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Aan 008

1) As humidity increases, the concentration of oxygen in air decreases due to water vapor displacing some of the oxygen. 2) Alphasense oxygen sensors can operate in low and high humidity environments but extended use in very low or high humidity and temperatures outside specifications is not recommended. 3) Rapid changes in humidity can cause temporary changes in sensor output as humidity levels increase and decrease, but the sensors are designed to minimize these effects.

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43 views2 pages

Aan 008

1) As humidity increases, the concentration of oxygen in air decreases due to water vapor displacing some of the oxygen. 2) Alphasense oxygen sensors can operate in low and high humidity environments but extended use in very low or high humidity and temperatures outside specifications is not recommended. 3) Rapid changes in humidity can cause temporary changes in sensor output as humidity levels increase and decrease, but the sensors are designed to minimize these effects.

Uploaded by

MD FASIUDDIN
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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Alphasense Application Note AAN 008

AAN 008 HOW HUMIDITY AFFECTS OXYGEN SENSOR


OUTPUT

Introduction
As the relative humidity of air increases, the volume concentration of oxygen in air
(nominally 20.9% in dry air) is reduced by the increasing water vapour pressure.

Alphasense Oxygen Sensors and Humidity

22

21

20
%Oxygen

100 % RH
19
50 % RH

25 % RH
18
10 % RH

17 0 %RH
2
%O2 (100%rh) = 20.641+ 0.019T -0.0008T

16
0 10 20 30 40 50 60
T (°C)
Figure 1 shows how oxygen concentration in air is diluted by humidity at different
temperatures.

Due to the very small capillary dimension in Alphasense oxygen sensors, our oxygen
sensors can be used in low and high humidity environments (see relevant data
sheets). Extended operation in low humidity and high temperature outside the
quoted ranges is not recommended due to evaporation or absorption of water from
the electrolyte through the capillary.

© Alphasense Ltd Page 1 of 2 Issue 12


Sensor Technology House, 300 Avenue West, Skyline 120, Great Notley. Essex.CM77 7AA. UK
Tel: +44 (0) 1376 556700 - Fax: +44 (0) 1376 335899
Email: sensors@alphasense.com - Web: www.alphasense.com
Alphasense Application Note AAN 008

Transient humidity performance

Changing output due to slow humidity changes can be understood as dilution, as


shown in figure 1; however, rapid humidity changes cause transient performance as
shown for an O2-A1 oxygen sensor in figure 2 below. Peaks are negative when
humidity increases and positive when humidity decreases; the peak height increases
as the humidity change increases. Alphasense oxygen sensors are designed to
minimise humidity transient effects so even a large transient such as 10% to 90% rh
will not set a gas detector into alarm.

22

21.5
Output (uA)

21
50% rh
10% rh 10% rh 75% rh 90% rh 10% rh
10% rh

20.5

20
0 50 100 150 200 250 300 350
t (s)

Figure 2. Transient humidity response of Alphasense O2-A1.

The effect shown in figure 2 is greatest for low output sensors: the O2-E1 shows the
least effect, while the O2-A2 showed the strongest effect. Alphasense has modified
the O2-A2 to specifically improve transient humidity spikes- it now has similar
response as the O2-A1 shown above.

Contact Alphasense for advice on any specific application where humidity may be of
concern.

© Alphasense Ltd Page 2 of 2 Issue 12


Sensor Technology House, 300 Avenue West, Skyline 120, Great Notley. Essex.CM77 7AA. UK
Tel: +44 (0) 1376 556700 - Fax: +44 (0) 1376 335899
Email: sensors@alphasense.com - Web: www.alphasense.com

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