AD-1252 Thermal Dispersion Probe Airflow Measuring System Installation Instructions
15
GAIN
This option adjusts the gain for the average velocity
calculation. Press ENTER from the Options menu to
access the GAIN adjustment submenu. Use UP and
DOWN to adjust the desired gain value
(Range = 0 to 99). Press ENTER to accept the value.
See Figure 20.
OFFSET
This option adjusts the offset for the average velocity
calculation. Press ENTER from the Options menu to
access the OFFSET adjustment submenu. Use UP and
DOWN to adjust the offset value (Range = 0 to 1000).
Press ENTER to accept the value. See Figure 21.
Field Calibrating GAIN and OFFSET
One-Point Field Compensation Using Gain
Adjustment
Use this method for calibrating a device that is being
controlled to a single flow rate setpoint (for example,
minimum outside air flow or intended operating
setpoint).
•
Control the airflow to one fixed value during the
calibration process.
•
Set the fan speed, dampers, and VAV boxes (if
possible) on the unit to a fixed speed or position
when measurements are taken and record all
setting.
Complete the following steps to calculate the gain for
the controller.
1.
Set the in controller values for gain equals 1.0 and
the offset equals ZERO, and set to display CFM (L/
S) or FPM (M/S), depending on what is measured.
(FACTORY RESET sets Gain = 1, Offset = 0, and
velocity units to FPM.) If the units displayed are for
volume (CFM and L/S), make sure that the area
calculation is correct for each respective area
where measurements are being taken.
2.
Record the flow rate displayed on the controller
during the time that reference measurements are
taken.
3.
Record reference measurements of the flow rate.
Make sure that the units (FPM, CFM, M/S, and L/S)
are the same for all measurements. If the units are
for volume (CFM and L/S), make sure that the area
calculated is correct for each area where
measurements are being taken.
4.
Calculate the gain by dividing the value recorded in
Step 3 by the value recorded in Step 2.
5.
Set the gain in the controller to the value calculated
in Step 4 above.
6.
Make sure that the offset remains at 0.0.
Two-Point Field Compensation Using Gain and
Offset Adjustments
Use this method for calibrating a device that is
controlling a flow across a range (for example, volume
matching or high and low operating setpoints).
Select two airflow rates within the expected operating
range. Do not select extremes that are outside
expected normal operating conditions. For example, if
winter design conditions are approximately 65% and
summer design conditions are 95%, those two points
would be calibration points.
Figure 20: Gain Submenu
UP
SW3
DOWN
SW4
ENTER
SW5
ENTER
SW5
GAIN
GAIN VALUE
:1.00
OFFSET
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Figure 21: Offset Submenu
UP
SW3
DOWN
SW4
ENTER
SW5
ENTER
SW5
OFFSET VALUE
:0
ZERO CUTOFF
OFFSET
F
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