Types of Transducer

There are of many different types of transducer, they can be classified based on various criteria as:

Types of Transducer based on Quantity to be Measured

• Temperature transducers (e.g. a thermocouple)
• Pressure transducers (e.g. a diaphragm)
• Displacement transducers (e.g. LVDT)
• Oscillator transducer
• Flow transducers
• Inductive Transducer

Types of Transducer based on the Principle of Operation

• Photovoltaic (e.g. a solar cell)
• Piezoelectric transducer
• Chemical
• Mutual induction
• Electromagnetic
• Hall effect
• Photoconductors

Types of Transducer based on Whether an External Power Source is required or not

Active Transducer

Active transducers are those which do not require any power source for their operation. They work on the energy conversion principle. They produce an electrical signal proportional to the input (physical quantity). For example, a thermocouple is an active transducer.

Passive Transducers

Transducers which require an external power source for their operation is called as a passive transducer. They produce an output signal in the form of some variation in resistance, capacitance or any other electrical parameter, which than has to be converted to an equivalent current or voltage signal. For example, a photocell (LDR) is a passive transducer which will vary the resistance of the cell when light falls on it. This change in resistance is converted to proportional signal with the help of a bridge circuit. Hence a photocell can be used to measure the intensity of light.

Above shown is a figure of a bonded strain gauge which is a passive transducer used to measure stress or pressure. As the stress on the strain gauge increases or decreases the strain gauge bends or compresses causing the resistance of the wire bonded on it to increase or decrease. The change in resistance which is equivalent to the change in stress is measured with the help of a bridge. Hence stress is measured.