SIEMENS /WAGO difficulties

[RClem]

I have a peculiar problem with an analog input. First off I'm using a CPU315-2 PN/DP and Wago 750-343 bus couplers via profibus. My analog input is a 750-466 4-20mA single-ended, connected to an IFM PN2021 pressure transducer scaled 0-2700 PSI.
I am also using a Wago 750-554 analog output to a PD6000 display. The problem I have is I am able to input the signal, transfer to a temp variable and then transfer that to the output module. The Display and transducer will read correctly. I also use the temp variable to perform a logic comparison to load/un-load pumps. What I am able to monitor from the input is absolute garbage. Sometimes it will read as a negative integer and/or other random numbers that do not follow a pattern. The odd thing is display will read correctly on the signal pass-thru. I have mocked this system up prior to installation on the bench and simulated the input with a current calibrator and everything worked correctly. Now that the system is installed I have this problem. I have attached the function in PDF form. Thanks for your time.

 

[danw]

My analog input is a 750-466 4-20mA single-ended.

I have mocked this system up prior to installation on the bench and simulated the input with a current calibrator and everything worked correctly. Now that the system is installed I have this problem.

If your programming worked on the bench with a calibrator, which was probably battery powered(?)and 'floating', but you now have a problem with a field connected device to a single ended input, I suspect that you have a ground loop/common mode problem.

Is the IFM a 3 wire device? Is one side of the power supply grounded?

 

[RClem]

The IFM is a three wire device, the problem though is still there even if I connect the calibrator to the input module, and the signal transfers to the output module just fine.

 

[danw]

>simulated the input with a current calibrator and everything worked correctly.

I thought that meant that when the calibrator is connected to the analog input, you could read a correct process value from the input card. Is that the case, or not?

Is the calibrator an electrical calibrator, a 4-20mA signal?

 

[RClem]

It is a 4-20mA calibrator, when connected the PLC does not indicate a correct value, however it passes the signal from the input module to an output module and the process indicator reads correctly. The analog value seen by the PLC is in error, negative integers, random steps high and low between values. I have verified the current input to the module both with the transducer and the calibrator. Both values are appropriate with the system pressure or the calibrator output.

 

[RClem]

Update
I believe the problem resides in the hardware config on my Wago Profibus bus couplers. During a hardware config download the process data representation defaulted to INTEL instead of MOTOROLA, this would reverse the LSB/MSB of the word. I will have to wait until this weekend to upload the new configuration and test the results.

 

[shooter]

the 750-466 can have an output in siemens format but also in simple word format. see datasheet for this on the wago site.
or you have a grounding problem.

 

[RClem]

The problem was in the process data representation, after the change all I needed to do was scale the word to my process.