Primary thermometry and standards
The laboratory maintains and disseminates the national standards for contact thermometry, i.e. the International Temperature Scale (ITS-90) of 1990 up to 962 °C. This scale defines a limited number of phase transitions (triple points, melting points and freezing points) called fixed points and, as interpolation instrument, the Standard Platinum Resistance Thermometer (SPRT).
The two sections of the laboratory, the Cryogenics and the Medium Temperatures, are distinguished by the type of thermometer used and the type of fixed points:
- the Cryogenics laboratory for temperatures below 0 °C (4 K - 273.15 K), realises the 4 gaseous fixed points defined in this range and uses capsule SPRTs, which are mounted inside cryostats along with the fixed point(s);
- the laboratory for Medium Temperatures, for the temperature range from - 196 °C to + 962 °C, uses long-stem SPRTs, which are inserted in the 9 fixed points defined in this range. These 9 fixed points are mounted in dedicated cryostats/thermostats/furnaces.
The laboratory realises and maintains the International Temperature Scale (ITS-90) above the fixed-point of silver (961.78 °C) up to 2500 °C by realising radiation scales at wavelengths between 0.65 mm and 0.95 mm. The laboratory participates to the international comparisons promoted by CIPM and EURAMET to support their own CMCs.
- High-temperature eutectic metal-carbon fixed-points (Co-C, Pd-C, Pt-C, Ru-C, Re-C) are investigated to be used for the realisation of radiation thermodynamic scales at high temperature for the new mise-en-pratique of the kelvin (MeP-K).
- Infrared temperature scales at 1.6 mm for approximating the ITS-90 are realised between the indium point (156.5985 °C) and the silver point (961.78 °C) with an expanded uncertainty (k = 2) of 0.08 °C.
- Techniques of radiation thermometry are investigated and implemented to be used both in primary thermometry and scientific and technological applications at high temperature. A multi-spectral measuring system to be operated between 0.35 mm and 0.95 mm designed and realised in the framework of the EMRP project HiTeMS is available.
- The laboratory is also involved in the measurement of thermal radiative properties (emissivity and reflectivity) of solid materials by employing reflectometric techniques in the temperature range between room temperature and 1000 °C in the spectral range from 0.65 mm and 15 mm. A sodium heat-pipe based absolute reflectometer for the room temperature characterisation of solid materials has been realised and is operative in the laboratory.
- An original measurement technique, the so called hybrid technique, which combines reflectometric and direct measurements for investigations of materials at temperatures between 250 °C and 1000 °C has been developed and implemented.
The laboratory allows to achieve state-of-the-art measurements of:
- speed of sound and refractive index of pure gases and mixtures over the pressure range between 50 kPa and 7 MPa, at temperatures between 25 K and 500 K with relative uncertainties in the order of a few ppm;
- relative humidity, i.e. composition of humid gaseous mixtures for water mole fractions above 100 ppm volume
Available instrumentation and experimental apparatus include generation, measurement and control systems for acoustic and microwave signals, temperature, pressure, flow of pure gases and mixtures. Namely,
- cylindrical, spherical and ellipsoidal acoustic and microwave resonators (steel, copper, gold plated) with internal volumes between 125 cm3 and 3 litres;
- lock-in analysers (up to 125 kHz) and network analysers (up to 20 GHz);
- 2 liquid-bath isothermal thermostats: temperature range -40 °C to 160 °C; stability and uniformity < 5 mK; useful experimental volume 40 litres;
- cryogen-free pulsed tube cryostat: temperature range 4 K to 300 K; stability and uniformity < 5 mK; experimental volume 20 litres;
- adiabatic furnace: temperature range 30 °C to 500 °C, stability and uniformity 50 mK; experimental volume 20 litres;
- electropolished stainless steel manifolds and purification systems (getters, zeolites, cryotraps) to maintain impurity levels in gaseous samples below 1 part per million level (ppm);
- medium to high vacuum pumping systems, leak detector, residual gas analyzer;
- quartz and capacitive absolute and differential pressure transducers with relative accuracies down to 50 ppm.