SCUV – Step controller unit with velocity input

Block SymbolLicensing group: STANDARD

Function Description
The block SCUV substitutes the secondary position controller SCU in the step controller loop when the position signal is not available. The primary controller PIDU (or some of the derived function blocks) is connected with the block SCUV using the block inputs mv, dmv and SAT.

If the primary controller uses PI or PID control law ( $CWOI = off$ ), then all three inputs mv, dmv and SAT of the block SCUV are sequentially processed by the special integration algorithm and by the three state element with parameters thron and throff (see the TSE block, use parameters $ep = thron$ , $epoff = throff$ , $en = -thron$ and $enoff = -throff$ ). Pulse outputs of the three state element are further shaped in such a way that the minimum pulse duration time dtime and minimum pulse break time btime are guaranteed at the block outputs UP and DN. The parameter RACT determines the direction of motor moving. Note, the velocity output of the primary controller is reconstructed from input signals mv and dmv. Moreover, if the deviation error of the primary controller with $icotype = 4$ (working in automatic mode) is less than its dead zone ( $SAT = on$ ), then the output of the corresponding internal integrator is set to zero.

The position pos of the valve is estimated by an integrator with the time constant trun. If signals from high and low limit switches of the valve are available, they should be connected to the inputs HS and LS.

If the primary controller uses P or PD control law ( $CWOI = on$ ), then the deviation error of the primary controller can be eliminated by the bias ub manually. In this case, the control algorithm is slightly modified, the position of the motor pos is used and the proper settings of thron, throff and the tracking time constant tt are necessary for the suppressing of up/down pulses in the steady state.

There is also a group of input signals for manual control available. The manual mode is activated by the $MAN = on$ input signal. Then it is possible to move the motor back and forth by the MUP and MDN input signals. It is also possible to specify a position increment/decrement request by the mdv input. In this case the request must be confirmed by a rising edge (off $\to$ on) in the DVC input signal.

The overall control function of the SCUV block is obvious from the following diagram:

The complete structures of the three-state controllers are depicted in the following figures:

Inputs

mv	Manipulated variable (controller output)	Double (F64)
dmv	Controller velocity output (difference)	Double (F64)
ub	Bias (only for P or PD primary controller)	Double (F64)
SAT	Internal integrator reset (connected to the SAT output of the primary controller)	Bool
HS	Upper end switch (detects the upper limit position of the valve)	Bool
LS	Lower end switch (detects the lower limit position of the valve)	Bool
MUP	Manual UP signal	Bool
MDN	Manual DN signal	Bool
mdv	Manual differential value (requested position increment/decrement with higher priority than direct signals MUP/MDN)	Double (F64)
DVC	Differential value change command (off $\to$ on)	Bool
MAN	Manual or automatic mode	Bool
	off .. Automatic mode on ... Manual mode

Outputs

UP	The "up" signal	Bool
DN	The "down" signal	Bool
pos	Position output of motor simulator	Double (F64)
MR	Request to move the motor	Bool
	off .. Motor idle ( $UP = off$ and $DN = off$ ) on ... Request to move ( $UP = on$ or $DN = on$ )

Parameters

thron	Switch-on value $↓$ 0.0 $⊙$ 0.02	Double (F64)
throff	Switch-off value $↓$ 0.0 $⊙$ 0.01	Double (F64)
dtime	Minimum width of the output pulse [s] $↓$ 0.0 $⊙$ 0.1	Double (F64)
btime	Minimum delay between two subsequent output pulses [s] $↓$ 0.0 $⊙$ 0.1	Double (F64)
RACT	Reverse action flag	Bool
	off .. Higher mv $\to$ higher pv on ... Higher mv $\to$ lower pv
trun	Motor time constant (determines the time during which the motor position changes by one unit) $↓$ 0.0 $⊙$ 10.0	Double (F64)
CWOI	Controller without integration flag	Bool
	off .. The primary controller has an integrator (I, PI, PID) on ... The primary controller does not have an integrator (P, PD)
tt	Tracking time constant $↓$ 0.0 $⊙$ 1.0	Double (F64)

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