Measuring a 4-20ma Input With a Voltage Input Device
we will assume that a 0-10Vdc input will be used to measure 4-20ma signal.
Ohms law states: R=V/I where V is the Voltage, I is the current and R is the resistance
R=10V/.020A = 500 Ohms
When 20ma flows through a 500 Ohm resistor, it will drop 10 volts
When 4ma flows through a 500 Ohm resistor, it will drop 2 volts
Therefore, 4-20ma signal through a 500 ohm resister will drop 2 to 10 volts
PLC
if you’re using instrument with 4-20mA and connect it to:
1. range 0-20mA – your value of the instrument will be from that 5529 to 27648, value from 0 to cca 5500 will be not showed, but it depends on instrument.
2. range 4-20mA – your value of instrument will be from 0 to 27648.
References
https://www.omega.co.uk/techref/das/4-20ma.html
https://support.industry.siemens.com/tf/WW/en/posts/analog-input-evaluation/146749?page=0&pageSize=10
https://www.omega.com/en-us/resources/data-acquisition-measuring-420-input-with-voltage-device
