Application scheme of photoelectric level sensors in the control of casting liquid level in rolling mills

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For cast rolling production, it is necessary to maintain a continuous supply of material in order to ensure normal and stable operation; therefore, level control is very important. In traditional level control systems, operators are required to make frequent inspections to detect any abnormalities in the liquid level in a timely manner, so as to adjust it as needed. If an operator is careless, if the discharge outlet becomes blocked, or if the liquid level in the insulation furnace is too low, it can result in the liquid level in the front tank not being at the proper level. This leads to repeated interruptions in production, causing unplanned shutdowns and affecting production progress. Currently, some cast-rolling manufacturers also use level control systems. Such systems enable effective monitoring of the liquid level, but operators still need to make adjustments based on the level, which results in a waste of labor resources. The level control method based on the casting device of the rolling mill involves using an adjustment rod to control the level of the molten metal. During the casting process, due to factors such as skin formation, the height of the adjustment rod gradually increases over time. Once the runner and skin formation are cleaned manually, the height of the adjustment rod drops significantly, making it impossible to maintain its position. Existing liquid level control methods typically involve installing a support rod on the adjustment rod, as well as a conical plug on that same adjustment rod; the support rod is used to control the position of the conical plug at the liquid leakage opening, thereby regulating the flow rate of the molten metal and consequently controlling its level. However, during the casting process, the size of the conical plug changes due to the formation of a coating on it, and the single support rod mechanism results in inaccurate level control. A level sensor can provide a switch signal to detect the presence or absence of liquid. Its operating principle is total internal reflection; inside the plastic dome at the front of the device, there is an LED and a detector. When no liquid is present, all light from the LED is reflected from inside the dome cover toward the detector. When the liquid covers the dome, the effective refractive index at the boundary between the dome cover and the liquid changes, causing some of the light emitted by the LEDs to escape. As a result, less light reaches the voltage level switch, and the presence or absence of liquid is indicated by the high and low switch signals. A British SST industrial-grade photoelectric level sensor/photoelectric level switch from Gongcaiwang – the LLC210D324-003 – features single-point detection and outputs digital signal at TTL-compatible levels. This sensor is suitable for high-power output systems, and it can directly drive incandescent indicator lights, sound alarms, relays, or other devices. -An infrared LED light source and a phototube detector are precisely mounted on the base at the sensing end, ensuring excellent light coupling in air. When the sensing tip is immersed in a liquid, infrared light passes through the conical surface, and the light intensity received by the phototube decreases, resulting in a change in the output level. Diverse output circuits can meet different application scenarios. Measurement principle: The photoelectric level switch utilizes the principles of light refraction and reflection, causing light to be reflected or refracted at the interface between two different media. When the liquid being tested is at a higher level, a boundary layer is formed between the liquid and the switch; when the liquid is at a lower level, another boundary layer is formed between the air and the switch. Due to the significant difference in refractive indices between the plastic hemisphere of the switch and air, the intensity of the reflected light received by the light-sensitive crystal inside the switch differs at these two boundary layers, corresponding to two different switch states.