5698-25 Working Standard SPRT

The 5698 Working Standard SPRT is a true SPRT. It meets the ITS-90 ratio requirements for SPRTs with a Hart-designed, completely strain-free platinum sensor


All the features you expect in a world-class SPRT

  • Conforms to ITS-90 SPRT guidelines
  • Drift rate typically 0.003 °C
  • Calibration options by fixed point
  • Unmatched performance-to-price-ratio

SPRTs. Art or science? It takes, in fact, quite a bit of both. The one thing not involved is mystery. That’s why Hart SPRTs always include detailed published specifications, including drift rates.

Our newest SPRT is no exception. It was designed by the same Hart metrologists who have created a dozen different SPRT designs used in national labs around the world. And it performs just like we say it does.

The 5698 Working Standard SPRT is a true SPRT.

It meets the ITS-90 ratio requirements for SPRTs and includes a Hart-designed, completely strain-free platinum sensor. With a 485-mm quartz sheath, this 25-ohm SPRT covers a temperature range from –200 °C to 670 °C. Long-term drift, which we define as the change in output resistance at the triple point of water after 100 hours at 670 °C, is (after converting to temperature) less than 6 mK—typically less than 3 mK.

The 5698 is the perfect companion to a Fluke 1595A Super-Thermometer, which reads 25-ohm SPRTs to within 0.015 mK at 0 °C and includes a number of convenient features for working with SPRTs. Requiring 1 mA of excitation current, the 5698 can also be used easily with a Fluke Black Stack, or even a Chub-E4 Thermometer.

If you need your SPRT calibrated by a reputable calibration lab, we offer appropriate calibration options by fixed-point in our NVLAP-accredited lab. Our calibration prices are as reasonable as our instrument prices, so you get maximum value from your SPRT.

Why buy critical temperature standards from companies unwilling to publish complete specifications? At Fluke Calibration, we not only provide excellent post-purchase support so you have the best possible ownership experience, we also provide you all the information we can before you purchase—including detailed performance specifications.

Maybe there is some art mixed with our science. But that doesn’t mean we keep secrets. Trust your lab standards to Fluke Calibration.





Temperature Range –200 °C to 670 °C
Nominal RTPW 25.5 Ω (± 0.5 Ω)
Current 1.0 mA
Resistance Ratios W(234.315 K) ≤ 0.844235
W(302.9146 K) ≥ 1.11807
Sensitivity 0.1 Ω/°C
Drift Rate < 0.006 °C/100 hours at max temperature (typically < 0.003 °C)
Self-heating at TPW < 0.002 °C under 1 mA current
Reproducibility ± 0.0015 °C or better
RTPW Drift After Thermal Cycling < 0.001 °C
Diameter of Pt Sensor Wire 0.07 mm (0.003 in)
Protective Sheath Quartz Glass
Diameter: 7 mm (0.28 in)
Length: 485 mm (19.1 in)
Lead Wires Four sensor wires



Model Name


5698-25 25 Ω Working Standard SPRT 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:



1912-4-7 PRT Calibration, –200 °C to 660 °C, NVLAP Accredited


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