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TEMPERATURE & HUMIDITY

MM1 Temperature

Introduction


introduction

Temperature measurement may span a wide range, from ultra-low temperatures of –273 °C up to temperatures of several thousands of °C. A precise and accurate knowledge of temperature measurement is important in science, technology and industry where precision and pushed limits are targeted. Humidity measurement is established by temperature and pressure measurement, can be expressed using a few definitions; the most commonly one is "relative humidity". It has imperative impact in industries such as (gas industry, food and drug industry, corrosion,) and in measurements of climate changes.

Temperature and Humidity Laboratory is responsible for establishing, maintaining and disseminating national reference temperature and humidity standards to ensure all relevant measurements are traceable to SI units. Traceable and accurate measurement is vital for many applications in particular for manufacturing processes and quality control processes so that the products is consistent with international accepted standards. The dissemination can be achieved through calibration and verification of measuring instruments from industry directly and by providing traceability to calibration and testing laboratories and in turn to manufacturers, consumers and other stakeholders through them.

Primary thermometry, based on the well-understood physical systems, including a set of internationally recognised standards and defined international temperature scales and their realizations, represent an important basis for all applications, and for science and innovation.

Secondary thermometry is involved with all kinds of instruments depending on the application: resistance thermometers, thermocouples, radiation thermometer, thermal cameras, thermometers containing alcohol or mercury (the latter successively abandoned for environmental reasons) and so on. The accuracy of these thermometers varies depending their applications and method of use.

Temperature and humidity measurements are involved in a large range of areas and applications in industry, such as metallurgy, chemistry and biochemistry, quantum computing, the health sector (e.g. medical ablation techniques in human tissue by thermal heating), environment monitoring and climate change (e.g. monitoring and prevision of climate and climate changes in up-air, soil and water).

Currently, the International Temperature Scale 1990 (ITS-90) provides the basis of traceability for these industry thermometers. While the humidity measurement equipment are evaluated against reference humidity generators.

LATEST NEWS

  • Open cell fixed point standards have been established in NMC Temperature and Humidity Laboratory from Indium point to Aluminium point since 2018.
  • NMC has expanded its dew point measurement capability down to -100 °C frost point and up to 95°C dew point by establishing two new reference dew point generators.

MEASUREMENT STANDARDS AND DISSEMINATION

Temperature and Humidity Laboratory is responsible for establishing, maintaining and disseminating national reference temperature and humidity standards to ensure all relevant measurements are traceable to SI units in Singapore. Beyond measurement traceability dissemination, these measurement standards open up opportunities for local and overseas sensing instrument developers and manufacturers to understand their device performance through comprehensive characterization. The temperature and humidity metrology at NMC involves various areas namely Temperature Fixed Point standard, Standard Platinum Resistance Thermometer, Mini Temperature Fixed Point Standards, Noble Metal Standard Thermocouple, Primary Standard Radiation Thermometer, Transfer Standard Radiation Thermometer, Standard Humidity Generator, Climatic Chamber and Reference Dew Point Meters, with various Temperature and Humidity Calibration Services.

Temperature Fixed Point Standard

In International Temperature Scale of 1990 (ITS-90), between the triple point of equilibrium hydrogen (13.8033 K) and the freezing point of silver (1234.93 K), T90 is defined by means of Standards Platinum Resistance Thermometers (SPRTs) calibrated at specified sets of defining fixed points and using specified interpolation procedures.

The table below lists the defining temperature fixed point standards of ITS-90 maintained in NMC: 

Substance and its state

Defining point

K

°C

Triple point ofArgon

83.8058

−189.3442

Triple point ofMercury

234.3156

−38.8344

Triple point ofWater

273.16

0.01

Melting pointofGallium

302.9146

29.7646

Freezing pointofIndium

429.7485

156.5985

Freezing pointofTin

505.078

231.928

Freezing pointofZinc

692.677

419.527

Freezing pointofAluminum

933.473

660.323

Freezing pointofSilver

1,234.93

961.78

Services Provided:

  • Resistance thermometer

Standard Platinum Resistance Thermometer

Standard platinum resistance thermometer (SPRT) is the defined interpolating equipment in the range from the triple point of equilibrium hydrogen (13.8033 K) to the freezing point of silver (961.78 °C) of ITS-90 

  • In this temperature range, ITS-90 temperature is defined by means of SPRT, which meets certain criteria, calibrated at specified sets of defining fixed points and using specified reference and deviation functions for interpolation at intervening temperatures
  •  Under this temperature range, several sub-ranges are defined and NMC is able to realise ITS-90 in the sub-ranges from the triple point of Argon (83.8058 K) to the triple point of water and from 0 °C to the freezing point of silver (961.78 °C)
  • NMC maintain a number of SPRTs carrying ITS-90 realisation which are the references for many of our calibration services

Services Provided:

  • Resistance thermometer
  • Thermocouple including both noble metal and base metal thermocouple
  • Liquid-in-glass thermometer

Mini Temperature Fixed Point Standards

  • Mini temperature fixed points are generally made using the same metal and techniques as those used for ITS-90 realisation but smaller in size and therefore with reduced costs. 
  • They are suitable for calibration of thermometers with slightly less accuracy as compared with those used for the ITS-90 realisation, such as industrial platinum resistance thermometers and noble metal thermocouples.
  • NMC has a set of these mini fixed points for this purpose including indium, tin, zinc, aluminum, silver and copper.

Services Provided:

  • Resistance thermometer
  • Thermocouple including both noble metal and base metal thermocouple

Noble metal standard thermocouple

  • Among thermocouples, noble metal thermocouples are relatively more stable and can achieve a satisfactory accuracy when handled with care. They are used as standard thermometers particularly at high temperatures.
  • In general, they are calibrated at several temperatures and the corresponding values of thermoelectric voltage are then compared with the defined reference function. A deviation function can be obtained by interpolating the measurement results using a polynomial.
  • NMC maintains a set of noble metal thermocouples, including Au/Pt thermocouple (up to 1000 °C); Pu/Pt thermocouple (up to 1300 °C) Type R and Type S thermocouple (up to 1100 °C); Type B thermocouple (up to 1500 °C). They are calibrated using mini fixed points for temperature below 1100°C, and against reference radiation thermometer for temperature above 1100°C.

Services Provided:

  • Thermocouple including both noble metal and base metal thermocouple
  • Radiation thermometer

Primary Standard Radiation Thermometer

  • The NMC primary standard radiation thermometer is used for realising the ITS-90 above the silver point temperature (961.78°C) with working wavelength at both 0.65 µm and 0.9 µm and a Si detector
  • The thermometer is characterised in terms of following necessary parameters:

    • - Relative spectral response using NMC spectral response calibration system
    -     Size-of-source effect using integrating sphere
    -     Non-linearity by using double-flux method

  • The thermometer is calibrated at the silver point (961.78°C) and/or copper point (1084.62°C) as a comparator or in terms of its output signal
  • The realisation is then transfer to a working standard radiation thermometer to facilitate the day-to-day operation

Services Provided:

  • Thermocouple including both noble metal and base metal thermocouple
  • Radiation thermometer

Transfer Standard Radiation Thermometer

  • The transfer standard radiation thermometer is used for approximating ITS-90 from the In point temperature (156.5985 °C) to the silver point temperature (961.78 °C) and/or copper point temperature (1084.62°C ) by using a set of fixed points and an interpolation equation.
  • The thermometer works at 1.6 µm and uses a InGaAs detector
  • The use of such reference standard enable to largely reduce the measurement error as compared with using a contact thermometer due to non-uniformity of the blackbody sources

Services Provided:

  • Radiation thermometer
  • Blackbody
  • Ear thermometer
  • Thermal imager

Standard Humidity Generator

  • The humidity generator is based on two-pressure principle and is capable of continuously supplying air with accurately known humidity values
  • The humidity generator is suitable for calibration and evaluation of various hygrometers, such as dew point meters and relative humidity meters
  • The humidity generator covers the relative humidity from 12 % relative humidity to 95 % relative humidity at temperature range from 0 °C to 70 °C.

Services Provided:

  • Dew point meter
  • Relative humidity hygrometer

Standard Low Humidity Generator

  • The low humidity generator is based one two-pressure and two-temperature principle and is capable of continuously supplying nitrogen gas with accurately known humidity values
  • The low humidity generator is suitable for calibration and evaluation of various hygrometers, such as dew point meters and trace moisture analyser
  • The low humidity generator covers the frost/dew point range from -100°C +10°C (traceability above -80 °C only).

Services Provided:

  • Dew point meter
  • Relative humidity hygrometer

Standard High Humidity Generator

  • The high humidity generator is based one two-pressure and/or one pressure principle and is capable of continuously supplying air with accurately known humidity values
  • The high humidity generator is suitable for calibration and evaluation of standard dew point meters such as chilled mirror dew point meters.
  • The high humidity generator covers the frost/dew point range from -20°C + 95°C.

Services Provided:

  • Dew point meter
  • Relative humidity hygrometer

Climatic chamber and reference dew point meters

The reference dew point mirror is used as reference in the climatic chamber. Various humidity sensors such as hygrometer, psychomotor, Rh sensor and etc. are calibrated against the chilled mirror standard.

Services Provided:

  • Dew point meter
  • Relative humidity hygrometer
  • Psychometer

Other Temperature & Humidity Calibration Services

  • Digital thermometer
  • Surface probes

TRAINING COURSES

training courses

The Temperature and Humidity Laboratory also provides trainings on current and emerging technologies for Temperature and Humidity measurements and monitoring. These trainings also act as a platform to educate scientists and engineers working in the fired on the fundamentals of Temperature and Humidity metrology, and the importance of measurement comparability and traceability for international recognition of measurement and test results.

Temperature and Humidity Metrology Trainings Courses conducted in the past:

  • Humidity Measurements: Principle, Standards, Calibrations and Applications
  • Resistance Thermometry and Calibration
  • Calibration of Environmental Chamber and the Calculation of Measurement Uncertainty
  • Thermocouple - Measurement Principles & Calibration
  • Liquid-in-glass calibration
  • Clinical thermometers calibration
  • Temperature Measurement for Green Building
  • Clinical Thermometers and How to Make Sure the Accurate Measurement
  • Radiation Thermometry

International Comparisons

To ensure the international equivalence of CMCs, the Temperature and Humidity Laboratory pilot and participate in many international comparisons in both the temperature and humidity domains. NMC is currently the member in the Consultative Committee for Thermometry (CCT) and also the member in the Asia Pacific Metrology Programme (APMP) Technical Committee for Thermometry (TCT).

Completed International Comparison in recent years:

  • CCT-K8: High dew point from 30 °C to 90 °C
  • APMP.T-K8 High dew point from 30 °C to 90 °C
  • APMP.T-S6: Industry platinum resistance thermometer
  • APMP.T-S11: Fixed points for radiation thermometry
  • APMP.T-S12: Radiation thermometer
  • APMP.T-S15: APMP supplementary comparison on ear thermometer calibration

On-going comparisons:

  • APMP.T-K4.2: Comparison of Realization of the Aluminium Freezing Point
  • APMP.T-K6: APMP key comparison on dew point (pilot)
  • APMP.T-K9: SPRT Comparison from Ar to Zn (Ar, Hg, TPW, In, Ga, Sn, and Zn)
  • APMP.T-S14: Relative Humidity comparison
  • APMP.T-S16: Type-R thermocouples calibration
  • APMP. T-S17: Air Thermometer

research projects

research projects

The Temperature and Humidity Laboratory also carries out R&D and consultancy for industry and other stakeholders to develop and apply temperature and humidity measurement techniques for various applications.

Some of the projects in Temperature and Humidity laboratory:

  • Brain Temperature Measurement
  • In-situ Melt Pool Temperature Monitoring and Close-loop Control for Laser Aided Additive Manufacturing (LAAM)
  • To Develop Environmental Validation Platforms for testing of Photonic Gas Sensor
  • Evaluation on QTG Heat Transfer Medium using heat pipe as benchmark
  • Development of a calibration system for “DTS chip on board” using chamber with isothermal box
  • Cooling performance of ERS Heat Removal Module (HRM) in data-center

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