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GSS - gas sensing solution application note

This application note reviews the important considerations for choosing a pump as part of a gas sampling system.

Some GSS sensors such as the SpintIR®-R, are designed to sample gas via a flow port adaptor. The gas can be derived from a sample bleed from high pressure system, or from a pump that is used to induce flow. Ideally, there should be a match between the required gas sampling speed and the gas flow rate

GAS FLOW RATE

The gas flow rate and sensor sampling speed have a major influence on the fidelity of the gas measurements and the response time of the sensor. As a rule of thumb, 5 x the volume of gas in the system is required to be fully exchanged in order to ensure ‘fresh’ gas is being sampled by the sensor. For example, if the gas sample volume is 20ml, you will need to flow 100ml of sample gas into the sensor measurement chamber to flush the chamber with the new gas.

In practice the amount of gas needing to be replaced is the volume of the complete sample system, including tubing, filters, pump, and sensor. The response time will be improved by minimising the volume of the complete system.

PUMP SELECTION

There will be many criteria for pump selection including the required flow rate, but also air tightness, size, cost, reliability, noise, weight, power consumption, material composition and lifetime. The priorities will be specific to the application but should start with pump flow rate.

CONTAMINANTS

GSS sensors, like almost all NDIR sensors, rely on the sample gas being in direct contact with optical surfaces. Whether that surface is a window, lens or reflective, all are susceptible to contamination by dry or wet contents that are contained in the sample gas. In the case of GSS, the flow path contains a reflective optic and the sample gas supplied to the sensor is required to be clean. If the source gas not already clean, some type of filter and/or water trap will be required.