AFA4000/E VAV Airflow Controller / p.130
The ideal setting is to select a value that is as small as
possible which gives stable control of the damper or inverter
without ‘hunting’. (Refer to section 0 for a practical
explanation of how to set this value on a fume cupboard).
Example Prop Band gain settings:
The Prop Band gain is 0 – 100% of full scale (1.00 m/sec), so
if a Prop Band of 50% = 0.5 m/sec, the output will be at zero
when the airflow is 0.5 m/sec below the set point and be at
100% when the airflow is 0.5 m/sec above the set point.
The Integral Time is the correction action of the control
system. If only proportional control (prop band) is used, any
error is between the actual measured face velocity and the
set point face velocity. The Integral action takes this error
and adjusts the control output in a series of small steps to
bring the measured value to the same as the set point value.
The time taken to correct the measured value depends on
how many times the controller makes the small adjustments
over a period of time.
The Integral Time action is shown on the menu in Seconds.
Increasing the value will give a faster correction time.
If the value is set too low, it will take a long time for the
measured value to reach the set point. If it is set too high,
the measured value will correct very quickly but may
‘overshoot’ in each direction and cause ‘hunting’.
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