Active transducers


Active transducers are self generating transducers taht do not require external power source to work. They are of four types.

Thermocouple & thermopile

Principle: An emf is generated across the junction of two dissimilar materials ( metals or semiconductors) when that junction is heated.
Application : Temperature,heat flow, radiation

Moving coil generator

Principle: Coil moving in a magnetic field generates voltage
Application : Velocity, vibration

Piezoelectric pickup

Principle: External force acting on certain crystals called piezoelectric crystals (Eg. Quartz) can generate a emf .
Application: Pressure change, Sound, vibration, acceleration


Principle: Incident light stimulates semiconducting materials, constituting a cell, to generate voltage across their junctions.
Application : Solar cell, light meter.

Disadvantages of active transducers

Rather than being disadvantage, these are the differences in active and passive transducers in terms of output, that can be exploited for a completely different set of applications.

  1. Low Resolution,
  2. Low output amplitude.

Mostly used in devices that use very low voltages, read microelectronics, for working.


Active Transducers Passive transducers
Do not require external power supply Requires an external power supply
Compact systems Bulkier to accommodate the power supply
Outputs are current or voltage generated proportional to the input Physical inputs are mostly converted to resistance, capacitance or inductance.
The signal conversion is simple as output is directly measurable Complex signal conversion as additional conversions are needed for measurable voltage or current
Simple design Complex design
Resolution is less, A large input is to be measured for very less change in output High resolution, slight change in input is translated to the output
Feeble output would need amplification Amplification is not always necessary

Resistance Thermometer (RTD), types, materials and characteristics and calibration
Principles and applications of Thermo electric effect