Det-Tronics PW9200x Pathwatch IR Gas Detection System - Manual (Page 23)

SYMPTOM: Voltage at NUMERATOR (blue) test
jack relative to GROUND (green) is not within
0.3 to 0.5 vdc after proper alignment and out-
put zero adjustment.
POSSIBLE CAUSE: Improper preamplifier gain
setting for path length.
REMEDIAL ACTION: See Step 14 of “Optical
Alignment/Signal Strength” procedure.
SYMPTOM: RATIO is noisy or erratic.
POSSIBLE CAUSE: Instrument not optically
aligned.
CHECK: Voltage at NUMERATOR test jack.
Voltage should be 0.3 to 0.5 vdc.
REMEDIAL ACTION: If NUMERATOR voltage
is low, realign as described in “Optical
Alignment” procedure.
SYMPTOM: RATIO voltage is negative or 4 to 20
ma output is below 4 ma.
POSSIBLE CAUSE: The ZERO adjustment poten-
tiometer located on the front panel is not set
properly.
CHECK: Setting of ZERO potentiometer.
REMEDIAL ACTION: Adjust ZERO poten-
tiometer until RATIO output is 0.1 ± 0.1
vdc.
POSSIBLE CAUSE: Instrument malfunction.
CHECK: NUMERATOR and DENOMINATOR
voltages when a bare flashlight bulb or
bare 60 watt light bulb is held in front of
receiver window.
REMEDIAL ACTION: Replace each printed
circuit board (one at a time) and recheck
voltages. Contact factory if fault cannot
be located.
SYMPTOM: RATIO voltage is steady and does not
appear to be responding to heavy hydrocar-
bons within the monitored path.
POSSIBLE CAUSE: Malfunction of signal pro-
cessing circuitry.
CHECK: Response of RATIO when a piece of
plastic film (roughly 8 mils thick) is placed
in front of the receiver window. The
RATIO voltage should increase to at least
+2 vdc.
REMEDIAL ACTION: Substitute spare boards
and assemblies until defective part is
located and RATIO responds properly to
plastic film. Defective part can be
returned to factory for analysis and repair.
POSSIBLE CAUSE: Object in beam.
REMEDIAL ACTION: Remove obstruction.
SYMPTOM: HC Alarm does not activate when
hydrocarbon vapors are present in monitored
path, or HC Alarm activates too often.
POSSIBLE CAUSE: Improper HC Alarm threshold
setting.
CHECK: Voltage at HC ALARM SETPOINT
jack relative to GROUND. Refer to
Calibration graph in APPENDIX for con-
centration indicated by alarm threshold
setting.
REMEDIAL ACTION: Adjust setpoint if
required. See “Hydrocarbon Vapor Alarm
Threshold Adjust-ment” procedure.
POSSIBLE CAUSE: Malfunction of HC Alarm cir-
cuitry.
CHECK: RATIO voltage relative to voltage on
HC ALARM SETPOINT jack. If RATIO
voltage exceeds alarm setpoint and alarm
does not activate, a malfunction of alarm
circuitry exists.
REMEDIAL ACTION: Replace rear panel p.c.
board and HC alarm relay on
connector/relay board.
SYMPTOM: RATIO output obtained during calibra-
tion check is not within the range indicated by
the calibration graph.
POSSIBLE CAUSE: Excessive hydrocarbon
background at installation site.
CHECK: Hydrocarbon background along
instrument path length with an indepen-
dent hydrocarbon vapor analyzer.
REMEDIAL ACTION: Wait until hydrocarbon
background along path length of instru-
ment is low, then recheck calibration.
POSSIBLE CAUSE: Calibration shift after factory
calibration due to some parameter within the
instrument, or to some change in the installa-
tion parameters.
CHECK: Calibration to be sure that calibra-
tion check was performed properly and
calibration point obtained is repeatable.
REMEDIAL ACTION: If calibration check is
repeatable and not within calibration
range, adjust CALIBRATION ADJUST-
MENT potentiometer on front panel with
calibration tube filled and installed.
21 95-8400