The major difference between active and passive transducer is that an active transducer has the ability to convert one form of energy into another form (electrical) without using an external source of power. On the contrary, a passive transducer converts a form of energy into another (electrical) by making use of an external source of power.
Active transducers are also known as self-generating transducers while passive transducers are known as externally energized transducers.
We will discuss some other important differences between active and passive transducer but before that have a look at the contents to be discussed under this article.
Content: Active Vs Passive Transducer
|Parameter||Active Transducer||Passive Transducer|
|Operating Principle||Operational energy is derived from quantity being measured.||Operational energy is taken from external power source.|
|Alternatively known as||Self-generating transducer||Externally powered transducer|
|Output generated||Electrical current or voltage.||Variation in quantity associated with passive elements is observed.|
|External energy||Not required||Required|
|Further amplification||Needed||Not needed|
|Example||Piezoelectric crystal, Thermocouple etc.||Potentiometer, Thermistor etc.|
Definition of Active Transducer
An active transducer is a self-generating type transducer that has the ability to generate electrical voltage or current as its output without using any external source of power.
These transducers draw the energy needed for their operation from the measuring system itself. It is noteworthy in case of active transducers that the output produced is very small thus further amplification is required in its case.
The various examples of active transducers are as follows:
- Tachogenerators – These are basically used to measure angular velocity.
- Thermocouples – Temperature measurement is accomplished using thermocouples.
- Piezoelectric crystals – These converts charges generated by application of force into electric potential.
Definition of Passive Transducer
These are externally powered transducers, that induces variation in the parameters associated with the electrical circuits, with the variation in the applied input signal.
Here, energy conversion is established by the use of an auxiliary power source. In these type of transducers, changes in voltage, current or frequency are noticed when electrical parameters such as inductance, capacitance or resistance associated with the circuit changes. A passive transducer sometimes may draw energy from the measuring system itself.
The output of a passive transducer is not that much low which requires further amplification. However, sometimes amplifiers are employed in such transducers also.
The various examples of passive transducers are:
- Potentiometer – It is a device that converts displacement into voltage.
- Thermistor – These produce voltage with change in temperature.
Key Differences Between Active and Passive Transducer
- The key difference between active and passive transducer is that in an active transducer, the energy required for its operation is taken from the quantity that has to be measured. On the other side, in passive transducer energy needed for operation is derived from an external source.
- Active transducers basically produce electrical current or voltage as its output while passive transducers show variation in passive parameters as its output.
- On the basis of their working active transducers are known as self-generating transducers whereas passive transducers are known as externally powered transducers.
- A very low amplitude signal is produced at the output by an active transducer thus requires amplification. As against, high amplitude signal is generated by a passive transducer thus signal amplification is not required.
- The system design of an active transducer is simple whereas passive transducer holds a complex system design.
- Active transducers do not need an external supply of power while the passive transducer requires an external energy source.
A thermocouple is the category of active transducer that is used for temperature measurement. It is one of the simplest and widely used devices for temperature measurement.
It works on the principle of energy conversion. These are basically designed to measure temperature in the form of EMF. Seebeck effect is the basis of working of the thermocouple.
A thermocouple is formed by combining two dissimilar metals in such a way that their ends form 2 junctions after combination. The figure below shows the general arrangement of a thermocouple having two different metals.
Seebeck effect states that when two wires of dissimilar metals form an electric circuit on joining, then current flows through that circuit if there exists a temperature difference between the two junctions. It is to be noted here that no any current will flow through the circuit when the temperature difference of the circuit becomes equal.
Any rapid change is the circuit is efficiently measured by a thermocouple thus it is widely used for temperature measurement.
Thermistor, a semiconductor device is a type of passive transducer in which variation in temperature causes a corresponding change in resistance. Thus, variation in temperature produces an analogue voltage. As these are thermally sensitive resistors thus also termed as thermal resistors.
The figure below shows the rod form of a thermistor
Due to their temperature sensitive nature, thermistors have various applications in temperature measurement field. It can be a positive temperature coefficient thermistor or negative temperature coefficient thermistor depending on the variation of resistance wrt temperature.
An extremely non-linear characteristic is exhibited by the thermistor for resistance versus temperature curve. As it is inexpensive and highly sensitive device thus has numerous applications.
When we talk about transducers, then these are meant to convert a form of energy into other. However, active and passive transducers show a variation on the basis of energy conversion principle. As one does not need external energy while other require a power source of its operation.
Thus due to the variation in their working principle active and passive transducers are termed as self-generating and externally powered transducers respectively.
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