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In world class metrology, the most important consideration is the quality of the fundamental measurement. ASL's F18 AC bridge technology represents the 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 F18 Precision Digital Thermometry Bridgeis 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. Practical measurements involve cables, connectors and imperfect operating environments, the F18 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 0.2 ohms to 390 ohms. This equates to a temperature measurement accuracy of 5 micro K for a 25.5 ohm SPRT referenced to a 25 ohm reference resistor. AC bridge technology will always out-perform measurements made using DC technology with slow current reversal. These benefits are inherent to the fundamentals of electrical measurement and not just the implementation. The F900 includes a wide range of features specifically tailored for temperature metrology. These include 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.