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MAN0889_Issue 3_03/13
2.2 Transmitter and Receiver Unit
Air Shield
Gas In/Out
Gassing Cell
2.2.1 Transmitter
The Transmitter produces an intense, collimated infrared beam from a Xenon arc flashlamp. The Transmitter
window is heated to minimise condensation and frosting. During particularly cold operating conditions, the
heating of the Transmitter window is increased to turbo levels. The turbo mode can be disabled if not required.
Electrical connections to the Transmitter are made via wires which run through the protective, flexible conduit.
There are three Transmitter wires, red (+24V), black (0V) and green/yellow (GND).
Note: The infrared beam is invisible and eye safe.
2.2.2 Receiver
The Receiver collects infrared radiation from the Transmitter and performs measurements to enable methane
gas in the beam path to be detected.
The Receiver output signal is 4 - 20mA available as a source or sink option. The output is calibrated for a
range of 0 to 100% LEL methane.
Note: The detector uses the duct width in the calculation of gas reading – it is essential that this is
specified correctly during installation (See Appendix B.2 for the explanation of how open path gas
detectors measure gas concentration)
Output signal levels below 4mA are used to indicate Fault (0mA), Inhibit (2mA), Beam Blocked (2.5mA) and
Low Signal (3mA).
The Receiver communicates with the SHC1 Handheld Interrogator using an RS485 output. The SHC1 is used
to perform commissioning, functional testing and diagnostic procedures.
The Receiver window is heated to minimise condensation and frosting.
Electrical connections to the Receiver are made via wires which run through the protective flexible conduit.
There are six Receiver wires, red (+24V), black (0V), white (4 - 20mA), orange (RS485 A), blue (RS485 B) and
green/yellow (GND).
2. Overview
Mounting Block
Transmitter
10
Searchline Excel Cross-Duct Technical Handbook
Slot for test filter
Beamsplitter
Receiver
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