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Closed loop cycling method 82 – Red Lion TCU User Manual

Page 90

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Closed Loop Cycling Method

An alternative to auto-tuning is manual tuning. This tuning method

induces oscillations into the process in the same way as the controller’s
auto-tune function. If oscillations are not acceptable, the open-loop tuning
method can be used.

The following is a manual tuning procedure for determination of the PID

control constants.
1. Connect a chart recorder to log temperature and set the paper speed

appropriate for the process.

2. Set the controller to automatic (auto) control mode.
3. Set proportional band to 999.9%. (maximum setting)
4. Set integral time and derivative time to 0 seconds.
5. Decrease proportional band (increase controller gain) by factors of two

until process just begins to oscillate and the oscillations are sustained.
Make a small change in setpoint to provide a stimulus for oscillations.
Allow adequate time for the process to respond. If oscillations appear to
grow, increase proportional band. Adjust the proportional band until
steady oscillations appear.

6. Note the peak-to-peak amplitude of the cycle (a) in degrees and the period

of oscillation (t) in seconds.

Parameter

Fast Response

Damped

Response

Slow

Response

Proportional Band (%)

200a/range

400a/range

600a/range

Integral Time (sec)

1t

2t

3t

Derivative Time (sec)

0.2t

0.25t

0.25t

Output Power
Dampening (sec)

t/40

t/30

t/20

82

Figure 44, Closed Loop Tuning