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13.5.2.
Analog Output Control
The analog output on the M3 unit controller (P2594) is set to closed loop PID or staged control when configured for
Constant Air Volume bypass damper (Configuration ID 2, position 7 must be set to Y). The closed loop PID method used
by the M3 unit controller has three constants manual resets; proportional (P), integral (I) and derivative (D) as shown in
figure 1. The PID control constants, as well as the output values for minimum and maximum, may be adjusted if
necessary.
No.
Screen Name
41
SUPPLY MANUAL RESET
31
SUPPLY PID P CONST
32
SUPPLY PID i CONST
33
SUPPLY PID D CONST
13.5.2.1.
Supply Manual Reset — Parameter 41
Supply Manual Reset is used when the output values for PID P, I, and D constant values are all set to 0 (OFF). This is the
approximate output expected which allows quicker settling at set point. On Constant Air Volume units with bypass
damper, this is also the damper position when blower is off. Supply Manual Reset can be adjusted between 20 to 100%.
Default setting is 52%.
13.5.2.2.
Supply Proportional Constant (P) — Parameter 31
To handle the present, this is the value of the "gain' that is multiplied times the error. The error is the difference between
the output and the set point. A large value of "P" will cause the output to reach the set point faster, however, this faster rate
can cause the output to overshoot the set point. On the other hand, a low value of "P" will reduce overshoot, but will cause
the output reaction to be too slow. The "P"constant parameter value can be adjusted between 0 –127 with 0 being off and
127 being the highest value.
13.5.2.3.
Supply Integral Constant (I) — Parameter 32
To handle the past, this gain is proportional to the amount of time that the error is present. This gain tries to integrate out
any offset. A high value of "I" can provide fast correction but can cause overshoot and ringing. The "I' gain should be set to
the lowest value possible that corrects the offset. "I" can be adjusted between 0127 with 127 being the lowest value. The
"I" constant parameter value is inverted. A value of 0 turns the integral factor off. A value of 127 is the minimum and 1 is the
maximum.
13.5.2.4.
Supply Derivative Constant (D) — Parameter 33
To handle the future, this gain is proportional to the rate of change of the error and provides a damping factor. The "D"
constant parameter value can be adjusted between 0 127 with 0 being off and 127 being the highest value. Most M3 unit
controller applications do not require using any "D" gain.
M3 Unit
Controller
Static
∑
Pres. SP
Feedback
Static Pres. Sensor
(A30 P267−7
Figure 12. PID Operation Diagram for CAVB Air Delivery
Table 38. Summary of PID Constants Parameters
CAVB Air Delivery PID Constants
Min
Default
Max
20.0
52.0
100.0
0
17
127
0
12
127
0
0
127
P Gain
I Gain
∑
Bypass Damper
D Gain
Units
Description
%
Manual reset value.
Counts
CAVB supply PID Proportional constant.
Counts
CAVB supply PID Integral constant.
Counts
CAVB supply PID derivative constant.
57
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