Micrologix Analogue Input

forqnc

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Jul 2009
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Elizabeth City
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Hi all,
This is my first time programming an analogue input. I understand how the SCP instruction works, and have set the channel to 4-20mA. Using a meter that gives 4-20mA, when I increase the mA, the PLC maxed out at around 17.12mA.
External Dip switches are set to ON (current), what am I missing to get to the full 20 mA without the PLC hitting 32767. See picture, Input is on I:1.0.

DSCF9698.JPG
 
Hard to troubleshoot from afar. It may help if you can tell us the complete catalog number of your analog card (module) and if you can show us a diagram of how you have the meter connected. What is generating the ma?
 
Hard to troubleshoot from afar. It may help if you can tell us the complete catalog number of your analog card (module) and if you can show us a diagram of how you have the meter connected. What is generating the ma?

Not sure where the complete catalog number is located so see attached pictures. The meter I am using is a Martel Electronics IVC-222HP
https://www.ebay.com/p/Martel-Electronics-Ivc-222hp-Voltage-Current-Calibrator/1583110512?iid=183013047100&chn=ps
Connection is +ve from the meter to IN0+ and -ve from the meter to IN0-, meter connections are the back set for mA output.

have you tried 0-20mA?

If you mean Input Min = 0 and Input Max = 20 in the SCP instruction, then this faults the PLC, due to the input value being higher than the set parameters. I also tried, in the program, to subtract 6300 (start value for 4mA) from the input to see if that would "trick" the PLC to going up to the 32767, but it stopped again at 17mA with a value of 26400.

Have you tried different scaling for the analog channel?
View attachment 48956

Yes, change the scaling and the value stopped at 17400 and 17.14mA. Also tried changing the filter values, still no joy.
Just for troubleshooting I tried the other 3 channels, got the same results.

Attached are 2 pictures when I am online, first is my reading at 4mA from the meter and the second is at 17.15mA when the PLC reaches 32767, maybe I don't understand the SCP instruction.

DSCF9700.jpg 4mA.PNG 17mA.PNG
 
you are not considering 0-3.999 Ma in your scaling but the module still does.

So, if you are only concerned with 4-20 ma then your SCP should then use 6394 as its "zero" point i.e. Input Min = 6394.

FWIW
Scaled Raw is 0-32767 which is kinda awkward to work with but more precise I suppose.
Scaled for PID is, I think, 0-10000 and is simpler to visualize if you want to try that for fun.
 
you are not considering 0-3.999 Ma in your scaling but the module still does.

So, if you are only concerned with 4-20 ma then your SCP should then use 6394 as its "zero" point i.e. Input Min = 6394.

FWIW
Scaled Raw is 0-32767 which is kinda awkward to work with but more precise I suppose.
Scaled for PID is, I think, 0-10000 and is simpler to visualize if you want to try that for fun.

Setting Input min to 6394 only gives me a -ve output for 0-3.99mA, but still with Input max at 32767 it stops at 17.2mA input.
I may have to see if I can find another source for a 4-20mA signal or insert my meter in series to measure the signal.
 
The output you are looking at will only go to 32767 thats the upper limit of the AD conversion in the module

The scaled output is 0-500 and N7:3 should equal 0 at 4ma and 500 at 20ma Thats what SCP does
 
If memory serves me correctly this module has a range of -21 to 21mA but I can not remember the raw values to scale by. Try Input Min at -32767 and input Max at 32767
 
See pdf for your cards raw data format.

Can you post the .rss file (zip it first) or a snap shot of how you have the input module (1762-IF4) configured?

Do you have another meter to verify the accuracy of the ma? (you did say you were going to try that)

Have you tried another channel?
 
Last edited:
See pdf for your cards raw data format.

Can you post the .rss file (zip it first) or a snap shot of how you have the input module (1762-IF4) configured?

Do you have another meter to verify the accuracy of the ma? (you did say you were going to try that)

Have you tried another channel?

Thank you all the replies and feel I owe an apology for wasting your time.
Connected my Fluke meter in series and PLC is doing exactly what it should 32767 at 20mA. The precision voltage/current calibrator, I'm using for my signal, it seems is not so precision. Last calibration 1995 :oops:
Thank you all again.
 
Actually if you have 32767 you would have to have 21 ma or greater.
20 ma should give you 31206 raw data count.

See PDF I posted above for raw data values for your 1762-IF4 analog module.

Thanks for posting to solution.
 
Last edited:

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