United Process Versapro, Installation And Operation Handbook

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VersaPro Temperature Controller Page 40
Copyright © 2013, United Process Controls Inc.
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13 Tuning
Before attempting to tune the instrument make sure you understand the Operation and Setup part of the
instrument. This section applies to the controller only.
13.1 What is tuning?
Tuning the controller means that the control characteristics of the controller are matched to those of the
process in order to obtain hold the process to setpoint. Good control means:

Stable, ‘straight-line’ control of the process variable at setpoint without fluctuation

No overshoot, or undershoot, of the process variable relative to setpoint

Quick response to deviations from the setpoint caused by external disturbances, thereby rapidly restoring
the process variable to the setpoint value.
Tuning involves calculating and setting the value of the parameters listed the following table. These
parameters appear in the Control Setup menu.
Table 11
Parameter Meaning or Function
Proportional band The bandwidth, in display units, over which the output power is proportioned
between minimum and maximum.
Integral time
(Reset)
Determines the time taken by the controller to remove steady-state error signals.
Derivative time
(Rate)
Determines how strongly the controller will react to the rate-of-change of the
measured value.
The Versapro uses the Proportional Band as a representation of the Proportion section of PID, the Reset as a
representation of the Integral section of PID, and the Rate as a representation of the Derivative section of PID.
Thus by following a simple procedure, PID tuning can easily be implemented in any control situation. A
suggested procedure is diagramed in the next figure.
All of the PID parameters may be altered by changing these parameters in the Setup / Ctrl menu. The
following procedure assumes the initial PID values for a typical batch furnace. You may be able to start with a
proportional band setting of 10 or less for a smaller box or temper furnace.
If, after following the procedure, the process continues to oscillate, it may be necessary to change the HIPO or
LOPO parameters. Make sure that the control output is linear through the full range from LOPO to HIPO. In
situations where the system is difficult to tune, it is most likely the output is not linear or there is too much lag
time between the control command and measurable changes in the process. Test the system in manual
mode to verify the output is linear.