model 2704 controller installation and operation handbook - Soliton

2704 Controller Tuning
Typical automatic tuning cycle
PV
Setpoint
Calculation of the cutback values
Low cutback and High cutback are values that restrict the amount of overshoot, or
undershoot, that occurs during large step changes in PV (for example, under start-up
conditions).
If either low cutback, or high cutback, is set to ‘Auto’ the values are fixed at three times the
proportional band, and are not changed during automatic tuning.
Time
8.4. CASCADE TUNING
In the 2704 controller a cascade loop can be tuned using the autotune feature.
The cascade autotuner tunes to the local setpoint of the auxiliary loop. This value should be
set to the value at which the process is typically operated. For example, for a furnace
typically used around 1000 o C, set ‘Local SP’ (Aux) to 1000 o C. The autotune will take place
at a level below this to ensure that the process operating conditions are not exceeded.
Similarly, since autotune applies the full range of the output signal to the process it may in
some cases be desirable to limit this range to protect the process.
Cascade autotune tunes the slave loop first followed by the master. For a more detailed
description of cascade autotune or tuning of cascade loops manually, see the 2704
Engineering Handbook, Part No. HA026933.
8.4.1. Automatic Tuning of a Cascade Loop
1. On the loop overview page, set ‘Local SP’ to the value at which the process typically
operates. Alternatively, this value can also be set in the LPx SETUP (SP(Aux)) page.
2. Set ‘Tune OL’ and ‘Tune OH’ (if necessary) to the required limits for the process.
These parameters can be found in the AUTOTUNE page.
3. From the AUTOTUNE page header, choose the parameter ‘Autotune Loop’ and select
‘LPx (CSD)’.
Cascade control is described in Chapter 9
Installation and Operation Handbook. Part No HA026502 Issue 1.0 Apr-00 8-5