Red-lion TCU User Manual download pdf (Page 78)

The following additional parameters are calculated and set as a result of

Auto-Tuning of the secondary:

Secondary Proportional Band (Pb-2)

Secondary Integral Time (It-2)

Secondary Derivative Time (dt-2)

Secondary Output Power Dampening (OPd2)

Auto-Tuning of the secondary presents two different control points at

which the controller cycles power. In Automatic mode of operation, the

secondary control point is the setpoint directed by the primary at the instant

Auto-Tune is started. In Manual mode of operation, the secondary control

point is the secondary process value reading at the instant Auto-Tune is

started. The secondary is normally Auto-Tuned with the controller in the

Manual mode of operation unless the process is reasonably under control.

Prior to tuning the Secondary, it is essential that it is scaled to match the actual

secondary process range. This is important for proper Auto-Tuning of the

primary. Subsequent changes made to scaling values may require re-tuning.

The following procedure may be used to initially tune an Internal Cascade

controller:

1) Place the controller into Manual (USEr) mode of operation.

2) Adjust output power level until primary variable is close to primary

setpoint. (± 10% of range)

3) Auto-Tune the secondary.

4) Auto-Tu ne th e primary.

5) Place controller into Automatic (Auto) mode of operation.

6) Initial tuning is complete.

After the process has stabilized, the primary and secondary may be

re-tuned in Automatic mode of operation. Normally, the primary requires

re-tuning whenever the secondary PID constants are changed.

Auto-Tune Of External Cascade Systems (Remote Setpoint)

External Cascade systems involve the use of two controllers, the Primary

and the Secondary, that have a Remote Setpoint Input. In such a system, the

Secondary controller is normally tuned f irst followed by tuning of the

primary controller. Prior to tuning the Secondary controller, it is essential

that the Remote Setpoint is scaled to match the actual secondary process

range. This is important for proper Auto-Tuning of the primary controller.

Subsequent changes made to scaling values may require re-tuning. The

following procedure may be used to initially tune an External Cascade

controller:

1) Place the Secondary controller into Local Setpoint mode and Manual

(USEr) mode of operation.

2) Adjust output power level o f the secondary until primary variable is close

to primary setpoint. (± 10% of range)

3) Key-in secondary setpoint value equal to secondary process v alue.

4) Auto-Tune the secondary controller while in Local Setpoint mode.

5) Place the secondary controller into Remote Setpoint mode and Automatic

(Auto) mode of operation.

6) Auto-tune the primary controller while the primary is in Automatic mode

of operation.

7) Initial tuning of system is complete.

After the process has stabilized, the primary and secondary may be

re-tuned in Automatic mode of operation. Normally, the primary requires

re-tuning whenever the secondary PID constants are changed.

Note: For Remote Setpoint controllers, the Auto-tune control point is derived

from the Remote Setpoint when in Remote Setpoint mode and it is derived from

the Local Setpoint when in Local Setpoint mode.

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Red-lion TCU User Manual Page 78

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