User guide

Temperature Controller iB6 / iB12

6.0 PID Controller Tuning

6.4 Manual Tuning (Zeigler-Nichols PID Method)

6.4.1 Introduction

This tuning method may be used if the spread between initial process temperature and process

operating temperature is small, or if the process is too slow for Autotuning. Manual tuning requires

that zones be tuned one at a time and that the PV be tracked over time. (Graph the displayed PV

against time manually.) All zones should be running while manually tuning one zone.

After you have finished manual tuning, you can change the Startup Mode parameter setting and

enable soft start (recommended).

6.4.2 Procedure

To do manual tuning:

1) After configuring any parameters that apply to your control strategy, enter a setpoint that is

representative of the setpoint you expect to use when the selected zone is in Normal operation.

2) Go to the Control Config menu.

3) For now, leave the Proportional Band set to 13 °C (24 °F), but change the Derivative (PID rate) to

0 seconds.

4) In the Control Config menu, set the PID Autotune parameter to Disable.

5) Return to the standard operating display and watch the behavior of the displayed process value.

When the temperature reaches setpoint, plot a graph of the displayed process value against time

or record the time period between temperature peaks. (Be patient. It may be several minutes

before you see up and down changes (oscillation) in the process value for a manifold zone.)

6) If the temperature (process value) will not oscillate, then decrease the proportional band value

by repeatedly halving the value (dividing it by 2) until a small, sustained temperature oscillation

is seen.

Alternatively, if the temperature (process value) oscillates severely, double the proportional

band value (multiple it by 2) repeatedly until a small, sustained temperature oscillation is

observed.

7) Measure the period in seconds of one cycle of oscillation (“T” on the diagram below).

8) Divide the period of oscillation (T) by 8. The resulting number (quotient) is the correct Derivative

parameter value (rate) time in seconds.

9) Access the Control Config menu and enter the Derivative value obtained in Step 8. The integral

time will be set automatically to 6 times the rate. (You cannot view the integral term value.)

10) If the process is stable, manual tuning is completed. However, if slight oscillation is observed,

multiply the current proportional band value by 1.66 and enter the product as the new PID

Proportional Band value to complete the tuning procedure for this zone.