Allen Bradley Analog Module problem

Hey guys!!!

Im building a pressure chamber with automatic control. Im using a Micrologix 1100 with a 1762-IF2OF2 analog module to control 2 proportional valves that have a command signal of 4-20mA.

I have configured my PLC and my module to recieve a 0-10V analog signal from a pressure transmitter and control the valves through a PID instruction.

The problem im dealing with is the current signal. When the output value is 0 the reading i have is 0 mA instead of 4 mA. I have tested increasing the value from 0 and 16383 (Scaled value for PID) and the current output goes from 0 to 20 mA.

The module is working properly and I have to scale the value myself?? Or I have missed a configuration to make this module function form 4 to 20mA

Thanks very much for the help!!!

Welcome to the forum.

Scale your output to operate from 3277 to 16383. You can do this with the SCP instruction. Set the SCP instruction input min at 0% command and input max at 100% command and make output min 3277 and output max 16383.

Don't send the PID CV directly to the analog output, send it to an intermediate register and use that address as the source for the SCP instruction that writes to the analog output.

I believe you will find the data format closer to the values below. Try them a see for your self. Using the SCP instruction as described by TConnolly above.

Thank you very much for your help.

I thought there would be a configuration option for making the output go from 4 to 20mA.

Well I will scale the value before sending it to the output as you recommend.

Thanks again!!

PLC.EC said:

Thank you very much for your help.

I thought there would be a configuration option for making the output go from 4 to 20mA.

Well I will scale the value before sending it to the output as you recommend.

Thanks again!!

Click to expand...

Let us know how it works out. I am not 100% sure about the data format I provided.

Final Results

Good morning my friends

I used the SCP instruction to scale my PID output value. I also did several tests to determine the exact resgister values to get the 4-20mA current output of my 1762-IF2OF2. The final results are the following:

0 ----------- 0mA
3070 --------- 4mA
15630--------- 20mA
16383--------- 21mA

Hope this helps anyone using this module.

Thanks for the help again!

Thanks for the info. That's very close the the published data format.