Capability Improvements of the NMISA Humidity Laboratory Capability Improvements of the NMISA Humidity Laboratory Regina Mnguni, NMISA 31 July 2017 TQM-5134-1

Outline Introduction What is humidity? Current capabilities Improvements Conclusion TQM-5134-1

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. TQM-5134-1

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 TQM-5134-1

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. TQM-5134-1

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. TQM-5134-1

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. TQM-5134-1

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 TQM-5134-1

Improvements Water activity measurements Calibration of the meters using unsaturated salts. In the process of acquiring accreditation TQM-5134-1

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 TQM-5134-1

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. TQM-5134-1

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. TQM-5134-1

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. TQM-5134-1

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