Det-Tronics PW9200x Pathwatch IR Gas Detection System - Manual (Page 16)

1. Attach the Flowmeter Outlet Hose to the appropri-
ate hose fitting on the Calibration Tube as shown
in Figure 8.
2. Remove the two protective caps from the
Calibration Tube. To make certain that it is com-
pletely free of any residual hydrocarbon vapors,
purge the Calibration Tube with oil-free com-
pressed air at no more than 5 psi and 10 SCFH
for 2 minutes. Do not block the vent. Do not
pressurize or evacuate the calibration tube while
purging.
3. Remove the receiver window assembly. Set the
MODE switch on the front panel to the OPERATE
position. If 4 to 20 ma output option is used, set
the OUTPUT SELECT switch on the front panel to
V and break the connection at the junction box
between the RATIO output (terminal 1) and its
field wire to remove the current load.
4. Install the Calibration Adapter on the transmitter
window mounting ring with the four 10-32 x 3/4
inch screws provided with the adapter.
5. Insert the calibration tube into the adapter, so that
the flowmeter is vertical on the right side of the
tube. Make sure that the tube is seated squarely
and securely in the adapter.
6. Attach the vent hose and flowmeter inlet hose to
the calibration tube as shown in Figure 8. For
heavier than air gases, the flowmeter outlet hose
is connected to the hose fitting on the bottom of
the calibration tube and the vent hose is connect-
ed to the hose fitting on the top. For lighter than
air gases, these two connections are reversed.
7. Adjust the OUTPUT ZERO potentiometer on the
receiver until the RATIO voltage is 0.1 ± 0.1 vdc.
8. Attach the calibration gas cylinder to the flowme-
ter inlet hose, making sure that the regulator is
shut. At the junction box, attach a digital volt-
meter with a resolution of at least 1 millivolt dc
between the RATIO output (terminal 1) and SIG-
NAL GROUND (terminal 2).
WARNING
DO NOT pressurize or evacuate the calibration
tube. Make sure vent hose is not blocked or
crimped.
9. With the gas cylinder regulator set at no more
than 2 psi, open and adjust the regulator and flow
meter valves so that the flow indicator on the cali-
bration tube reads 5 SCFH.
10. Wait at least five minutes and observe the RATIO
output voltage. The reading should be within the
range indicated on the calibration graph. If the
RATIO output is not within the calibration range,
use the CALIBRATION ADJUSTMENT poten-
tiometer on the front panel of the receiver to bring
the RATIO output within the desired range.
11. Close the gas regulator. Remove the flowmeter
inlet hose from the gas cylinder regulator.
12. Remove the calibration tube from the calibration
adapter and replace the protective end caps.
Remove the calibration adapter from the window
mounting ring.
13. With clean air present in the path, re-adjust the
OUTPUT ZERO potentiometer on the receiver so
that the RATIO voltage is 0.1 ± 0.1 vdc.
14. If the 4 to 20 ma output option is used, return the
OUTPUT SELECT switch on the front panel to the
MA position. Reconnect the RATIO field wire in
the junction box.
USE OF THE CALIBRATION GRAPH
The instrument output is related to the presence of
hydrocarbon vapor in the path in terms of a unit
called PPM-Meters (PPM-M). Because it is an open
path system, the instrument’s measurement is a func-
tion of the gas concentration (expressed in PPM)
times the length of the vapor cloud (expressed in
meters).
In interpreting the instrument’s output, two possible
conditions exist:
A. The hydrocarbon vapor cloud is larger than the
path length.
14
HOOK-UP FOR
LIGHTER-THAN-AIR GASES
HOOK-UP FOR
HEAVIER-THAN-AIR GASES
A
A
B
B
C
C
HOSE IDENTIFICATION
A. FLOWMETER INLET
B. FLOWMETER OUTLET
C. VENT
REAR VIEW OF CALIBRATION TUBE
(INSTRUMENT SIDE)
A1493
Figure 8—Calibration Hookup