Design Of High Precision And High Resolution Digital Systhensis AC Voltage Standard Source

With the improvement of the industrial manufacturing,the calibration requirements for the accuracy of the multimeter are getting higher and higher,AC voltage standard source is a standard device for calibrating a multimeter.However,the research and development of related products in China is at an early stage,and the related products have poor stability and low resolution,which is difficult to meet the current market demand.Therefore,this thesis studies the accuracy and resolution enhancement technology of voltage standard,develops corresponding metering devices,and solves the problem of localization of imported instruments.The specific research questions of this thesis are as follows:Firstly,the standard source requires extremely high stability,so this paper studies the key technologies of the AC standard source.After deep analysis and derivation,a number of closed-loop feedback control links were designed.The feedforward-feedback control improves the speed of adjustment,avoids integral saturation,and improves the accuracy of standard source.The use of negative feedback technology reduces the distortion of the power amplifier,improves linearity,and broadens the frequency band to 100 kHz.And based on the dual-channel pulse width modulation technology,the voltage high resolution adjustment is realized.Secondly,develop an overall plan to complete the circuit design.The circuit mainly includes a reference source circuit,a double DA circuit,and a broadband amplifying circuit.The reference source circuit uses charge pump technology to invert the reference voltage,replaces the digital-to-analog converter with pulse width adjustment,and extends the voltage output range to-7V~+7V.The dual DA circuit converts the sinusoidal digital wave generated by the FPGA into amplitude and frequency adjustable analog wave;The wide-band amplifier uses the cascade technology to broaden the frequency band,uses a constant current source load to reduce harmonic distortion,and has a protection circuit to prevent overcurrent damage of the device.Then combine the power amplifier with the transformer to amplify the output voltage.Thirdly,the internal logic of the digital synthesis system of FPGA is designed.The AC voltage is generated by digital frequency synthesis technology.The causes of harmonic generation are analyzed and improved in the FPGA logic design by increasing the number of phase accumulator and improve the frequency resolution,And truncate its high position for addressing,while compress the ROM space to reduce the ROM space requirements.Finally,the high-precision AC standard voltage source test and verification platform was built.The AC standard source was tested and calibrated with an eight and a half 8508 A high-precision digital multimeter.The upper computer was programmed by Labwindows/CVI to realize the whole process automation.And use the error compensation algorithm to reduce the system error.The short-term stability and the output of each range were tested,and the uncertainty was evaluated.The results show that the developed AC standard source output meets the requirements of the specifications.