15 fault repairs of electronic platform scales
The electronic platform scale is visually inspected to check whether the instrument casing, switch and keyboard are normal, whether the display and the scale body are disconnected, and the sensor simulator can be used instead of the sensor to determine whether the instrument is faulty, or the electronic scale scale body is faulty, so that you can quickly Find the fault location accurately.
1. No display after booting, no self-test. First check whether the power supply fuse is blown, whether the 5V, 15V three-terminal integrated voltage regulator block has a normal output, whether the clock pulse has a normal output, and whether the single-chip channel is damaged. Then check whether the digital tube pin is unsoldered from the circuit board, and whether there is a disconnection between the latch and the driver. Show whether the driver HA16617 integrated block is working properly. When it is working normally, touch the surface with your hand, there should be a slight heat feeling. Whether the display is burnt out and air leaks (after the fluorescent tube leaks, the black spots on both ends turn white).
2. There is a self-test after booting, but the display is not bright after the self-test. The keyboard is not reset, or the keyboard is damaged.
3. The flashing keeps turning on. Whether the electronic scale is affected by wind and vibration, whether there is an object in contact with the scale, whether the sensor plug is in good contact, and whether the sensor wire is disconnected or virtual connected.
4. Howling at startup. CPU computer is not working properly, check whether the DC power supply voltage is normal, try to replace a good CPU, if there is an external program, you should also check the program, and check the CPU and EPROM interface circuit.
5. After flashing at startup, zero is not displayed. There is no load on the scale, whether the sensor plug is in good contact, and whether the sensor is disconnected. After some sensors are used for a period of time, the resistance of the resistance strain gauge changes and the initial value changes. Adjust the initial value.
6. The function key fails. First check whether there is dust and moisture in the contact area between the circuit board and the button. If there is, clean and dry it with alcohol. Check if the connection between the keyboard and the circuit board is broken. Whether the diode is damaged when connected, and whether the contact of the 4049 pin of the six inverter is firm. Check whether the keyboard and the instrument shell are installed correctly, that is, whether there is a card or squeeze, which affects the keyboard's working phenomenon.
7. When weighing and loading, there is no weight display on the weighing display. No bridge voltage is applied to the input end of the load cell bridge, or the sensor cable socket is not in good contact, and the sensor signal cable has an aging and breakage phenomenon, which causes the amplifier to have no input signal. Or there is a foreign object between the sensor and the scale body, which hinders the deformation of the elastomer.
8. Adjustment of indication error. The load-bearing system of the scale body is damaged due to external forces, which deforms and breaks the mechanical structure, and generates an angle with the axis of the load-bearing force of the sensor, resulting in unrealistic forces, which should be repaired or replaced if there are weighing errors. Due to the long-term use of electronic scales, the elastic modulus and temperature coefficient of its sensor elastomer will change, or errors will occur due to the different acceleration of gravity in different regions. The elimination method is that some electronic scales are adjusted by pulling the two sets of binary switches inside the instrument, some are calibrated by adjusting the adjustable resistance, and other electronic scales are adjusted by the keyboard function keys.
9. The display shows that the data fluctuates too much. That is, when the same weighing load is added to the electronic scale, the displayed value of weighing several times is different. The cause is generally the virtual connection of the cable between the weighing instrument and the sensor, the insulation layer is aging, the shield is damaged, and the insulation resistance between the core wires decreases, which makes the transmission signal fluctuate too much. Or it may be caused by the welding and virtual welding of the filter capacitor and the circuit board. Find the breakpoint and re-weld. Or because the humidity of the environment is too high, the weighing instrument is damp, and it is dried with an electric hair dryer, and the fault can be eliminated. The characteristic of the sensor resistance strain gauge is not good, the adhesive is deteriorated, the strain gauge and the elastomer are not well pasted, the sensor is aging, and the sensor is generally replaced.
10. Non-linear error. Generally, the installation of the sensor is not good, the distance between the limit screws is too small, or there is a foreign object between the load-bearing plate and the scale body.By adjusting the limit spiral, the foreign body is removed, and the contact between the load-bearing plate and the scale body is checked to see if it is reasonable solve. There is a problem with the first-order low-pass filtering of the amplifier. The R and C values ​​of the amplifier are changed, which causes the interference frequency to be amplified. After entering the integrator, the integrated waveform is unstable, and the linear compensation resistance is adjusted.
11. The output is unstable, skip words. The power supply is unstable, and the AC ripple of the power supply for the integrator and zero detector is too large. The double integral is unstable, the integral capacitor loss increases and the electric leakage. The phenomenon caused by the sensor is that the measurement results are inconsistent for many times, and the zero drift and creep are measured with a multimeter. It has been damaged and should be replaced in time.
12. The four corners of the load-bearing table are inconsistent (four corner errors). First check whether the sensor screw is tight and whether the gap between the limit screw and the scale body is reasonable. If the above problems are still inconsistent, you can use a small file to gently file the inner hole of the sensor.The principle is: the corresponding value with the smaller display value The side hole file is thin, increasing the amount of change in the elastomer. Be careful not to file too much at one time during maintenance. It should be adjusted gradually in several times to prevent damage to the sensor.
13. Display the missing segment. The display is not in good contact with the circuit board. The virtual soldering is broken, the PCU segment selection signal transistor and the latch are damaged, the display is shorted internally, and the display is replaced.
14. Zero drift. It is not good to return to zero after each use of electronic platform scales, causing drift. Whether it is affected by external influences such as vibration, wind and power interference. The insulation resistance of the circuit board drops, there is dirt, clean with alcohol. The anti-interference ability of the amplifier is reduced and self-excited. If the zero detector fails, the insulation resistance of the integral capacitor decreases and aging causes an increase in loss. Replacement experiments can be used to eliminate the fault during maintenance.
15. Elimination of clever interference. In the industrial production process, due to the large number of electrical equipment, sometimes there are a lot of electricity, magnetism, interference and electrostatic interference in the environment of the electronic scale, which makes the display value of the electronic scale in an unstable state, affecting the weighing speed and making the work efficiency Reduce, for this we check the filter and found that the filter is damaged. After the replacement, a special stabilized power supply for weighing instruments is added in the use place with large interference environment, and the power cord is shielded and effectively grounded, and the effect is good after the treatment.
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