PC33 & 52 User’s Manual
20
97238 Issue 2, October 2013
appendix d
•
Clean environments are always best for humidity measurements, but this is
especially critical at very low humidity. Even fingerprints harbour water. High
purity cleaning agents are recommended: Analytical Reagent (AR) quality
solvents for oil-based contaminants, and purified water (distilled or de-ionised)
for salts. Cleaning should be followed by thorough drying by a clean method.
•
Sample tubing should be as short in length as possible. The surface area should
be minimised by using the narrowest tubing that the flow conditions will permit.
•
Avoid leaks. Minimising the number of connections (elbows, tees, valves, etc.)
helps with this.
•
Adequate flow of the gas sample should be ensured, to minimise the influence of
sources of stray water in the flow path.
•
‘Dead ends’ should be avoided, as they cannot easily be flushed.
•
back-diffusion of moisture should be minimised, e.g. by fast flow rates of gas,
long exhaust tubes after the sensor, or by valves which isolate the low-humidity
region from ambient air.
Practical recommendations for specific types of hygrometer
Relative humidity capacitive sensor
•
Care should be taken to avoid mechanical shock (impact) or thermal shock
(sudden temperature changes). Sensors should be protected from steam or
water sprays, and from direct sunlight.
•
Where a sensor is at risk of exposure to dust, droplets, or the occasional knock
during handling, the appropriate guard or filters for the sensor head should be
used.
•
Any temptation to breathe on the sensor, or to wave it over cups of tea, etc.
should be resisted. Filters and saturation guarding may protect the sensor, but
these actions carry a risk of damage by condensation or other contamination.
•
Protective filters can slow the response time of sensors. This can be avoided by
removing any filter, but the benefit must be weighed against the risk of damage
to the sensor.
•
Sensors should not normally be submerged in liquids. In the case of a resistive
(electrolytic) sensor, water or other liquids would certainly damage the sensor
beyond repair.
•
Salt solutions are especially commonly used for calibration of electrical sensors,
and should be provided with traceability directly or via a calibrated hygrometer.
Protection of sensors from direct contact with salt or solution is most important
as contamination would destroy or seriously impair the sensing element.
Содержание PC33
Страница 14: ...PC33 52 User s Manual 8 97238 Issue 2 October 2013 appendix a Appendix A Technical Specifications...
Страница 16: ...PC33 52 User s Manual 10 97238 Issue 2 October 2013 appendix B Appendix B EC Declaration...
Страница 19: ...PC33 52 User s Manual Michell Instruments 13 appendix C Appendix C Quality Recycling Warranty Information...
Страница 27: ...PC33 52 User s Manual Michell Instruments 21 NOTES...
Страница 28: ...http www michell com...
