Eventually all resistance thermometry refers back to one or more fixed resistors. These are a key element in any laboratory which measures temperature. The resistors need to be very stable with time, temperature and transportation, and they need to have negligible inductance and capacitance.
They also need to have a long and successful history of use. Wilkins and Swan at our National Physical Laboratory (NPL) developed a resistor design flexible enough to allow windings with various resistance values to be made available and stable enough to be accepted world-wide as resistance standards. Particularly important is that the AC/DC characteristics are the same up to about 1000 Hz.
This design has been licensed to H. Tinsley & Co. who have been producing (and have made further improvements to) this product since 1970. Isotech are pleased to be able to offer this design of resistor made for us by Tinsley with 1 of 2 calibration possibilities:
UKAS with an uncertainty of ±0.3ppm (SRA models). NPL with an uncertainty of ±0.1 ppm (dependant on resistance value).
|Type SRA Values||1, 10, 25, 100 Ohms, 400 Ohms to special order|
|Type SRB Values||1000 10,000 Ohms|
|Calibrated Uncertainty||0.3ppm (see UKAS schedule)|
|Accuracy of Adjustment||±20ppm|
|Stability||2ppm/year (0.5ppm/ year to special order)|
|Temperature coefficient of resistance||2ppm / °C 0.5ppm made to special order|
|Recommended Dissipation||10 mW|
|Maximum Dissipation||1 Watt|
|Approximate load coefficient||6ppm/ Watt|
|A.C./D.C. transfer error at 1kHz||1ppm 10Ω – 10kΩ. 5ppm – 1Ω|
|Element||Strain free, immersed in dry oil (no. 4 Kerosene)|
|Top Panel||Bakelite with PFTE inserts and engraved lettering|
|Terminal – current||0BA Copper|
|Terminal – Potential||4BA Copper|
|Dimensions||Container 114 x 74mm dia. Overall 140 x 83mm dia.|
|How to order||Standard resistor. Please specify type, resistance value and calibration option.|