M172 Expansion Module Calibration

[JeffBiser]

Hello everyone!  We have a project with some existing M172 PLCs that all have a TM172E28R expander module attached.  I've observed that several of the expander's AOs are not quite calibrated correctly.  They characterize nice and linear, but the gain and offset need adjustment (errors of 5-20% at the low end around 2V, much better around 10V).

I would like to calibrate the gain and offset properly with BIOS parameters, as one would with AOs on the main PLC, but I cannot find a way to access those.  Is connecting with a TM171ADMI cable through the Installer interface the only realistic option?  If even that won't work, we can always accomplish it with software scaling, but that's not as nice of a solution.

Thanks!

[FedericoM · Accepted solution]

Hello,

I think what you have seen is due to the load of the actuator you are using.

The configurable AO can work only as source, while in your case it should likely work as sink.

So far this issue has been always solved adding a 1Kohm resistor to the output.

Try and let me know

[JeffBiser]

It looks like that's the case.  Everything looks good in the field on a real system, I was only seeing this effect during bench testing with a multimeter.  Thanks for the sanity check!