S7 Analogue values not steady

Hi everyone,

This is my first thread after joining here. so not sure about the search option if there is any, I actually preferred to start a new thread on my issue;

The analogue inputs on the OPC Scout (and therefore on the other OPC clinets) does not stay on a steady value whilst the analogue voltage on the input is steady, why that can be?

Sia

The question is, is it really steady? i would say no.

ps. search you can find up and right. please use it always.

I'm not 100% sure as it has been a while, but on the 300 series Siemens analog input cards, we had to jumper the commons to terminal 11 to keep the values steady, and in some cases to make them work at all.

Like I said it has been a while and I can't remember if this was for two or four wire devices.

Hope this helps.

It is called "noise".
With an analog meter, the signal may appear to be steady, but in reality noise enters the signal path in some way.
Grounding one side is quite common.
Shorting unused channels is also quite common.
Also check if the ground is good enough.
Are your analog cables screened ?
Check if the screen is properly connected to ground.
Are there noise-generating equipment such as VFDs nearby ?
Does cables run in parralel with VFD cables ?
Is the main supply noise-free ?
etc etc.

well as far as noise is of concern, I have no VFD around, and even osciliscope does not show such fluctuation, but I take your replies as there is no particular arrangment apart from the standard care, I'll try and see... thanks anyway...

Particular care related commnets would be welcome.

Sia