CIE A Level Physics (9702) 2019-2021

Revision Notes

24.2.1 Digital and Analogue Meters

Output Devices

  • An op-amp circuit creates a constant gain or amplification in voltage or current
  • An output device may be required to monitor the output of an op-amp circuit

 

  • Examples of these are:
    • Transducers (a device that changes energy from one form to another)
    • A diode
    • A microphone
    • A loudspeaker
    • Digital meter (eg. voltmeter)
    • Analogue meter

Calibration of Digital and Analogue Meters

  • When digital or analogue meters are used as output devices for measuring the output of an op-amp (eg. voltmeters), calibration may be needed
    • This is because the output voltage of an op-amp is unlikely to be exactly proportional to the physical quantity being measured eg. temperature
  • With a digital voltmeter, calibration for temperature is done by placing the temperature sensor and a thermometer in a water bath at a number of different temperatures
  • A calibration curve is then used to change any voltmeter reading into a value for the physical quantity being measured (ie. temperature)
  • Therefore, a scale can be obtained
    • For example, an increase of 2 V = increase of 0.5 oC
  • Calibration curves are often used to convert measurements made on one measurement scale to another measurement scale
  • With an analogue voltmeter, calibration is done in the same way except the result will cause a change in the linearity (linear proportionality) of the scale

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