5699 High-Temperature Metal-Sheath SPRT

Designed and manufactured by our primary standards metrologists, the strain-free sensing element in the 5699 meets all ITS-90 requirements for SPRTs.


Affordable working standard SPRT

  • Range to aluminum point (660 °C )
  • Inconel™ and platinum sheaths guard against contamination
  • Less than 8 mK/year drift
  • Many calibration options available including by fixed point
  • Fifth wire provides shield ground

SPRTs designed by Fluke Calibration are known for their outstanding reliability and minimal long-term drift. They have been calibrated by national (and other primary) laboratories and proven repeatedly to outperform competitive models. Now Fluke Calibration’s 5699 Extended Range Metal-Sheath SPRT combines all the advantages of a Fluke Calibration-designed sensor with the protective sheathing materials that allow your SPRT to be used in virtually any furnace or bath with temperatures as high as 670 °C.

Designed and manufactured by our primary standards metrologists, the strain-free sensing element in the 5699 meets all ITS-90 requirements for SPRTs and minimizes long-term drift.

After one year of regular usage, drift is less than 0.008 °C (< 0.003 °C is typical). Even lower drift rates are possible depending on care and handling. A fifth wire for grounding is added to the four-wire sensor to help reduce electrical noise, particularly for AC measurements. Finally, you can get an improved version of an old industry-standard Inconel-sheathed SPRT.

The 5699 is constructed with a 0.219-inch-diameter Inconel sheath for high durability and fast response times. Inside the sheath, the sensing element is protected by a thin platinum housing that shields the sensor from contamination from free-floating metal ions found within metal environments at high temperatures. Reduced contamination means a low drift rate—even after hours of use in metal-block furnaces at high temperatures.

If you choose not to calibrate the 5699 yourself, a wide variety of options are available from Fluke Calibration’s own primary standards laboratory, including fixed-point calibrations covering any range between –200 °C and 661 °C.

At Fluke Calibration, we use SPRTs every day. We design them, build them, calibrate them, use them as standards, and know what it takes to make a reliably performing instrument. Why buy from anyone else?





Temperature Range –200 °C to 670 °C
Nominal RTPW 25.5Ω (± 0.5Ω)
Current 1 mA
Resistance Ratio W(302.9146 K) ≥ 1.11807
W(234.3156 K) ≤ 0.844235
Sensitivity 0.1 Ω/ °C
Drift Rate < 0.008 °C/year
(< 0.003 °C/year typical)
Repeatability < 1 mK
Self-heating at TPW < 0.001 °C under 1 mA current
Reproducibility ± 0.001 °C or better
RTPW Drift After Thermal Cycling < 0.001 °C
Diameter of Pt Sensor Wire 0.07 mm
(0.003 in)
Lead Wires Four sensor wires plus grounding wire
Protective Sheath Inconel
Diameter: 5.56 mm ± 0.13 mm (0.219 in ± 0.005 in)
Length: 482 mm (19 in)
Insulation Resistance > 100 MΩ at 661 °C
> 1000 MΩ at 20 °C



Model Name


5699-S Extended Range Metal-Sheath SPRT with Maple carrying case

Accessories common to all models:



1911-4-7 PRT Calibration, –200 °C to 660 °C, NVLAP Accredited


Request a quote - Shop

  • Any additional requirements? Please let us know.
  • This field is for validation purposes and should be left unchanged.

Call Now Button