OT: Signal Conditioner 4-20mA to 0-20mA

Hey folks,

I have a situation where I need to connect a 4-20mA transmitter to an AI card that only does 0-20mA. On top of that it only has 8 bit resolution (256 states). So if I change scaling to handle the 4-20 signal, I loose too much resoultion.

Automation direct has a Signal Conditioner that appears to maybe work, has anyone used the FC-33? Can it change a 4-20 to a 0-20?

I have standardized on using PR Electronics 4114 and 4116 Universal Transmitters.


The cost can't be beat for the functionality. They take mV, VDC, mA, thermocouple, RTD, and potentiometer inputs and give a lot of output options. Also the scaling can be done in the signal conditioner - I have one set to voltage reading (half) the voltage of my solar batteries, but displaying the actual voltage and the 4-20mA output is ranged to 4mA = 9.5V, 20mA = 16V.


The 4116 has an internal relay that can be set to trip at high, low, or midrange.

Note that 1 part out of 201 (256*0.8) is ±0.49%. 1 part out of 256 = ±0.39% Based on the resolution and accuracy of the transmitter you should ask yourself if that difference is worth the cost.

If you look at the specs on the FC-33 it says "Field configurable input and output ranges of 0-5V, 0-10 V, 0-20 mA and 4-20 mA"

There is not much you can do about the resolution it is what it is unless you change the AI Card.
Just remember that is 8 bits for the full scale of 0 to 20ms. If the input signal is 4 – 20 ma you will definitely lose about 20% of the range. Can you work with the 8 bit resolution if ot then you will have to change the card.
I prefer to use a 0-20ma AI even when I have a 4-20ma signal I just scale it to -20% of the full range.
Some 4-20ma AI cards will read any signal below 4 ma as 0 (Zero) the same value as if it were reading 4 ma
With using the 0-20ma input scaled for -20% range should the signal be lost completely it will be read as a negative number and I can alarm on that, and the control will work accordingly usually shutting everything off.

This signal conditioner may work. I like these due to the amount of I/O they support. Plus supporting both 115/240VAC or 19-30VDC for power. Very universal.
https://www.automationdirect.com/adc/shopping/catalog/process_control_-a-_measurement/signal_conditioners/universal_input/scu-8400