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Problem vvith PT100 measuring.

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Greeatings . 

I have one problem vvith measuring temperature vvith pt100.

I use v1210 and expansion module pt400 , i have pt 100 vvith tvvo pt100 , problem is vvhen i start my inverter temperature value get some crazy value not good , vvhen motor is off 

temperature is ok .

Have someone this problem on this module ?


Thank you

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  • MVP 2023

You are describing a classic case of interference from the inverter.  Inverters need to be installed very carefully with regards to the interference they create.

  • Physically and Electrically Isolated as much as possible from the PLC, even to the point of being in their own enclosure etc;
  • All control lines done exactly as specified to minimise interference, generally as very well shielded;
  • The motor they are driving having the same things in place to limit interference; often shielded lines and reactors.
  • The machine the motor is in is all earthed very well to the PLC earth.  0 volts need to be well commoned.

The list is sort of endless on solving this type of issue.  One odd thing I have seen that is sometimes beneficial is if the inverter is 3 phase supply, find what phase it's control circuit  is on, and ensure that the plc is on the same one. (edit...by changing input lines on the inverter around as necessary)   Although this isn't meant to make a difference, I've found that sometimes it does.....I think it really relates to how well made the inverter is in the first place. This is one area where cheaper is often more expensive in the long run.

No doubt others will chime in soon with further thoughts and specifics.

cheers, Aus

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OK, some things that I have ran into, oh the fun of phantom currents!

- Are you using the correct type of extension wire?
- Do you have it in a tray with motor wires?
     -If so, is it separated by a metal divider?
     -Did you coil up excess wire anywhere near a motor wire in the tray?
 -Do you have it going in a standard din connector?
- Did you have an exorcism to drive away spirits? Sacrificing a goat is frowned upon in this society, bummer) 
-Do you power your DC rectifiers through a transformer and not off of a phase?
- Sometimes if I am still having issues we run all out motor wires in BX (this we actually do this all the time now on long runs)
- is only one side of the wire grounded?

Just some random thoughts


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  • MVP 2023
7 hours ago, viscoelastic said:

Sacrificing a goat

Very funny Visco!   🤣  

Seriously, that's how it is sometimes....magical gremlins. 

I have attached a link to another issue that sometimes arises that is also important, that of bearing failure.  Inverters are capable of doing vaguely similar sort of damage you do if you arc weld using the bearing as part of the circuit.  (I have often seen qualified welders put an earth clamp on a hub and then weld on something on the chassis/main frame!  "That hub's the easiest connection point!")  Page 19 gets into the solutions summary, if you can't be bothered reading it all.  Which you should.

cheers, Aus


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