I'm experiencing an obvious linear correlation between "battery voltage" and outputted pH measurements. The measurements are conducted with a two wire current transmitter (+power), (-current signal) and (shield). To convert outputted current (4-20 mA) to a voltage I have installed the 100ohm resistor CURS100 over "H" and "L" on the CR1000. I'll try to explain my wiring ""=CR1000 ()=current transmitter
"H";Curs100H;(-current signal)
"L";Curs100L;"G"
"AG";Curs100G
"12V";(+power)
"G";(Shield) and Curs100L
What can I do to get a stable reading?
Best regards from Karl Martin
That should work OK but there are a number of possible problems you can run into:
1) check the minimum supply voltage for the transmitter. It would need to be more than 9.5 V for your configuration. (=12V - 2.5 V, the latter being the voltage drop across the 100 ohm resistor at 20 mA.)
2) try increasing the settling time and/or the intergration time in the voltage measurement instruction in the logger. It is possible the signal is a little noisy and the logger can see this whilst many slow meters/displays will not.
3) check the shield is isolated from the power supply in the transmitter otherwise the connection might have created a ground loop.