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September 27, 2011 / abdelhezzinipewa

Photoelectric Sensors: Tips and Tricks

As an Application Engineer, one of the most common technical questions I see with photoelectric sensors is, “How can I reduce interference between photoelectric sensor?”

In the search for an answer, we must first grasp a better understanding of the question. When multiple photoelectric sensors are mounted in close proximity to one another, an unstable operation can result from “cross talk” or influence from other photoelectric sensors. This result is known as mutual interference and is most common in thru-beam photoelectric sensors.

Here are some tips and tricks to avoid mutual interference:

1. Use sensors incorporated with interference prevention function.
Interference prevention among multiple sensors is available by using sensors incorporated with interference prevention function. There are different types of models for interference prevention such as the automatic type or the emitter-frequency-selectable type.

2. Mount the sensors far enough apart to prevent interference.
Calculate the sensing operating point i by the setting distance L from either the parallel deviation characteristics or sensing area characteristics. Then mount the sensors more than double the distance of i.

3. Mount with polarizing filter. (thru-beam type only)
As for red LED, interference prevention is available with the use of a polarizing filter. However, as light is decreased by the filter, sensing range will be below the specified value.

 4. Narrow beam-envelop with hood and slit.thru-beam type only
In this case, although the beam has been narrowed down, you should be careful that the sensing range has decreased. As for models with optional slit, please confirm both sensing ranges when one side is mounted and when both sides are mounted as mentioned in the catalog.

5. Alternate emitter with receiver. (Thru-beam type only)
Alternating the emitter with the receiver will reduce interference since the emitting direction is alternately opposite. However, there is a possibility where the 2nd receiver receives light from the 1st emitter when the sensors are close. In such case, countermeasures such as adding light shields can be taken.

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