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[August 2006]
New Precision Thermometer Claimed to Offer Unrivalled Accuracy and Stability
Isothermal Technology Ltd (Southport, Merseyside, England) – known generally as Isotech – has introduced a new type of precision thermometer which it claims will set new world standards for accuracy and stability. Designed for a wide range of highly accurate industrial and scientific calibration applications, the instrument uses a completely new measurement technique to achieve accuracies better than 0.4 ppm - equivalent to 0.0004°C - when used with a standard platinum resistance thermometer (SPRT).Designed and manufactured in Britain, MicroK is believed to be the only instrument of its type in the world which will work to this precision with all three commonly used sensors: platinum resistance thermometers (PRTs); thermocouples; and thermistors. In terms of long-term stability, MicroK is said to achieve zero drift for resistance ratio measurements and an annual drift of only 3 ppm for voltage measurements.
While using sophisticated software and specially developed circuitry, the MicroK is easy to use and has a comprehensive range of built-in features. It uses a 6.4-inch VGA colour touch screen as the main user interface, providing a number of graphically presented user options and controls. The underlying operating system is Microsoft Windows CETM, facilitating direct reading of temperature for all sensor types, data logging, export of data into Microsoft ExcelTM applications and graphing facilities.
Measurement Best Practice guidelines recommend the use of two separate reference thermometers when carrying out temperature calibrations. For that reason the designers of the MicroK have incorporated three channels, enabling users to achieve best practice without having to invest in additional multiplexers. The instrument also includes 'keep-warm' current sources to maintain the power in a PRT when it is not being measured. This feature effectively eliminates uncertainty resulting from power coefficients, says Isotech.
A key to achieving such high accuracies and stability is the use of a specially designed analogue to digital converter (ADC) within the instrument measurement circuits. In conjunction with a digital signal processor (DSP) this uses a unique adaptation of existing advanced sigma-delta ADC techniques to achieve linearity better than 0.4 ppm. A further major benefit of this ADC technique is its low noise performance and the designers claim that electronic noise is reduced by a factor of 32 over conventional sigma-delta ADC circuits.
A further break with convention is that the instrument uses no mechanical switches, relays or potentiometers whatsoever (other than the main power on/off switch), relying on solid state switching to route voltage and current signals internally. Comparative instruments in this class have used high quality mechanical relays for this purpose, a technique which inherently introduces inaccuracies arising from thermal EMFs and degrades reliability, explains the company. By using the latest semiconductor technology, performance has been enhanced, component counts have been reduced and reliability considerably improved.
www.isotech.co.uk
ENDS