PID advanced beta

[ChrisDevicix]

Hello,

I am using the adnvanced PID with the beta for reducing sensitivity to setpoint noise. (PID toolkit 8.5)

I have noticed that the beta in the NI advanced PID simply multiplies the SP by the beta, then caculates the error with beta by subtracting the PV (process variable). It then uses this error for the proportional term.

Should this actually include Perror = Kp(PVt - PV(t-1))?

It seems that unless your setpoint is acting around the zero value then the VI would not work correctly. If your setpoint is 30 and your beta is 0.1, then your setpoint used for the proportional term is 3, while the derivative term will be trying to drive the process variable to 30.

Thanks,

Chris

[Eric_R]

Hi Chris,

I think your error equation is a little off. If you refer the manual for the PID control toolkit you can find more detailed information regarding this.

The following formula represents the current error used in calculating
proportional, integral, and derivative action.

e(k) = (SP PVf)(L+(1 – L)*|SP – PVf|/SPrange)

where SPrange is the range of the setpoint, β is the setpoint factor for the Two
Degree of Freedom PID algorithm described in the Proportional Action
section of this chapter, and L is the linearity factor that produces a nonlinear
gain term in which the controller gain increases with the magnitude of the
error. If L is 1, the controller is linear. A value of 0.1 makes the minimum
gain of the controller 10% Kc. Use of a nonlinear gain term is referred to as
an Error-squared PID algorithm.

For more information check out section 2-4 of the PID Control Toolkit User Manual (http://www.ni.com/pdf/manuals/372192b.pdf),

Thank You,
Eric Reid

[Duffmanen]

This post is a little old, In case anyone was looking for the same answer the updated link for the manual is here: PID control manual