Introduction To Heat/Cool Control - ABB COMMANDER 1911 Operating Manual

5.10

Introduction to Heat/Cool Control

Note.Refer to sections
5.10.2 and 5.10.3
Derivative Action
Note. Refer to Sections 5.10.2 and 5.10.3 for Crossover Value and Transition Bandwidth Value examples.
Information.
• P.I.D. Output – is the output value calculated by the controller. The output is divided into two different control
elements one for raising the product temperature (heat output) and one for lowering the product temperature
(cool output).
• Transition Bandwidth – used to transfer smoothly from one set of control terms to the other.
• Crossover Value – defines the changeover point between heat output active and cool output active. The
crossover value is also the centre of the transition and off hysteresis bands.
• Output Off Hysteresis Band – for the majority of applications Outputs 1 and 2 have opposing control actions
i.e. one is direct acting and the other is reverse. In this configuration both outputs are at 0% within the off
hysteresis band. The band setting is used to prevent oscillation of control changes.
• Heat/Cool Outputs – refer to
100
90
80
Max. Cool
Output = 75%*
70
Cool
60
Output
(%)
50
40
30
20
10
0
0 10 20
Crossover
Value (33%)
0%
Proportional
Band (Cool)
25.0%
Integral Action
Value (Cool)
Value
, above.
P.I.D. Output
Fig. 5.18 Heat/Cool Control – Principle of Operation
Q Heater = 1.5kW
Q Cooler = 0.75kW
Output Off
Hysteresis Band
=15%*
30 40 50 60
*User definable limits
P.I.D. Output (%)
Transition
Bandwidth
20%
5 CONTROL OPERATION...
100
Max. Heat
Output = 88%*
Heat
Output
(%)
0
70 80 90 100
100%
Proportional
Band (Heat)
20.0%
Integral Action
Value (Heat)
Derivative Action
Value
31