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Isotech Model 670 SPRT

-200°C to 670°C

The 670SQ is our latest thermometer, to be specifically designed to give optimum performance up to the aluminium point.

  • 25.5 Ohm SPRT
  • Outstanding Performance


The 670SQ is our latest thermometer, to be specifically designed to give optimum performance up to the aluminium point. Its construction permits the four internal platinum lead wires to expand and contract in the same manner as those of silver-point thermometers. The all-quartz construction of the support members gives the most stable performance with minimal drift, and a unique platinum radiation shield prevents heat radiating up the inside of the sheath.

The construction, including the coiled sensing element, heat-shunt baffles and light scattering barriers, creates a thermometer of unsurpassed stability.

Because the 670SQ goes beyond the temperature range of oxide growth to the level at which the oxide dissociates, the 670 is filled with a unique argon/oxygen mixture. A 2.5 metre length of low thermal EMF, high temperature, screened cable is connected in the handle, via a strain-relieving transition, to the all pure platinum construction of the thermometer.

Gold-plated U-shaped terminals complete the cable construction, and the 670SQ is delivered in an elegant soft lined carry-case of our own design. A 670SQ is supplied only after a stabilising process which is complete when the reproducibility of RTPW is within 0.0005°C after excursions to the extremes of its temperature range. Values of RTPW and Wga are routinely provided with the 670SQ.

The 670SQ can be supplied with RTPW and Wga only or with full UKAS calibration. “With calibration” means that you will get an Internationally accepted Fixed Point calibration. For best accuracy, recommended maximum measuring current for the 670SQ is 1mA for the 25.5Ω(Ro).

A comprehensive handbook and tutorial will help you get the very best performance and stability from your 670SQ.

The 670SQ 650mm long is our recommended SPRT offering ultra stability, vibration, shock, immersion and self heating characteristics. From the success of the original Model 670 SPRTs we have introduced new models into the 670 range offering metal sheathed and low temperature models.

Copper Point SPRT

Download Datasheets


Models 670SQ, 670SH, 670SL
Measuring Range -200°C to 670°C
Nominal Resistance 25.5Ω Ro
Resistance Ratio Wga > 1.11807 as required by ITS-90
Sensitivity 0.1Ω / °C (25.5Ω)
Long term drift from 0.001°C / year depending on use

Over the temperature range -38.8°C to 29.76°C, typical drift rate 0.0003°C over 100 hours

Reproducibility Over the temperature range -38.8°C to 29.76°C
TP Mercury 0.0003°C (0.3mK)
TP Water 0.0001°C (0.1mK)
Gallium 0.0002°C (0.2mK)
How to order Models 670SQ, 670SH, 670SL / 25.5 or 670SQ, 670SH / 100. State “with UKAS Calibration” or “without UKAS Calibration”.