Development of a New NIST Calibration Service Using the Comparison Method for Vacuum

Influencing the "injection barriers" into prototype molecular wires through metal-molecule Context: Many NIST customers using our vacuum calibration services spanning the pressure range from 0.65 Pa to 133 kPa (5 millitorr to 1000 torr) desire direct traceability to NIST but cannot justify the cost of calibration against relative to the NIST NIST Ultrasonic Interferometer Manometers (UIMs). These customers are typically using less accurate gauges, such as Thermal Conductivity Gauges 1-2 (TCGs), or the newer combination type gauges that have 2 sensors combined with an electronic processor that averages or selects which sensor is being utilized depending on the pressure being sensed. A new calibration service based on a secondary pressure transfer standard spanning this pressure range is being developed at NIST. It is designed to add a lower accuracy level service consistent with the needs of these customers and will follow a model where a less accurate, and less costly, service is offered to customers who do not require the lowest uncertainty available from NIST. Introduction: The Comparison Method Vacuum Gauge calibration service under development at NIST has been designed with the NIST calibration customer in mind. From the onset, the goals for this project were to reduce turnaround time , calibration cost, and to provide an on-demand vacuum gauge calibration service. This new services is aimed at a class of pressure instruments whose accuracy capabilities are significantly less than that of the NIST standards currently used for calibration. Use of calibration standards consistent with the performance capabilities of this instrument class and utilizing extensive computer automation as part of the design conceptconsists of: • A high-stability Transfer Standard Package (TSP) that provides traceability to NIST primary pressure standards and • An automated test stand where the high-stability TSP and customer gauges can be compared with a series of computer-controlled pressure test points spanning the barometric pressure range of 0.65 Pa to 130 kPa. At the core of the Comparison Method Vacuum Gauge calibration service is a NIST-designed, built, and tested TSP, consisting of two different gauge technologies: Resonant Silicon Gauges (RSGs) and Capacitance Diaphragm Gauges (CDGs). The RSG technology has demonstrated superior long-term stability (drifting less than 0.01% per year) while the long-proven CDG technology provides superior low-pressure resolution at pressures below 133 Pa (1 torr). High-stability TSPs have been periodically calibrated against the NIST 160 kPa UIM and 140 Pa Oil UIM Primary Pressure Standards as part of …