Analogue Value Fluctuations RTD.

Dear Experts,

In the plant I am working is having S7-400H(6ES7417-4HT14-0AB0) system for conveyor applications. 

Here with this PLC we are having 2 Nos of RIO panel with IM153-2(6ES7153-2BA02-0XB0).

In both this RIO panel we have 2 Nos of Analog RTD(6ES7 331-1KF02-0AB0) modules each.

now all this RTD modules are taking Motor bearing and winding temperature,it was running perfectly and showing proper values since almost 6 years.

However from last 1 month value of RIO1 RTD is getting fluctuated when we start the conveyor.

When check we found that, when we remove the RTD connection from module and check the resistance value of RTD  in running condition, it dose not fluctuate,but when we connect with our module it starts getting fluctuated.

So we have interchange the modules of RIO1 and RIO2 but problem was not swapped it stayed with RIO1 only.

Also the programming of this AI is in locked block with simulation function,one of my technician suggested to check the programming,can this be a programming issue??

If this is earthing/shielding issue then it should also fluctuate when i have removed the RTD cable from module, but it is not.

so where should i look.

kindly guide.

Hi hsnaik,

Connect the new RTD to RIO1 module & test. Try to test in ideal conditions like free from harmonics, steady temperature etc.