Maintenance of 12 major faults of electronic scale
HENGQUASI:2023-02-21 14:42:24

1. No display and self-inspection at startup:
First, check whether the fuse of the power supply is burnt out, whether the 5V and 15V three-terminal integrated voltage stabilizer block has normal output, whether the clock pulse has normal output, and whether the channel of the single-chip microcomputer is damaged. Then check whether the digital tube pin is desoldered from the circuit board and whether there is an open circuit with the latch and driver. Display whether the driver integrated block works normally. When it works normally, touch its surface with your hand, and there should be a slight heat feeling. Check whether the display is burnt out or leaked (after the fluorescent tube leaks, the black spots on both ends turn white).
2. Zero drift:
The electronic platform scale does not return to zero after each use, resulting in drift. Whether it is affected by vibration, wind blowing, power interference and other external factors. If the insulation resistance of the circuit board drops and there is dirt, clean it with alcohol. The immunity of amplifier is reduced and self-excited. The zero detector is faulty, and the insulation resistance of the integral capacitor decreases and ages, resulting in increased loss. During maintenance, replace the test to eliminate the fault.
3. Removal of smart interference:
In the process of industrial production, due to the large number of electrical equipment, sometimes there are a lot of electrical, magnetic, interference and electrostatic interference in the environment where the electronic platform scale is located, which makes the displayed value of the electronic platform scale in an unstable state, affects the weighing speed, and reduces the working efficiency. Therefore, we check the filter and find that the filter is damaged. After replacement, the special stabilized power supply for weighing instrument shall be added at the place where the interference environment is large, and the power line shall be shielded and effectively grounded, with good effect after treatment.
4. The buzzer will keep on ringing:
If the CPU computer is not working properly, check whether the DC power supply voltage is normal. Replace a good CPU and try it. If there is an external program chip, check the program chip and check the CPU and EPROM interface circuit.
5. After the power on flashes, zero is not displayed:
Check whether there is load on the scale, whether the sensor plug contacts well, and whether the sensor is disconnected. After some sensors have been used for a period of time, the resistance value of the resistance strain gauge changes, resulting in the change of the initial value. Adjust the initial value.
6. Function key failure:
First, check whether there is dust and moisture at the contact part between the circuit board and the key. If any, clean and dry it with alcohol. Check whether the connection between the keyboard and the circuit board is broken. Check whether the diode is damaged during connection and whether the pin contact of the six inverters 4049 is firm. Check whether the keyboard and the instrument shell are installed correctly, that is, whether there are jamming, squeezing and other phenomena that affect the keyboard operation.
7. When weighing and loading, there is no weight display on the weighing display screen:
No bridge supply 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 is aging and broken, resulting in no input signal of the amplifier. Or there is foreign matter between the sensor and the scale body, which hinders the deformation of the elastomer.
8. Adjustment of indication error:
The weight bearing system of the scale body is damaged due to external force, resulting in deformation and fracture of the mechanical structure, and the angle between the mechanical structure and the force axis of the sensor, which causes the force to be unreal, and thus the weighing error should be repaired or replaced. Due to the long-term use of the electronic scale, the elastic modulus and temperature coefficient of its sensor elastomer will change, or the error will occur due to the different gravity acceleration in different regions. The elimination method is that some electronic scales are adjusted by pulling two sets of binary switches inside the instrument, some are calibrated by adjusting the adjustable resistance, and others are adjusted by keyboard function keys.
9. The display data fluctuates too much:
That is, when the same heavy load is added to the electronic scale, the displayed values of several weighing times are different. The cause is generally the virtual connection of the cable between the weighing instrument and the sensor, the aging of the insulation layer, the damage of the shield, and the reduction of the insulation resistance between the core wires, resulting in excessive fluctuations in the transmission signal. Or it is caused by the disconnection or faulty soldering between the filter capacitor and the circuit board. Find the breakpoint and re-weld it. Or due to excessive humidity in the use environment, the weighing instrument is damp and dried with a hair dryer. The fault can be eliminated. The resistance strain gauge of the sensor has poor characteristics, the adhesive deteriorates, the strain gauge and elastomer are not well bonded, and the sensor is aged. Generally, replace the sensor.
10. Nonlinear error:
Generally, the sensor is not installed properly, the spacing between the limit screws is too small, or there is a foreign matter between the bearing plate and the scale body. The problem can be solved by adjusting the limit screw, removing the foreign matter, and checking whether the contact between the bearing plate and the scale body is reasonable. There is a problem with the first order low-pass filter of the amplifier. The R and C values of the amplifier are changed, which causes the interference frequency to be amplified, and then the integrator is inserted to make the integral waveform unstable, and the linear compensation resistance is adjusted.
11. Output is unstable, word skipping:
The power supply is unstable, and the AC ripple of power supply for integrator and zero detector is too large. The double integral is unstable, the integral capacitance loss increases and leakage occurs. The fault caused by the sensor is that the measurement results are inconsistent for many times, and the zero drift and creep. Use a multimeter to measure the input and output impedance of the sensor, the m number of the empty scale, and whether the insulation resistance is normal. If the indicated values are out of tolerance, it means that the sensor is damaged and should be replaced in time.
12. Inconsistent weighing at four corners of the bearing table (four corner error):
First of all, check whether the sensor screws are tight, and whether the clearance between the limit screw and the scale body is reasonable. If the above problems are still not consistent, you can file the inner hole of the sensor gently with a small group file. The principle is: file the side hole corresponding to the smaller displayed value to increase the change of the elastomer. Pay attention not to file too much at one time during maintenance, and gradually adjust it several times to prevent damage to the sensor.