System Design Of Multifunction Calibrator And Research On Accuracy-Improving Strategy

Multifunction calibrator is an important part of electronic measurement system,which is widely used in various measurement stations and scientific research institutes.The multi-function calibrator can generate common basic electrical standard signals,such as AC/DC voltage,AC/DC current and impedance.It has wide range and simple operation.It is very friendly to users and plays an irreplaceable role in the calibrator of digital multimeters.Aiming at the gap between domestic multi-function calibration and foreign advanced products,and promoting localization of precision instruments,this topic makes an in-depth study on the structure and DC reference part of multifunction calibrator,designs and draws the system supporting plate of multi-function calibrator,and provide hardware basis for multifunction calibrator system;The adjustable DC reference with high resolution and high stability is designed and implemented,which can achieve the output noise voltage index of 1u V resolution and 6.5u Vpp.The specific contents include:Firstly,the overall structure of the multifunction calibrator is analyzed from the overall point of view of the system.The structure of the overall base of the multifunction calibrator is described from the position distribution of each sub-board and the arrangement and transmission of digital and analog signals in the multifunction calibrator system.At the same time,the functional requirements and performance indexes of the multifunction calibrator are defined.The key circuit which determines the output accuracy and stability of the multi-function calibrator is found out through error distribution and synthesis.Secondly,aiming at the high resolution and high stability adjustable DC reference source of key parts of the multifunction calibrator,a realization scheme based on Dual PWM modulation is proposed.The transmission and calculation of noise voltage of all levels of circuits in adjustable DC reference are analyzed,and the feasible scheme to realize high resolution and high precision is described,According to the requirements of the index,the reference source chip and the precision operational amplifier are selected.Thirdly,the hardware circuit and software of adjustable DC reference with high resolution and high stability are designed and implemented.The hardware circuit includes the reference circuit based on LTZ1000,charge pump phase-inversion circuit,drift-free filter and so on.The circuits are simulated in the simulation software LTSpice and Multisim.The software part includes the programming of upper computer,the format of serial communication command protocol,and the design and implementation of correction and compensation algorithm.Finally,the test platform of adjustable DC reference source is built by using eight and a half digital multimeter and upper computer software.The output of each circuit of adjustable DC reference source is repeatedly measured,and the test results before and after correction and compensation are compared.The test results show that the design of adjustable DC reference meets the requirements of resolution and stability.