Some humidity
measurement examples
A few basic examples of how instruments might be used in particular applications are as follows:
| Room humidity monitoring |
| Requirement: Long-term record of temperature and humidity in a moderate range |
| Consider: Unsupervised operation? Would data at intervals be enough e.g. hourly? Real-time information needed, or record to view later? |
| Possible solution: Automated "data logger" whose readings can be downloaded easily to a computer. |
| An industrial oven |
| Requirement: Humidity measured at high temperatures to show progress of heat treatment such as drying or baking. |
| Consider: Will there be dust, or other vapours apart from water? |
| Possible solution: Relative humidity probes can be used (but only those specified for high temperatures). It may be possible to extract a sample flow of gas to a cooler temperature (but avoiding condensation). Check sensitivity to any chemicals given off during heating. |
| A compressed air supply line |
| Requirement: Monitor air supply inside a pipeline to confirm level of dryness. May have some level of dust or oil in the gas stream. |
| Consider: Unsupervised operation? Reading remotely? Any alarms needed? |
| Possible solution: Typically a dew-point capacitive probe would be used. The sensor usually has a sintered filter (and upstream filtering of the gas flow may help to protect the sensor). Dew-point probes vary in their speed of response and long-term performance. |
| Note: The dew-point reading in a pressurised gas line is known as "pressure dew point". The same gas expanded to atmospheric pressure would have a lower dew point. |
| A climatic test chamber |
| Requirement: A range of temperatures and humidities. May need to track rapid changes. There may be condensation at times (depending on the test performed). |
| Consider: Response time. Robustness of instrument at hot and wet extremes. Check the actual planned range of test conditions. |
| Possible solution: A few relative humidity sensors (probes) are designed to cope with a wide humidity and temperature range. Wet-and dry-bulb hygrometers (psychrometers) can be suitable, although they need careful setting up and maintenance. |
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