AccuMac – AM1968 Capsule SPRT

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  • Rtpw Drift < 1 mK after thermal cycle
  • Temperature range: -260 ?C (13K) to 100 ?C (373K)
  • Short term stability < 1 mK
  • Nominal Rtpw: 25 ohm at 0 ?C

AM1968 Platinum Capsule SPRT covers temperatures from -260°C to 100 °C. The capsule construction makes this SPRT a preferred primary standard for cryogenic applications and other applications where space is limited or stem conduction is a concern for a long stem SPRT.
The sensing element is made of pure platinum wires with a temperature coefficient of 0.003925Ω/Ω/°C. The coiled platinum wires are mounted in a way that is strain free and enclosed in a platinum capsule, which is sealed by glass. The special sealing glass has a thermal expansion coefficient that matches with that of the platinum wire to ensure the capsule SPRT is sealed permanently in the entire temperature range. A uniquely designed support structure provides excellent performances of stability, mechanical shock, and thermal cycle performance. The SPRT achieves a high level of stability and repeatability in performance and fully meets ITS-90 criteria for reference thermometers.

Temperature Range
-260°C to 100°C
Resistance at 0.01 °C
Nominal 25 Ω
Temperature Coefficient
0.003925 Ω/ Ω/°C
Drift of R(tpw)*
< 0.003°C at TPW after 1 year, < 0.001°C typical
Short Term Stability
Thermal Shock
±0.001°C after thermal cycles from minimum to maximum temperatures
0.0015 °C at 1 mA current
Resistance Ratios
W(Ga)>=1.11807, W(Hg)<=0.844235
Measurement Current
1 mA
Sensor Length
42 mm
Filling Gas
Sheath Material
Sheath diameter 5mm, glass head diameter 7mm, length 60mm
External Leads
Teflontm –4 platinum wires, 30mm
  *Long-term drift rate is for reference only. It could be affected by such facts as handling, application, and maintenance, etc.


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