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Thermocouple characteristics are sufficiently smooth to allow interpolation of deviations from the reference table to be carried out over fairly wide temperature spans without introducing unacceptable errors. In world class metrology, the most important consideration is the quality of the fundamental measurement. ASL's F900 AC bridge technology represents a new peak of performance in resistance thermometer measurement and exploits the inherent advantages of AC bridge technology to maintain repeatable measurements of the highest precision under practical operating conditions. The Model F900 Precision Digital Thermometry Bridge is designed specifically for resistance thermometry to provide you with the best possible accuracy. The 25 Hz or 75 Hz operating frequency provides fast, continuous measurement with high immunity to thermal emfs and supply frequency noise sources. The F900 achieves its full specification under a wide range of real operating conditions. For example, you can add cable probe extensions and extra terminal junctions without concern for thermal emfs generated by the temperature gradients in your laboratory. Design features such as the unique input guard ensure that you really can obtain the specified accuracy of 20 ppb over the range of 0.2Ω to 390Ω. This equates to a temperature measurement accuracy of 5 micro K for a 25.5Ω SPRT referenced to a 25Ω reference resistor. AC bridge technology will always out-perform measurements made using DC technology with slow current reversal. The F900 includes a wide range of features specifically tailored for temperature metrology including accurate programmable excitation current, 2 current, analogue outputs, selectable source impedance matching, gain and filter bandwidth. Manual or automatic bridge balancing together with manual or automatic control (IEEE interface) of the instrument ensure that the F900 can provide solutions in a wide range of measurement applications.