Marathon Monitors Inc.

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

Pb

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

band

 

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

rEL

Only present if cooling has been configured and a module is

gain

 

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

 

 

value divided by the rEL value.

 

 

 

AACC 2000 Carbon

53

Nov. 1, 1997

Page 53
Image 53
Marathon Computer AACC 2000 manual Tuning, Parameter Code Meaning or Function