This document discusses carbon monoxide detection using non-dispersive infrared instrumentation. It describes CO as an odorless, colorless gas that is toxic above 35 ppm. The instrument works by measuring the absorption of infrared light at 4.6 micrometers by CO molecules in a gas cell. A reference gas is generated by oxidizing CO to CO2 to eliminate interference from other gases. The analyzer provides accurate, stable measurements with automatic ranging from 0-100 ppm CO concentration.

2. Basics about carbon monoxide (CO)
Instrumentation
Working principle
Specifications

3.  Carbon monoxide (CO) is a colourless, odourless, and tasteless gas that is
slightly less dense than air. It is toxic to humans when encountered in
concentrations above about 35 ppm.
 Wavelength absorption at 4.6µm(4600 nm)
 In the atmosphere, it is spatially variable and short lived, having a role in the
formation of ground level ozone.
 Carbon monoxide is produced from the partial oxidation of carbon containing
compounds; it forms when there is not enough oxygen to produce carbon
dioxide (CO2), such as when operating a stove or an internal combustion
engine in an enclosed space.
 Worldwide, the largest source of carbon monoxide is natural in origin, due to
photochemical reactions in the troposphere that generate about 5 × 1012
kilograms per year.
 Other natural sources of CO include volcanoes, forest fires, and other forms
of combustion.

4. Structure of analysing unit
Absorption spectra of various
gaseous in infrared region.
INSTRUMENTATION

5.  The reference gas is generated by purging the sample through an oxidation
process, where an oxidizing catalyst burns the CO to CO2.
 These features eliminate interference from other elements, resulting in highly
accurate measurements.
 It does not use such components as reflecting mirrors, which attract foreign
matter.
 This means the optical bench stays clean assuring you of stable results over
long periods of time.
 Cross-flow modulation provides measurements, which are stable and accurate
with the client reducing significantly instruments maintenance costs. Solenoid
valves open and close continuously to alternately with the unique cross-flow
modulation method, introduce sample gas and a reference gas at a constant
flow rate into the sample cell.
 The APMA-370 uses an AS type (anti shock) interference-compensating
detector, and a purified reference gas.

6. NON DISPERSIVE INFRARED METHOD
 Non dispersive infrared method depends on the characteristics
energy of absorption of CO molecule at wavelength of 4.6micro meter
(4600 nm).
 IR energy is also absorbed by the other gases like CO2, CH4,SO2,
etc..
 co analyser based on IR absorption would give grater sensitivity with
larger cell path lengths.
They are calibrated by passing a known ppm conc. Of CO in the
nitrogen into the sample cell. The zero is set by using a pure nitrogen as
a sample.

7. The unit analyser consists of a infrared source lamp, a measurement
cell, an optical filter and condenser micro detector with interference
compensation detector.
The detector is comprised of two parts, a detector for measuring CO
(the target component of the measurement) and an interference
compensation sect ion for measuring the interference gas.
When measuring atmospheric gas, a typical example of interference 'gas'
is moisture.
The reference gas is created by refining the sample gas with an oxidation
catalyst.

8. By changing CO in the sample gas to CO2 using the oxidation catalyst, it
becomes possible to obtain an accurate measurement by comparing and
cancelling out the effects of interference from other gases, even if the
other gases have a large potential of interfering components.
However, when the concentration of interference gas changes, since
there is a time gap for the sample gas and the reference gas to reach the
measurement cell, influence due to interference gas may occur.
In order to over come such a change in interference gas concentration,
APMA-370 measures the concentration of interference gas component
with an interference compensation detector and corrects its influence on
the output signal of the measurement detector, therefore highly accurate
measurements are possible.

9.  Range: Standard 1 0 ppm to 10/20/50/100 ppm Automatic range switching
Standard 2 0 ppm to 5/10/20/50 ppm Automatic range switching
Optional Max. 5 ranges between 0 and 5/100 ppm, Maximum range ratio: 10
 Minimum detection sensitivity: For ranges of 10 ppm or less: 0.05 ppm
For ranges exceeding 10 ppm: 0.5% of the F.S.
 Reproducibility (repeating accuracy): ±1.0% of the full scale
 Linearity (readout error): ±1.0% of the full scale
 Zero drift: ±1.0% of the full scale/day or ±0.1 ppm/day (whichever is larger)
±2.0% of the full scale/week or ±0.2 ppm/week (whichever is larger)
(ambient temperature change: within 5°C)
 Span drift: ±2.0% of the full scale/day
±3.0% of the full scale/week (ambient temperature change: within 5°C)
 Response rate: 60 s or shorter
 Interference effect: Moisture (25°C 80%) : ±0.3 ppm
CO2 0.1%: ±0.3 ppm
 Sample collection rate: Approximately 1.5 L/min
 Flow rate of calibration gas: Approximately 2.5 L/min