

• They give very small output and use of amplifier is essential.

• Examples: Tachogenerator, Thermocouple, Piezo-electric crystals, photovoltaic cell etc.

• The transducers in which, the electrical parameters i.e. resistance, inductance and capacitance changes with change in input signal. 

• They require external power source for energy conversion.

• In this, electrical parameters causes a change in voltage, current or frequency of the external power source.

• They may draw some energy from the system under measurement.

• Examples: Resistive, Inductive and Capacitive transducers

• Analog transducer converts input signal into output signal, which is a continuous function of time.

• Examples: Thermistor, Strain gauge, LVDT, Thermocouple

• Digital transducer converts input signal into output signal of the form of pulses e.g. it gives discrete output.

• These transducers are becoming more popular.

• Sometimes, analog transducer combined with ADC (Analog-to-Digital Converter) is called digital transducer.

• Examples: Encoders, Hall effect sensors

• When input signal is directly sensed by transducer and physical phenomenon is converted into electrical form directly then such transducer called primary transducer.

• Examples: Thermistor

• When input signal is directly sensed first by some sensor and then its output being of some form other than input signal I given as input to a transducer for conversion into electrical form, then it’s called secondary transducer.

• Examples: LVDT for used pressure measurement by using bourdon tube 

• It is a device that converts a non-electrical quantity into an electrical quantity.

• Examples: Thermocouple, Pressure gauge, Strain gauge, Photovoltaic cell

• It is a device that converts an electrical quantity into non-electrical quantity.

• It is a precision actuator having an electrical input and low-power non-electrical output.

• A most useful application of inverse transducer is in feedback measurement systems.

• Examples: Piezo-electric crystal

• A device which converts linear or angular motion into electrical output signal is known as displacement transducer.

• Examples: LVDT, RVDT, Gyroscope

• A device which converts pressure or force into electrical output signal is known as pressure or force transducer.

• Examples: Strain gauge, Piezo-electric transducer, Bourdon tube transducer

• A device which converts transducer into electrical output signal is known as pressure or force transducer.

• Examples: Thermocouple, Thermistor, RTD

• A device which converts flow into electrical output signal is known as pressure or force transducer.

• Examples: Ultrasonic flowmeter, Hotwire anemometer

• A transducer which works on the resistive principle is known as resistive transducer.

• Examples: Potentiometer, Strain gauge, RTD, Thermistor, Hotwire anemometer

• A transducer which works on the inductive principle is known as resistive transducer.

• Examples: LVDT, RVDT, Synchro

• A transducer which works on the capacitive principle is known as resistive transducer.

• Examples: Capacitor microphone