Precautions In Measurement - Fluke Comark N8004 Manuel D'utilisation

8. PRECAUTIONS IN RH MEASUREMENT
Apart from the need to take reasonable care when using the N8004/6
as described already, there are precautions to be taken in measuring
humidity, regardless of the instrument being used.
AIR CIRCULATION
Without air circulation there will be humidity differentials across the
room or chamber.
TEMPERATURE
The temperature differences that exist across a room or chamber,
though small, will have a large effect on Relative Humidity. In a typical
case 0.5%RH for a temperature difference of 0.1°C (0.2°F).
AIR VELOCITY
Some air velocity is necessary to ensure accurate results and fast
response time.
ATMOSPHERIC PRESSURE EFFECTS
These are often neglected, but can be significant. As an example, for
the same temperature, air measured at 1050mB (millibars) may give an
RH of 70%RH, whereas the same air at 950mB will read 77%RH.
CONDENSATION
This can occur at high RH when the probe is below the ambient dew-
point. Though the N8004/6 humidity sensor will recover from this, it
should be avoided if possible.
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