Special failure of metering electronic weighing instrument

1、 With the rapid development of science and technology, electronic weighing apparatus plays an important role in production and management In order to play their role better, we must guarantee their reliability and measurement accuracy However, no matter the newly installed electronic weighing instrument or the electronic weighing instrument which has been used for many years, there will be some failures, which will cause them to be unable to work normally The faults of electronic weighing apparatus can be divided into two types: common faults and special faults However, no matter what kind of fault, it is caused by weighing display, weighing sensor, power supply, connecting circuit and mechanical transmission mechanism The reason of its failure is caused by unreasonable installation design, improper use and natural damage The following are some special troubleshooting experiences we have encountered in the installation and maintenance of electronic weighing apparatus Second, the inherent deficiency of electronic weighing device electronic ground weighing device is a kind of electronic weighing device that we use more Zui, and we have experience in installation and debugging However, when a billet scale is installed and debugged in a steel rolling plant, a phenomenon never occurs That is to say, when the test weight is used for calibration after installation, it is found that the weight displayed on the display instrument does not change according to the weight applied, but varies from time to time, and the quantity displayed on the instrument is also related to the placement position of the weight, so normal calibration cannot be carried out The weighing sensor of the scale is connected in parallel After careful inspection, the connecting circuit of the sensor is correct (the sensor is connected according to the color code of the wiring diagram in the manual) And the display instrument and mechanical part have no fault After careful analysis of the above phenomena, we think that the problem still appears on the sensor In order to find out the reason further, we first calibrate the display instrument with a simulator, then connect it to the sensor, and then use a weight to press the four corners of the scale respectively The results show that the three corners are positive, while the other is negative Therefore, we conclude that the internal wiring of the sensor at this angle is wrong After the bridge voltage of the sensor or the positive and negative lead of the signal wire are replaced, the angle also shows a positive value Because the positive and negative electrodes of bridge voltage or internal lead of signal are connected reversely when the sensor is packaged before leaving the factory, the above-mentioned fault occurs when the sensor is connected according to the normal color code during installation After the connection is changed, it is recalibrated, and the above phenomenon is eliminated Another example is that the scale can not work normally (the display shows under load phenomenon) after replacing four sensors and calibrating the sensor junction box during the overhaul Since both the sensor and the junction box are newly purchased, when finding the cause of the fault, the connecting line is mainly checked, but there is no wrong connection in the connecting line, but when the ground wire is disconnected, the display instrument shows normal, and the above fault occurs again after the ground wire is connected Disconnect the display instrument and check the bus with a multimeter It is found that the signal positive pole is connected to the ground wire Therefore, when the sensor bus is connected to the display instrument system, the signal positive pole is short circuited to the bridge voltage negative pole, which destroys the normal working state of the sensor bridge Therefore, the above phenomenon occurs Next, disconnect all the sensors and check whether the results are normal There is no doubt that the problem is in the sensor junction box When using a multimeter to check the sensor junction box separately, find out the short circuit between the ground terminal of the junction box and the signal positive terminal of the sensor in the junction box Check carefully to find out that there is a short circuit on the printed circuit board in the junction box The problem is caused by the product quality of the junction box (it is analyzed that the junction box has not been carefully inspected before leaving the factory, otherwise the above problems should not occur.) After cutting the short circuit with the blade, the above problems can be eliminated Third, the problem of unreasonable design and installation program-controlled hopper scale is applied in our company When we installed and debugged two program-controlled hopper scales in the No.2 electric furnace branch, we found that the two scales interfered with each other, and the control system sometimes failed to work according to the specified procedures, often resulting in misoperation The scale is designed according to the design scheme of a Design Institute for two sets of batching systems in the second electric furnace branch During the installation and debugging, the above phenomenon appeared After repeated tests and analysis, we found out that the cause of the fault was the power supply problem Because the control part and instrument part of the two scales are connected to the lighting power supply, then the control part is connected to the power supply, and the instrument part is still connected to the lighting power supply, the above problems are solved, the commissioning of the program-controlled hopper scale is completed, and the normal work of the feeding system is ensured Another two 30t truck scales are installed and debugged by a manufacturer It is installed in summer, but the scale is out of tolerance in winter After analyzing and finding out the reasons, we found that the two scales are all connected according to the four wire system Because we are located in the north cold area, and the temperature difference is large in winter and summer, we analyzed and determined that the error is caused by the change of wire resistance with the change of temperature (the principle is brief, otherwise specifically discussed in the article) After we changed the four wire system to the six wire system, the problem was solved IV the troubles occurred in use our electronic truck scale without foundation pit once had such problems in winter: the weight of the display instrument was not the same due to the different stop position after the truck scale was put on When the car with known weight is put on the weighing platform, * times stop at the front of the weighing platform, the weighing result is slightly higher than the actual weight, while the second time, stop at the back of the weighing platform, the weighing result is lower than the actual weight, so the scale can not measure and check the weight normally After careful inspection, the weighing display instrument and connecting circuit are normal When the car is on the scale platform, it can be seen that the scale body swings weakly, indicating that there is no foreign matter stuck on the scale body Through analysis and judgment, it is possible that there is a hard object on the ground at the bottom of the scale body to hold the scale body, and the weight on the load cell is not the actual gravity, so the weight displayed by the instrument is less than the actual weight In order to confirm this judgment, we stretched the iron hook to the bottom of the scale body for inspection, and found that there was a foreign object at the bottom of the scale body The foreign matters are the powder coal, dust and other deposits blown into the bottom of the scale by the wind, mixed with rain and snow, forming a hard mixture against the scale body when it is frozen, reducing the positive pressure borne by the two sensors at this end, resulting in inaccurate measurement data of the truck scale, and the scale returns to normal after the removal of the foreign matters In addition, the electronic weighing instrument often shows the phenomenon of unstable data (variable) in use Some of the faults are caused by the bad performance of the instrument or sensor, but most of them are caused by the water and damp at the junction of the wire box or the wire But in the electronic weighing apparatus we used, the above phenomenon is not caused by the above reasons, but the multi strand wire at the welding part of the connector connecting the sensor and the junction box is broken due to the long-term corrosion of residual welding oil, leaving only two or three strands of wire connection (it is difficult to find the appearance) After careful search, we found the above fault After reconnection, we removed the fault V conclusion the above several failures are the more special failures and handling experience we have experienced in the installation and maintenance of electronic scales for many years In order to ensure the normal use of electronic weighing apparatus and better play their role in production and operation, it is necessary to constantly summarize and accumulate experience, and timely eliminate all kinds of failures in the installation and use of electronic weighing apparatus