- Transducer Definition: A transducer is a device that converts physical quantities into proportional electrical signals, which can be used for further control or display.
- Types of Transducers: Transducers vary based on what they measure, their operating principles, and whether they need external power.
- Active Transducers: These transducers do not need external power and work by directly converting physical inputs into electrical signals.
- Passive Transducers: Passive transducers require external power and typically convert physical changes into signals via resistance, capacitance, or other electrical changes.
- Application in Instrumentation: Transducers are crucial in instrumentation systems, which are central to controlling industrial processes by measuring various variables.
What is a Transducer?
An electrical transducer is a device which is capable of converting physical quanties into a proportional electrical quantity such as voltage or electric current. Hence it converts any quantity to be measured into a usable electrical signal. This physical quantity which is to be measured can be pressure, level, temperature, displacement etc. The output which is obtained from the transducer is in the electrical form and is equivalent to the measured quantity. For example, a temperature transducer will convert temperature to an equivalent electrical potential. This output signal can be used to control the physical quantity or display it.
Instrumentation is the heart of industrial applications. Instrumentation is the art and science of measuring and controlling different variables such as flow, level, temperature, angle, displacement etc. A basic instrumentation system consists of various devices. One of these various devices is a transducer. A transducer plays a very important role in any instrumentation system.
Any device that converts one form of energy to another is known as a transducer. For instance, a speaker is a transducer that changes electrical signals into sound waves. An electrical transducer specifically converts physical quantities to electrical signals.
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 that need an external power source are called passive transducers. They generate output signals by changing resistance, capacitance, or another electrical parameter, which is then converted to a current or voltage signal. For example, a photocell (LDR) varies its resistance based on light exposure, and this resistance change is converted to a signal to measure light intensity.
The figure above illustrates a bonded strain gauge, a passive transducer that measures stress or pressure. As the stress varies, the strain gauge flexes, altering the wire’s resistance. This resistance change, corresponding to the stress change, is measured using a bridge circuit to accurately gauge stress levels.
