Microcomputer testing system for electric paramete

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Microcomputer testing system for electrical parameters of washing machine Abstract: testing electrical parameters of washing machine with microcomputer can improve the automation level of washing machine production. This paper presents the hardware and software of the washing machine electrical parameter testing system composed of microcomputer and PLC, and the measures taken to improve the reliability of the system. The actual operation of the system has received good results

key words: washing machine; Testing; Microcomputer; PLC; Reliability

after the parts of the washing machine are assembled into a complete machine on the assembly line, the electrical safety parameter test shall be carried out. Only when the technical indicators meet the requirements can they be qualified. The test system is mainly used for the parameter test of washing machine. The test performance of the microcomputer test system meets the relevant requirements of the national standard; The system can automatically complete each test item, automatically complete data collection, quality judgment (qualified, unqualified), result display, print commodity inspection card, test report and quality statistics report; It can handle shutdown recovery and automatically identify empty trains. The application of Microcomputer in the electrical safety parameter test of washing machine can improve the automation of washing machine production, increase productivity and reduce the labor intensity of workers; Avoid the randomness of manual test and improve the accuracy of test parameters

1 hardware design

structural block diagram of the test system, as shown in Figure 1, the test line is equipped with a circulating chain, and 8 stations are arranged at equal intervals on the line. Three core sockets are fixed on the circulating chain at equal intervals according to the length of the stations. The length of one station is 1.2m. The washing machine is transported from the assembly line to the circulating chain by a manipulator and placed between the two sockets. The washing machine moves along with the circulating chain. Each time, the moving distance is one station long, and then it stops for parameter test. After the test, it moves. The washing machine moves to the last station and is carried by the manipulator to the water adding test line

Figure 1 system structure block diagram

the hardware of the test system includes a parameter tester, a programmable controller and a microcomputer system. The hardware block diagram is shown in Figure 2

Figure 2 system hardware block diagram

1.1 microcomputer system

uses 586 microcomputer, which is equipped with two printers, one on the machine room to print statistical reports, and one on the outlet to print commodity inspection cards. The two printers use the same parallel port through the sharer, and select a printer to connect with the computer through switching. The barcode scanner is connected to the microcomputer through RS-232C serial port. The mains supply power to the system through the voltage stabilizer and uninterruptible power supply (UPS). On the one hand, the power supply quality is improved. On the other hand, when the mains supply is abnormal, the UPS is used to supply power and save the data, so as not to lose useful data due to power failure

1.2 parameter tester

parameter tester includes grounding resistance tester, insulation resistance tester, withstand voltage tester, current and power tester and noise tester. Each tester adds the test signal to the washing machine for parameter test. The test signal and test result are displayed digitally on the front panel of the tester during the elastic modulus test of materials and sent to the microcomputer through the interface unit. The measurement method of grounding resistance is 10A constant AC power supply. The grounding resistance is obtained by measuring the AC voltage. In order to improve the measurement accuracy, the measurement method uses the four terminal principle, as shown in Figure 3. The insulation resistance measurement method is to add 500V DC voltage to the phase line, zero line and ground line of the washing machine. The sampled voltage is processed by double integration and compared with the reference voltage to obtain its corresponding value. Leakage current measurement is to measure the leakage current between the live line or zero line and the ground line of the washing machine

Figure 3 principle of grounding resistance measurement

the withstand voltage test is to add high voltage to the phase line, zero line and ground line. Under the specified high voltage, if the current value exceeds the specified value, an overcurrent signal will be generated on the sampling resistance. Through comparison and amplification, the relay will act, automatically cut off the high voltage and alarm at the same time. The power measurement is to measure the voltage value added to the washing machine by the voltage transformer, and the current value flowing through the washing machine by the current transformer. The voltage value and current value are converted into power value by the power converter

in order to reduce the impact of environmental noise, the noise measurement is carried out in the noise room. A noise probe is installed in the noise room. The noise room has a good sound insulation effect. The inlet and outlet of the washing machine are well sealed with felt. The noise meter converts the noise into DC voltage. The principle block diagram of the noise meter is shown in Figure 4

Figure 4 principle block diagram of noise meter

1.3 programmable controller

Mitsubishi F1 series programmable controller is selected. The controller has 24 inputs and 36 outputs, and the input and output points can be expanded. The programmable controller receives the photoelectric switch, travel switch and button signals, judges whether the chain body stops, whether there is a washing machine on the station, controls the measurement time, controls the start and stop of the tester, and sends the arrival signal to the microcomputer. The microcomputer welcomes your call and support after receiving the arrival letter! Read the test results after No. After all parameters are tested, the microcomputer will judge whether the washing machine is qualified. If the parameter is unqualified, the judgment result will be sent to the programmable controller, which will display the judgment result at the outlet

1.4 A/D conversion and digital display

the test signal and test result of each tester are digitally displayed after a/D conversion and sent to the microcomputer. The analog-to-digital converter used is that the BCD code output by icl71357135 is decoded and drives five seven segment code displays to form a 4-bit and a half display. The 7135 outputs one bit BCD code each time, and the microcomputer reads it five times continuously to get a conversion result

1.5 interface and bus

connect each tester and programmable controller to the microcomputer through 40 core flat cable. The 40 flat cable is connected to the interface board inserted into the microcomputer expansion slot. Each tester is connected to the flat cable through the interface unit, and the programmable controller is connected to the flat cable through the communication interface. The interface board is a 16 bit digital quantity input and 16 bit digital quantity output board, and the digital quantity output has the locking capability. The communication interface is used for two-way data transmission between the microcomputer and the programmable controller. Both directions are photoelectrically isolated. The communication parties do not affect each other and can communicate reliably. The interface unit has the ability of photoelectric isolation and three state output. Four bits of the 16 bit digital quantity output by the interface board are used as the address signal. The address is decoded in the interface unit. The selected interface unit is connected with the flat cable. The unselected interface unit is in a high resistance state

2 software design

the software is compiled in the form of modules in C language. The software has the function of interactive response. Chinese characters are prompted on the screen. The Chinese character display method is to read the font in the font, draw the dot matrix graphics of Chinese characters with the point drawing function, and enlarge and rotate Chinese characters. The flow chart of the main program is shown in Figure 5. The screen displays the main menu during program execution. The main menu has six options: parameter setting, parameter test, shutdown recovery, parameter query, report printing and system exit. Parameter setting is used by the operator to set the qualified range of each tested parameter. Parameter test is the main part of the software. When the parameter test is selected, the screen displays the second level menu. The second level menu is used to set the coding method. One coding method is to scan the bar code of the washing machine, and the other coding method is to automatically add 1 code. In this way, the code of the first washing machine to be tested is sent to the microcomputer, and the code of the next washing machine to be tested is the previous one plus 1. During the parameter test, the screen simulates the movement of the washing machine on the test line, and the measured parameters corresponding to the washing machine are displayed on the screen. With the movement of the washing machine, the screen gives the time to start the test. At present, as more Chinese sports brands join the trend of upgrading from solvent based shoe adhesive to waterborne polyurethane shoe adhesive, how many have been tested, of which how many are qualified and how many are unqualified, Test the number of sets and other statistical parameters. When the washing machine reaches the outlet, the microcomputer will judge whether it is qualified according to the measured parameters and the qualified range. The judgment results will be displayed on the display and sent to the programmable controller. The test results will be stored in the file in the disk and sent to the outlet printer to print the commodity inspection card of the washing machine. During the test, because the test system may be abnormal (such as power failure), the measurement has to be stopped. At this time, some parameters of the washing machine on the test line are measured. The UPS power supply is used to save these parameters. When the system returns to normal, the measurement can be continued. This can avoid repeated measurement from the beginning. Shutdown recovery can complete the above functions. Parameter query displays the code and parameters of the tested washing machine for query

Figure 5 main program flow chart

3 anti interference measures

in order to improve the reliability of the system, the following measures are taken:

(1) the stabilized current and uninterruptible power supply are used to improve the power supply quality of the system. The test system is powered separately to avoid using the same power source as other power equipment. The machine room is equipped with an independent grounding wire, the grounding resistance is less than 4 Ω, and the system is grounded at one point

(2) shielded cable shall be used, and the signal line and power line shall be laid separately, with a distance of 15cm

(3) for accurate test, the microcomputer can read the test results only after the test signal is stable, such as measuring the grounding resistance. The value of the grounding resistance can be read only when the AC current is stable to 10A. The read value is taken as the final test value after digital filtering. The method of digital filtering is to read 8 values, remove the two large numbers and two decimal places, and take the arithmetic mean of the four values

(4) photoelectric isolation technology is adopted, and the microcomputer is isolated from the programmable controller and each tester with photoelectric coupler

4 conclusion

the test system has been officially put into operation and works well. With a little modification, it can be used to test the electrical safety parameters of other electrical appliances

about the author:

Zheng Changbao graduated from the Department of electrical engineering of Hefei University of technology in 1990 with a master's degree. Now he works in the Department of automation of Anhui University. His research direction is microcomputer application and intelligent control


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