Marathon Computer AACC 2000 Manual Do Utilizador

AACC 2000 Carbon                                                                       Nov.  1, 1997

53

 

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.

 

 

 

 

 

 

 

 

 

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.