The Development Of Portable Multifunctional Calibrator

With the coming of the new century,in order to deal with the increasingly serious problems such as energy exhaustion and power grid quality degradation,the construction of power grid has ushered in the era of smart grid aiming at efficiency,economy,security and reliability.In order to ensure accurate and stable operation of electrical measuring instruments in various fields of power grid structure,whether it is the factory calibration or the regular inspection in use,it is an indispensable step.However,the common checking platform or device is bulky,which is not conducive to carrying it on site.Therefore,on this basis,it is of great significance to develop a portable calibrator that can verify different functional electric meters.The portable multifunctional calibrator developed in this paper,using the standard source method as the basic principle,separate isolation technology for voltage and current,the signal can be output through the power amplification circuit without transformer,able to check ac/dc meters and electric energy meter.At the same time,switch from check mode to external ac/dc signal measurement mode by relay,the main function is calibration and the auxiliary function is measurement.The calibrator adopts a dual-ARM architecture,with STM32F407ZGT6 as the central processing unit for each piece of ARM,the function is divided into waveform output MCU and sampling communication MCU,data exchange through SPI communication.Waveform output MCU control two-stage D/A: the first stage 20-bit DAC MAX5719 produces a reference signal with adjustable amplitude;second stage 16-bit digital-to-analog converter DAC8811,write 1024 waveform points generated by formula method.Finally,with the cooperation of two-stage D/A,the MCU outputs the standard source signal with adjustable amplitude and frequency.In the sampling communication MCU,when the calibrator is in the calibration mode,synchronous sampling of standard source signals was completed by 18-bit successive approximation ADS8699,the sampled data are calculated as the standard value,and transmitted to the waveform output MCU for closed-loop adjustment,cooperate to complete ac/dc meter calibration.AD9833 converts the calculated power value into a frequency pulse,through pulse comparison method cooperate with MCU to complete the inspection of electric energy meter.When the calibrator is in the measurement mode,the ADS8699 and AD7710 respectively complete the asynchronous sampling of external ac signal and the acquisition of dc signal,the sampled data of ADS8699 by adding four-term and fifth-order Nuttall cosine window function,FFT operation and interpolation correction,then get the electrical parameters.The calibrator is equipped with serial display screen and serial upper machine for communication,control and display,sampling communication MCU receives instructions and parses them,cooperate with the of waveform output MCU to complete each function instruction,and return to display in real time.In this paper,starting from the background and significance of multifunctional calibrator instrument development,combined with the current situation of domestic and foreign inspection platform,and the actual application requirements in the power grid structure.Put forward the research content,the performance and index of the calibrator,then detailed introduction related algorithm principle,hardware structure and software design flow thought of calibrator during the design process.Under the comprehensive test of Fluke 8845 A meter and various electric meters,the calibrator has reached the expected design requirements.Finally,some improvement measures are put forward in view of the shortcomings in the development of the calibrator.