Marathon Computer AACC 2000 TUNING

Marathon Monitors Inc.

AACC 2000 Carbon Nov. 1, 1997

TUNING

Before tuning, please read Chapter 2, Operation, to learn how to select and change a

parameter.

This chapter has five topics:

• WHAT IS TUNING?

• AUTOMATIC TUNING

• MANUAL TUNING

• COMMISSIONING OF MOTORISED VALVE CONTROLLERS

• GAIN SCHEDULING

WHAT IS TUNING?

In tuning, you match the characteristics of the controller to those of the process being

controlled in order to obtain good control. Good control means:

• Stable, ‘straight-line’ control of the process variable at setpoint without fluctuation

• No overshoot, or undershoot, of the process variable 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 in Table 4-1.

These parameters appear in the ‘Pid’ list.

Parameter

Code

Meaning or Function

Proportional

band Pb The bandwidth, in display units, over which the output power is

proportioned between minimum and maximum.

Integral time ti Determines the time taken by the controller to remove steady-

state error signals.

Derivative time td Determines how strongly the controller will react to the rate-of-

change of the measured value.

High Cutback Hcb The number of display units, above setpoint, at which the

controller will increase the output power, in order to prevent

undershoot on cool down.

Low cutback Lcb The number of display units, below setpoint, at which the

controller will cutback the output power, in order to prevent

overshoot on heat up.

Relative cool

gain rEL Only present if cooling has been configured and a module is

fitted. Sets the cooling proportional band, which equals the Pb

value divided by the rEL value.