Three-Step Control - Siemens SIMATIC S7-1200 Function Manual

9.4.3.4

Three-step control

Three-step control
In "Three-step control" mode, it is possible to generate three statuses of the actuating signal.
For this, the status values of the binary output signals QPOS_P and QNEG_P are assigned
to the respective operating statuses of the actuator. The table shows the example of a
temperature control:
Output signals
QPOS_P
QNEG_P
The pulse duration is calculated from the input variable via a characteristic curve. The form
of the characteristic curve is defined by the minimum pulse duration or minimum interval and
the ratio factor. The normal value for the ratio factor is 1.
The "doglegs" in the curves are caused by the minimum pulse duration or minimum interval.
Minimum pulse duration or minimum interval
A correctly assigned minimum pulse duration or minimum interval P_B_TM can prevent short
on/off times, which reduce the working life of switching elements and actuators. Small
absolute values of input variable LMN that would otherwise generate a pulse duration shorter
than P_B_TM are suppressed. Large input values that would generate a pulse duration
longer than PER_TM - P_B_TM are set to 100% or -100%.
The duration of positive or negative pulses is calculated by multiplying the input variable (in
%) by the period duration:
Pulse duration = INV / 100 * PER_TM
PID control
Function Manual, 03/2017, A5E35300227-AC
Heat
TRUE
FALSE
Off
FALSE
FALSE
Instructions
9.4 PID basic functions
Cool
FALSE
TRUE
465