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

Each electronic scale of batching and weighing system in mixing station is composed of batching bin (scale body), weighing sensor, junction box, control instrument and connecting line. The common faults such as instability, drift and linear out of tolerance of batching scale in use affect the normal work of mixing station.

The line fault shows that the value indicated by the controller overflows, the error message is displayed, and the signal suddenly interrupts or jumps when weighing. There are two reasons.

One is the quality of the sensor itself. 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 the outgoing line falls off; Sensor zero temperature compensation or sensitivity temperature compensation resistance false 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 circuit. This kind of external fault is mainly caused by improper installation and use. If the input and output resistance of the sensor is checked with a multimeter, the resistance value is normal. The cause of the fault is: the connecting wire is broken, causing the open circuit; The joint of connecting line is loose or not soldered with tin.

Recently, the author went to a mixing station for on-site service and found that the value of the aggregate scale controller jumped disorderly, resulting in the failure of calibration. After on-site debugging, the sensor was suspected to have a problem. The input and output resistance and voltage of T4 sensors were measured after the author arrived at the site, which were normal, so as to judge whether the sensors were in good condition; When the control instrument was replaced, the fault was still not eliminated, and it was preliminarily determined that the connection line was faulty. After the inspection, it was found that the excitation power line output from the control instrument to the sensor was loose at the wiring plug, which led to the instability of the sensor power supply.

The zero point abnormality of electronic scale is also a common fault. One of the reasons is that the sensor does not make temperature compensation. The zero point and sensitivity of the sensor change with the ambient temperature of the powder, which leads to the zero point failure of the electronic scale. According to the international standard, there is a temperature compensation process in the production process of the sensor, which should be compensated by using the high and low temperature box to simulate the ambient temperature change of the sensor. However, many domestic sensor manufacturers do not have high and low temperature boxes at all, The sensor cannot be compensated for temperature; The second reason is that the sensor is seriously overloaded, resulting in plastic deformation of elastomer and sensor damage.

Recently, the author found in a mixing station that the zero point of an orthopedic scale became larger soon after it was installed, and it was unable to accurately measure t and determine the cause of the failure. The author carefully observed four S-shaped 2T sensors and found that one of them had obvious impact marks on the iron chain connected with the scale body, so it was determined that the sensor was overloaded. The zero point output of four sensors is measured respectively, and the zero point output of the sensor is four times of that of the other sensors. Replace the overload damaged sensor and remove 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 the connecting line and suspecting that the control instrument is faulty, a good instrument can be used to replace it and observe whether the fault phenomenon disappears. After replacing the new control instrument, the relevant parameters must be set and calibrated.

The author has dealt with a control instrument fault not long ago. When a company installed and debugged a medium-sized mixing plant for customers, it was found that the water scale and additive scale could not be calibrated normally. The fault shows that the value indicated by the water balance controller is stable and the loading response is very slow; The indication value of additive scale controller is stable, but there is no reaction during loading.

After the initial check of the sensor and the connecting line, it is determined that the problem is likely to be in the control instrument. The control instrument is integrated, and all the sensors of the sub scale share one power supply. Because there is no other control instrument to replace on site, the fault location cannot be determined accurately. And two sub scale problems at the same time, I suspect that the power supply is not stable. The sensor is powered by the voltage stabilized power supply, and the output signal of the sensor is transmitted to the control instrument, and the fault phenomenon disappears.

In addition, the junction box water, moisture, niuhua or electrical resistance may lead to the breakdown.

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