Hello all! :)

I have a question about the limits of a tag: in the online help page, it sais that 'if a process value exceeds the upper limit value, WinCC grays out the value and does not process it any more'. What does this mean exactly? I don't understand what the process implies when a tag exceeds its limits...

Thanks in advance! :)

Hello ToVerm;

For WinCC Process Tags (external tags linked to a PLC register value) you can define Hi- and Lo-limit values as part of the tag properties. These limits should be related to the process instrumentation, for example.

Take as an example a pump, controlled through a WinCC screen, that you choose to run a frequencies between 20 and 50 Hz (for adequate control of the process). Say the operator tries to enter 10 Hz as a setpoint by mistake, and you have set a Lo-limit of 20 Hz on the specific process tag controlling the pump frequency. The setpoint would not be accepted (and not be processed), the input field would turn grey until you write a new setpoint above the Lo-limit of the tag.

See the attached extract from the Working with WinCC v7.3 manual, below.

https://support.industry.siemens.com/cs/ww/en/view/102754925

Hope this helps,

Daniel Chartier

Okay, thanks for the answer.

What happens when you set a limit value for the pressure on a piston, and it exceeds it's limits? I.e. the under limit is 2 bar, and it got to 1.5 bar (because for example a pneumatic hoze sin't connected good). What does happen then?

Hello ToVerm;

It seems I am not the only one scratching my head on this issue.

I have only used the Limit property of tags in such a fashion as I described earlier.

It might be that if the process value exceeds a parametrized limit, the tag becomes unreachable. But that wouldn't really help you out in your process information. This would be a case for an analog alarm, linked with alarm messages, to warn operators and log the time of the limit crossing.

Hope this helps,

Daniel Chartier

You can create a output I/O field. In runtime and in design time the resut is the same. If the tag vaue is out limits you only can see several asteriscs. WinCC programers think that is better to see asteriscs than the outer-limits real value.

I think that is an "i d i o t" idea but...

dcharter: I'm already using analog alarm msgs, but I have to use 2 kinds of warning: one especially warning, but then there's no interruption in the machine running (when the analmog value exceeds a limit but for a shorter time); and a second that kind of interrupts the mahcine' (when an value is exceeded in already a long time)...

F.Abril: I just want to mkae sure that I 'don't loose my tag' when it goes off limits... But I'll try with another internal tag, then I'll see what happens...