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
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.
- Low Resolution,
- 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|