5S MKIII CO2 Sensor. Performance and benefits. Analox Sensor Technology Ltd. 15 Ellerbeck Court, Stokesley Business Park North Yorkshire, TS9 5PT, UK

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1 5S MKIII CO2 Sensor Analox Sensor Technology Ltd. 15 Ellerbeck Court, Stokesley Business Park North Yorkshire, TS9 5PT, UK T: +44 (0) F: +44 (0) W: E:

2 List of Contents 1 Introduction How does an infra-red sensor work? What s different? Performance graphs Accuracy Long term drift... 5 Page 2

3 1 Introduction The 5S3 CO 2 sensor is Analox s next generation infra-red gas sensor. It was developed in response to improving standards in the diving industry and on the back of improvements in infra-red detector technology and micro-electronics. Various models are available covering a wide selection of gas measurement ranges, ppm being the most popular for use in the diving industry. 2 How does an infra-red sensor work? Gas ports Detector Lamp Aluminium bench Carbon dioxide (CO 2 ) gas absorbs light at certain specific wavelengths. Inside an infra-red sensor there is a lamp and a detector held a short distance apart by a rigid tube (called a bench in optics parlance). The lamp flashes, emitting infra-red light. Inside the detector the light is passed through filters which are tuned to the wavelength of infra-red light which CO 2 absorbs (similar to how green stained glass only allows green light through). So with no CO 2 inside the bench, much of the light reaches the detector, but with CO 2 inside the light is absorbed before it reaches the detector. Less light means more CO 2. 3 What s different? Compared to our previous CO 2 sensors, and those of many of our competitors, the Analox 5S3 offers several advantages: Dual channel detector. One channel is sensitive to CO 2 concentration while the other monitors the lamp output. Changes in light output are thus measured and compensated for. Stable mechanical design. Various features of the mechanical design make this sensor extremely stable, even when subjected to rapid temperature fluctuations. No need for drift compensation. Some of our competitors CO 2 sensors assume that they will see 400ppm from time to time and compensate for drift by resetting their reading to 400ppm when this happens. Our sensor drifts by less than 100ppm/year without such trickery. Page 3

4 Wide operational temperature range. Full specification performance is maintained over a -5 C to 55 C temperature range. Advanced micro-electronics. An ARM7 core and an ADC from the market leader combine to give precise measurement of the sensor signals and copious processing power for sophisticate digital signal processing techniques. On board pressure sensor. The errors caused by normal weather related changes in atmospheric pressure are greater than most people realise. Using a miniature pressure sensor the Analox 5S3 automatically compensates its readings. Industrial EMC immunity. The Analox 5S3 complies with the EMC requirements for CE marking for both the light industrial and heavy industrial standards. Rapid response time. The twin port sensor provides a large area for gas diffusion into the bench, giving a rapid response to changes in gas concentration. 4 Performance graphs 4.1 Accuracy Our 5000ppm units comply with the requirements of DNV for use in commercial diving to a depth of 350m and across the following variations in environmental conditions: Temperature range: -5 C 55 C (23 F 131 F ) Ambient pressure: 950mbar 1050mbar (712.5mmHg 787.5mmHg) Humidity: 0 99% non-condensing Vibration: Compliant to DNV OS-D201 Oct 2008, Section 3 B201 The sensor error is less than 25ppm plus 1% of the sensor reading plus 2.5ppm/ C of shift from the temperature of calibration (see graphs below). Max error, ppm CO CO2 error at constant temperature assuming calibration at 20 C CO2 max 0 C CO2 max 20 C CO2 max 30 C ppm CO2 Page 4

5 Max error, ppm CO CO2 error over temperature for different CO2 levels CO2 = 0ppm CO2 = 250ppm CO2 = 500ppm CO2 = 1000ppm CO2 = 2500ppm CO2 = 5000ppm Temperature C 4.2 Long term drift The graph below shows a log from three sensors monitoring atmospheric CO 2 over an eight month period. There is a significant swing during each weekday (less so in the summer when the windows are open) but the baseline remains steady at just below 400ppm as one would expect. Specified long term drift is < 100ppm / year. Page 5