PIDAT – PID controller with relay autotuner

Block SymbolLicensing group: AUTOTUNING

Function Description
The PIDAT block has the same control function as the PIDU block. Additionally it is equipped with the relay autotuning function.

In order to perform the autotuning experiment, it is necessary to drive the system to approximately steady state (at a suitable working point), choose the type of controller to be autotuned (PI or PID) and activate the TUNE input by setting it to on. The controlled process is regulated by special adaptive relay controller in the experiment which follows. One point of frequency response is estimated from the data measured during the experiment. Based on this information the controller parameters are computed. The amplitude of the relay controller (the level of system excitation) and its hysteresis is defined by the amp and hys parameters. In case of hys=0 the hysteresis is determined automatically according to the measurement noise properties on the controlled variable signal. The signal TBSY is set to onduring the tuning experiment. A successful experiment is indicated by and the controller parameters can be found on the outputs pk, pti, ptd, pnd and pb. The c weighting factor is assumed (and recommended) c=0. A failure during the experiment causes $TE = on$ and the output ite provides further information about the problem. It is recommended to increase the amplitude amp in the case of error. The controller is equipped with a built-in function which decreases the amplitude when the deviation of output from the initial steady state exceeds the maxdev limit. The tuning experiment can be prematurely terminated by activating the TBRK input.

Inputs

dv	Feedforward control variable	Double (F64)
sp	Setpoint variable	Double (F64)
pv	Process variable	Double (F64)
tv	Tracking variable	Double (F64)
hv	Manual value	Double (F64)
MAN	Manual or automatic mode	Bool
	off .. Automatic mode on ... Manual mode
TUNE	Start the tuning experiment	Bool
TBRK	Stop the tuning experiment	Bool

Outputs

mv	Manipulated variable (controller output)	Double (F64)
de	Deviation error	Double (F64)
SAT	Saturation flag	Bool
	off .. The controller implements a linear control law on ... The controller output is saturated
TBSY	Tuner busy flag	Bool
TE	Tuning error	Bool
	off .. Autotuning successful on ... An error occurred during the experiment
ite	Error code; expected time (in seconds) to finishing the tuning experiment while the tuning experiment is active	Long (I32)
	1000 . Signal/noise ratio too low 1001 . Hysteresis too high 1002 . Too tight termination rule 1003 . Phase out of interval
pk	Proposed controller gain	Double (F64)
pti	Proposed integral time constant	Double (F64)
ptd	Proposed derivative time constant	Double (F64)
pnd	Proposed derivative component filtering	Double (F64)
pb	Proposed weighting factor – proportional component	Double (F64)

Parameters

irtype	Controller type (control law) $⊙$ 6	Long (I32)
	1 .... D 2 .... I 3 .... ID 4 .... P 5 .... PD 6 .... PI 7 .... PID
RACT	Reverse action flag	Bool
	off .. Higher mv $\to$ higher pv on ... Higher mv $\to$ lower pv
k	Controller gain $K$ . By definition, the value 0 turns the controller off. Negative values are not allowed, use the RACT parameter for such a purpose. $↓$ 0.0 $⊙$ 1.0	Double (F64)
ti	Integral time constant $T_{i}$ . The value 0 disables the integrating part (the same effect as disabling it by the irtype parameter). $↓$ 0.0 $⊙$ 4.0	Double (F64)
td	Derivative time constant $T_{d}$ . The value 0 disables the derivative part (the same effect as disabling it by the irtype parameter). $↓$ 0.0 $⊙$ 1.0	Double (F64)
nd	Derivative filtering parameter $N$ . The value 0 disables the derivative part (the same effect as disabling it by the irtype parameter). $↓$ 0.0 $⊙$ 10.0	Double (F64)
b	Setpoint weighting – proportional part $↓$ 0.0 $⊙$ 1.0	Double (F64)
c	Setpoint weighting – derivative part $↓$ 0.0	Double (F64)
tt	Tracking time constant. $↓$ 0.0 $⊙$ 1.0	Double (F64)
hilim	Upper limit of the controller output $⊙$ 1.0	Double (F64)
lolim	Lower limit of the controller output $⊙$ -1.0	Double (F64)
iainf	Type of apriori information $⊙$ 1	Long (I32)
	1 .... No apriori information 2 .... Astatic process (process with integration) 3 .... Low order process 4 .... Static process + slow closed loop step response 5 .... Static process + middle fast (normal) closed loop step response 6 .... Static process + fast closed loop step response
k0	Static gain of the process (must be provided in case of $iainf = 3, 4, 5$ ) $⊙$ 1.0	Double (F64)
n1	Maximum number of half-periods for estimation of frequency response point $⊙$ 20	Long (I32)
mm	Maximum number of half-periods for averaging $⊙$ 4	Long (I32)
amp	Relay controller amplitude $⊙$ 0.1	Double (F64)
uhys	Relay controller hysteresis	Double (F64)
ntime	Length of noise amplitude estimation period at the beginning of the tuning experiment [s] $⊙$ 5.0	Double (F64)
rerrap	Termination value of the oscillation amplitude relative error $⊙$ 0.1	Double (F64)
aerrph	Termination value of the absolute error in oscillation phase $⊙$ 10.0	Double (F64)
maxdev	Maximal admissible deviation error from the initial steady state $⊙$ 1.0	Double (F64)

It is recommended not to change the parameters n1, mm, ntime, rerrap and aerrph.

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