3 Ways of Knowing the Right Photoelectric Sensors for You

If you are part of the management team in a manufacturing company and are tasked with selecting technology to enhance both safety and productivity, it is crucial to thoroughly understand how the chosen technology works and its potential benefits. This article focuses on photoelectric sensors, explaining the three main types, their individual functions, and operations.

A photoelectric sensor is an industrial sensor designed to detect changes in light intensity. It consists of a light source, amplifier, signal converter, and output. The three major types of photoelectric sensors are as follows:

1. Thru-Beam (Opposed Mode):

   • This mode employs separate housings for the transmitter and receiver. It detects objects when an object interrupts the light beam between the two sensors.

2. Retroreflective:

   • In this mode, the light source and receiving device are housed together. The sensor emits light aimed at a reflector, and the reflected light is received by the sensor. The presence of an object is detected when the light path is interrupted.
   • Retroreflective mode for clear object detection: These sensors utilize a low hysteresis circuit to detect slight changes in light, which commonly occur when sensing clear objects.
   • Retroreflective mode with foreground suppression: This mode is suitable for detecting shrink-wrapped pallets, as a standard retroreflective sensor may mistake the glossy covering for a reflector and not change state.

3. Diffused (Proximity Mode):

   • In this mode, the transmitter and receiver are housed together. The diffused mode has a shorter sensing range compared to retroreflective and thru-beam modes due to the targets' angle and ability to reflect light.
   • Diffused Mode with Background Suppression: This mode can operate at a fixed or variable distance.
   • Diffused Convergent Beam Mode: In this mode, the transmitter lens is focused on a precise point in front of the sensor, and the receiver lens is also focused on the same point.
   • Diffused Mode with Mechanical Background Suppression: This mode employs two receiving elements in the photoelectric sensor, one of which receives light from the target, and the other receives light from the background.

To compare the three modes, let's highlight their advantages and disadvantages:

• Through-Beam:

  • Advantages: Most accurate, longest sensing range, detect objects regardless of color or surface.
  • Disadvantages: Requires two-point installation (emitter and receiver).

• Retroreflective:

  • Advantages: Space saver (light emitter and receiver in one housing), faster installation with only one device for wiring and mounting, cost-effective with a single device.
  • Disadvantages: May cause false triggers on highly reflective surfaces, sensing distance is less than through-beam.

• Diffused:

  • Advantages: Space saver (light emitter and receiver in one housing), faster installation with only one device for wiring and mounting, cost-effective with a single device.
  • Disadvantages: Shortest sensing distance compared to through-beam and retroreflective modes, less accurate due to energy loss caused by the target's angle and reflectivity.