| Building by external force,mechanical equipment operation will produce vibration signal.The vibration signal contains a large number of structures and equipment operating status information,through the analysis of these vibration information can be a good understanding of its operating state,when in its subtle failure but will not have a greater risk before the fault diagnosis,to avoid the hidden danger result to the larger losses.So the vibration signal acquisition and analysis is necessary.At present,the cable vibration signal acquisition and analysis instrument has been mature and perfect,but the study of vibration signal acquisition of wireless transmission is not mature and perfect,so this paper carries on the research of the vibration signal acquisition instrument based on WIFI.This paper analyzes and studies the basic principle and implementation of LwIP protocol stack,and improves the LwIP protocol stack according to the features that the vibration acquisition card upstream sent a large amount of vibration signal data,the amount of instructions sent to the downlink data is small.By reducing unnecessary functions in the protocol stack,optimizing the update algorithm of the blocking window value of the protocol stack,and transferring the sampling data pointer,the transmission efficiency of the vibration signal data is improved.In the hardware design,this paper designs a multi-type programmable sensor interface circuit,which can be programmed to set the signal input type,such as single-ended voltage input,differential voltage input,ICP input,AC-DC coupling.Can access displacement,ICP acceleration and speed sensors and other types of sensors.Using 24-bit high-precision A/D,so that the sampling has a relatively high amplitude relative accuracy.Sampling frequency and channel gain programmable control,for the adaptive gain and sampling rate control provides a hardware guarantee.Design SDIO_WIFI module interface circuit,the signal can be realized WIFI wireless transmission.In the software design,transplante real-time operating system uC/OS-II and improved LwIP protocol stack.The realization of the wifi-based vibration data upload and configuration commands to receive.At the same time,the design of the ARM and computer-side data acquisition protocol,the realization of the circuit parameters and the effective transmission of sampling data.According to the characteristics of the input signal,changing the gain of the acquisition channel and A/D sampling frequency,improve the accuracy of signal acquisition and transmission efficiency.Through the final test,this design of the vibration signal acquisition card can be a very good realization of the function.It can realize the acquisition of the vibration signal in the frequency range of 0～40kHz,the relative accuracy of the sampling amplitude is less than 0.2%,and the WIFI transmission distance can reach 100m in the open environment.At the same time,the system can improve the transfer rate of WIFI up to 4.5Mbps and packet loss rate of less than 0.01%after the improvement of LwIP protocol stack,which obviously improves the problem of low sending rate when the vibration data is large. |
