SAP PCo 15.4 Listening Problems

[neha1609]

Hi Experts,

I am observing some issues with the listening capabilities of PCo. It does seem to be ignoring the changes in the tag values once in a while. I understand If the data at the device changes faster than either the OPC update, or the PCo update, those changes will not be detected and this can be cause of issue.

Anyone else noticed the same and able to resolve issue with some settings? It tried changing value of below parameter and it worked few times but not always.

I am using PCo 15.4.

Thanks,

Neha

[Kevin_Hunter]

Hi Neha,

You are correct, the most common cause of this issue is the sample rate. I typically quote Nyquist-Shannon sampling theorem (look it up on Wikipedia as I cant add the URL here !) . For a digital signal the crazy math can be simplified by saying that your sample rate has to be a minimum of twice the frequency of your data if the duty cycle is 50%. If the duty cycle isnt 50% then you have to be careful of the pulse width, for example a signal may switch from low to high every 1 second and you might think the frequency needs to be 500ms, but if the pulse width is only 100ms then the sample rate should 50ms. For analogue signals its much much higher.

Also remember that this sample rate also applies to any 3rd party tools that you are using to convert the machine data into OPC (eg if you are using Kepware etc)

Is it a digital signal you are monitoring? If so do you know the frequency, duty cycle and pulse width?

Hope this helps and sorry i missed your skype.

Kevin

[neha1609]

Hi Kevin,

Thanks for reply.

PCo is getting signals from equipment according to event triggers. Even though I reduced scan rate to low, we are missing signals. Is there any other setting with which scan rate can be reduced further? Maybe I'm missing something.

Thanks,

Neha