A
i
r
F
l
o
w
T
un
i
n
g
P
I
D
S
t
a
t
u
s
:
32400
c
f
m
S
e
t
po
i
n
t:
32000
c
f
m
I
n
t
eg
r
a
t
i
on
T
i
m
e
:
300
s
B
a
nd
Per
F
a
n
:
300
c
f
m
D
e
r
i
v
a
t
i
v
e
T
i
m
e
:
15
s
C
u
rr
e
n
t
D
e
m
a
nd
:
38
%
Note: The Fan Air Flow screen is only displayed when CW or DX fan mode is set
to modulate to maintain Air Flow.
The dap4 uses a proportional integral derivative algorithm (PID) to maintain air
flow. The description of the settings offered below is only a guide. The difference
between the set point and the actual measured air flow is called the error.
Status: This is the display of the current airflow in cubic feet per minute.
Setpoint: This is the airflow set point in cubic feet per minute.
Integration Time: Used to slowly shift the fan speed level as a result of an error
between set point and t he measured a ir f l o w. If the Integral time is set too low
the f an s peed level could c ha ng e quickly, causing oscillation. If Integral time
s e tti n g is too long, the fan speed may become sluggish to change. A setting
of 0s puts the algorithm in a proportional only mode. Range of adjustment is 0 to
999s with a default setting of 50s.
Band Per Fan: This setting is effectively the “sensitivity” of the PID algorithm. The
smaller the band, the more the algorithm will try to correct the error. If the band
setting is too low, the system will oscillate by being over-responsive. If the band
setting is too high, fan speed may lack responsiveness. Ideally, the band
s et t ing s hou ld be as lo w a s possible without causing oscillation. Range of
adjustment is 0 to 32767cfm with a default of 650cfm.
Derivative Time: Causes a sudden change in fan speed to correct the error as a
result of a quick change in measured air flow. Typically, the derivative setting is
about a sixth of the Integral time setting. Range of adjustment is 0 to 9999 with a
default of 5. A setting of 0s (default) puts the algorithm in a P+I mode without
derivative function.
Current Demand: This indicates what percentage of the maximum speed that fan
is currently being driven.
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