Fluke
Fluke 5681/ 5683/ 5684 Quartz-Sheath SPRTs
Manufacturer: Fluke Calibration
Model: 5681/ 5683/ 5684
Features
Drift rates as low as 0.0005 K
Proprietary gas mixture ensures high stability
Most experienced SPRT design team in the business
Specifications
| Specifications | 5681 | 5683 | 5684 |
| Temperature Range | –200 °C to 670 °C | –200 °C to 480 °C | 0 °C to 1070 °C† |
| Nominal RTPW | 25.5 Ω | 0.25 Ω | |
| Current | 1 mA | 14.14 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 | |
| Sensitivity | 0.1 Ω/°C | 0.001 Ω/°C | |
| Drift Rate | < 0.002 °C/100 hours at 661 °C (typically < 0.001 °C) | < 0.001 °C/100 hours at 480 °C (0.0005 °C typical) | < 0.003 °C/100 hours at 1070 °C (typically < 0.001 °C) |
| Sensor Support | Quartz glass cross | Quartz glass strip with notches | |
| Diameter of Sensor Pt Wire | 0.07 mm (0.003 in) | 0.4 mm (0.016 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-ohm SPRT be used below 0 °C.
