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Electronic weighing instrument common faults and maintenance
I. Overview
Electronic weighing instrument (abbreviated as electronic scale) is a weighing instrument equipped with electronic devices, including full electronic scales and electromechanical combination scales. Its working principle is as follows:
When the weighing object or truck is parked on the weighing platform, the load passes through the scale body, and the weight is transferred to the weighing sensor. The elastic body of the weighing sensor is deformed, so that the electronic strain gauge stuck on the elastic body generates strain. The bridges that the strain gauges are connected to lose balance and generate electrical signals. The signal is amplified by a preamplifier, filtered by a second-order filter, and then added to an analog-to-digital converter to convert the analog quantity into a digital quantity. After processing by the CPU microprocessor, the weight of the object is displayed by the display.
If the user needs to print the record, the data is input in ASCII code and the dot matrix printer prints the record.
We know that the development of weighing instruments has gone from manual to automatic, from mechanical to electronic development, especially in the 1990s. New, highly integrated electronic components are also emerging. Now, mechanical weighing devices have gradually faded out of the market, and electronic weighing devices occupy an absolute dominant position. The reason for this is that full electronic scales have significant advantages over traditional mechanical lever scales:
1. The load-bearing device has a simple structure, small size, light weight, convenient installation and testing, strong adaptability, various forms, and is limited by installation.
2, weighing a wide range, as small as a few kilograms or even hundreds of grams, as large as tens of tons or even hundreds of tons. The use of a wide range, to meet the needs of different occasions, such as high temperature, high humidity, high dust, high noise, radiation and other environments.
3, no leverage ratio requirements, no blade and knife bearing wear, maintenance is simple, the workload is small, reducing the daily investment.
4, weighing speed, simple operation, thereby increasing work efficiency.
5, high resolution, repeatability, and intuitive.
6, electronic weighing device can achieve dynamic measurement or with certain operations at the same time, (such as dynamic electronic track scale, that is, during the operation of the train, at the same time to complete the weighing work, and such as electronic belt scales, dynamic cars, etc., in the completion of transport At the same time, weighing and metering are completed, which greatly shortens the working time, reduces the labor intensity, and improves the efficiency.
7. The intelligent electronic weighing instrument has many functions such as weighing, metering, control, verification, and communication. The application of the microcomputer software is more convenient for management. Therefore, its application field is continuously expanding, which is also a mechanical weighing apparatus. Unprepared.
It is because of the many advantages of electronic weighing devices that their market share continues to rise. Of course, it also brings various problems to our verification, repair and maintenance. Electronic scales mainly consist of scale bodies, sensors, weighing displays, large screens (or computers, printers, etc.), and those parts that are prone to problems are also included.
Second, the scale body common faults and maintenance
Common faults of the scale body are generally manifested as partial load overload or inconsistent indications of partial load points. The reasons for this may be:
1. If it is a newly-installed or first-certified electronic weighing instrument, first check the rigidity of the scale body, mainly to see if the thickness of the countertop panel or the like with the naked eye or with a simple appliance meets the specified requirements, or after pressing with a heavy object, the weight will be heavy. When the object is removed, see if the scale returns to zero within a short period of time. If it does not return to zero or returns to zero after a long time, it may not be rigid enough. In this case, the scale body must be replaced as a whole.
2, limit screw top dead
Check whether the limit screw is in contact with the scale body under empty scales and weighing conditions. Under normal circumstances, there should be a certain gap, and there is still a gap after the load is loaded. If the top dead or the gap is too small, it should be adjusted.
3, if there is no problem in the above two aspects, you should check the installation quality of the scale by: using a horizontal ruler or transparent hose to check whether the angle is in the same horizontal plane, the horizontal error of each angle should not exceed 10mm, if found If the loading point is not horizontal, the scale body should be lifted. After adjusting the level with the pad, the problem can generally be solved.
4, there is sensor damage
The standard weights are placed at each offset point, and it is found that the error at one point is particularly large, and it may be that the sensor at this point is damaged. The inspection method is: disconnect the power, open the junction box, disconnect the terminal of a sensor, close the power supply, add the standard weight to the sensor point when the scale is in the weighing state, if its value and the original If the standard weight value is equal or similar, the sensor is bad. If the value is far from the original standard weight value, the sensor has no problem. To judge whether the sensor is good or bad, you can also use the following simple method: Put the multimeter in the 20M ohm file, place the rod on the shielded wire or shell, and rest on the other wire. If 1 is displayed, the sensor is good, otherwise The sensor is bad. If this is not the case, it may be that the terminals of the sensor in the terminal box are loose or the contact points have poor rust. In this case, the rust can be properly treated or the terminal can be connected.
Third, the instrument common faults and maintenance
Instrumentation is an important part of electronic weighing instruments. With the continuous development of electronic technology, its degree of integration is getting higher and higher, and at the same time it plays an increasingly important role. In many cases, many failures of electronic weighing instruments can be directly displayed on the instrument, which brings great convenience to our fault diagnosis. We usually encounter difficulties in the inspection process. It is recommended that we carefully read the technical specifications of the instrument first, and then apply the right medicine to the disease, which can effectively avoid blindly judging faults, avoid detours, and save time.
1, first of all, to remind you to pay attention to the maintenance of the instrument:
1.1 Do not use the tweezers to randomly move the components so as not to disturb the original parameters of the instrument.
1.2 The multimeter's test leads should be thin to avoid short-circuiting the pins and damaging the device during measurement.
1.3 welding integrated film, soldering iron temperature should not exceed 200 °C, welding time does not exceed 10 seconds.
1.4 It is not possible to remove or solder the components from the printed circuit board under power-on condition.
1.5 During operation, it is strictly prohibited to hot plug sensors, printers and other external devices.
1.6 During the inspection, do not expand the fault to avoid future maintenance difficulties.
1.7 When you change the integrated chip, you should be familiar with the performance and pin arrangement of the integrated chip to avoid burnout due to plug-in. In general, the 1st pin on the bottom left of the integrated chip is 1 pin, and then it is arranged counterclockwise, as shown below:
2, determine the instrument is good or bad
Suspected instrument failure, can be judged by the following methods:
2.1 Connect the meter with the simulator and observe the changes in the indication. For example, whether there is drift, presence or absence of display, etc. If the indication is stable and there is no drift, the instrument is good.
2.2 Replace the spare PCB board, input the original parameters to the new PCB board or re-commission the board, use the same method to observe the change of the indication value to judge whether the instrument has any fault.
3, the instrument is fully dark after boot
Sometimes check the power supply first. They are the "source" of the instrument's operation. Therefore, troubleshooting should start here. Check if there is 220V AC voltage input. Use the electric pen or multimeter to measure the power supply circuit if there is no input. If yes, use a multimeter to measure the voltage at the output of the transformer. If no, the transformer is damaged. Replace the transformer to solve the problem. problem. If there is output voltage, inspect the integrated chip according to the instructions (or drawings) of the instrument for damage. If the conditions permit, it is better to replace the instrument with another instrument of the same type. The maintenance of integrated circuits is a tedious task. Sometimes the judgment of failure is still insufficient to measure. Therefore, a comprehensive inspection method is introduced here. This method is also applicable in the following other troubleshooting.
Visual, audio, touch and smell comprehensive inspection methods:
"View" is to see the display, sometimes the meter can show the cause of the malfunction.
"Listening" means listening to a beep, a beep sounds, no sound, and a long sound. The cause of the malfunction can be judged by a beep.
"Touch" is to touch the device by hand. The purpose is to find hot and hot devices in time and trouble-shoot.
"Smell" is the strange smell on the line. When the device is short-circuited, hot, and burnt, strange odor will be emitted. Carefully observe and touch the site where the odor occurs.
4, after the boot, weighing instrument indicates that the value is not stable
After powering on, the weighing instrument indicates that the value is unstable, indicating value gradually jumps upward, jumps back to a certain extent, and then jumps again. This situation is generally not well shielded. Check the instrument to see if the shielded wire (the thickest) falls off. If it does not come off, connect it. If it does not fall off, there may be a problem with the grounding wire. The test grounding resistance should be less than 4 ohms. If it cannot be reached, increase the number of piles until Grounding resistance meets the requirements and generally solves the problem.
If there is still drift, you should take the following measures: Open the junction box, clean it with alcohol and blow dry, check the communication cable is broken, take the line, if any, connect the broken line, remove the connection, unplug the nine-pin plug Blow dry and the meter should display normally. If there is drift, the PCB board or sensor may be damaged. The inspection method is the same as above, you must replace the PCB board or replace the sensor.
5, display weight is not accurate
In this case, there may be several situations in general:
5.1 Sensor failure. The failure inspection method has been described above.
5.2 Loss of original calibration data. If it is determined that there is no problem with the sensor, recalibrate the instrument according to the technical manual of the display instrument or re-enter the original calibration parameters, which will generally solve the problem.
5.3 Mechanical Failure. To see if it is a mechanical failure, the main inspection: 1), to see whether the unloading bolts contact the sensor, adjust the gap to less than or equal to 2mm; 2), whether the scale body is damaged or the scale body sinks; 3), under the scale body is Foreign matter, if any, remove foreign matter.
Fourth, software system failures and maintenance
1, boot the mouse drift
Sometimes in normal connection, the power-on mouse drifts to the side of the screen and the mouse cannot be used normally. This phenomenon is when the computer is self-checking, and the meter's communication data is mistaken for the mouse's data. The solution is usually to unplug the communication line, restart the computer, and then plug in the communication line, the computer's mouse will return to normal. You can also open the computer first, and wait until the computer is fully started before turning on the meter.
2, can not open the software
You can run Instdrv.exe in the DRIVER folder under the installation CD to reinstall the dongle driver. After restarting the computer, you can enter the software interface.
3, serial communication problems
The computer always shows no weight. How to deal with it?
First check whether the connection between the instrument and the computer is correct. Second, check whether the setting parameters in the software (such as baud rate, serial port settings, etc.) are correct. Generally, the problem can be solved.
4, can not enter the management system
This situation generally belongs to the database and loses information. Solution: Reinstall the software installation disk again, re-enter the staff and user permissions.
5, can not print
Solution: 1), re-set (install) the printer; 2), if the printer fails, it may be damaged, you can replace the printer.
6. After the management system has been used for a period of time, some strange problems have appeared. Generally, reinstalling will solve the problem.
Author: Yu Yong Yong Source: Science and Fortune 2014 6