September 24, 2020

What impact do Gas Standards have on my Testing Measurements?

Customer feedback has shown us that many measurement errors are caused by a mismatch between the gas standards used by the device under test and the analyzer used for testing.

Keep in mind both the devices are measuring the same gas flow but each device can be set to apply an offset to the displayed values. Those offsets are convenient for the operator but they can be a challenge for the test technician.

The most commonly used gas standards are:

STP: Standard Temperature and Pressure – the device does a conversion based on a dry gas flow, at 21.1°C, and at an ambient pressure of 1013.25 mbar.

ATP: Ambient Temperature and Pressure – the device does a conversion based on gas flow at current humidity and temperature and local ambient pressure.

BTPS: Body Temperature and Pressure – the device does a conversion based on gas flow saturated with moisture (100% RH) at body temperature (37°C) and flowing at local ambient pressure.

However, there are many more gas standards in the industry and our analyzers can be set to apply any one of seventeen different standards.

Each manufacturer can stipulate which gas standard their device uses.  BTPS is often used in the ventilation environment.

 Here’s an example from our headquarters in Buchs, Switzerland 450 meters above sea level (960mbar) at a sunny window space with a temperature of 28°C and a relative humidity of 50%. The device in this example supplies a steady flow of 100 liters per minute (LPM.)

With the following gas standard applied:

STP: displays 100 LPM

ATP:  displays 110.19 LPM

BTPS: displays 119.04 LPM

The error is quickly at 19% or in this example 19.04 liters per minute.  Which is why it is essential to select the same gas standard on each device before comparing their displayed measurement values…lesson learned!


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