Optical Switch Sensors Successfully Operate Using Snell’s Law

Snell’s Law is used to predict how a light beam will refract or change it’s direction when traveling from one substance to another. θ represents (left figure) the angle between the direction of the light beam and a normal line (defined as the line perpendicular to the two surfaces at the point where the light ray passes from one substance to another. When light moves from a medium of a refractive index into a second medium with refractive index, both reflection and refraction of the light may occur.
 

Optical switches work by sensing the difference in the refraction index between various mediums, causing different degrees of refraction. When the liquid is not in contact with the sensor, all transmitted light is reflected back to the receiver. When the sensor is immersed in liquid, the light disperses throughout and less is returned to the transistor. The amount of returned light to the transistor affects output levels, making point level sensing possible.

Ultrasonic Optical Liquid Level Sensor

Strain Measurement Devices’ optical liquid level sensors consist of two main parts: an infrared LED coupled with a light transistor, and a transparent prism tip. The LED projects an infrared light outward; when the sensor tip is surrounded by air the light reacts by bouncing back within the tip before returning to the transistor. The main advantages of optical level sensors are their compact size, their lack of moving parts, and their low cost.

However, while extremely accurate for point level detection in high-stress environments, they’re less useful for continuous level measurement. In addition, optical level sensors are unsuited for applications where top mounting is necessary; when top-mounted, the accuracy optical level sensors may be adversely affected by moisture condensation.


Specialty combination sensors are a specialty at SMD Sensors, we have the ability to provide multiple sensors that work together in one application, and also have the ability to combine certain sensors together in small housing options to meet many detection needs in strict space requirements. The video below is a demonstration module created by engineers to highlight just some of the technology Strain Measurement offers and how our sensors can work seamlessly together.