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A high-voltage isolated DC voltage and current transmitter

the creativity is unlimited, and the instrument is a great invention. Today, I will introduce a national invention authorized patent - a high-voltage isolated DC voltage and current transmitter. The patent was applied by Nanjing Guodian Nanzi Rail Transit Engineering Co., Ltd. and was authorized and announced on January 4, 2016

content description

the invention relates to a voltage and current measuring device for high-voltage DC systems such as subway and light rail, in particular to a high-voltage isolated DC voltage and current transmitter

invention background

with the development of subway, light rail and other rail transit, DC system is more and more widely used, which brings the measurement of DC voltage and current. When DC analog signals are isolated by linear optocoupler, the cost is relatively high, and the isolation voltage is limited, which cannot meet the safety requirements. For example, in CNU, a circuit used to isolate analog signals, the linear triangular wave is the method of generating sawtooth wave through 555 circuit, and the sawtooth wave is realized through the filtering of square wave. Due to the charging and discharging characteristics of capacitor, the sawtooth wave generated will not be linear, which will lead to the duty cycle of subsequent PWM is not linear, thus introducing error to the system. PWM is a method of digital coding of analog signal level. By adjusting the duty cycle, the level of a specific analog signal is encoded. As long as the bandwidth is enough, any analog signal can be encoded with PWM. It is especially suitable for DC voltage conversion. The output voltage can be controlled by adjusting the duty cycle. PWM signal is a complete digital signal, which can easily realize signal isolation. However, in the circuit of PWM coding and PWM to DC voltage, the PWM duty cycle and the corresponding value of its output voltage usually show a nonlinear state, and this nonlinear state will lead to the decline of the accuracy of PWM in operation

content of the invention

in view of the problems existing in the existing technology that can also measure copper alloy materials, the purpose of the invention is to provide a high-voltage isolated DC voltage and current transmitter

the technical scheme of the invention is: a high-voltage isolated DC voltage shakes too much voltage and current transmitter, including the transmitter due to excessive accumulation of contradictions, opaque information, plus people's panic psychological main body and signal processing circuit. The signal processing circuit consists of a fixed frequency pulse generation circuit, a linear triangular wave generation circuit, a sampling signal modulation and amplification circuit, a photoelectric isolation circuit, a DAC conversion circuit and a v/i conversion circuit. The fixed frequency pulse can improve the success or prolong the life of the medical device based on its elasticity, and the impulse generation circuit is connected with the linear triangular wave generation circuit; The triangular wave generation circuit and the sampling signal modulation and amplification circuit are respectively connected with the comparator to form a PWM wave; PWM wave is connected with photoelectric isolation circuit; The photoelectric isolation circuit is connected with the DAC conversion circuit through the Schmidt trigger; One voltage output of DAC conversion circuit is connected with v/i conversion circuit

the above high-voltage isolated DC voltage and current transmitter is further characterized in that the linear triangular wave generation circuit uses a constant current source to control the capacitor charging speed on the basis of the generated fixed frequency square wave. In the later stage of charging, under the action of the fixed frequency square wave, it discharges rapidly, so as to achieve

it is further characterized in that the DAC conversion circuit is a DAC chip with two PWM inputs, which realizes PWM to V voltage output and ma current output

the invention realizes the sampling signal of ± 60mV, converts it into standard control signal of V or Ma, selects the corresponding isolation optocoupler and power supply according to the isolation level and requirements, and can realize the isolation of 10kV at most. At the same time, the delay of signal output is reduced, the error of the system is reduced, and the measurement result is more accurate

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