Photoelectric sensors: the tech sense

"Photoelectric sensors are devices which utilize photoelectric emitters and receivers and perform their own modulation, demodulation, amplification and switching. Their internals can be broadly classified into two parts – Optics and Electronics. Another commonly used term for a photoelectric sensor is a "Photoeye".

Photoelectric sensors or Photoeyes mainly serve the following two purposes:-
1. Detection of the distance between a point and an object
2. Determination of the absence or presence of an object by using a light transmitter

In manufacturing industries where automation is of paramount importance, photoelectric sensors serve a key role to play. These work in tandem with the other equipments in a manufacturing unit and reduce the time required for a manufacturing cycle to finish. These have three different functional types:-
1. Opposed
2. Retroreflective
3. Proximity sensing

An opposed arrangement comprises of a receiver located within the line-of-sight of the transmitter. The object gets detected when the light beam is blocked from getting to the receiver from the transmitter.

In a retroreflective arrangement, the transmitter and receiver are at the same place and use a reflector to bounce the light beam back from the transmitter to the receiver. The object gets detected when the beam is interrupted and fails to reach the receiver.

Finally, in a proximity sensing arrangement, the transmitted waves must reflect off the object in order to reach the receiver. The object gets when the receiver sees the transmitted source.

The characteristics to look for in a photoelectric sensor are
1. Detecting range
2. Sensing mode
3. Response time

The detecting range of a Photoelectric sensor is termed as its "field of view". It is the difference between the maximum and the minimum distance the sensor can retrieve information from. For example, if the sensor could measure between 15 and 45 cm, this window would be 30 cm. High quality sensors generally have a wide field of view. Sensors which have wide field of view cost more.

Sensing mode can be either presence/absence or position measurement. In the former mode, the sensor detects presence or absence of an object in an on/off mode. In the latter mode, the sensor can detect position in a linear region by the intensity of reflected light.

The response time happens to be the delay between the time of the target object entering the detection zone and the time when the sensor registers a detection signal. It’s preferable to have low response time in a photoelectric sensor.

Photoelectric sensors can have different body styles, a few of which happen to be threaded barrel, cylindrical, rectangular, ring and frame. Each of these styles is suitable for a particular type of application which is the main deciding factor."