Agilent Fully-Automatic DMM Calibration System - White Paper 5991-1270EN c20140603 [11] free download

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Keysight Technologies Fully-Automatic DMM Calibration System White Paper Abstract This paper describes a fully-automatic calibration system for digital multimeters (DMMs), and uncertainty estimation of the DCV measurements of the system. A connection mechanism whose rating is more than 1000 V/1 A/1 MHz was developed for the system. By using compressed air to drive the mechanism, we were able to eliminate operator bias, as well as improve the thermal electromotive force and measurement repeatability of the system. For the standard in the system, an 8 1/2 digital multimeter was used, which was calibrated by the standards laboratory of Keysight Technologies Japan Ltd. The measurement uncertainty was estimated by referring to the ISO Guide to the Expression of Uncertainty in Measurement[1] (GUM). Introduction Issue for Designing Fully-Automatic DMM Calibration System There are some points to be considered in order to design a digital multimeter (DMM) calibration system, such as traceability to an upper level standards laboratory, selection of a stable standard, and evaluation of the measurement repeatability. Furthermore, for a fully -automatic DMM calibration system, it is necessary to consider signal switching mechanisms, system noise, and countermeasures for abnormal conditions. Generally, a relay switch is used to route test signals between the unit under test (UUT) and signal sources. However, a relay switch isn't suitable for precision measurement of low voltage because thermal electromotive force (thermal-emf) is caused by self-heating due to the driving current of the relay. Therefore, a commercially available low thermal-emf scanner is widely used for a precision measurement system for a standard cell or a Zener voltage standard. On the other hand, as maximum DC voltage and DC current of the DMM calibration are 1000 V and 1 A, the scanner whose maximum rate is 24 V 0.5 A is unlikely to be used in the fully-automatic DMM calibration system. Besides, a fully-automatic calibration system is physically larger than a manual calibration system. Because the cables between the equipment become long and are easily affected by environment noise, the problem of measurement repeatability can occur. Furthermore, as the fully-automatic calibration system can perform calibration without operators, it is important to take countermeasures for unexpected damage to the equipment or the software into consideration. Authors: Yuko Hirota, Tos hiaki Aoki and Masao Noguchi Keysight Technologies Japan, Ltd. 2000 NCSL Workshop & Symposium Design for Fully-Automatic DMM Calibration System We developed the fully-automatic system in order to improve upon operation quality and throughput of 81/2-digit DMM calibration, considering the above- ment