液面传感器.ppt

压力（静水头） 表面反射 折射率的变化 应用 液面传感器 毋明旗 Level sensors Introduction Level sensors are categorized as switches for high/low level and leak detection or as magnitude sensors for actual liquid level. Fiber optic devices have found more applications in the former category. Liquid level is one of the prime process control parameters, especially in the petrochemical and chemical industries. The explosive nature of many of the processes makes fiber optics especially desirable. Leak detection and fuel level are required in many military applications. The immunity to EMI and RFI is the driving force for fiber optic usage in these applications. Fiber optic sensors that use light interaction with the media for which the level is being measured work best in relatively clean and clear liquids. Dirty or somewhat opaque liquids such as crude oil and paints tend to foul the optics and blind the sensors, as do solids in the powder form. Level measurement for these type materials is best achieved by sensors that are used in pressure-related level measurements. The concept that can be used in conjunction with fiber optic level sensors include: (1)Sight glasses (2)Force(buoyancy) (3)Pressure(hydrostatic head) (4)Reflective surface (5)Refractive index change 液面传感器主要用作高/低液面的开关和泄漏检测器或者实际液位传感器。光纤设备在第一类中有诸多应用。 液位是一个重要的过程控制参数,尤其是在石油和化学工业。由于许多过程易爆的特性，这使得光纤设备显得尤为可取。泄漏检测和燃料液面的检测在军事中有诸多的应用。对EMI（电磁干扰）和RFI（射频干扰）的免疫使光纤常被应用于军事方面。 光纤传感器利用光与介质的相互作用来进行液面测量，尤其在相对干净和清晰的液体中，它可以很好的工作。浑浊或有些不透明的液体,如原油和油漆，往往阻塞和弄脏光学传感器，在固体粉末中也一样。对于这些类型材料的液位测量，最好使用与压力相关的传感器来进行。 光纤液位传感器利用的相关的概念包括： （1）视镜 （2）力（浮力） （3）压力(静水头) （4）反射面 （5）折射率的变化 Sight glass liquid level sensor Boilers generally use a bi-color visual sight gage for water level. A prism is used in such a way that if steam is in the gage port, red light is observed. Water in the port causes the red light to be refracted, with only green light transmitted. Such a device is shown in Figure 10-1.The location of the sensing device