PCM-2 Manual.pdf - Voss Associates

is selected. If desired, both inlets may be connected to the same gas source with
a "T" fitting.
Adjust the gas control to obtain a flow of 800 cc/minute as indicated by the
second flowmeter (Note that the flow indication may require 2-3 minutes to
stabilize. Do not permit the flow rate to exceed 1000 cc/min at any time).
Maintain this rate for about 4 hours minimum to ensure that the detectors are fully
purged, then decrease flow rate to 200 cc/minute as indicated by the first
flowmeter. If the hand probe option is installed, a third flow meter is provided;
purge this probe at 25 cc/minute for 1-2 hours, then decrease its flow to 5-10
cc/minute for normal operation.
If a gas manager is installed, refer to the Gas Management System (Option 12)
portion of the Options Section for proper gas adjustment instructions.
Accessing The
Computer
Either the front panel keypad or the main computer keyboard may be used to
control the instrument, however for calibration it is suggested that the larger
keyboard be deployed next to the CRT display. To access the computer, press the
ESCAPE key, then type the high-level system password (default value = 9999)
followed by the ENTER key. This will give access to the main menu.
Using the four arrow keys, select the OVERRIDE PARAMETERS screen which
is located under the EDIT heading of the main menu. Press the ENTER key to
open this screen, and enter a typical high voltage setting for gas proportional
detectors operating at your altitude, followed by ENTER. Press ESCAPE to
leave this screen and store the new voltage setting. Use the arrow keys to select
the BACKGROUND AVERAGES screen under the main menu DATA heading.
Background count rates for all detectors will be displayed within 1-2 minutes and
will be updated regularly thereafter. Once these values have stabilized, the unit is
ready for calibration and gas flows may be reduced as described above.
Before proceeding, use the arrow keys, ENTER and ESCAPE to navigate through
the various menus and submenus of the PCM-2 program. Examine each screen
and learn where various functions are located. Refer to the technical manual for
explanations of anything which is unclear.
Detector Voltage
Selection
Two high voltage plateau programs are provided, and it is recommended that both
be run before the instrument is put into service. Both are selected from the
CALIBRAnON menu.
Due to the large number of detectors on the PCM-2, it is not practical to run a
full voltage plateau on each. The BACKGROUND PLATEAU routine uses
natural background radiation as a calibration source and can run all detectors at
the same time. This test should be run over a wide range of voltages (typically
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