How to eliminate glitches or false signal?

[John_Ess]

I need some help with my 820-DC-RC program that controls a water pump...

I have this 0-10V input coming from a pressure transmitter that continuously monitors water pressure during pumping operation. Obviously there is some water hammer (or pipe vibration) when the pump turns OFF, and that creates a sudden pressure spike that I would like to ignore in my program.

Any ideas how?

Thanks,
John

[Spellbreaker]

Do you get a Signal or something when the Pump turns off?

[Maikky]

Dear John.

You may use the signal smoothing filter function block during that period.

Regards
Maikky

[John_Ess]

Do you get a Signal or something when the Pump turns off?

Yes I do, as the pump starts at "low" pressure level and has to stop at the certain "high" pressure level.
And that's when the sudden pressure spike occurs. So it's kind of chicken and egg scenario

Ideally I would like to ignore in my program any pressure changes during the pump OFF action and 3 seconds immediately after the pump's stopped.

[John_Ess]

Dear John.

You may use the signal smoothing filter function block during that period.

Regards
Maikky

Hi Maikky,

I looked into http://www.trainingscenter.moeller.net/functions/easySoft/easy-800/PT1-signal-smoothing-filter.html

and I still have no clue how to use it in my particular situation - can you help a bit

Thanks,
John

[Maikky]

Dear John.

The filter is normally used to smooth a signal and reduce ripples and peaks.
The "degree" of smoothing is set by the parameter TG (recovery time).
Additionally there is a parameter KP (proportional gain), which should be set
to 100.
 
In your case with a rising and - during that time - relatively smooth signal you
may set TG to the lowest value TG = 1 with the smallest delay between original
and smoothed signal.
At "pump stop" you should set TG to 0 for 3 seconds. A value of 0 freezes the
output to the last input.

As a second option you may use the value limitation function block VC.
If you set the upper limit value SH, all inputs larger than SH will create an output
of the upper limit.

Regards
Maikky
     

[John_Ess]

At "pump stop" you should set TG to 0 for 3 seconds. ..

    

So can I simply set the "recovery time" value TG=30 (for 3 seconds delay) instead?
Are you sure about setting TG = 0 ?

[Maikky]

Dear John.

From your earlier statements I assumed, that you do not need a signal for the 3 seconds,
where the peaks occur. For this scenario a value of 0 at parameter TG is freezing the last
input value.

Now I understand, that you need the input for a high alarm observation so forget the earlier
recommendation with value 0 or with function block VC. This will not work.

You still may use the smoothing filter but you have to "play" a little with the parameter TG.
The impact of this parameter is not directly predictable. A higher value results in a smoother
and more delayed output, a lower value results in a more rippled and shorter delayed output.

If you have an input signal which jumps from 0% to 100% a TG value of 30 means, that
the output will reach 63% after 3 seconds. This is predictable but you will not have such
inputs in reality.

A second option to do your high alarm observation is to use an on-delayed timing relay.
If the input signal is higher than the set point for more than 3 seconds it will cause an alarm.

Regards
Maikky

[John_Ess]

A second option to do your high alarm observation is to use an on-delayed timing relay.
If the input signal is higher than the set point for more than 3 seconds it will cause an alarm.

Thanks Maikky, something like this - right?

[Maikky]

Dear John.

This solution will work.

Regards
Maikky

[John_Ess]

@Maikky,
Thank you for your feedback. It was helpful.