Det-Tronics PW9200x Pathwatch IR Gas Detection System - Manual (Page 14)

ALIGNMENT
View the transmitter through the receiver alignment
scope to verify that the cross hairs of the scope are
centered on the target attached to the transmitter
mount. If the cross hairs are not centered on the tar-
get, alignment has changed. Adjust the pan and/or
tilt of the receiver until the cross hairs of the alignment
scope are centered on the target. Check the transmit-
ter alignment scope to verify that the cross hairs are
centered on the target attached to the receiver mount.
If not centered, adjust as with the receiver.
NOTE
Accurate alignment must be maintained for reli-
able operation of the instrument. If alignment is
changing, the vertical mounting pipe may not be
sufficiently stable, or it is being moved during
operation. This problem must be corrected to
ensure that alignment is maintained.
SIGNAL STRENGTH
The NUMERATOR output read from terminal 3 in the
junction box should be between 0.3 vdc and 0.5 vdc.
If the NUMERATOR voltage is less than 0.3 volts,
realign the instrument as described in the “Optical
Alignment/Signal Strength” procedure. If the NUMER-
ATOR output obtained exceeds 0.5 volts, the pream-
plifier gain must be adjusted as described in Step 14
of the “Optical Alignment/Signal Strength” procedure.
OUTPUT ZERO
The OUTPUT ZERO (RATIO) is factory set for hydro-
carbon-free air. The OUTPUT ZERO should be
checked periodically and the ZERO potentiometer
should be adjusted when necessary.
1. With the instrument viewing hydrocarbon-free air
and both transmitter and receiver windows in
place, record the RATIO voltage at the junction
box. If the RATIO voltage is not 0.1 ± 0.1 vdc, the
OUTPUT ZERO potentiometer should be adjusted
as described in the following steps.
2. Remove the receiver window and locate the OUT-
PUT ZERO potentiometer on the front panel.
3. If the RATIO voltage recorded in step 1 was high-
er than 0.1 ± 0.1 vdc, rotate the ZERO poten-
tiometer counterclockwise until the RATIO voltage
is within the desired range.
4. If the RATIO voltage recorded in Step 1 was lower
than 0.1 ± 0.1 vdc, rotate the ZERO potentiometer
clockwise until the RATIO output is within the
desired range.
HEAVY HYDROCARBON RESPONSE
CONFIDENCE TEST
To verify that the instrument is responding to the pres-
ence of heavy hydrocarbon vapor in the path:
1. With power applied to the instrument, connect a
digital voltmeter between the RATIO (brown) and
SIGNAL GROUND (green) test jacks on the front
panel.
2. Hold a piece of clear plastic (roughly 8 mils thick)
in the path of the light beam. Be careful not to
block the beam with anything other than the plas-
tic film.
3. The RATIO voltage should increase sharply. If
the RATIO voltage does not increase, contact the
factory for assistance.
4. Repeat Steps 1 and 2 and check the resistance
between terminals 6 and 7 in the receiver junction
box. The resistance should increase from zero to
infinity.
STATUS ALARM CONFIDENCE TEST
To verify that the instrument status alarm circuit is
working properly:
1. With power applied to the instrument, block the
beam with an opaque object.
2. The Status Alarm should activate within 120 sec-
onds. The resistance between terminals 4 and 5
in the receiver junction box should increase from
zero to infinity. If the status alarm does not acti-
vate, contact the factory for assistance.
INSTRUMENT OUTPUT
The 0 to 10 vdc RATIO output is available on all
PW9200 instruments at the RATIO test jack (brown)
on the front panel and at the receiver junction box
when the OUTPUT SELECT switch is set to position V.
An optional 4 to 20 ma output can be ordered with the
instrument or can be field installed at any time after
purchase. The 4 to 20 ma output option converts the
standard 0 to 10 vdc RATIO output to a 4 to 20 ma
output. If installed, the 4 to 20 ma output will be avail-
able at the receiver junction box when the OUTPUT
SELECT switch on the front panel is set to the MA
position. The 4 to 20 ma current may be tested by
opening the user installed RATIO wire in the junction
box (terminal 1) and connecting a current meter
between the RATIO wire and terminal 1. The 4 to 20
ma output will drive a user supplied load of 0 to 500
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