4 Oct 2016
Why a copper point SPRT? In our research at the copper point we had been using noble metal thermocouples to intercompare Copper freeze point cells. For a Type R thermocouple the voltage sensitivity at the copper point is 14μV/°C; a change of 1 μV is equivalent to a voltage change of 71mK. When using thermocouples electrical noise limits the ability to follow small changes in the copper freezing plateau and so attention was turned to the development of a new resistance thermometer allowing better copper measurements to be made.
R0 is nominally 0.25Ω the same as the silver point SPRT but the platinum winding is held in place on a new type of synthetic sapphire mandrel. The thermometer sheath is made of alumina which is air filled and hence surrounded by 20% oxygen. Uniquely the sheath is connected to a small air pump to pressurise the 108462 with air so that any leakage is outwards, whilst maintaining an oxygen rich atmosphere around the winding. This is what gives the thermometer its stability.
Following its launch in 2014 we have been getting very positive feedback.
Our friends at Klasmeier Kalibrier have been using the device - they calibrated the thermometer in their silver cell and sent it to PTB for a report to be made. PTB used a different cell, different bridge and made an identical measurement - astonishing! Both labs reported an identical WAG value - which is truly remarkable.
We also supplied a Model 108462 to a large petro-chemical company; they wanted better performance in their horizontal thermocouple calibration furnace as the reference thermocouples they had been using were drifting too much. (Conventional quartz sheath SPRTs are unsuited to horizontal use at 1000 °C.)
On its return for recalibration, after 1 year the drift in the thermometer's WTP from its previous calibration was less than 1 mK. This is as good as our Premium 670SQs. The client had selected our standard calibration service which is 40mK at the Silver Point; the thermometer value was within 9mK of the original calibration value!
For further information, or to discuss your application please contact us