Introduction - Honeywell Searchline Excel Open-Path Technical Handbook

MAN0530 Issue 09 October 03
2104M0506
Searchline Excel is a hydrocarbon gas detection system that is available in two versions:
• Searchline Excel Open-Path Gas Detector
• Searchline Excel Cross-Duct Gas Detector
Searchline Excel Open-Path Gas Detector (OPGD) consists of a Transmitter unit that sends an
infrared beam to a Receiver unit up to 200 metres away, and can be located where a flammable
hydrocarbon gas cloud is likely to occur.
The Cross-Duct version of Searchline Excel is used where the path length is less than 5 metres,
for applications such as air intake ducts. Most of the installation and operating instructions for
the Open-Path Excel apply to the Cross-Duct Excel, but see Chapter 4 for specific information
about the Cross-Duct version.
Both types of gas detector operate on the principle of infrared (IR) absorption. Gases absorb
light at specific wavelengths depending on their molecular composition. Hydrocarbon gases
absorb in the infrared region of the spectrum. If a cloud of hydrocarbon gas is present, part of
the infrared light is absorbed by the gas, causing a reduction in the signal received that is
proportional to the amount of gas in the beam.
The Searchline Excel Transmitter unit produces the infrared light, and the Receiver unit features
optical detectors and signal processing electronics. Each unit is housed in a robust stainless
steel housing. The Receiver produces a 4 - 20mA analogue output equivalent to 0 - 5 LEL.m
(Lower Explosive Limit metres) of gas.
NOTE: THE INFRARED BEAM IS INVISIBLE AND EYE SAFE.
Searchline Excel is designed for use in the most demanding environments/applications and
provides a sensitive, fast and reliable response. The sophisticated open-path technology provides
immunity to sunlight and minimises the effects of environmental factors such as rain, fog, ice,
snow and condensation.
The Transmitter and Receiver units incorporate heated optics designed to minimise the build
up of humidity, condensation, snow or ice on the glass windows, that could obscure the optics
in extreme conditions.
The system is microprocessor controlled with integral self-diagnostics and fault finding facilities.
Local communication between an operator/technician and the gas detector system is made via
an associated Handheld Interrogator that uses the Receiver s inbuilt RS485 serial link. The
interrogator provides the user with a menu-style interface to select and invoke commands for
commissioning and configuring the system, and for viewing the system state and measurements.
The interrogator is connected to the Receiver via one of Zellweger Analytics' DVC100/DX100/
DX100 (M) types of Termination Unit, or via other types of junction box using the optional SHC
Protection Device. The DVC100 and DX100 are passive junction boxes whereas the DX100
(M) features an active digital interface that allows a remotely located control centre to monitor
the gas detector's signal output and perform basic commands using the Modbus Remote Terminal
Unit (RTU) protocol over an RS485 link.

1. INTRODUCTION

7
Searchline Excel