Fluke Calibration

5681 / 5683 / 5684 / 5685 Quartz-Sheath Standard Platinu...

Four world-class SPRTs to cover the ITS-90 temperature range of 200C to 1070C

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Fluke Calibration has four quartz-sheath SPRTs covering the ITS-90 range of –200°C to 1070°C. The 5681 is used from –200°C to the aluminum point at 660.323 °C. The 5683 is used from –200°C to 480 °C with greater long term stability. The 5684 and the 5685 cover higher temperatures up to 1070 °C and can be calibrated at the silver point.

All have gold-plated spade lugs, a strain-relieved connection to the four-wire cable, convection prevention disks, the finest quartz glass available, delustered stems, and the purest platinum wire available.

• Drift rates as low as 0.0005 K
• Proprietary gas mixture ensures high stability
• Most experienced SPRT design team in the business






Temperature Range

-200°C - 670°C

-200°C - 480 °C

0°C - 1070°C

0°C - 1070°C

Nominal RTPW

25.5 Ω

0.25 Ω

2.5 Ω


1 mA

14.14 mA

5 mA

Resistance Ratio

W(302.9146 K) ≥ 1.11807 and
W(234.3156 K) ≤ 0.844235

W(302.9146 K) ≥ 1.11807 and
W(1234.93 K) ≥ 4.2844


0.1 Ω/°C

0.001 Ω/°C

0.01 Ω/°C

Drift Rate

< 0.002°C/100 h at
661°C (typically < 0.001°C)

< 0.001°C/100 h at
480°C (0.0005°C typical)

< 0.003°C/100 h at 1070°C
(typically < 0.001°C)

Sensor Support

Quartz glass cross

Quartz glass
strip with notches

Quartz glass cross

Diameter of Sensor
Pt Wire

0.07 mm (0.003 in)

0.4 mm (0.016 in)

0.2 mm (0.008 in)

Protective Sheath

Quartz glass, Diameter: 7 mm (0.28 in), Length: 520 mm (20.5 in)

Quartz glass, Diameter: 7 mm (0.28 in), Length: 680 mm (26.8 in)


The official maximum temperature of an SPRT as a defining interpolation instrument of the ITS-90 is 961.78°C, but these types of SPRTs were found to be stable up to at least 1070°C. The annealing temperature during the stability test was 1085°C. The lower temperature limit of these types of SPRTs can be as low as -200°C.
In general, it is suggested that a 25 Ω SPRT be used below 0 °C.