# Rate Of Change in a certain time

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i am looking for block to measure the rate of change for sine wave at normal operation the ROC = 0 during short circuit the current is increasing to very high level ... during this increasing i need some function to calculate the ROC and tell me if this increasing is a short circuit case

best regards

A.R

I believe this is answered in the Support section of the Plexim site, under "Why is there no “derivative” block in the PLECS component library?".  You can define a value for your short circuit current ROC limit, and use a comparator with that constant value to determine if you're shorted.  If that's not what you're looking for, please clarify.

answered Mar 26 by (43 points)
edited Mar 31 by angrmgmt

i asked PLEXIM support and they provide a block for di/dt ... but  i can not use it or in right way i dont know how i can use it ...

i am not looking to compare the current by a certain value , if exceed ,, So that mean i have short circuit ... so time the current it high but still lower than the diecrmental value by few limits ...

So i need another function can monitor the rise of current ,,, comparing to time ,,, if this rising is exceed the normal value it mean that  have short circuit ,, so that i dont have to wait until the current reach to the discremental vlaue

best regards

A.R
You have some signal with values of di/dt that fall within a particular range during normal operation.  If the di/dt value is greater (in magnitude) than this range, you have a short circuit, correct?  So using the information I suggested, you can set up a comparison between the value you select for the limit (di/dt = 1000000 A/s, for example) and your measured di/dt, and if the output of your di/dt block is greater than that value, you can do whatever it is you need to do to resolve that problem (open a switch, insert a shunt, etc.).

I don't know what you mean by "time the current it high but still lower than the diecrmental value by few limits" or "until the current reach to the discremental vlaue".  I assume you're talking about exactly what is in the first paragraph of this comment, though.  Please clarify if I have not understood you correctly.
you are completly right ..but if i did that i still detect the short circuit current by changing in magnitude .not the rate of rise

let us supposed  that the short circuit level is (id) = 5000 A , once the current reach to 5000 A , a magnitude comparator works, and i can take action ,....

but some times the current reach to 4500 A . it is very high value but lower than the sitting value. So the comparator will not work , but that this value is not desired ...

So i am looking to add another why for detection the short circuit ... (di/dt) ...  if the nominal currnet = 100 A,  i am lookig to detect the change in magnitude during the rising from the rated value (100A) to the short-circuit value , and if we found that the Rate of change is very high we dont have to wait the current until reach a (id) we take action imeadialty

hope that i did clear explain .. and hope you find something to help me