Control Modes & Algorithms 94
Outputs
PID control block
Set point
Control mode
Deviation
Control period
Minimum On time
Overtime
Control output
Control enabled
Rate time
Reset time
Dead Band
Dead Band Gain
• Control output as 0 to 100 %
Update rate “‑” = Control period
Enabled by
• Settings
• Controller status
Figure 37: PID Control Block
The transfer function of a PID Control is modeled as follows:
Kp
+ Ki
/s + s Kd
= Kp
(1+1/(s Ti) + s Td)
with:
Ti = Kp/Ki, Td = Kd/Kp
where:
` the first term is the Proportional action
` the second term is the Integrative action
` the third term is the Derivative action
Proportional action can be set by means of the Proportional Band (PB). PB is expressed in percentage of the
input range and is related to Kp with:
Kp = 100/PB
Figure 38: Proportional Action by Means of Proportional Band
The proportional action is set directly as Deviation (D) in control parameter units.
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