Digital Panel meters are available in LED or LCD display. LED (Light Emitting Diode) displays are the easiest to see even in small character heights and are available in color. LCD (Liquid Crystal Display) can be either unlighted “transflective” that depends on ambient lighting or Backlighted and can be hard to read at certain angles & lighting. Since Digital Panel meters actually measure voltage in discrete steps, all inputs must be scaled to match the full count range of the meter. A 3 digit Digital Panel Meter has a count range to 0-999 where a 3-1/2 digit doubles the count to 1999 for very little extra electronics. Scaling for the Digital Panel Meters is accomplished by using a Voltage divider usually dividing down the input by a factor of 10, 100, 1000 although there are other factors used.
Most Digital Panel Meters have a basic input based on the max count such as 99.9mV for a 3 digit, 199.9mV for a 3-1/2 digit etc. by using the input voltage divider the meter can be display full scale of 9.99V or 99.9V or more. Accuracy and resolution is dependant on the Analog to Digital Conversion process that controls the minimum voltage difference between the least valued digit. Digital Panel meters used to display current have a fixed resistor called a “Shunt”. The voltage drop developed across this known resistance is then converted and displayed. The Shunt can be either internal or external. AC Digital Panel Meters work much the same way with the exception that the AC voltage is first converted to a DC. Signals from low level sources such as thermocouples and strain guage require a amplifier to bring the input to a readable level. Some uses require meters that are not standard or would have hazardous inputs. In this case we use “Scaling” resistors, voltage dividers, Current Shunts (DC Amps), Current Transformers (“CT” AC Amps) or Potential Transformers (“PT” AC Volts) to set the input to the Digital Panel Meter specifications.