D8 Series User’s Guide
Chapter 5: Tuning and Control
90
Heat and Cool Outputs
Each loop may have one or two outputs. Often a heater is controlled according to the feedback
from a thermocouple, in which case only one output is needed.
In other applications, two outputs may be used for control according to one input. For example,
a system with a heater and a proportional valve that controls cooling water flow can be controlled
according to feedback from one thermocouple.
In such systems, the control algorithm avoids switching too frequently between heat and cool
outputs. The on/off algorithm uses the control hysteresis parameter to prevent such oscillations
(see Hysteresis on page 115). When PID control is used for one or both loop outputs, both the
hysteresis parameter and PID parameters determine when control switches between heating
and cooling.
Setting Up and Tuning PID Loops
After installing your control system, tune each control loop and then set the loop to automatic
control. When tuning a loop, choose PID parameters that will best control the process. This section
gives PID values for a variety of heating and cooling applications.
NOTE!
Tuning is a slow process. After adjusting a loop, allow about 20 minutes for the
change to take effect.
Proportional Band Settings
Table 5.1 shows proportional band settings for various temperatures in degrees Fahrenheit
or Celsius.
Table 5.1
– Proportional Band Settings
TEMPERATURE
SET POINT
PB
TEMPERATURE
SET POINT
PB
TEMPERATURE
SET POINT
PB
-100 to 99
20
1100 to 1199
75
2200 to 2299
135
100 to 199
20
1200 to 1299
80
2300 to 2399
140
200 to 299
30
1300 to 1399
85
2400 to 2499
145
300 to 399
35
1400 to 1499
90
2500 to 2599
150
400 to 499
40
1500 to 1599
95
2600 to 2699
155
500 to 599
45
1600 to 1699
100
2700 to 2799
160
600 to 699
50
1700 to 1799
105
2800 to 2899
165
700 to 799
55
1800 to 1899
110
2900 to 2999
170
800 to 899
60
1900 to 1999
120
3000 to 3099
175
900 to 999
65
2000 to 2099
125
3100 to 3199
180
1000 to 1099
70
2100 to 2199
130
3200 to 3299
185
As a general rule, set the proportional band to ten percent of the set point below 1000° and five
percent of the set point above 1000°. This setting is useful as a starting value.
