Sample Gas Processor

iGA Sample Gas Processor cropped2

The Sample Processor Slave Module is used to manage the sample and calibration gases being sent to the CO2 Slave and O2 Master analysers.

All HMCS Sample processors are fitted with an internal sample gas pump.  The sample pump is used typically in SAT control chamber applications where there is sometimes insufficient pressure from the chambers (e.g. at the end of a decompression) to allow a suitable sample flowrate.  Under these conditions, the pump is switched on (either automatically or manually) to draw a sample through the unit.  Note that the pump does NOT operate when the calibration gases are online – as it is assumed there will always be sufficient pressure in the calibration gas supplies.

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On the rear panel of the Sample Processor there are five quick-connect couplings.  The Analyser system requires a supply of calibration gas to verify performance on a periodic basis, and these calibration gases are typically:

    1. Zero Calibration Gas (pure helium) for checking/calibrating the zero reading of analyser sensors.
    2. Low-Span Calibration Gas (a mixture of O2 and a small trace of CO2 with the balance gas being helium).  Typical concentrations may be around 4% O2 and 500ppm CO2.  This gas is used for checking analysers when the diver’s gas (chambers or masks) is of a similar low S.E. concentration.
    3. Mid-Span Calibration Gas (a mixture of O2 and a small trace of CO2 with the balance gas being helium).  Typical concentrations may be around 10% O2 and 1000ppm CO2.  This gas is used for checking analysers when the diver’s gas (chambers or masks) is of a similar medium S.E. concentration.
    4. High-Span Calibration Gas (a mixture of O2 and a small trace of CO2 with the balance gas being helium).  Typical concentrations may be around 15% O2 and 3000ppm CO2.  This gas is used for checking analysers when the diver’s gas (chambers or masks) is of a similar high S.E. concentration.

Different concentrations are used depending on company policies and available supplies, but it is the responsibility of the operations personnel to ensure that suitable calibration gas supplies are available at all times.  The different calibration gases are also used to verify the correct linearity of the O2 and CO2 sensors (this is done automatically by the HMCS system during the 12-hourly calibration procedure).