| Pneumatic braking system is the most common type of dynamic braking system. Its stable braking performance and strong braking force make it widely used in heavy vehicles.The national standard makes corresponding mandatory standard for the braking performance of different vehicle. In order to test whether the braking system meet these standard, it is necessary to test the parameters of the system through a variety of instruments or test bench. Designers do not need to master all the parameters of the vehicle in the design of their own systems,, and even only need to measure some of the parameters they interest in the static state of the vehicle. The characteristics of the measuring device are used frequently, the test results are relatively simple, easy to carry and install.The main content of this research is to develop a small embedded system, which can measure the pneumatic force and distance of the brake pedal, the pressure value of pipeline, and displayed on monitor in real time. In addition, connected to the computer through the data line, the computer software can draw the three measurement objects real-time curve, and can store the results of repeated measurements, which is easy to used any time. The device has the advantages of small volume and light weight, and can be directly carried out by hands.The design of the device is mainly from two parts,the handheld devices and computer software. the handheld devices, including the hardware circuit and the program loaded on the single chip microcomputer, has the function of signal acquisition, data processing and display. The signal of the sensor is adjusted by the analog signal to enter the AD converter, becomes the 12 bit digital signal and then entering the 51 SCM. As the detection field exists all kinds of noise, in order to ensure the accuracy of measurement data, the microcontroller makes anti-jamming process to the acquired signal through program, that is certain extent digital filter, then converse the data after the filter into the actual value according to the output voltage characteristics of the sensor, then the result can be sent to LCD display or serial buffer. LCD display driven by the T6963C drive, with the function of display graphics, and thus can display Chinese characters. Serial interface using the commonly used RS232 interface, not only able to transfer the binary number, but also the direct transmission of characters. Computer software can perform the bidirectional transmission of data with the SCM, the graphic display area can display real-time curve of the measured data, also has the editing function,such as curve zoom and curve move, and can store the data, and to open the curve from stored data.The hardware circuit of the hand holding part comprises a single chip microcomputer module, a signal acquisition module, a LCD display module, a RS232 module and the like. the software of the hand holding part includes start convert and reading data from AD converter, data filtering and numerical conversion, then drive and data refresh timing of LCD display, timing to send data to the serial port and processing the received data. The software on the computer mainly contains searching port could be used, the controlling of serial data transmission, and the various buttons and a graphic display area which can be used to open the file. the program loaded in SCM written in C51 language. Programming software is KEIL, which can directly generate the completion of the program to HEX files. The software running on the computer is written in VB language. |
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