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6. OPTICAL BENCH DESCRIPTIONS

6.1 Introduction

This section describes the basic construction and operation of the various types of bench that

may be fitted in an instrument. All the infrared types rely on a characteristic of heteroatomic

gases to absorb energy at specific wavelengths in the infrared spectrum, and, follow the

operating principles described in Section 1.6.1.

Each bench type makes use of a different technique. To recommend a type of bench best suited

to the requirements will generally relate to the type of gas measured and/or the accuracy and

sensitivity of measurement.

6.2 GC Bench (when fitted)

The GC (Gas Correlation) infrared bench is a non-dispersive single beam analyser in which the

gas to be measured is passed through an optical cell continuously. Although the instrument

output is in terms of gas concentration, this type of analyser operates as a comparator. That is,

its output is not absolute, but is established by standardising with a known gas mixture at a

point on the calibrated scale See section 4.

Motor

Sensor

Filter Wheel

Source

Lens

Optical

Filter

Window

Gas Entries

Lens

Analysis Cell

Detector

Figure 13 The Gas Correlation optical bench

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ADC MGA3000 series Specifications

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