Displacement sensor interference faults and solutions

Displacement sensor interference faults and solutions The hydraulic pressure control system (referred to as hydraulic AGC system) of the 2500mm four-high reversing mill was reconstructed. The control system was designed, commissioned, and put into use by the National Key Laboratory of Northeastern University. After the transformation, the hydraulic AGC system will further increase the same-plate and differential-to-plane differences of the steel plate, and better realize the improvement of the physical quality of the steel plate.

Hydraulic AGC System This system consists of a two-level computer control system. One of them is the HAGC (HYDRALIC AUTOMATIONALGAUGECONTROL) basic automation system for rolling mills; the second is the HAGC process control system for rolling mills. The process computer of the mill AGC process control system adopts one COMPAQ server system from the United States and a mirror disk array of 3*40GB. The process computer is connected to the basic automation PLC through industrial Ethernet, and two terminals are connected at the same time. They are installed on the rolling mill and the process machine respectively. One for each room for process monitoring and control.

The main functions of basic automation in the rolling zone are AGC and controlled rolling; Siemens S7-400/FM458 PLC and PROFIBUS-DP remote I/O ET200 system are used. The top hat sensor and hydraulic cylinder displacement sensor used in this system are magnetostrictive digital absolute displacement sensors of MTS Systems Corporat, which have high precision (resolution of 2μm), high temperature resistance, high degree of protection, non-contact, no wear and tear. Calibration, SSI interface output characteristics. The top hat sensor is used to measure the displacement of the press screw, one each on the operating side (OS) and on the drive side (DS). The sensor is installed on the top of the press screw, and the screw center hole can directly measure the static and dynamic displacement of the screw, which is non-contact measurement.

Two MTS displacement sensors are installed in each hydraulic cylinder and installed in an external diagonal position to not only measure the displacement of the hydraulic cylinder but also measure the yaw of the hydraulic cylinder. This external installation method is convenient for inspection, maintenance and replacement. The German HYDAC hydraulic pressure sensor used in this system has the characteristics of high precision and stable output. The hydraulic cylinder displacement sensor is used as the position feedback of the hydraulic pressure-reducing system. If the position feedback is inaccurate, it will directly affect the pendulum roller gap in the steel rolling process, which will cause the roller gap anomaly to directly affect the production of the medium plate mill.

Problems and exclusion methods Roll gap display is not allowed On March 25, 2003, the Japanese plant pulled out the hydraulic cylinder on the operating side to change the spherical pad. On the afternoon of March 26, the operator of the rolling mill reported that the gap between the roller gap was inaccurate and there was a phenomenon that the roller gap ran. PLC online monitoring and analysis, we found that the operating side of the hydraulic cylinder exit MTS displacement sensor readings in the displacement does not change the situation began to jump phenomenon, the jump value is typically jumped from 70 to 60, sometimes can immediately jump Going back, sometimes it will be stable at this position for a period of time, and this transition does not have any regularity. It can occur in the rolling process, it can also occur in the steel rolling gap, it can happen at the moment of biting steel, and it can happen at the moment of steel throwing. In the case of a rolling mill, it can also happen when the motor is pressed down. This instability of the hydraulic position leads to instability of the roll gap, which seriously affects the normal production, forcing us to stop the use of the hydraulic press system. Only electric rolling can be used. By tracking we have obtained a trend chart of sensor readings, as shown in Figure 2. We have taken several approaches to troubleshooting.

Troubleshooting (1) Measure four cylinder displacement sensor clock signals and data signals. The clock signal is about 2.8V DC, and the AC is about 0.123V. The data signals are about 2.8V DC, and the AC is about 0.245V. From this, it can be determined that the PLC clock and the MTS data bit receive and send pulse circuits are all normal.

(2) Check the mounting screws of the exit sensor on the operating side, all intact. There is no problem with the installation of the sensor.

Figure 2 MTS displacement sensor reading trend (3) Check the sensor's external cable, neither short-circuit phenomenon is also excellent insulation to the ground. Check the wiring in the hydraulic cylinder junction box and the top box of the archway, the wiring conditions are good, and the shield layer of all signal lines is reliably grounded. The phenomenon remains.

(4) The operating side outlet displacement sensor is replaced, and the reading of the new displacement sensor still shows a random jump.

(5) The wiring of the operation-side inlet and outlet displacement sensors was aligned in the junction box and it was found that the exit MTS still experienced random jumps. There is no problem with the cable from the top box of the archway to the hydraulic cylinder junction box.

(6) The operating-side outlet displacement sensor and the transmission-side inlet displacement sensor are reversed, and it is found that the operation-side outlet MTS still undergoes a random jump and the inlet sensor is normal. The transmission side sensor is also normal. Explain that the MTS displacement sensor is good.

(7) In the PLC cabinet, the channels connected by the two displacement sensors on the operation side are aligned, and it is found that the export MTS still has random jumps and the entrance sensor is normal. There is no problem with the template channel.

(8) Replace the MTS sensor on the operating side from the top of the arch to the dedicated line between the junction box of the hydraulic cylinder and find that the MTS on the operating side still has random jumps and the entrance sensor is normal. Again, there is no problem with the cable.

(9) In the PLC cabinet, the channels on the operation side and the transmission side displacement sensors are overall aligned, and it is found that the MTS on the operating side of the hydraulic cylinder still undergoes random jumps, and other sensors are normal. There is no problem with the template.

(10) We carefully analyzed each test process and the installation position of the sensor and found that the ambient temperature of the hydraulic cylinder outlet displacement sensor on the operating side was the worst. Therefore, the operating side outlet sensor is connected to the cooling water, and the phenomenon of rapid jump is disappearing immediately. The hydraulic system continues to be used, and the exit sensor on the operation side can begin to jump after four or five days.

(11) All the FM458 and EXM438 templates were replaced with new ones, and the operation-side exit MTS still experienced random jumps, further demonstrating that there is no problem with the PLC template.

(12) Take out a new MTS displacement sensor to fix its position and connect it directly to the terminal junction box at the top of the mill archway. After the system is powered on, we observe that the sensor whose position is fixed should not change its reading. However, random jumps occur with the rolling process. So we took the sensor directly behind the PLC electrical cabinet and directly connected to the PLC template channel. After continuous tracking observation, we found that the sensor's reading thread was not moving and was very stable. From this we concluded that only from the PLC electrical cabinet to the top of the mill archway Cables between the terminal junction boxes do have unpredictable interference.

Treatment method All the connecting cables of the MTS displacement sensor are re-layed on the individual bridges, all the cables are replaced, the cover of the bridge is covered, and all the shielding layers are reliably grounded to completely eliminate the interference signals. Facts have proved that after the improvement measures are completed, no similar phenomenon has occurred again.

Concluding remarks When installing, the hardware must be strictly controlled to prevent the hardware from hiding hidden dangers. Should be recorded in detail after a failure, in order to prevent false signals or phenomena, resulting in feelings of paralysis, affecting the actual troubleshooting, the only way we can maintain each device.

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