The transducer is devices comprises of the circuit which converts input energy to particular output energy. The physical quantities (output) are represented in terms of electrical quantities such as voltage and current. The mechanical stimuli (input) can be pressure, temperature, displacement, distance extra. Various sensing devices such as loudspeakers, microphones, and like a pressure transducer that will convert pressure measured into an equivalent electrical quantity or a speaker that can convert electrical signals into sound are simple examples of transducers. The output which is produced is not restricted only to electrical current or voltage; it can be pneumatic or hydraulic output.
Sensors are also a transducer but the difference is that the sensor senses the physical changes whereas transducer converts the physical quantity or nonelectrical quantity into electrical signals.
There are various kinds of transducers and are classified as follows:
Active electrical transducer and passive electrical transducer
• An active transducer is that which generates voltage and current directly as output. The thermocouple is an example of the active transducer.
• The passive electrical transducers produce a change in electrical quantity in passive elements such as resistance, capacitance, and inductance.
The quantity that they measure and on the principle of operation
• Temperature transducers:
Temperature transducers convert thermal or heat into mechanical energy or into electrical equivalents. They are used to measure heat flow and temperature.
There are two types of temperature transducers:
Contact temperature sensor
Non- contact temperature sensor
Contact temperature sensor:
The device is directly in contact with the thermal source and by the process of conduction, the thermal energy is transferred.
Non- contact temperature sensor:
As the name suggests in these device’s sensing element is not in direct contact with the thermal source and they follow the process of convection for thermal energy flow.
Thermocouples are an example of active temperature transducers with two metal junctions, in which one junction is kept at constant temperature and is called a reference junction and the other is varying temperature junction called measuring junction.
The dissimilarity between the temperatures develops a voltage across the junction which is used for measuring temperature. These are linear temperature transducers and their operating range is 0 to 200 degrees Celsius.
The accuracy is less in these temperature transducers, so for high accuracy and precision, we choose thermistors.
The thermistor stands for thermal resistor which is made of semiconductors. Due to their high sensitivity, its resistance changes as the temperature changes and is widely used. They have a negative temperature coefficient meaning as temperature increases resistance decreases. The range of temperature varies from -60 degrees to 15 degrees.
• Pressure transducers:
Pressure transducers are devices that convert pressure which is applied to electrical stimuli. The most commonly used pressure transducer is a strain-gage based transducer. The pressure is converted into electrical pulses and signal by the physical deformation of strain gage which is bounded into the diaphragm (force collector) of the transducer and wired into a Wheatstone bridge configuration.
There are various types of pressure transducer such as absolute pressure sensor, gauge pressure sensor, vacuum pressure sensor, differential pressure sensor, and sealed pressure sensor.
There are different type of sensing technology which are used for selection and designing, the first one is force collector type: this type uses various type of force collector for measuring strain. Examples of force collectors are diaphragm, piston, bellow extra. The other type uses other parameters such as density to infer the pressure of gases or liquids.
• Displacement transducers:
This type of transducers is used for converting linear motion into an electrical signal, these transducers intend to convert the motion of an object into signals (example: electromagnetic, magnetoelectric or electrostatic signals). Linear variable displacement transducer is an example of displacement transducers.
Types of displacement transducer:
Linear potentiometer measures linear motion. The capacitive sensor used for measuring movement, pressure and other parameters, it is a passive transducer.
Displacement transducer finds its application in various industries such as machine automation, aircraft and aerospace, turbines and in hydraulics.
Designing drones, missiles and space vehicles involve the use of displacement transducers.
• Oscillator transducers:
Oscillator transducers used for measure force, pressure, distance and convert it into electromagnetic, magnetoelectric or electrostatic signals. Oscillator transducers have four parts:
Mechanical linkage provides a link between input and transducer, oscillators consist of an LC circuit and are used for generating frequency. The output of the oscillator is given to the modulator that is frequency modulator, the force summer is used for transferring pressure to mechanical linkage. The advantage of using this oscillator is that it measures both dynamic and static phenomena but its thermal stability is very less with less precession and accuracy.
• A photovoltaic cell or solar cell:
A photovoltaic cell or solar cell is used to convert light energy into electrical energy. It can conventionally understand as basic p-n junction diode but in this layer of semiconductors are employed. A layer of p-type semiconductor is attached with n-type semiconductor;
electrical contacts are created on p-type semiconductor side and photons of light fall on the n-type semiconductor. The P-n junction is created between a p-type semiconductor and n-type semiconductor. Silicon, GaAs, CdTe are used for making solar cells. The advantage of using solar cells is that it is environment-friendly, causes no pollution and no maintenance cost but the installation cost is high, you cannot use it on a cloudy day or rainy day which makes it less efficient.
• Piezoelectric transducers:
This type of transducer uses a piezoelectric effect for measuring the change in pressure, temperature, force extra and convert it into electrical stimuli or charges. Piezoelectric materials are that material which produces voltage difference when you press them. These are used in microphones, automobiles, in kitchen lighter and in various medical applications. Example of piezoelectric material used for designing transducer is barium titanate, lead zirconate titanate, and Rochelle salt. The disadvantage of using piezoelectric transducers is that it is not good for measuring static conditions, it is highly affected by temperature variation, the output is low and to give the desired shape to the material used is very difficult.