Temperature
For the safe and effective operation of industrial processes, accurate measurement of temperature is crucial. Some industries that require accurate temperature measurement are metal fabrication, power generation, chemical, and pharmaceutical. Temperature measurements also play an important role in the evaluation of energy efficiency in, for example, building insulation.
The Thermometry laboratory of the NMISA calibrates contact thermometers from -196 °C to 1555 °C: platinum resistance thermometers (PRTs) can be calibrated from -196 °C to 660 °C (for quartz-sheathed standard PRTs) or 550 °C (for other PRTs), thermistors from 0 °C to 60 °C, thermocouples from -80 °C to 1555 °C and liquid-in-glass thermometers from -25 °C to 280 °C.
The laboratory calibrates infrared radiation thermometers from 0 °C to 1600 °C and blackbody radiation sources from 0 °C to 2000 °C.
Traceability for contact thermometry is obtained from thermometric fixed point cells from the triple point of argon (-189.344 2 °C) to the freezing point of copper (1084.62 °C). (Pt-Rh thermocouples are calibrated at the melting point of palladium (1553.5 °C) using the wire-bridge method.)
Traceability for radiation thermometry is obtained from contact thermometers up to 500 °C and from a spectrally characterised monochromatic radiation thermometer calibrated at the freezing point of silver (961.78 °C) or copper (1084.62 °C) from 600 °C upwards.
Temperature Involvement in Metrology
- Provides expertise to the SANAS Specialist Technical Committee for Temperature Metrology and performs technical assessments and inter-laboratory comparisons on behalf of SANAS
- Represents South Africa on the CIPM Consultative Committee for Thermometry (CCT) and its associated working groups, ensuring equivalence of measurements
- Supports the development of metrology infrastructure in AFRIMETS through training, assessment and piloting comparisons
Humidity
The presence or the absence of water vapour in air or other gases influences a vast range of physical, chemical and biological processes. Humidity measurements are important for a wide range of industries and to some, such as pharmaceuticals and food; they are a critical aspect of business costs, product quality, and health and safety.
The Humidity laboratory of NMISA maintains the national measurement standards for humidity, in the sub-fields of relative humidity (%rh) and dewpoint temperature (°C).
The Hygrometry laboratory of the NMISA maintains measurement standards for dew point (from -75 °C frost point to +20 °C dew point) and relative humidity (from 5 %rh to 95 %rh, over the temperature range 5 °C to 60 °C). Traceability for dew point measurements is obtained from chilled mirror hygrometers that are regularly calibrated at another NMI that is a signatory of the CIPM Mutual Recognition Arrangement (MRA). For relative humidity, unsaturated salt solutions (calibrated at an accredited laboratory traceable to the national measurement standards of a country that is a signatory to the CIPM MRA) are used as the starting point of traceability.
The laboratory is in the process of developing a standard humidity generator, which will allow traceability of the relative humidity standards to the standards of temperature and pressure.
Humidity Involvement in Metrology:
- Provides expertise to the SANAS Specialist Technical Committee for Humidity Metrology and performs technical assessments and inter-laboratory comparisons on behalf of SANAS
The Temperature and Humidity Laboratory Supports:
- Commercial calibration laboratories and regional National Metrology Institutes (NMIs), by providing them with traceability
- Fair trade, by underpinning an internationally respected measurement infrastructure in South Africa
- Environmental, Health & Safety regulation, in those areas (e.g., validation of sterilising autoclaves, measurement of heat stress) where accurate temperature measurement is required
