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

[MMS79]

hi,

i am using Labview for water level control setup (working on Autotune Controllers).

using Arduno Uno for communication purpose with hardware.

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, as right now controllers efforts are much more making PID controlller useless.

please suggest how to calculate or set suitable dt(s) value in program.

Thanks

[hrh1818]

What is this dt(s) value you need help with?   How are you using dt(s)?

hfrh212

[MMS79]

Thanks hrh212 for reply,

i mean dt(s) is the sampling frequency in labview.

Regards.

[hrh1818]

The requirements for sampling frequency depend upon the size of your tank and the inflow and out flow rates. A small tank and large inflow and outflow rates requires a high sampling frequency.  Where as a big tank and low inflow and outflow rates can use a low sampling frequency. 

On approach for calculating a sampling frequency is to use your design's accuracy requirement. Your accuracy requirements determine the acceptable variations in the tank level.  Then using your tank's dimensions and maximum flow rates calculate how long it will take for the level to change by an amount equal to the maximum acceptable variation.  This time is the sampling period.  The reciprocal of the sampling period is the sampling frequency,  

A second approach is don't calculate a sampling frequency.  Instead just let the time required to measure the tank level and change an inflow or outflow rate set the sampling frequency.  Communication overhead limits the maximum sampling frequency of LIFA to approximately 50 samples per second.

hrh212