Detailed description
Original instructions
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Structure of the controller
Structure of the two-point controller:
Principle of the two-point controller
The actual two-point controller will have 2 dynamic feedback paths (PT1-element) added. Through appropriate selection of the time constants of the feedback element, the two-point controller maintains dynamic behavior that corresponds to the behavior of a PID controller.
Feedback
The feedback parameter set, made up of the feedback gain and the feedback time constants lag_neg and lag_pos, allows universal usage of the two point controller.
The following table provides more exact information about it:
Feedback
lag_neg
lag_pos
2-Point-Behavior (without feedback)
= 0
= 0
negative feedback
> 0
= 0
negative + positive feedback
> 0
> lag_neg
Warning, regeneration (neg. feedback with lag_pos)
= 0
> 0
Warning, regeneration (pos. feedback switched off)
> lag_pos
> 0
Set feedback gain greater than zero!
Enter xf_man (meaning 0% to 100%) values between 0 and 100!
Hysteresis
The parameter hys indicates the switching hysteresis, i.e. the value that the effective switch value ERR_EFF outgoing from control point hys/2 must be reduced by, before the output Y is reset to"0". The dependence of the output Y depending of the effective switch value ERR_EFF and the Parameter hys, becomes clear in the picture Principle of the two-point controller. The value of the hys parameter is typically set to 1% of the maximum control area [max. (SP - PV].
Operating modes
There are three operating mode selectable through the man and halt parameter inputs:
Operating mode
man
halt
Meaning
Automatic
0
0
The function block will be handled as described above.
Manual mode
1
0 or 1
The output Y is set to the value YMAN. xfl and xf2 are calculated using the following formula:
xf1 = xf_man * gain /100
xf2 = xf_man * gain /100
Halt
0
1
Output Y will be held at the last value.
xf1 and xf2 are set to gain * Y.