FB 59 TCONT_S works without a position feedback signal (see following block diagram).
The I-action of the PI algorithm and the assumed position feedback signal are calculated
in an integrator (INT) and compared as a feedback value with the remaining P-action.
The difference is applied to a three-step element (THREE_ST) and a pulse generator
(PULSEOUT) that forms the pulses for the valve. Adapting the response threshold of the
three-step element reduces the switching frequency of the controller.
To prevent overshoot, you can weaken the P-action using the "proportional factor for set-
point changes" parameter (PFAC_SP). Using PFAC_SP, you can now select continuously
between 0.0 and 1.0 to decide the effect of the P-action when the setpoint changes:
n PFAC_SP = 1.0: P-action has full effect if the setpoint changes
n PFAC_SP = 0.0: P-action has no effect if the setpoint changes
A value for PFAC_SP < 1.0 can reduce the overshoot as with the continuous controller if
the motor run time MTR_TM is small compared with the recovery time TA and the ratio
TU/TA is < 0.2. If MTR_TM reaches 20 % of TA, only a slight improvement can be ach-
ieved.
A load can be added at the DISV input.
With LMNS_ON, you can change between manual and automatic mode. In manual
mode, the actuator and the integrator (INT) are set to 0 internally. Using LMNUP and
LMNDN, the actuator can be adjusted to OPEN and CLOSED. Switching over to auto-
matic mode therefore involves a bump. As a result of the GAIN, the existing error leads to
a step change in the internal manipulated variable. The integral component of the
actuator, however, results in a ramp-shaped excitation of the process.
PI Step Controller Algo-
rithm
Weakening the P-Action
when Setpoint Changes
Occur
Feedforward Control
Manual Value Processing
(LMNS_ON)
VIPA SPEED7
Standard
PID Control > FB 59 - TCONT_S - Temperature Step Control
HB00 | OPL_SP7 | Operation list | en | 18-30 877
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