how to calculate suitable dt(s) value for a program.

[MMS79]

hi,

I am using Labview for water level control setup (working in relay autotune controllers),

using Aurduno uno for communication purpose.

i am using 500ms dt(s) with no specific reason,

but came to know that if i will put proper dt(s) value, PID parameters which i will receive will be more accurate.

Please suggest how to calculate suitable dt(s) value for a program.

Thanks

[Bob_Schor]

It depends on the frequency characteristics of your signal.  You have to sample at twice the highest frequency you want to analyze in your signal, and many advocate sampling about 10 times higher than the highest signal-of-interest.  You should also have what my engineering friends call an "anti-aliasing filter" on the signal to remove high frequency "noise" before you sample it.

dt = 500ms corresponds to a frequency of 2 Hz, which means that the signal you are measuring needs to have essentially all of its energy below 1 Hz, i.e. be a pretty slow process (I suppose a Water Level controller might fit that bill ...).  Expect changes to take seconds (meaning "units of time", not "ordinal position").

Bob Schor

[natasftw]

If he's only worried about the frequency, the ten times rules isn't important.  That's only to see the shape.

[MMS79]

Thanks for the reply Bob_Schor  and natasftw ,

Is there any code/ block at which i will connect my input signal (level).

and i will get the sampling frequency of signal.

And than i will keep my d(t) sampling rate 10times greater than that.

Regards.