Troubleshooting of Inaccurate Measurement in Batching And Weighing System of Mixing Plant

Each electronic scale of the batching and weighing system of the mixing plant is composed of batching bin (scale body), weighing sensor, junction box, control instrument and connecting line. Common faults such as instability, drift and linear out of tolerance of the preparation scale in use affect the normal operation of the mixing plant.
The line fault shows that the indicated value of the controller overflows and displays error information. The signal is suddenly interrupted or jumps randomly during weighing. The reasons are as follows.
First, there is a problem with the quality of the sensor itself. It shows that the input and output resistance of the sensor changes. Under normal conditions, the input resistance of the sensor is 400 Ω± 10 Ω and the output resistance is 350 Ω± 3 Ω. The main fault of the sensor is that the solder joint of the wiring terminal or outgoing line falls off; Sensor zero temperature compensation or sensitivity temperature compensation resistance faulty welding or desoldering; The sensor is not well sealed and the internal chip is damp.
Second, the connecting line between the sensor and the control instrument is open. This external fault is mainly caused by improper installation and use. If the multimeter is used to check the input and output resistance of the sensor, the resistance value is normal. The cause of the fault is: the connecting line is broken, resulting in open circuit; The connector of the connecting wire is loose or not soldered.
When I went to a mixing plant for on-site service a few days ago, I found that the indicated value of the aggregate scale controller jumped randomly, resulting in failure to calibrate. After many inspections by the on-site commissioning personnel, it was suspected that there was a problem with the sensor. After the author arrived at the scene, the input and output resistance and voltage of T4 sensors were measured respectively, which were normal, so it was judged that the sensors were intact; After replacing the control instrument, the fault phenomenon has not been eliminated, and it is preliminarily judged that the connecting line is faulty. After inspection, it was found that the excitation power line output from the control instrument to the sensor was loose at the wiring plug, resulting in unstable power supply to the sensor.
Abnormal zero point of electronic scale is also a common fault. One of the reasons is that the sensor is not temperature compensated, and the zero point and sensitivity of the sensor change with the change of the ambient temperature of the powder, resulting in the failure of the zero point of the electronic scale. According to the international standard, there is a temperature compensation process in the sensor production process, which should be compensated by simulating the change of the ambient temperature of the sensor through the high and low temperature box. However, many domestic sensor manufacturers do not have high and low temperature boxes at all, Unable to compensate the temperature of the sensor; The second reason is that the sensor is seriously overloaded, resulting in plastic deformation of the elastomer and damage to the sensor.
Recently, the author found at the site of a mixing plant that the zero point of an orthopedic scale became larger soon after installation, and it was impossible to accurately measure t and judge the cause of the fault on site. The author carefully observed four S-shaped 2T sensors and found that one of the iron chains connected with the scale body had obvious impact marks, so it was judged that the sensor had been overloaded. The zero output of four sensors is measured respectively, and the zero output of the sensor is another 4 times. Replace the overload damaged sensor and eliminate the fault.
The fault of control instrument can be judged by substitution method. After preliminarily judging that there is no problem with the sensor and connecting line and suspecting that the control instrument has a fault, a good instrument can be used to replace it and observe whether the fault phenomenon disappears. After replacing a new control instrument, the relevant parameters must also be set and calibrated.
The author handled a control instrument fault not long ago. When a company installed and commissioned a medium-sized mixing plant for customers, it was found that the water scale and admixture scale could not be calibrated normally. The fault shows that the indication value of the water scale controller is stable and the loading response is very slow; The value indicated by the admixture scale controller is stable, but there is no reaction under loading.
After preliminary inspection that the sensor and connecting circuit are free of fault, it is determined that the problem is likely to be caused by the control instrument. The control instrument is integrated, and the sensors of all sub scales share a power supply. Since there are no other control instruments to replace on site, the fault location cannot be determined accurately. The two sub scales have problems at the same time. The author suspects that the power supply is not stable enough. The portable regulated power supply is used to supply power to the sensor, and the sensor output signal is transmitted to the control instrument, and the fault phenomenon disappears.

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