Det-Tronics PIR9400 PointWatch Infrared Hydrocarbon Gas Detector - Manual (Page 9)

7 95-8440 9.3
5. The sensor should be accessible for maintenance.
6. Excessive heat or vibration can result in premature
failure of any electronic device and should be
avoided if possible.
NOTE
For additional information on determining the
quantity and placement of gas detectors in
a specific application, refer to the article titled
“The Use of Combustible Detectors in Protecting
Facilities from Flammable Hazards” contained
in the Instrument Society of America (ISA)
Transaction, Volume
20 , Number 2 .
0 TO 100% LFL LINEaRIzED OUTPUT OPTIONS
The PointWatch IR Detector is provided with five field
selectable “standard gas” signal processing program
settings. These settings create a linearized scale for
methane and other gases like ethane, propane, butane,
ethylene, or propylene, and are defined as linearized
PointWatch gas measurement outputs. This means
that the detector is capable of providing an analog
signal output that is directly proportional to the % LFL
concentration for these gases, provided the proper gas
setting has been selected, and the it has been calibrated
with the proper calibration gas type.
The PointWatch Detector is factory configured for 0 to
100% LFL methane. To re-configure the detector for one
of the other gases, remove the electronic module from
the housing and select the desired gas by changing
the setting on the rotary gas selection switch. (Refer
to “Changing Linearized Output Gas Selection.”) The
detector must then be calibrated using a
50% LFL
mixture of the selected gas.
NOTE
Failure to calibrate the device with a 50% LFL
mixture of the selected gas will result in a sensor
fault and improper operation of the detector.
Response of Methane-Calibrated PointWatch Detector
(Factory Setting) to Other Gases
Figure
8 shows the signal output of a PIR 9400 that has
been properly calibrated for methane in response to
other gases. This data should be used as a reference
only. It is recommended to always calibrate the detector
with the type of gas to be detected.
PointWatch Model PIR 9400 Transfer Curves
The gas detector, when set for methane, provides
detection of other hydrocarbon vapors at higher LFL
readings (see Figure
8 ). In addition to the standard gases
previously mentioned, the PointWatch Detector is capable
of detecting and measuring many other hydrocarbon
gases and vapors. Although linear detector outputs are
not offered for most of these gases, an accurate gas
concentration measurement can be made by using a
cross-reference data sheet known as a “transfer curve.”
(Available upon request.) The transfer curve data sheet
is always based upon the following:
1. The data applies to one specific gas/vapor type
only.
2. The data is collected at a specific test temperature.
(Significant differences in ambient hazard area
temperature as compared to test temperature may
impact transfer curve accuracy.)
3. The data compares actual hazardous gas
concentration in %LFL to the detector signal output
level, using all five standard gas settings.
The transfer curve data is then used:
1. To select the optimum detector standard gas
setting.
2. To select the appropriate setpoint levels for proper
alarm relay actuation. This will ensure that external
alarm response action occurs as required.
0
0 10 20 30 40 50 60 70 80 90 100 110
10
20
30
40
50
60
70
80
90
100
110
%LFL GAS
RESPONSE OF METHANE CALIBRATED POINTWATCH TO OTHER GASES
POINTW
A
TCH OUTPUT (% LFL)
ETHANE
PROPANE
ETHYLENE
PROPYLENE
C2019
Figure 8—Response of Methane-Calibrated
PIR9400 (Factory Setting) to Other Gases, at
Tamb = 25°C