Photoelectric Through Beam with Fiber-Optics


Photoelectric sensors are often used with fiber-optic cables in the through-beam/opposed mode.  While there are numerous advantages/trade-offs associated with the through-beam mode, the advantages include the ability to install the sensing tips of each of the two fiber-optics into tight, space-constrained areas, keeping the sensor itself from direct exposure to heat, water, or physical harm from the machinery itself, and experience a difference in optical performance that the sensor itself may not provide without a fiber-optic being used (as in the case of a fixed lens on two separate sensors (sender and receiver).  Of course, using a fiber-optic also allows the sensor to be remote from the point of sensing, and allow physical adjustment of the sensor parameters as needed for the application.

One of the more challenging applications encountered is to detect a small size part at significant span distance (the distance between sender and receiver fiber-optic cables).  The challenge is that the small part is best sensed with small aperture fiber-optic cables.  However, the manufacturer’s specs regarding maximum span distance for fiber-optic cables are typically based on the largest, 0.125 inch standard aperture.  If smaller aperture through-beam fiberoptic cables are best for sensing a smaller part, then the span distance is significantly reduced as the aperture is reduced from the standard 0.125 inch.


Tri-Tronics offers through-beam glass fiber-optic cables with different apertures.  When a small part needs to be sensed, and the application requires a large span, the combination of one Tri-Tronics fiber-optic with  standard 0.125 inch aperture can be used with the second Tri-Tronics through-beam fiber-optic cable with a aperture that is selected relative to the size of the part.  Specifically, if the part to be sensed is, for example, a 0.062 inch diameter rod, use one Tri-Tronics fiber at 0.125 inch aperture, and the other corresponding Tri-Tronics fiber with an aperture as close to the size of the part as possible.  In this case the second Tri-Tronics fiberoptic cable could be 0.062-inch aperture.

One theory is that the Tri-Tronics sender fiber should be the larger fiber to project as much light from the sensor’s LED source, and the smaller Tri-Tronics diameter fiber could be the receiving fiber.  The shadow cast by the 0.062 diameter rod would fall on the smaller receiving fiber, and theoretically block a significant portion of its smaller, sensing/receiving face.

Note that using a lens on the end of a through-beam fiber application does significantly increase the span achievable, but the tradeoff is the corresponding reduction in its ability, or complete inability to sense a small part.

Net Value to our Customers:

Whether you have an easy, or more challenging type application, give us a call.  Chances are we may have either the sensor and/or the experience to solve it.  Excel Automation, and Eagle Sensors & Controls, have years of experience, and are application-oriented Authorized Distributors of numerous products for Industrial Automation, and LED Lighting.

Eagle Sensors & Controls - A Division of Excel Automation LLC