LX Series Unit Ventilator Controller User's Guide 57
Gain
Gain is a multiplication factor that adds weight to the integral part of the PID loop.
The integral gain is similar to the proportional gain. The error is multiplied by the
value you entered as integral gain. If the gain is equal to 5% per °F and the error is
2F°, the integral output is 10% of the maximum possible output signal.
The integral gain differs from the proportional gain in that the output is increased
the longer that the error persists. This situation occurs because the product of the
error multiplied by the integral gain is periodically added to the output. When you
enter the time, you are entering the length of the time period over which the error is
added.
Time
Time is the cycle period for the integral part of the PID loop. The cycle period is
the time necessary for the integral error to attain the same value as the proportional
error.
How It Is Used
Imagine a building in a cold climate where the temperature of a certain space is
never quite warm enough. A log of the temperature of this space would produce a
graph such as Figure 23.
In Figure 23, the temperature never quite falls low enough to turn on the
proportional heat.
Temperature
Time
Setpoint
Heat is ON
Heat is OFF.
Space Temperature
8:00 8:30 9:0010:00
Figure 23: Never Quite Warm Enough:
Using Only a P Controller
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