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Cascade control—first stage
CNT-APG002-EN 35
®
Figure 25: TGP program for discharge-air temperature setpoint in cascade control
If you use the settings shown in Table 14, you should not have to tune the
loop. These values can be used in almost any cascade control application
without change. The proportional and integral gains are high to respond
aggressively to the error and change in error. The minimum and maxi-
mum output values keep the output between 50°F (10°C) and
120°F(49°C).
Figure 26 on page 36 shows an example of the relationship between the
calculated discharge-air temperature setpoint and the space temperature.
The discharge-air temperature setpoint reacts strongly to small changes
in error because of the high proportional gain.
If space temperature sensor has
failed, switch control to space
temperature setpoint
Table 14: Settings for discharge-air temperature setpoint
PID setting Initial value
Proportional gain 20.0
Integral gain 5.0
Derivative gain 0.0
Error deadband 0.5
Action Reverse
Sampling frequency 60 seconds
Minimum output 50°F
Maximum output 120°F