# Active transducers

**URL:** <https://forumautomation.com/t/active-transducers/4938>\
**Category:** Field Instrumentation\
**Created:** [October 16, 2018, 3:58am UTC](https://forumautomation.com/t/active-transducers/4938 "2018-10-16T03:58:36Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![divyasree](https://forumautomation.com/letter_avatar_proxy/v4/letter/d/edb3f5/32.png) [@divyasree](https://forumautomation.com/u/divyasree)\
**Post date:** [October 16, 2018, 3:58am UTC](https://forumautomation.com/t/active-transducers/4938/1 "2018-10-16T03:58:36Z")

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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

## Photovoltaic

**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.

## Comaprison

| 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 |