1. Capability Improvements of the NMISA Humidity Laboratory
Capability Improvements of the NMISA Humidity Laboratory Regina Mnguni, NMISA July 2017
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2. Outline Introduction What is humidity? Current capabilities
Improvements
Conclusion
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3. Introduction
NMISA Humidity laboratory maintains the national humidity standards and disseminate the traceability to industry.
The laboratory has been SANAS accredited since the year 2004.
The lab’s capabilities cover the low dewpoint temperature range and relative humidity parameters only.
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4. Introduction continue…
The humidity lab wants to increase/improve the capabilities:
To include high dewpoint temperature range
Establish traceability of relative humidity to temperature, pressure and dewpoint temperature
To include water activity parameter
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5. What is Humidity?
Humidity is the amount of water vapour present in air or other gases.
Humidity terms/parameters
Relative humidity - the ratio of actual vapour pressure to the saturation vapour pressure at the same temperature, expressed as a percentage (%)
Dewpoint Temperature – the temperature at which dew/frost or condensation forms on a cooling gas. The temperature at which air becomes saturated in equilibrium with water.
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6. What is Humidity? continue
Water activity – the ratio of the vapour pressure of water in a material to the vapour pressure of pure water at the same temperature. It is the same as equilibrium relative humidity (ERH) except that it is expressed on a scale of 0 to 1.
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7. Current capabilities Relative humidity
5 %rh to 95 %rh range covered at 5 °C to 55 °C.
Unsaturated salts are used at the temperature range 15 °C to 30 °C.
Thermohygrometer is used at 5 °C to 55 °C in a controlled chamber.
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8. Current capabilities continue
Dewpoint temperature
The range covered is from -75 °C to +17 °C
A pressure swing dryer, flow mixing generator and two chilled mirror hygrometers used as a system.
Hygrometer
Hygrometer
Flow mixing generator
Pressure swing dryer
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9. Improvements Water activity measurements
Calibration of the meters using unsaturated salts.
In the process of acquiring accreditation
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10. Improvements continue…
Two pressure humidity generator/chamber procured together with a dewpoint meter.
To replace the old climatic chamber of 20 years
Old controlled chamber
Two pressure generator/chamber
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11. Improvements continue…
To be used for the calibration of relative humidity instruments (i.e. data loggers, weather stations, indoor air quality monitors and thermohygrometers).
To extend the dewpoint temperature range to +70 °C.
The temperature range of the chamber is -10 °C to +70 °C.
The principle of operation (2 pressure) is that the gas is humidified at elevated pressure then expanded to a lower pressure at the given temperature.
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12. Improvements continue…
The chamber will be used concurrently with the calibrated dewpoint meter to give traceability for relative humidity calibrations.
This will replace the traceability to salt solutions and make NMISA comparable with other NMIs in RH.
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13. Conclusion
With the new method/equipment, UoM for relative humidity will be improved.
NMISA humidity lab to offer calibration of dewpoint meters of a higher range.
NMISA humidity lab will offer traceability for the water activity meters.
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