Analysis of the basic principle, structure and circuit maintenance of the electronic multihead weigher

Author: Smartweigh– Multihead Weigher

1 The basic principle and structure of the multihead weigher The basic principle of the multihead weigher is that after the object is loaded into the scale, the weighing sensor converts the net weight signal into a proportional electronic signal output, and then the multihead weigher amplifies, filters, A/D converts, and digitally processes the digital signal output by the sensor and displays it on the display. The multihead weigher can be divided into four parts, as shown in Figure 1. The basic principle, structure and circuit maintenance analysis of weigher table: First, the weighing sensor part, whose main function is to convert the net weight signal added to the weighing platform into an electronic signal output of percentage; second, the digital display part, whose main function is to display the digital signal output by the sensor on the display after amplification, filtering, A/D conversion and digital processing; third, the scale body part, whose main function is to load, and the mechanical system can also be divided into the scale platform, offset limit switch, and gong bolt; the electrical equipment is equipped with terminals, communication cables, etc.; fourth, the peripheral part, which refers to the equipment connected to the signal output port of the digital display instrument and receiving the output signal of the instrument panel; common peripherals include printers, large-screen displays, and computer intelligent management systems; in addition, there are analog input and output, optical fiber output, intermediate relay output, etc. Electronic scale electronic multihead weigher table can be divided into two categories according to the type of signal, namely, analog multihead weigher table and digital multihead weigher table. Analog multihead weigher table The weighing scale receives digital signals, and the scale body uses analog sensors, which convert the weight added to the scale into a proportional electronic signal output through the deformation of the elastic body to cause the resistance of the resistor strain gauge; the digital multihead weighing scale is an instrument that combines modern electronic information technology, micro-processing technology, digital compensation technology and traditional strain gauge weighing sensors. It can calculate the weight through a computer and display, store, copy and transmit it by providing a communication interface and protocol that matches the digital sensor. 2 Maintenance methods of electronic multihead weighing scales and sensor circuits Electronic multihead weighing scales There are various fault conditions of weigher tables, and there are many factors that cause faults. And the same fault condition often has different reasons. Because of the need for fault detection, we must first try to find and determine the location of the fault. The fault search is mainly based on the fault condition summarized during the fault and the functions of the system components, electronic devices, connectors, and parts. Combined with the fault types summarized during the usual troubleshooting, all factors that cause the fault are checked and analyzed. Then, relying on the multimeter, video signal instrument panel, through various methods, check the abnormal position one by one, and finally determine the location of the fault. 2.1 Failures caused by environmental factors Changes in environmental factors can cause the weighing of electronic scales. The main factors include changes in the power supply. Vibration, wind speed, lightning strikes, etc., which cause the electronic scale to work unstably. Therefore, the electronic scale should be started as little as possible in windy and thunderstorm weather. At the same time, the lightning protection measures and protective grounding of the electronic scale should be done well. For vibration, shockproof measures such as buffer devices and protective trenches can be used to reduce its impact. The power supply of the electrical system cannot be used to independently wire the electronic scale or modify the parameter regulated power supply. 2.2 Equipment failure at the scale body level Equipment failure at the scale body level mainly includes deformation of the scale support, the scale body being pressed by dirt, limit switch equipment failure, and weighing sensor support nodding failure. Electronic scales often move materials in long-term use, and materials are constantly scattered. Mechanical parts are supported for a long time. Damage can easily cause damage to mechanical parts. Failures of mechanical parts of electronic scales can usually be observed directly with the eyes, or can be easily identified by whether the scale body shakes flexibly to eliminate the faults. 2.3 Sensor failures The weighing sensor is the core component of the electronic scale. It has the function of converting force into electronic signals. Failures in the weighing sensor can easily lead to large deviations in the weighing of the electronic scale. The scale cannot return to zero. The wheel weight deviation is large. The repeatability is poor, etc. 1) If there is a large deviation in the weighing of the electronic scale, first observe whether the code value is stable, whether there is friction at each position of the sensor, whether the adjustable regulated power supply is stable, and whether the op amp circuit is normal. , use standard weights to check whether the four legs of the scale weigh evenly. According to the instructions, further analyze the instrument panel or calibrate the net weight. 2) If the electronic scale cannot return to zero, first check whether the sensor output signal value is within the standard (A/D total variable code/application code range/bottom code range). If the signal value is not within the standard, adjust the sensor adjustable resistance to adjust the signal value to the standard. If it cannot be compensated, please check whether the sensor is defective. After ensuring that the sensor output is normal (the scale body is stable), lock the instrument panel constant. If there is a fault, it is usually caused by the amplifier circuit and the A/D conversion circuit. Then, according to the circuit principle, we should first check whether the power supply is normal, then connect the signal input to the video signal, adjust the input size of the video signal, and see whether the voltage after the increase is normal. Then use the digital oscillator to check whether the active crystal oscillator is oscillating, check whether the output of each point is normal, and finally check the optocoupler circuit and other output circuits to find the fault. 3) The electronic scale has a large wheel weight deviation or poor repeatability. This situation is similar to the situation of being unable to return to zero. Most of the time, it may be due to the change of the small signal input range. According to the method of being unable to return to zero, if no problem is found, first check the power supply. Whether the A/D circuit is normal, and then check the sensor output. In addition, the dynamic measurement method can be used to check the common fault of the sensor. The solution is to properly connect the sensor wiring to the motherboard, use the DCV gear of the digital meter (four and a half digits or more is best), and measure the S+ to Are the working voltages of ground and S- to ground the same (preferably 0 deviation)? If not, the sensor needs to be compensated. The method is that if the sensor output signal is too high, please add a variable resistor between the "E+S-" of the sensor to make the signal value within the normal range (the lower the resistance, the lower the sensor output signal). If the sensor output signal is too low or -ERR, please add a variable resistor between the "E+~S+" of the sensor to make the signal value within the normal range (the lower the resistance, the higher the sensor output signal). 2.4 Electronic scale multihead Other common faults and repairs of weigher meter 1) When the electronic scale cannot be turned on, first check the electronic scale's main power switch, power plug, voltage conversion switch and other supply and demand balance power supply parts. If there is no problem, then check whether the transformer has AC input and AC output. If the instrument panel has a battery, take out the battery and then start it with AC power to avoid faults caused by insufficient battery voltage. Finally, check whether the inverter circuit, voltage regulator circuit and display optocoupler circuit are abnormal. If these are normal, check whether the CPU and auxiliary circuits are burned out. 2) The electronic scale screen displays an error code. Remove the original display circuit and replace it with a normal display circuit to see if it is normal. If the display If the information is displayed normally, it means that there is a problem with the display circuit. If it is abnormal, check whether the optocoupler circuit has a fault, and finally check whether the CPU display output pin is in the valid output range. 3) The function key is not working properly or not working. First, check whether there is a leak at the function key position, resulting in a short circuit or short circuit; second, check whether the function key plug and the power socket are in good contact and whether there is any looseness; third, check whether the function key socket is well welded; fourth, check whether the electronic scale power socket and the CPU electrode connection line have a short circuit or short circuit. If the fault is still not found, the fifth is to accurately measure whether the diodes and resistors on the function keys and CPU circuits have short circuits or short circuits. In short, the cause of electronic multihead There are many common faults in weigher scales, and the fault conditions are also very complicated. Sometimes several faults occur at the same time. Electronic multihead weigher scales are the same as other electrical products. As long as you understand its structural principles and circuits, you can carry out maintenance. When solving the common faults of electronic multihead weigher scales, you should conduct in-depth analysis based on the actual common fault conditions, carefully check the stage that may cause the common fault, quickly and accurately identify the common fault location, and ensure that the electronic multihead weigher scale weighs accurately. Introduction: Compared with mechanical scales, electronic multihead weigher scales have many advantages such as fast weighing, intuitive display, and not easy to damage. Their application is becoming more and more extensive, and they have gradually replaced mechanical scales. In this paper, the structure and weighing principle of electronic multihead weigher scales are first discussed in connection with reality, and then the maintenance methods of electronic multihead weigher scales and sensor-attached circuits are discussed. 1 Principle and structure of electronic multihead weigher scales Electronic multihead weigher scales The basic principle of weigher is that after the object is loaded into the scale, the weighing sensor converts the net weight data signal into an electronic signal of percentage output, and then the multihead weigher table amplifies, filters, A/D converts, and digitally processes the digital signal output by the sensor and displays it on the display. The weigher table can be divided into four parts, as shown in Figure 1. The first is the weighing sensor part, whose main function is to convert the net weight signal added to the weighing platform into an electronic signal output of a percentage; the second is the digital display instrument part, whose main function is to amplify, filter, A/D convert, and display the digital signal output by the sensor on the display after digital processing; the third is the scale body part, whose main function is to load, and the mechanical system can also be divided into a weighing platform, a displacement limit switch, and a gong bolt; the electrical equipment is equipped with terminals, communication cables, etc.; the fourth is the peripheral part, which refers to the equipment connected to the signal output port of the digital display instrument and receiving the output signal of the instrument panel; common peripherals include printers, large-screen displays, and computer intelligent management systems; in addition, there are also analog input and output, optical fiber output, intermediate relay output, etc.

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