Reading 4-20mA on Micrologix 1000 Analog

Hello all. I have a problem trying to read 4-20mA into a Micrologix 1000 Analog PLC. Not sure if my issue is with wiring, or an option within the PLC, or even the PLC itself.

I scoured the message boards and found a wiring schematic for creating 4-20mA using a potentiometer.

One leg of the Pot wired in series to 950ohm resistors.
Wiper of the pot wired in to the IA/2(I+).
Last leg of the pot wired to the 0VDC bus. IA(I-) wired to the 0VDC bus.

24VDC -----(950ohm)---+
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|
(5k pot)-------- to PLC input IA/2(I+)
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0VDC -----------------+------------ to PLC input IA(I-)

When I check my circuit with a meter, I am able to read 4-20mA fine, but when I connect to the PLC and check my inputs with RsLogix (in online mode), I:0.6 just seems to flipflop between 0 and 1, and doesn't seem to change no matter what direction I rotate the pot knob.

I've checked the IO Configuration>IO Setup>Input Enables and made sure that Input #2 is turned on. So not quite sure what else I can do to read the signal into the PLC.

Any suggestions are appreciated.

Thank you and blessings!
Mark.

Doesn't seem the drawing came out the way I'd hoped. So to clarify the 950ohm resistors are in series with the pot. Just a clarification.

Thank you.

Can you provide the complete catalog number of your ML1000, please?

And post your program if you can. It's .rss file, zip it first.

1761-l20bwa-5a

What you're describing is an ordinary voltage divider; you should set this up as a Voltage input.

Use a 7K resistor instead of the 950 ohm resistor, and you'll get a voltage input to the MicroLogix between 10 and 0 volts.

Sorry Mickey, I missed the last part of your post. I don't have a program yet for doing anything with the signal, I'm just looking at the input status on the data files.

In the process of learning how to read a 4-20mA signal so I can actually implement something using it. But having trouble reading that signal on the PLC.

Without a PLC and using a meter, I can read 4-20mA just fine, but not getting anything on either current analog channel which makes me wonder what I may have missed. Maybe an option in some screen somewhere.

Thanks guys!

Check to see if the channels are enabled. See picture.

Don't discount Ken's post. Do you see 4-20ma when connected to the PLC? The internal (load) resistance of the input card will change your voltage divider circuit.

The internal input impedance of the ML1K is 260ohms, so I've factored that in. With the pot cranked to full resistance i get 4mA, and to the least resistance I read 19.8mA. Verified with a meter.

I have checked the input enables all on, all off except input used, and still the result is the same.

I cannot read any change to the input when online. Changing the radix from binary to decimal result is the same. So still scratching my head at what I'm missing.