First, the general structure of electronic weighing instruments Electronic scales Electronic weighing instruments according to the type of signal source generally divided analog weighing instruments and digital weighing instruments. The following briefly introduces the structure of the two instruments.
Analog weighing instrument. The analog weighing instrument receives the analog signal and the scale body uses an analog sensor. Analog weighing instruments typically include small-signal amplification circuits, A/D conversion sections, microcontrollers or processors, display circuits, keyboards, data output sections (including parallel output or RS232 serial output or RS485 output), and other peripherals (such as Current loop output, analog output, dry contact output, etc.). The signal output by the sensor or signal source is relatively small, generally between 0 and 2mV. A/D conversion cannot handle such a small signal, so it is to be amplified by a small-signal amplifying circuit, and some A/D conversion chips are built-in. Amplifier circuit, so you can save the small signal amplification. After amplification, the small signal is converted into a digital signal by an A/D conversion circuit and then output to the processor. The processor digitally filters the data and processes it to output the data to the display circuit and other output peripherals. Digital weighing instrument. Digital weighing instruments receive digital signals, so they can only be connected to digital sensors. There are many types of digital sensors and there are various protocols, but they all communicate via RS422 or RS485. The famous German HBM, Japan's Kubota sensor, domestic DMP, Admiralty scale's Admiralty SP type sensor. Digital weighing instruments do not need small-signal amplifying circuits and A/D conversion parts. These functions are performed in digital sensors. The function of digital weighing instruments is to provide communication interfaces and protocols corresponding to digital sensors, and includes display circuits and keyboards. , Data output part (including parallel output or RS232 serial output or RS485 output), other peripherals (such as current loop output, analog output, dry contact output, etc.).
Second, the electronic scale electronic weighing instrument general failure and maintenance methods understand the basic structure of the electronic weighing instrument principle, if there is some basic knowledge of electronic circuits (will look at the circuit diagram), we can carry out the maintenance of electronic weighing instrument . Whether it is maintenance of instruments or other electronic products generally have two ideas, one is to identify the fault circuit to the problem, this is a common method, and often effective. If it is a more complex circuit, this method will often lead to misunderstandings, and the result will be less effective. At this time, we need to calm down and use the second method—the investigation method. The investigation method is based on normal inspection methods, one by one, and finally finds the problem. The troubleshooting steps are as follows.
(1) First check the power supply. The power supply is the main incentive for the entire circuit work. Before checking the circuit, we must first check whether the power supply is normal.
(2) Next check the input section, which is the small signal amplification section. Connect the signal input to the signal source, adjust the input size of the signal source, and see if the voltage after amplification is in accordance with the law.
(3) Check if the processor is working. Use an oscilloscope to test whether the crystal oscillator has started and test whether the output of each point is normal.
(4) Check the drive circuit and other output circuits.
In the maintenance process, we must use the combination of visual inspection, component removal, and confirm maintenance to complete our maintenance work. As long as it is confirmed which part of the circuit is faulty or damaged, we can proceed with the next step to solve the problem. After these steps can basically find the problem. The following describes the common faults and solutions of electronic weighing instruments.
(1) Failure analysis after the weight has been removed and cannot be returned to zero Check that the sensor output signal value is within the standard (A/D total amplifying code/use inner code range/base code range) if the signal value is not in the standard Inside, adjust the adjustable resistance of the sensor and adjust the signal value to the standard. If it can not be compensated, check if the sensor has any problem. If the sensor output is normal (the scale body is stable), then the instrument fault is locked. Generally, the amplifier circuit and A/ The D conversion circuit has a problem, and then judges the test analysis one by one according to the circuit principle, so as to finally solve the problem.
(2) Weigh inaccurate fault analysis Observe whether the internal code value is stable, whether there is friction in each part of the sensor, whether the regulated power supply is stable, and whether the op amp circuit is normal. Use weights to test whether the four-foot weighing scale of the weighing pan is average. According to the instruction manual, further instrument local analysis or weight correction.
(3) Faults that cannot be turned on First determine the problems caused by non-fuse, power switch, power line, and voltage switch. Check whether the transformer has AC voltage input and AC output. If the meter has a battery, remove the battery and turn it on with AC power to see if it is caused by a low battery voltage. Secondly, check whether the rectifier circuit, voltage regulator circuit, and display driver circuit are abnormal. If there is no problem, check whether the processor and auxiliary circuit are burned out.
(4) Display garbled The original display circuit is removed and replaced with a normal display circuit to see if it is normal. If the normal display shows a problem with the display circuit, if it is abnormal, check whether the driver circuit is faulty. Finally, check whether the output pin of the processor is within a reasonable output range.
(5) The button is not good to use the new button to test first, if the new button function is normal, it can be judged as bad button contact, measure whether the line between the button and the CPU is broken, false welding. Check the key support for poor contact. Measure whether there is a short circuit or open circuit between the button and the diodes and resistors on the CPU circuit.
(6) It cannot be said that full load and zero return are almost the same, most of which may have changed due to the small signal input range. According to the method that cannot be returned to zero, if no problem can be found, first detect whether the power supply, A/D circuit is normal, and then detect the sensor output.
(7) Sensor failure identification method 1 Static measurement method: Use the multimeter's ohm range to measure whether the sensor's E+ to S+, S- (or E-to-S+, S- may) resistances are the same, In general, the error needs to be compensated if it is more than 0.5Ω. If the error is too large (more than 2Ω), it is recommended to replace the sensor.
2 Dynamic measurement method: Connect the sensor wiring back to the motherboard correctly and use a digital meter (more than four and a half or better) on the DCV. Measure whether the S+ voltage is equal to the S-to-ground voltage (preferably 0). Errors) Sensor compensation if not equal.
(8) Sensor compensation sensor output signal is too high, please add a resistor to the sensor's "E+S-" between the signal value to the normal range (lower resistance value, the sensor output signal is lower).
Sensor output signal is too low or -ERR Please add a resistor to the sensor's "E+~S+" to bring the signal value to the normal range (the lower the resistance, the higher the output signal of the sensor).
The method of detecting the A/D circuit's amplifying code adjusts the electronic scale to the internal setting state (makes it display the current internal code state) and applies the full weighing weight to record the amplifying code value. Their relationship: the bottom code value + full Weighing code + security area code.
(9) Failure analysis of digital instruments Maintenance of digital instruments is relatively simple. It only needs to detect the power supply circuit, communication circuit, CPU micro-processing circuit, storage circuit and display circuit. According to the instructions in the instruction manual, different error phenomena and actual The measurement result is judged by solving the problem. The premise is to ensure the normal performance of digital sensors.
Third, summarize electronic weighing instruments and other household appliances, as long as they are familiar with its structural principles and circuits can be maintained, the general electronic weighing instruments are equipped with a microcontroller or processor, which shows that electronic weighing instruments are If there is a program, if the microcontroller or processor is broken, only the manufacturer will find the chip that will write the program. Because the circuit of the meter is various, each circuit has its own dedicated application, as long as the microprocessor The problem of the device (mainly software) is solved, and other problems are easily solved. Http://
Analog weighing instrument. The analog weighing instrument receives the analog signal and the scale body uses an analog sensor. Analog weighing instruments typically include small-signal amplification circuits, A/D conversion sections, microcontrollers or processors, display circuits, keyboards, data output sections (including parallel output or RS232 serial output or RS485 output), and other peripherals (such as Current loop output, analog output, dry contact output, etc.). The signal output by the sensor or signal source is relatively small, generally between 0 and 2mV. A/D conversion cannot handle such a small signal, so it is to be amplified by a small-signal amplifying circuit, and some A/D conversion chips are built-in. Amplifier circuit, so you can save the small signal amplification. After amplification, the small signal is converted into a digital signal by an A/D conversion circuit and then output to the processor. The processor digitally filters the data and processes it to output the data to the display circuit and other output peripherals. Digital weighing instrument. Digital weighing instruments receive digital signals, so they can only be connected to digital sensors. There are many types of digital sensors and there are various protocols, but they all communicate via RS422 or RS485. The famous German HBM, Japan's Kubota sensor, domestic DMP, Admiralty scale's Admiralty SP type sensor. Digital weighing instruments do not need small-signal amplifying circuits and A/D conversion parts. These functions are performed in digital sensors. The function of digital weighing instruments is to provide communication interfaces and protocols corresponding to digital sensors, and includes display circuits and keyboards. , Data output part (including parallel output or RS232 serial output or RS485 output), other peripherals (such as current loop output, analog output, dry contact output, etc.).
Second, the electronic scale electronic weighing instrument general failure and maintenance methods understand the basic structure of the electronic weighing instrument principle, if there is some basic knowledge of electronic circuits (will look at the circuit diagram), we can carry out the maintenance of electronic weighing instrument . Whether it is maintenance of instruments or other electronic products generally have two ideas, one is to identify the fault circuit to the problem, this is a common method, and often effective. If it is a more complex circuit, this method will often lead to misunderstandings, and the result will be less effective. At this time, we need to calm down and use the second method—the investigation method. The investigation method is based on normal inspection methods, one by one, and finally finds the problem. The troubleshooting steps are as follows.
(1) First check the power supply. The power supply is the main incentive for the entire circuit work. Before checking the circuit, we must first check whether the power supply is normal.
(2) Next check the input section, which is the small signal amplification section. Connect the signal input to the signal source, adjust the input size of the signal source, and see if the voltage after amplification is in accordance with the law.
(3) Check if the processor is working. Use an oscilloscope to test whether the crystal oscillator has started and test whether the output of each point is normal.
(4) Check the drive circuit and other output circuits.
In the maintenance process, we must use the combination of visual inspection, component removal, and confirm maintenance to complete our maintenance work. As long as it is confirmed which part of the circuit is faulty or damaged, we can proceed with the next step to solve the problem. After these steps can basically find the problem. The following describes the common faults and solutions of electronic weighing instruments.
(1) Failure analysis after the weight has been removed and cannot be returned to zero Check that the sensor output signal value is within the standard (A/D total amplifying code/use inner code range/base code range) if the signal value is not in the standard Inside, adjust the adjustable resistance of the sensor and adjust the signal value to the standard. If it can not be compensated, check if the sensor has any problem. If the sensor output is normal (the scale body is stable), then the instrument fault is locked. Generally, the amplifier circuit and A/ The D conversion circuit has a problem, and then judges the test analysis one by one according to the circuit principle, so as to finally solve the problem.
(2) Weigh inaccurate fault analysis Observe whether the internal code value is stable, whether there is friction in each part of the sensor, whether the regulated power supply is stable, and whether the op amp circuit is normal. Use weights to test whether the four-foot weighing scale of the weighing pan is average. According to the instruction manual, further instrument local analysis or weight correction.
(3) Faults that cannot be turned on First determine the problems caused by non-fuse, power switch, power line, and voltage switch. Check whether the transformer has AC voltage input and AC output. If the meter has a battery, remove the battery and turn it on with AC power to see if it is caused by a low battery voltage. Secondly, check whether the rectifier circuit, voltage regulator circuit, and display driver circuit are abnormal. If there is no problem, check whether the processor and auxiliary circuit are burned out.
(4) Display garbled The original display circuit is removed and replaced with a normal display circuit to see if it is normal. If the normal display shows a problem with the display circuit, if it is abnormal, check whether the driver circuit is faulty. Finally, check whether the output pin of the processor is within a reasonable output range.
(5) The button is not good to use the new button to test first, if the new button function is normal, it can be judged as bad button contact, measure whether the line between the button and the CPU is broken, false welding. Check the key support for poor contact. Measure whether there is a short circuit or open circuit between the button and the diodes and resistors on the CPU circuit.
(6) It cannot be said that full load and zero return are almost the same, most of which may have changed due to the small signal input range. According to the method that cannot be returned to zero, if no problem can be found, first detect whether the power supply, A/D circuit is normal, and then detect the sensor output.
(7) Sensor failure identification method 1 Static measurement method: Use the multimeter's ohm range to measure whether the sensor's E+ to S+, S- (or E-to-S+, S- may) resistances are the same, In general, the error needs to be compensated if it is more than 0.5Ω. If the error is too large (more than 2Ω), it is recommended to replace the sensor.
2 Dynamic measurement method: Connect the sensor wiring back to the motherboard correctly and use a digital meter (more than four and a half or better) on the DCV. Measure whether the S+ voltage is equal to the S-to-ground voltage (preferably 0). Errors) Sensor compensation if not equal.
(8) Sensor compensation sensor output signal is too high, please add a resistor to the sensor's "E+S-" between the signal value to the normal range (lower resistance value, the sensor output signal is lower).
Sensor output signal is too low or -ERR Please add a resistor to the sensor's "E+~S+" to bring the signal value to the normal range (the lower the resistance, the higher the output signal of the sensor).
The method of detecting the A/D circuit's amplifying code adjusts the electronic scale to the internal setting state (makes it display the current internal code state) and applies the full weighing weight to record the amplifying code value. Their relationship: the bottom code value + full Weighing code + security area code.
(9) Failure analysis of digital instruments Maintenance of digital instruments is relatively simple. It only needs to detect the power supply circuit, communication circuit, CPU micro-processing circuit, storage circuit and display circuit. According to the instructions in the instruction manual, different error phenomena and actual The measurement result is judged by solving the problem. The premise is to ensure the normal performance of digital sensors.
Third, summarize electronic weighing instruments and other household appliances, as long as they are familiar with its structural principles and circuits can be maintained, the general electronic weighing instruments are equipped with a microcontroller or processor, which shows that electronic weighing instruments are If there is a program, if the microcontroller or processor is broken, only the manufacturer will find the chip that will write the program. Because the circuit of the meter is various, each circuit has its own dedicated application, as long as the microprocessor The problem of the device (mainly software) is solved, and other problems are easily solved. Http://
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