The Development Of Voltage-Controlled Current Source

Intelligentization and automation of testing equipment are the developing trend at present.The traditional current-comparator bridge is balanced by adjusting the turns number of the coil,the operation is very troublesome.The adjustment of current is an effective way to achieve automatic balance of the current-comparator bridge.Voltage-controlled current sources can realiaze automatic adjusting current,because the voltage signal is very easy to achieve automatic adjustment by computer technology and analog-to-digital conversion.Therefore,the development of the voltage-controlled current source is an important foundation for automatic current-comparator bridge.The design of the voltage-controlled current source is background on the development of harmonic components of loss current measurement used for the diagnosis of water-tree in XLPE power cable.Considering the actual requirements of testing range and accuracy,designing coarse and fine-tuniing voltage-controlled current sources is needed.Coarse voltage-controlled current source is aimed to statify the testing range;fine-tuning voltage-controlled current source is aimed to meet the need of testing accuracy.The coarse voltage-controlled current source connects a hundred turns compensatory coil of the current-comparator bridge;the fine-tuning voltage-controlled current source connects one turn compensatory coil of the current comparator.According to the actual testing conditions,the operating frequency range of the voltage-controlled current source is determined.Then,the maximum current values of the coarse and fine-tuning voltage-controlled current sources are calculated.At the same time,the minimum changed amounts of current and testing capacitance are caculated also.According to the technical indexes,selecting electronic components and designing circuit are based on the principle of improved howland voltage-controlled current souce.Coarse and fine-tuning voltage-controlled current sources are simulated respectively by Multisim software.The simulation and analysis prove that the design of two standard voltage-controlled current sources is reasonable.Coarse and fine-tuning voltage-controlled current sources are made on a PCB-board.The performce of coarse and fine-tuning voltage-controlled current sources is measured,the load is respectively resistance or compensatory coils of the current-comparator bridge.The experimental result shows that the performance of developed coarse and fine-tuning voltage-controlled current sources satisfies initial design goals.