Optical sensor

They are another type of proximity sensors that work based on sending and receiving modulated light. Modulated light is pulses with a frequency between 5-30 kHz and the use of modulated light increases the detection range of the sensor and also decreases the effect of ambient light on the sensor, this light can range from visible green light to invisible light. Infrared.

Of course, 880mm wavelength infrared light is mostly used in the construction of optical sensors, the reason for this is the low interference of infrared light with ambient light and increasing the switching distance of the sensor. A potentiometer is installed on the optical sensors to adjust the sensitivity of the sensor

Optical sensors are divided into three categories as follows:

One-way optical sensors (Diffuse)
Retro-reflection optical sensors
Two Beam Optical Sensors
Diffuse optical sensors

One-way optical sensors work by modulating the transmission of light and receiving the reflection of this light from different levels. In this sensor, the transmitter and receiver sections are installed next to each other inside a case.

In a one-way light sensor, the light modulated by the transmitter is scattered directly in space, if this light hits an obstacle, it is reflected directly and indirectly, the amount of reflection of this light depends on the color, type of surface, Volume and angle are obstacles.

The reflection of light and polished surfaces is more than dark and non-polished surfaces, the reflected light is received by the receiver of this sensor and if the amount of this light is enough, the output changes position. Note that the switching distance of this type of sensor depends on the amount It has modulated light reflection so bright and polished surfaces can be detected from a distance.

The switching distance of this sensor is expressed on the basis of white cardboard with a smooth surface, and the correction factor can be used to calculate the switching distance for other objects.

As mentioned, the color of objects is very effective in detecting them. In general, one-way optical sensors are able to detect these bright objects with a refined surface of polished radiation such as the following objects:

Cardboard with bright colors
Fabric with bright colors
Clear glass
Clear plastics

Note that this type of sensor is not able to detect matte black plastics, black tires and dark fabrics, and to detect these objects can be used two other types of light sensors (reflector and two-way), of course, these objects can Power can also be detected by capacitive and ultrasonic sensors.

To install one-way sensors, care must be taken that the background behind the sensor absorbs or deflects light so that the light reflected to the sensor does not activate the sensor if there is no obstruction in front of the sensor. One-way optical sensor has the shortest switching distance among optical sensors, but this distance is much longer than the switching distance of inductive and capacitive sensors, the switching distance for one-way optical sensors is about 2m.

Retro-reflection optical sensors:

The reflector optical sensor operates based on light and receives the reflection of this light from the reflector. In this sensor, the transmitter and receiver sections are installed next to each other inside a case and the modulated light is emitted in space, a reflector is installed in front of the sensor and when this light hits the light reflector at a certain angle in a straight line The sensor is reflected to the receiver, if an obstacle is placed in the path of reflection of this light, it is no longer possible for the receiver to receive this light, so the sensor detects the presence of an obstacle and changes the sensor output.

The reflector optical sensor has a longer switching distance than the one-way optical sensor, but its switching distance is less than the two-way optical sensor. Normally, the switching distance of this sensor is about 10m.

Two Beam Optical Sensors (Through Beam):

The two-way optical sensor operates based on the transmission of light modulated in the transmitter and the reception of this light by the receiver that is installed in front of the transmitter. In this type of sensor, the transmitter and receiver are separate from each other and the modulated light is sent by the transmitter and the receiver that is installed in front of the transmitter receives this light and if there is an obstacle between the transmitter and the receiver, the other light They are not received by the receiver, so the sensor detects the presence of an obstacle and changes the sensor output. The two-way optical sensor has the longest switching distance among all types of optical sensors, the switching distance of this sensor in some cases reaches more than 100m.

Optical sensors with fiber optic cable:

The light of the transmitter and receiver of optical sensors can be controlled by using fiber optic cables. In fact, the light emitted by the transmitter section of the sensor can be directed to the desired points by using fiber optic cable. Optical sensors with fiber optic cable are used in many environments, but their main application is in environments where there is a risk of explosion, also with the use of fiber optic cable it is possible to use a one-way sensor. Used like a two-way sensor.

In general, the advantages of using a sensor with fiber optic cable are as follows:
-Detection of components in restricted environments (access through a small hole)
-Ability to install the sensor body away from hazardous environments (water, heat, radiation and the possibility of explosion)
-Ability to detect small parts with high accuracy
-Detection of moving parts
-Where to use a one-way sensor Similar to a two-way sensor