Line of Sight Infrared Hydrocarbon Gas Detector AutroPath HC800 , 116-P-HC800/IGB, Rev. A, 2016-03-03
P/N 95-8744, v4.2 , rev. 3/16
Autronica Fire and Security AS
Page 2
opERation ovERviEw
THEORY OF OPERATION
The AutroPath HC800 transmitter module uses a Xenon
flash lamp to produce a collimated IR light source. This
light source illuminates the path between transmitter
and receiver. The transmitter uses a filter to block
visible light emissions and is eye safe.
As flammable hydrocarbon gases intersect the light
beam between the two modules, certain IR wavelengths
are absorbed by the gas, while other IR wavelengths
are not. The amount of IR absorption is determined by
the concentration of the hydrocarbon gas. A pair of
optical detectors and associated electronics located
in the receiver module measure the absorption. The
change in intensity of the absorbed light (active
signal) is measured relative to the intensity of light at
a non-absorbed wavelength (reference signal). The
microprocessor computes the gas concentration and
converts the value into a 4–20 mA current output signal,
which is then communicated to external control and
annunciation systems.
The gas concentration is indicated by a 4–20 mA
signal, which corresponds to 0-5 LFL-meters. To better
understand the concept of LFL-meters, refer to Figure
1, which shows how three gas clouds of different size
and concentration would produce the same output of
1 LFL-meter by the line of sight gas detection system.
To convert a given LFL-m value to ppm-m for methane,
propane, or butane gas, refer to Table 1.
DETECTABLE GASES
The AutroPath HC800 is capable of detecting most
hydrocarbon gases and vapors including methane,
propane, and butane. Gas type and other operational
parameters are selected via HART or Modbus
communication. The AutroPath HC800 is factory
calibrated to methane, propane, and butane, and
comes from the factory set for methane. For detection of
gases other than the three selection settings (methane,
propane, and butane), performance characteristics /
transfer curves are available. Please contact the factory
for details.
DETECTION RANGES
The AutroPath HC800 is offered in two detection ranges
in order to meet customer needs, as listed below:
Short Range 5–60 meters
Long Range 30–120 meters
For installations with short separation distances (5-15
meters for the short range model and 30-40 meters for
the long range model), the range reduction aperture kit
(supplied) is required. Refer to “Aperture Kit for Short
Range Applications” section in this manual for details.
The correct range for the AutroPath HC800 must
be chosen to meet specific application needs. The
detection range of the AutroPath HC800 pair is
determined by the Receiver. Receiver units can be
converted from long to short or short to long range
in the field by replacing the front electronics module.
A single transmitter model is used for both detection
range options.
STANDARD OUTPUT
The
AutroPath HC800
receiver module provides an analog
4
–
20 mA signal output. HART and RS-485 Modbus serial
communication are available at either module.
The 4–20
mA current loop corresponding to 0–5 LFL-meters is
provided for connection to analog input devices such
as gas controllers, logic controllers, or distributed
control systems (DCS). To convert the mA reading to
LFL-meters, use the following formula:
mA Reading –4
X 5 = LFL-Meters
16
Figure 1—Detector Response to Three Gas Clouds
of Different Size and Concentration
1M @ 100% LFL = 1 LFL-M
2M @ 50% LFL = 1 LFL-M
10M @ 10% LFL = 1 LFL-M
HC800 OUTPUT EQUALS 1 LFL-M IN ALL THREE SCENARIOS
A2665
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