Discrete pid equation what unit is T in??

[bara_hence]

I wonder what unit the sample update time is in is it in minutes or seconds??

the equation: Un=Un_1+En(Kp+KiT+Kd/T)+En_1(-Kp-2*Kd/T)+En_2(Kd/T)


En=error
En_1 error previous
En_2 error before previous
Un=pid output
Un_1=previous pid output

 

[Singapore_Mats]

Here you find more info about PID:

http://www.plctalk.net/qanda/archive/index.php/t-237.html

 

[Peter Nachtwey]

I wonder what unit the sample update time is in is it in minutes or seconds??

the equation: Un=Un_1+En(Kp+KiT+Kd/T)+En_1(-Kp-2*Kd/T)+En_2(Kd/T)

What difference does it make? T can be either seconds or minutes but not both. The units must be consistent.

Why not write the PID like this:
u=u(n-1)+E*(Kp+KiT+Kd/T)+E(n-1)*(-Kp-2*Kd/T)+E(n-2)*(Kd/T)
Phil doesn't charge for using the multiply sign *. That way we know you are multiplying and not array indexing.

Singapore_Mats, it is good to see there are some that realize there is already wealth of information already on the forum and is only a search away.

 

[TimWilborne]

Singapore_Mats - Thanks for referencing the great thread. I miss Allen, he was very knowledgeable