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CHEMCO Exit Exam • Set 12 Question 5 of 30

Operating Principle of the Infrared instrument: identify the key principle that leads to detection of hydrocarbon gas,

✓

Direct Answer

Option D: When there is combustible gas present, there is a predictable drop in the output from measurement signal detector because the gas is absorbing light.

Infrared gas detectors operate on the principle that hydrocarbon gases absorb specific infrared wavelengths. When combustible gas is present, it absorbs the IR light, causing a predictable drop in the measurement signal detector's output. This reduction is directly proportional to the gas concentration, enabling accurate detection for safety, as per ISGOTT guidelines.

All Options

A
The amount of absorption is related to the concentration of the gas and is measured by a set of optical detectors and suitable electronic systems.
B
The change in the intensity of the absorbed light is measured relative to the intensity of light at a non-absorbed wavelength.
C
When there is no gas present the signals of reference signal detector and measurement signal detector are balanced.
D
When there is combustible gas present, there is a predictable drop in the output from measurement signal detector because the gas is absorbing light. (Correct Answer)

Detailed Explanation & Context

Infrared gas detectors operate on the principle that hydrocarbon gases absorb specific infrared wavelengths. When combustible gas is present, it absorbs the IR light, causing a predictable drop in the measurement signal detector's output. This reduction is directly proportional to the gas concentration, enabling accurate detection for safety, as per ISGOTT guidelines.

Relevant Framework: STCW 2010 Manila Amendments • DG Shipping E-Learning & Exit Exam Standards • Advanced Training for Chemical Tanker Cargo Operations (CHEMCO).

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