5686-B Glass Capsule SPRT

The 5686 is a true SPRT. The high-purity platinum wire is hand-wound on a glass cross frame in a strain-free design.


Designed for metrology work requiring small SPRTs

  • Temperatures from –260 °C (13 K) to 232 °C
  • Stability typically 0.001 °C over 100 °C range
  • Miniature capsule package eliminates stem conduction

Sometimes you would like to make SPRT measurements but traditional SPRTs are too long or awkward for a particular application. Now Fluke Calibration makes a miniature glass capsule SPRT, which is perfect for cryogenics, calorimetry, and other metrology work requiring small SPRTs.

The 5686 is a true SPRT. The high-purity platinum wire is hand-wound on a glass cross frame in a strain-free design. The glass capsule is designed to match the thermal expansion of the platinum wire to ensure a true seal at all operating temperatures. The capsules are pressure sealed and come protected in their own maple case.

The 5686 complies completely with ITS-90 and has the following resistance ratios:

W(302.9146 K) ≥ 1.11807


W(234.3156 K) ≤ 0.844235

The 5686 covers temperatures from –260 °C to 232 °C, so it’s perfect for cryogenic applications. It is 5.8 mm in diameter and 56 mm long. Fixed-point calibrations are available for the model 5686 from –200 °C to 232 °C.

These SPRTs are small but meet customary SPRT performance for reproducibility, reliability, and stability. They solve many of the problems associated with taking precision measurements in situations unsuitable for traditional-length SPRTs.





Temperature Range 5686: –260 °C to 232 °C (13 K to 505 K)
Nominal RTPW 25.5 Ω
Resistance Ratio W(302.9146 K) ≥ 1.11807
W(234.3156 K) ≤ 0.844235
Drift Rate 5686: < 0.005 °C per year over the entire range
Self-heating at TPW < 0.002 °C under 1 mA current
Reproducibility ±0.001 °C or better
R TPW Drift After Thermal Cycling < 0.001 °C
Filling Gas 5686: helium
Lead Wires Four platinum wires, 30 mm long (1.18 in)
Size 5686: 5.8 mm dia. x 56 mm long (0.23 x 2.2 in)



Model Name


5686-B Glass Capsule SPRT, –260 °C to 232 °C with Maple carrying case

(No calibration included. See recommended calibration options below. Contact your Fluke Calibration representative for additional calibration options.)

Accessories common to all models:



1911-4-9 PRT Calibration, –200 °C to 232 °C, NVLAP Accredited


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