Meaning of variable K:

The gain parameter must be greater than zero.

The parameter db sets the connection point for the outputs Y_POS and Y_NEG. If the effective switching value ERR_EFF = SP - PV - XR is positive and is greater than db, then the Y_POS output switches from "0" to "1". If the effective switch value ERR_EFF is negative and is less than db, then the output Y_NEG will switch from "0" to "1". The parameter db is typically set to 1% of the maximum control range (max. (SP - PV)).

The parameter hys indicates the connector-hysteresis, i.e. the value which the effective switch value ERR_EFF outgoing from control point db must be reduced by, before the output Y_POS (Y_NEG) is reset to "0". The connection between Y_POS and Y_NEG depending on the effective switch value ERR_EFF and the parameters db and hys is illustrated in the image "Principle of the three-point controller". The parameter hys is typically set to 0.5 % of the maximum control range (max. (SP - PV)).

Should the time constant ti = 0 or the proportional action coefficient gain ≤ 0 (configuration error), the block will still continue to operate. The functions feedback path is disabled however, so that the block operates as a conventional three-point switch.

If the time constant t_proc = 0 (configuration error), the block will still continue to operate. In this case t_proc is set to a preset value of t_proc = 60s (60 000 msec).