Repair technology for the scraper level sensor of pavers

During the construction process of a VoGELE-S1800 paver, the right scraper feeder suddenly failed to work properly. This machine adopts a proportional material conveying automatic control system, which is composed of a material level sensor and a proportional solenoid valve. The function of the material level sensor is to adjust the feeding speed proportionally according to the change in the height of the material pile.

The material level sensor is a contact-type magnetoresistive angular displacement sensor. It consists of two parts: the sensor and the controller, which are made as one. The main components of the sensor are magnetoresistive and permanent magnet. Magnetoresistors are made of semiconductor materials. The characteristic of this material is that its resistance can vary with the strength of the applied magnetic field (magnetoresistance effect). The permanent magnet is fixed on the rotating shaft connected to the sensor's rotating arm. When the height of the asphalt concrete pile changes and causes the sensor's rotating arm to rotate, it alters the distance between the magnet and the magnetoresistor, thereby changing the magnetic flux passing through the magnetoresistor. As a result, the output value of the magnetoresistor changes accordingly. This resistance value is input into the controller Through its electronic circuit, the voltage of the coil of the feeding variable pump proportional solenoid valve is adjusted at terminal 58R, thereby making the feeding speed change proportionally with the height of the material pile to maintain the basic constant height of the material pile.

Open the sensor side cover and rotate the arm to cause angular displacement between the permanent magnet and the magnetoresistor. However, the reading of the ammeter does not change. This phenomenon indicates that the controller can no longer adjust the voltage of the proportional solenoid valve coil, resulting in the feeder being unable to automatically control the height of the material push. The possible cause of this problem could be: malfunction of the controller's electronic circuit board; The magnetoresistor is damaged.

Unplug the four wires of the relevant sockets on the controller, measure the resistance values between each terminal with the resistance range, and compare the measured values with those obtained during normal operation. If the results match, it indicates that there is no abnormality with the controller's electronic circuit board, and the problem should lie with the magnetoresistor.

The resistance value of the magnetoresistor was measured, and the result showed that both the forward and reverse phases were only a few ohms. This situation indicates that the semiconductor material of the magnetoresistor has been broken down, causing its resistance value to not change with the rotation of the rotating arm, thus preventing the sensor from working properly.

Replace the magnetoresistor and plug in all the wires (connect the power supply and manually rotate the arm to achieve stepless speed regulation). At this time, the voltage value between 54 and 58R of the controller is the voltage value acting on the coil of this proportional solenoid valve. When the voltage reaches 21.8V, the scraper conveyor reaches its maximum rotational speed (the rotating arm rotates to the lower limit position of the baffle). When the voltage drops below 15.8V, the scraper conveyor stops rotating (the rotating arm turns to the upper limit baffle position). This repair work took less than 2 hours, ensuring the quality of the road surface paving and the progress of the project.