PID_LOOP is a module template that consists of a PID function block and seven alarm parameters for HighHigh, High, Low, LowLow, DeviationHigh, DeviationLow, and PV Bad alarms. Initially, only PV Bad alarm is enabled in PID_LOOP. Others can be enabled as needed.
The PID_LOOP module template has a single PID function block. The PID block has IO Reference parameters for the process variable input and control output. In most cases, you do not need to add additional function blocks to the module for a simple PID loop. But if, for example, your process variable is calculated or selected from several analog inputs, you can add this logic to the module after it is created from the template. You might need to add function blocks for feedforward control or tracking. The control output variable, IO_OUT, is typically a Device Signal Tag that specifies a Device Tag on an analog output channel and parameter. It could also be a discrete output channel (continuous pulse output) if you are doing time proportional output control.
Parameter |
Description |
|---|---|
CONTROL_OPTS |
SP-PV Track in Man is the only control option enabled as a default. Use this parameter to set the control action to Direct when necessary. Other control options to consider are SP-PV Track in LO or IMan, Track Enable, and Track in Manual. |
GAIN |
Proportional gain tuning parameter. The default is 0.5. You might want to set a better default based on the actual loop type prior to tuning. |
HI_LIM |
The high alarm limit value in engineering units. This is a Quick Config parameter because the HI_ALM alarm parameter is initially disabled. |
IO_IN |
An I/O Reference parameter for configuring the Device Signal Tag for the process variable input. |
IO_OPTS |
None of the I/O options are initially enabled. In the PID block, IO_OPTS is used to select the Increase to Close option for the control output (for example, for a fail open valve), or to enable the low cut-off function for the process variable input. |
IO_OUT |
An I/O Reference parameter for configuring the Device Signal Tag for the control output. |
L_TYPE |
Linearization type. The default is Indirect. This might be changed to Ind Sqr Root, for example, when flow is being determined from differential pressure. |
LO_LIM |
The low alarm limit value in engineering units. This is a Quick Config parameter because the LO_ALM alarm parameter is initially disabled. |
PV_SCALE |
This parameter is used to set the engineering unit value at 0 percent and 100 percent of scale for the process variable. The engineering unit descriptor can be selected from a list and the number of decimal places to be displayed can be set. Note that the number of decimal places to be displayed is applicable only for the faceplate and detail displays. The valid values for these displays are 0 to 3 decimal places. |
RESET |
The integral time constant tuning parameter in seconds (seconds per repeat). The default is 10 seconds. You might want to set a better default based on the actual loop type prior to tuning. |
SP_HI_LIM |
The high limit for the setpoint. Typically, this value should be changed when the EU 100 percent value is changed from the default in PV_SCALE. |
SP_LO_LIM |
The low limit for the setpoint. Typically, this value should be changed when the EU 0 percent value is changed from the default in PV_SCALE. |
Note that MODE is not a Quick Config parameter. The initial target mode for the PID function block in all of the analog control module templates is Manual. There might be other parameters that you need to configure that are not in the Quick Config view. If so, set the parameter filtering to Common Configuration (or Common Configuration and Advanced Configuration) to review or change other parameter values.