This module is intended to be used for control in the field, that is, when the control algorithm runs in fieldbus devices. The AI block is to be assigned to a transmitter and the AO block to a valve. The PID block can be assigned to either a transmitter or valve.
This module template is similar to PID_LOOP, the primary difference being that three function blocks are used instead of one. Both templates share the same dynamos in !Modules. Use either the PID LOOP 1 or PID LOOP 2 dynamo on your control display.
There are a few differences in the faceplate and detail display used by the two templates. The faceplates look identical, but the fieldbus faceplate bases the output indication fields on OUT of the AO function block rather than OUT_READBACK of the PID block. On both faceplates data entry for the output is written to the PID block OUT. Note that the OUT value field on the PID LOOP 1 dynamo is linked to OUT_READBACK of the PID block.
Another difference between the two faceplates is the rectangular button that appears next to the output value field in the fieldbus faceplate. This button is white when the target mode of the AO block is Cas (its normal mode). When the button is clicked, the target mode is changed to Auto which causes a value field to appear directly below the button. This value field is for the setpoint of the AO block. The button is cyan when the target mode of the AO block is Auto. Clicking the button again causes the target mode to change back to Cas and the setpoint value field to disappear. The button becomes white. This button is on the faceplate in the event that the PID block is in a transmitter that becomes unavailable. The AO block in the valve can still be manipulated in this event.
The detail displays of the two templates differ in some of the parameters shown, due to the differences in parameters in the DeltaV controller PID block and fieldbus device PID block.
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_OPTS |
SP_PV Track in Man is initially enabled. |
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. |
OUT_SCALE |
The high and low scale values, engineering units code, and number of digits to the right of the decimal point associated with OUT. |
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. |