Photoelectric sensor

Conceptual through-beam system to detect unauthorized access to a secure door. If the beam is interrupted, the detector triggers an alarm.

A photoelectric sensor is a device used to determine the distance, absence, or presence of an object by using a light transmitter, often infrared, and a photoelectric receiver. They are largely used in industrial manufacturing. There are three different useful types: opposed (through-beam), retro-reflective, and proximity-sensing (diffused).

Types

A self-contained photoelectric sensor contains the optics, along with the electronics. It requires only a power source. The sensor performs its own modulation, demodulation, amplification, and output switching. Some self-contained sensors provide such options as built-in control timers or counters. Because of technological progress, self-contained photoelectric sensors have become increasingly smaller.

Remote photoelectric sensors used for remote sensing contain only the optical components of a sensor. The circuitry for power input, amplification, and output switching is located elsewhere, typically in a control panel. This allows the sensor, itself, to be very small. Also, the controls for the sensor are more accessible, since they may be bigger.

When space is restricted or the environment too hostile even for remote sensors, fibre optics may be used. Fibre optics are passive mechanical sensing components. They may be used with either remote or self-contained sensors. They have no electrical circuitry and no moving parts, and can safely pipe light into and out of hostile environments.

Sensing modes

Classification of Photoelectric Sensors Based on Sensing Methods Photoelectric sensors can be divided into three categories based on their sensing methods: thru-beam, retro-reflective, and diffuse.

Thru-Beam Photoelectric Sensors Thru-beam photoelectric sensors, also known as through-beam sensors, rely on a light source and a light receiver to identify the presence or absence of an object. The light source and receiver are positioned on opposite sides of the target area and the light beam passes through the area, being received by the receiver.

When an object enters the target area, it obstructs the light beam, causing the light receiver to produce an electrical signal. This signal can then be used to initiate an action, such as turning on a motor, controlling a device, or activating an alarm.

Thru-beam photoelectric sensors are often used in situations where the target object is large, moves quickly, or demands high precision. They are also commonly used in applications where physical contact with the object is to be avoided.

Key features of thru-beam photoelectric sensors include a long sensing range, high accuracy, fast response time, and high resolution. These sensors are utilized in various industries, including the automotive, food and beverage, machine engineering, material handling, and pharmaceutical industries.

Retro-Reflective Photoelectric Sensors Retro-reflective photoelectric sensors are a type of photoelectric sensor that detect the presence or absence of a target object using a light source and a light receiver. They work by emitting a light beam from the source that is reflected back to the receiver by a retro reflector. The retro reflector is a small device that sends the light back to its origin.

The target object interrupts the light beam when it is placed between the light source and the retro reflector. The interruption is detected by the light receiver, which then generates an electrical signal that can be interpreted by the main circuit.

Retro-reflective photoelectric sensors are usually utilized in applications where the target object is far away from the sensor or moving. They are also commonly used in situations where avoiding physical contact with the target is important.

Diffuse Photoelectric Sensors Diffuse photoelectric sensors, also known as diffuse sensors, detect objects by measuring the scattered light reflected from the object. Unlike thru-beam or retro-reflective sensors, diffuse sensors do not need a direct line of sight between the light source and receiver. Instead, the light source directs light at the object, and the scattered light is detected by the receiver.

Diffuse sensors are often utilized in situations where maintaining a direct line of sight between the light source and target object is challenging or impossible. These sensors are commonly used in industries such as packaging, bottling, printing, and material handling.

Diffuse photoelectric sensors have a broad sensing range, making them suitable for various applications. To know more about Photoelectric senssor details check in the Guide.

Certain types of smoke detector use a photoelectric sensor to warn of smouldering fires.

Difference between modes

Name	Advantages	Disadvantages
Through-beam	Most accurate Longest sensing range Very reliable	Must install at two points on system: emitter and receiver May not detect translucent objects False triggers when misaligned.
Reflective	Only slightly less accurate than through-beam Sensing range better than diffuse Very reliable	Must install at two points on the system: sensor and reflector Slightly more costly than diffuse Sensing range less than through-beam May not detect objects with high albedo
LASER-Reflective	Single point installation Good for detecting small objects Clearly defined sensing ranges Very reliable	Blind to objects outside specified range Not good for mirror finishes
Diffuse	Only install at one point Cost less than through-beam or reflective	Less accurate than through-beam or reflective More setup time involved

See also

• List of sensors
• Photodetector
• Sensor
• Electric eye

External links

• Guide to Sensing, 2002, Banner Engineering Corporation, P/N 120236
• Guide to sensing