7 Difference Between Active And Passive Instruments

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What Are Active Instruments?

Active instruments are the instruments in which the quantity to be measured activates the magnitude of external power input source that produces the measurement. 

An example of an active instrument is a float-type petrol-tank level indicator. In this instrument, the change in petrol level moves a potentiometer arm and the output signal consists of a proportion of the external voltage source applied across the two ends of the potentiometer. The energy in the output signal comes from the external power source; the primary transducer float system is merely modulating the value of the voltage from this external power source.

What You Need To Know About Active Instruments

  1. Active instruments are the instruments in which the quantity to be measured activates the magnitude of external power input source that produces the measurement. 
  2. In the active instruments, the resolution can be adjusted by adjusting the magnitude of the external energy input.
  3. In the active instruments, additional external energy input source is required.
  4. Designing of the active instruments is quite involving (complex).
  5. Due to complexity in design and a higher number of elements, active instruments are costlier when compared to passive instruments.
  6. Active instruments have a high resolution.
  7. Examples of active instruments include liquid level indicator, flow indicator etc.

What Are Passive Instruments?

Passive instruments are instruments where the output is produced completely by the quantity that is measured.

An example of a passive instrument is the pressure measuring device. The pressure of the fluid is translated into movement of a pointer against a scale. The energy expended in moving the pointer is derived entirely from the change in pressure measured; there are no other energy inputs to the system.

What You Need To know About Passive Instruments

  1. Passive instruments are instruments where the output is produced completely by the quantity that is measured.
  2. In the passive instrument, the resolution cannot be easily adjusted.
  3. In passive instrument, additional energy input source not required.
  4. Passive instruments are simple to design.
  5. The passive instruments are cheaper hence economical.
  6. Passive instruments have a relatively lower resolution when compared to active instruments.
  7. Examples of passive instruments are pressure gauge, voltmeter,  Glass thermometer, ammeter etc

Difference Between Active And Passive Instruments

BASIS OF COMPARISON ACTIVE INSTRUMENTS PASSIVE INSTRUMENTS
Description Active instruments are the instruments in which the quantity to be measured activates the magnitude of external power input source that produces the measurement.    Passive instruments are instruments where the output is produced completely by the quantity that is measured.  
Resolution Adjustment In the active instruments, the resolution can be adjusted by adjusting the magnitude of the external energy input.   In the passive instrument, the resolution cannot be easily adjusted.  
Additional Energy In the active instruments, additional external energy input source is required.   In passive instrument, additional energy input source not required.  
Design Designing of the active instruments is quite involving (complex).   Passive instruments are simple to design.  
Cost Due to complexity in design and a higher number of elements, active instruments are costlier when compared to passive instruments.   The passive instruments are cheaper hence economical.  
Resolution They have a high resolution.   They have a relatively lower resolution when compared to active instruments.  
Example  Liquid level indicator, flow indicator etc.   Pressure gauge, voltmeter,  Glass thermometer, ammeter etc