Thermcraft XST-2-0-12-1V1-E28, Instruction Manual

Page: 202 / 260

Installation and Operation Handbook Tuning
4. Chapter 4 TUNING
Before tuning please read Chapter 2, Operation , to learn how to select and change a parameter.
This chapter has five main topics:
4.1 WHAT IS TUNING?
In tuning, you match the characteristics of the controller to that 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 restoring the
temperature rapidly 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
•
WHAT IS TUNING?
•
AUTOMATIC TUNING
•
MANUAL TUNING
•
COMMISSIONING OF MOTORISED VALVE CONTROLLERS
•
GAIN SCHEDULING
HA025041 issue 12 Aug 14 4-1