ITS-90 Fixed-Point Cells

Best cell uncertainties commercially available


Best cell uncertainties commercially available

  • Best cell uncertainties commercially available
  • Every ITS-90 fixed point available from argon to copper
  • Plateaus last days (gallium for weeks and TPW for months)
  • Manufactured and tested by Fluke Calibration’s primary standards scientists
Fluke Calibration scientists have designed and tested ITS-90 fixed-point cells for many years. Not only do we manufacture all the major fixed points, our metrologists have written extensively on the theory and use of cells and have created new designs covering a range of applications no other company can match. Our testing of fixed-point cells is also unmatched. The scope of our accreditation includes the testing of ITS-90 fixed-point cells. Each cell may be purchased with this intercomparison option, which includes comparing the equilibrium value of your cell against that of a reference cell.

Traditional freeze-point cells

If you want true primary temperature standards capability, you want metal freeze-point cells that are very close to the theoretical freezing temperature and provide plateaus that are both stable and long lasting.

Fluke Calibration's metal freeze-point cells are the culmination of more than 20 years of primary standards experience. No other company has as much experience in the development of metal fixed-point cells. That’s why you’ll find Fluke cells in many national metrology institutes around the world.

Each Fluke Calibration cell is carefully constructed in our ultra-clean, state-of-the-art lab, using high-density, high-purity graphite crucibles containing metal samples with purity of at least 99.9999 % (six 9s) and, in many cases, 99.99999 % (seven 9s). The crucible is enclosed within a sealed quartz glass envelope that is evacuated and back-filled with high-purity argon gas. A special sealing technique is used to seal the cell at the freezing point. We measure and record for you the precise pressure of the argon gas to ensure the most accurate corrections for pressure.

Once manufactured, all Fluke cells are tested and supplied with an assay of metal-sample purity. Every traditional size ITS-90 cell further undergoes more rigorous testing in our primary standards lab where we realize melt-freeze curves and perform a detailed “slope analysis" to confirm cell purity. If you want more data, we’ll give you an optional intercomparison with our own reference cells.

Gallium cells

Gallium cells are a great reference for validation of instruments subject to drift (like SPRTs), and they’re important for calibrating sensors used near room or body temperatures, in environmental monitoring, and in life sciences applications.

Fluke Calibration's 5943 Gallium Cell is sealed in a stainless steel envelope. High purity gallium (99.99999 %) is enclosed in a plastic and metal shell. The stainless steel container is then filled with pure argon gas at one standard atmosphere at the melting-point temperature.

Gallium expands by 3.1 % when it freezes requiring the cell to have flexible walls. Unlike some manufacturers’ cells, which are made from PTFE enclosure materials, our cells don’t need pumping and refilling because they’re not gas permeable. In fact, we guarantee our cells will maintain their uncertainty of < 0.1 mK for at least five years. Realization and maintenance of the cell is automated with our 9230 Maintenance Apparatus (see page 31). This apparatus will provide melting plateaus up to eight days and a convenient control to automatically achieve a new melt plateau each week with an investment of just five minutes. Never has the maintenance of a world-class gallium cell been easier.

Water cells

While simple ice baths are often used as a calibration point at 0 °C, their limitations include gradients, purity problems, repeatability issues, and variances in construction and measurement techniques. Triple point of water cells not only solve these problems; they represent the most used temperature on the ITS-90, and they’re inexpensive to own and use.

Fluke Calibration makes three traditional-size TPW cells that have been repeatedly proven in national labs to surpass their published uncertainty specification of ±0.0001 °C. Ice mantles may be formed using dry ice, LN2 , or immersion freezers and can last for up to two months when maintained in our 7012 or 7312 baths.

Open metal cells

Made from the same materials and with the same manufacturing techniques as their sealed counterparts, Fluke's new series of “open" metal fixed-point cells include a high quality valve for connecting to a precision pressure-handling system within your lab. Using such a system, the cell can be evacuated, charged, and purged several times with a pure inert gas, then charged again to a regulated pressure level while measurements are made with the cell.

Once assembled and tested, each Fluke Calibration ITS-90 open cell further undergoes more rigorous testing in our lab, unlike cells from some manufacturers who provide their open cells as a kit of parts, without any test data.

Because open cells allow users to measure the pressure within the cell, uncertainties due to pressure corrections may be minimized. Use of open cells is now being suggested by the CCT, and open cells can be used for demanding temperature-versus-pressure applications, as well as precision SPRT calibrations.

The height of these cells has been extended to allow easy access to the gas valve while the cells are in use. Pure quartz-wool insulation and four high-purity graphite discs prevent heat loss from the metal sample to the pressure regulation system while optimizing vertical temperature gradients within the cell. Each cell has an outside diameter of 50 mm (2 inches) and a height of 600 mm (23.5 inches)—(silver and copper cells are 700 mm [27.6 inches] tall).

When it comes to primary temperature standards, Fluke Calibration supplies more equipment than all of our competitors combined. If your goal is to reduce uncertainty, start by buying from the company that supports its products better than any other metrology company in the world. Why trust your primary standards to any other company?





Model Fixed Point Style Assigned Value ( °C) Outside Diameter Inside Diameter Total Outside Cell Height Depth‡ Cell Uncertainty (mK, k=2) Certification (mK, k=2)†
5900E Mercury Stainless Steel –38.8344 31 mm 8.2 mm 470 mm 200 mm 0.2 0.25
5904 Indium Traditional Quartz Glass 156.5985 48 mm 8 mm 285 mm 195 mm 0.7 0.7
5905 Tin Traditional Quartz Glass 231.928 48 mm 8 mm 285 mm 195 mm 0.5 0.8
5906 Zinc Traditional Quartz Glass 419.527 48 mm 8 mm 285 mm 195 mm 0.9 1.0
5907 Aluminum Traditional Quartz Glass 660.323 48 mm 8 mm 285 mm 195 mm 1.3 1.8
5908 Silver Traditional Quartz Glass 961.78 48 mm 8 mm 285 mm 195 mm 2.4 4.5
5909 Copper Traditional Quartz Glass 1084.62 48 mm 8 mm 285 mm 195 mm 10.1 12.0
5924 Indium Open Quartz Glass 156.5985 50 mm 8 mm 596 mm 195 mm 0.7 0.7
5925 Tin Open Quartz Glass 231.928 50 mm 8 mm 596 mm 195 mm 0.5 0.8
5926 Zinc Open Quartz Glass 419.527 50 mm 8 mm 596 mm 195 mm 0.9 1.0
5927A-L Aluminum Open Quartz Glass (long) 660.323 50 mm 8 mm 696 mm 195 mm 1.3 1.8
5927A-S Aluminum Open Quartz Glass (short) 660.323 50 mm 8 mm 596 mm 195 mm 1.3 1.8
5928 Silver Open Quartz Glass 961.78 50 mm 8 mm 696 mm 195 mm 2.4 4.5
5929 Copper Open Quartz Glass 1084.62 50 mm 8 mm 696 mm 195 mm 10 12.0
5943 Gallium Stainless Steel 29.7646 38.1 mm 8.2 mm 250 mm 168 mm 0.1 0.1
†Certifications at lower uncertainties are available for national laboratories. ‡Depth is measured from the bottom of the thermometer well to the top of the pure reference material.


Model Name


5900E Mercury Triple Point Cell, Stainless Steel
5904 Indium Cell, Traditional Quartz Glass
5905 Tin Cell, Traditional Quartz Glass
5906 Zinc Cell, Traditional Quartz Glass
5907 Aluminum Cell, Traditional Quartz Glass
5908 Silver Cell, Traditional Quartz Glass
Accessory Description
1904-Ag Accredited Cell Intercomparison, Silver
5909 Copper Cell, Traditional Quartz Glass
5924 Indium Cell, Open Quartz Glass
5925 Tin Cell, Open Quartz Glass
5926 Zinc Cell, Open Quartz Glass
5927A-L Aluminum Cell, Open Quartz Glass, Long
5927A-S Aluminum Cell, Open Quartz Glass, Short
5928 Silver Cell, Open Quartz Glass
5929 Copper Cell, Open Quartz Glass
5943 Gallium Cell, Metal Cased

Accessories common to all models:



2068-D Stand, Fixed-Point Cell, Black Delron

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