|An instance of
this function block type implements the reverse-acting PID
(Proportional+Integral+Derivative) control law
XOUT = -(Kp*e + ITERM/TR + TD*DTERM),
e = PV - SP, ITERM = ∫edt, and ETERM = de/dt.
The manipulated variable XOUT, the process variable PV and the proportionality constant KP are of type REAL, as are the internal terms ERROR, ITERM and ETERM. The reset time TR and derivative time TD are of type TIME. The set point SP and initial output value X0 are of type UINT since they are considered to be manually set, e.g., from an instance of the FACEPLATE type.
Provision is made for anti-reset windup and bumpless transer from MANUAL to AUTO mode through appropriate initialization of the internal ITERM and ETERM variables.