Research on Detection Method and Calibration Specification of Portable Digital Multimeter
Calibration method studies
According to the requirements of the relevant spirit, based on the principle of legal measurement, after investigating the actual use of the portable digital multimeter and the current situation of the measurement work, combined with the actual situation of the basic measurement work, the calibration method of the portable digital multimeter is studied, and a set of A practical and effective calibration specification that meets the needs.
At present, most of the portable digital multimeters in use are three-and-a-half-digit display or four-and-a-half-digit display instruments, the accuracy level is between 0.1 and 5.0, and the scope of use is basically to detect AC and DC voltage, AC and DC current, and resistance. Electrically measured parameters, and used for general measurement purposes. The calibration items formulated in conjunction with the calibration specifications include AC and DC voltages, AC and DC currents, and resistance. In order to ensure the accuracy and reliability of the value transfer and traceability work, while considering factors such as cost and operation convenience, there are direct comparison method and standard source method available.
1 Direct comparison method
From the perspective of the calibration method of the portable digital multimeter, the direct comparison method can also be called the standard digital multimeter method. It connects the input terminals of the standard digital multimeter and the portable digital multimeter to be connected to the output terminal of the external adjustable voltage and current source and the adjustable resistor. When the external adjustable voltage and current source and the adjustable When the resistor outputs a certain value, assuming that the displayed value of the portable digital multimeter to be calibrated is Ux, and the displayed value of the standard digital multimeter is Un, then the relative uncertainty r of the portable digital multimeter to be calibrated is
The wiring corresponding to the direct comparison method is shown in Figure 1.
The feature of the direct comparison method is that the accuracy of the external adjustable voltage and current sources and adjustable resistors is not high, but the technical indicators such as the stability of the adjustable device and the fineness of adjustment are high, and it should meet Calibration specification requirements for adjusting devices. The cost of a whole set of calibration equipment using this calibration method is relatively low.
