3 wire PT100 sensor connected to 4x AI RTD 1231 module

Hi. I'm really new to PLCs world and I'm trying to setup a PT100 3-wire sensor with my s7 1200 + sm 1231 x4 ai rtd module.

So far, I could connect the module to the cpu, but I can't figure out how to wire the pt100 sensor as I tried with channel 0, but all I get is a flashing red led. In the buffer log it says "broken wire" (it says in spanish "rotura de hilo", so that's my translation).

Any idea on how can I continue with this issue? I have no specs on the pt100 sensor wires to knkow which one needs to be connected where. Only 2 red wires and 1 white.

Thanks for any help! 

Hello petho;

And welcome to our forum.

First off, 3-wire connections for your RTD moduele can be found in this document, see the attachment below.:

https://public.eandm.com/Public_Docs/S71200_SM_1231_RTD_Product_info_en-US_en-US.pdf

Second point, there are many, many technical articles on the web that can help you sort out how the 3 wires need to be connected to the analog input card. For example:

https://instrumentationtools.com/difference-between-2-3-and-4-wire-rtds/

Hope this helps,

Daniel Chartier

Hi dchartier, thank you for your reply!

Yes, I've seen lot of documents even the ones you sent me, and I was missing a bridge wire between L+ and M+, that makes the "broken wire" error dissapear, but I get now a "lower limit overflow" which I suspect it's coming from the wrong wiring, as I couldn't find how to determine which wire goes into each terminal.

Edit: I've just switched colors and it's working now, thank you Daniel!