101
CONTROL MODES
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 34:
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 represents the Proportional action, the second is the Integrative action and the
third 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 35:
Proportional action by means of Proportional Band
The proportional action is set directly as Deviation (D) in control parameter units. The relation between
D and PB is:
D = Range * PB/100
Ti = Kp/Ki, Reset time
Td = Kd/Kp, Rate time
