Resistance Bridge Calibrator
- Isothermal Technology Ltd has signed a license to Develop, Sell and Produce IRL's Resistance Bridge Calibrator
Industrial Research Ltd of New Zealand (IRL) has developed and patented a Resistance Bridge Calibrator designed for quick and simple, in-house calibrations of AC and DC thermometry bridges, with an accuracy of better than 0.1 ppm at 100 Ω. The calibrators are supported by software for analysis of the results, and an extensive user manual with a complete description of the operating principles and an uncertainty analysis.
Isotech are a world recognised producer of instrumentation for both primary and secondary temperature measurement laboratories including electronic thermometers and bridges, ITS-90 fixed point systems, calibration baths and furnaces.
The calibrators are a result of research carried out at the Measurement Standards Laboratory of New Zealand, which operates within IRL. IRL is one of New Zealand’s National research institutes focused on the industrial application of science and engineering.
Rod White of IRL, who developed the bridge calibrator, says, “We’re really pleased that Isotech has agreed to take on the calibrator. We’re a national laboratory and we don’t have the resources to manufacture at low cost or distribute efficiently. Now we can focus on research and improvements.” “This arrangement is also good for thermometrists. In our experience, as many as 15% of thermometry bridges develop small faults but, like walking wounded, they continue to provide a plausible reading. Having access to a simple calibrator that can prove a bridge is operating correctly, within an hour or so, is very valuable.”
The operating principle of the calibrator is very simple. One way of checking a bridge is to measure the resistance of a pair of resistors separately, and then measure the two in series. Ideally, the series measurement should equal sum of the two individual measurements. The calibrator enables similar comparisons but with four precision resistors measured in up to 70 different series and parallel combinations. Because the interrelationships of all 70 combinations are known in terms of the four base resistances, the measurements can be analysed to provide up to 66 independent measurements of the bridge error.
To date, research models of the RBC have demonstrated accuracies better than 2ppb. Isotech have two models immediately available, one optimised for 25Ω thermometry and one for 100Ω thermometry accurate better than 0.1ppm at 100Ω.
John Tavener, President of Isotech comments, “I have known of the RBC for many years, in fact it has been invaluable for the development of the Isotech range of microK thermometry bridges, it is the only simple method for calibrating and verifying their performance. I am honoured that my organisation has the opportunity to work with IRL. We have some 90 distributors globally and are looking forward to helping laboratories worldwide to benefit from this technology.”