M_ANA function: How to DHm

Hello,

my question is, how to use DHm limits in the M_ANA-function. I don`t undersatnd to configure this limit. e.g. I want to monitor the steam-pressure speed change.

Is there a fromula to calculate the limit I need to set in the M_ANA-function.

Thanks

Mornu


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mornu   

asked 3 months ago
Closed



Best Answer

1

The M-ANA block determines the current rate of change of the applied measured value over the sampling cycle. This rate of change is then extrapolated to the set time interval (e.g., minutes, hours, ...). With a cycle time of 1s and a change in value of 2 / s, the result for DHm is 120 / min.

tr10091969   

answered 3 months ago


 


By mornu on 1/29/2018 | Like (0) | Report

thanks for you answer

that means the value I have to set, depends on the cycle time, OK.
example: I have a measurement range 0-200bar. DHm is 120 bar/min. the actual changerate is 5 bar/s will i get an alarm after 1 minute or immediatly?


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Answers

1

The M-ANA block determines the current rate of change of the applied measured value over the sampling cycle. This rate of change is then extrapolated to the set time interval (e.g., minutes, hours, ...). With a cycle time of 1s and a change in value of 2 / s, the result for DHm is 120 / min.

tr10091969   

answered 3 months ago


 


By mornu on 1/29/2018 | Like (0) | Report

thanks for you answer

that means the value I have to set, depends on the cycle time, OK.
example: I have a measurement range 0-200bar. DHm is 120 bar/min. the actual changerate is 5 bar/s will i get an alarm after 1 minute or immediatly?


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0

DHm expects a per minute change limit (DHs second, DHh hour)

positive limits detect high risings, negative limits detect high drops.

M_ANA calculates the difference of the IN value of the current execution with the value of the previous execution. It then normalizes it to the selected time base for the rate, considering the cycle time.

If your input would be in bar, your limit would be bar/Minute. Rises and drops need separate limits.

You can find more information in the help (click Help in the M_ANA configuration dialog): See section Functions and Function blocks : General description and overview : Hints on parameter definition of the blocks

Best regards

Jürgen

JuergenV   

answered 3 months ago


 


By mornu on 1/29/2018 | Like (0) | Report

Hallo Jürgen, danke für die Antwort. Die Hilfe habe ich breits durchgelesen, werde aber nicht so richtig schlau daraus. Da wäre ein Beispiel zum Verständnis nicht schlecht.


By JuergenV on 1/29/2018 | Like (0) | Report

Yes, this is what I thought too, when reading the help.
The rate is calculated during every cycle, the alarm will occur immediately. By the way, the calculation of the rate uses the configured cycle time, not the actual time since last execution. This is probably a reason why a task in equidistant mode is recommended.


By mornu on 1/29/2018 | Like (0) | Report

OK, thank you, we tried it on the plant and it looks good, thank you for help


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