How to use a digital panel meter

Digital panel meter or DPM

 

Anoying properties of DPM

  • Using multiple DPMs requires multiple power supplies
    • This is not entirely true.  If you are measuring voltages close to the same values it is ok. All the measured signal must be within the same range
      • Vsupply_positive - 1 > Vinputs > Vsupply_negative +1
  • Measured voltage must be isolated from supply power
    • Again not entirely true.  Voltage inputs must be between
      • Vsupply_positive - 1 > Vinputs > Vsupply_negative +1
  • Needed scaling resistors values are usualy non-standard values
    • i.e. for a measuring 200V signal you need a 9.99MΩ and 10kΩ
    • using a potentiometer or trimmer solves this
  • Can't display full value when signal is less than 19mV
    • i.e. 1.234mV displays as 1mV
    • Can be solved using op-amp (see below

Using an op-amp

Benifits

  • Filtering noise
  • Can be used to measure signals lower than DPM can measure alown (i.e. a 1.234mV signal can be displayed as 1234V, 123.4V, 12.34, 1.234, instead of 0001, 000.1, 00.01, 000.1)
  • Can adjust signals reference