BAM 1020-9800 Manual Rev W.docx
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within +/- 1 deg C. To calibrate it, enter the ambient room temperature from your reference
standard into the REFERENCE field and press the CALIBRATE soft key. The RESET soft
key can be used to revert to default calibrations and start over if difficulty is encountered.
Note: Never calibrate this sensor if the BAM inlet heater has been operating recently. The
heater causes this sensor to measures higher than ambient. See the notes about
equilibrating or removing the filter RH sensor for calibrations below.
7.19 RH Test Menu
– Filter Humidity Sensor Test and Calibration
The TEST > RH screen is used to check or calibrate the filter relative humidity sensor located
in the air stream beneath the filter tape. The sensor measures the RH of the sample air to
control the Smart Inlet Heater system, which turns up or down as needed to maintain the
sample near or below the RH set point value. See Section 6.9. The filter RH sensor (part
9278) should match ambient RH within +/- 4% when properly equilibrated. If the sensor fails,
it usually reads something impossible like -25% or 135% RH.
The FILTER RH Test Screen
Important Equilibration Notes:
It is difficult to effectively correlate an ambient RH
measurement to the filter RH reading, because the BAM has some self-heating from the
Smart Heater which causes the filter sensor to measure significantly lower than ambient RH.
For this reason it is usually best to leave the factory default calibration alone, unless you have
clear evidence that it needs to be calibrated. If the filter RH sensor is calibrated without first
being fully equilibrated to ambient, it will introduce a large artificial offset.
For example: The ambient RH is 50%, but the filter RH sensor reads 20% due to inlet heat. If
the filter sensor calibration is adjusted to that it matches 50%, this adds a +30% offset to all
RH readings. Now the filter RH data values are all 30% too high and it looks like the inlet
heater is not functioning and not regulating the sample RH when it actually is. In addition, the
inlet heater may run at full power trying to achieve regulation to the set point.
To equilibrate the sensor without removing it from the sample stream:
Enter the TEST >
FILTER RH screen. The BAM will raise the nozzle and turn the pump on to pull room air past
the RH sensor. Unplug the inlet heater and allow the BAM to cool completely to room
conditions. This might take an hour or more. Position your RH audit device as close as
possible to the BAM sample nozzle during calibration.
To remove the sensor from the flow system for calibration:
Unplug the inlet heater and
remove the BAM case cover. Remove the black 3-port compression manifold from the flow
path. It is located under the nozzle motor and holds the two filter sensors. This is easiest with
tool 9627 from the BX-308 tool kit. Leave the sensors plugged into the circuit board. Do not
touch the RH sensor element because it is ESD sensitive. Move the sensor manifold away
from the BAM so that an accurate ambient RH value can be obtained. Enter the TEST > RH
FILTER RH CALIBRATION
BAM: 32.5 %
REFERENCE: 33.1 %
CALIBRATE RESET Exit
