Thermcraft XST-3-0-36-3V - Manual (Page 73)

Installation and Operation Handbook Tuning
2408 and 2404 Controller 4-1
Chapter 4 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 temperature at setpoint without fluctuation
• No overshoot, or undershoot, of the temperature setpoint
• Quick response to deviations from the setpoint caused by external disturbances, thereby
rapidly restoring the temperature 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.
Table 4-1 Tuning parameters