Signal Acquisition Device Based On Micro-injection Method For Monitoring Distribution Cable Insulation State

With the development of urban modernization,distribution cables are widely used,but their long-term operation may suffer from insulation degradation,resulting in power outages,serious fires and threats to personal safety.Therefore,online monitoring of distribution cables is required.The micro-injection type on-line monitoring method for insulation degradation of distribution cables adopts the method of injecting ultra-low frequency low-voltage signals to realize the detection of cable insulation impedance.As an important part of the monitoring device,the acquisition device needs the acquisition device to achieve high-speed and accurate acquisition of weak signals.Therefore,the comprehensive performance of the acquisition device has an important impact on the evaluation of the insulation state.The micro-injection distribution cable insulation degradation online monitoring device originally used the NI 9202 and Lab View framework to complete data collection,and then sent the collected data to a computer for data processing.The scalability of this framework is poor.For example,the range cannot be flexibly changed according to the needs of users,and when the technology is widely promoted,its expensive hardware cost limits the cost performance of the entire monitoring device.The collection device based on the embedded system studied in this paper has the characteristics of low cost,small size,and strong ability to resist electromagnetic interference.It is more suitable for monitoring the insulation status of distribution cables in power distribution stations.In addition to the high-precision,high sampling rate,and high stability requirements of the real-time acquisition device,the micro-injection type distribution cable insulation degradation online monitoring device also requires the realization of multi-channel acquisition to reduce costs.Under the premise of multi-channel high sampling rate,to realize the continuous collection,storage,calculation and other functions of all data,the parallel control capability,memory space size,and calculation speed of the real-time collection device are a great test.Aiming at the above project requirements,this article firstly carried out the overall design scheme of the collection device.FPGA with strong general performance and parallel processing capability is selected as the control chip,and DSP with fast calculation speed and high precision is selected as the calculation chip.Since FPGAs can only perform fixed-point operations,highprecision measurement cannot be achieved if only FPGAs are used for control and calculation.Because the working mode of DSP is sequential execution,if only DSP is used for control and calculation,DSP will always work on receiving data from the analog-to-digital converter,and calculation cannot be performed.Therefore,this paper proposes a hardware architecture of 24-bit analog-to-digital conversion chip + FPGA + DSP,which makes full use of the advantages of FPGA and DSP to realize continuous data collection and transmission: FPGA has been receiving data all the time,and the received data is cached in memory and set In a fixed time period,each cycle sends the cached data to the DSP at a very high speed.The time it takes from the FPGA data to the DSP data reception is only a small part of the time period,and the remaining time is reserved for high-performance DSP performs high-precision floating-point operations.Relying on the above hardware architecture alone cannot achieve continuous data transmission,and it is also necessary to set the cache function at the software level,and the setting of the cache area cannot be unchanged,otherwise it will cause the data to be forcibly overwritten before reading.In order to solve this problem,this article proposes to use sacrificial space in exchange for a continuous method in time to set the cache area to ensure that data is read smoothly and continuously.Based on the above hardware architecture and software design,hardware and software development and corresponding debugging work have been completed.And based on a large number of test data,the measurement errors due to the hardware circuit itself and zero drift are corrected.Finally,the real-time acquisition device can continuously collect all sampled data and complete FFT and other related calculations in DSP.Finally,the performance test of the real-time acquisition device was carried out,and the test results showed that the main performance of the real-time acquisition device reached the design index requirements.