Types of Photosensitive Sensors
A photosensitive sensor is a device that converts radiant energy (light) into an electrical signal. These devices can be found in many different types of applications.
Light that radiates from LEDs oscillates horizontally and vertically. However, there are optical filters that constrain these oscillations to a single direction.
This allows for a much more precise focal point that can be mechanically adjusted for greater accuracy. This method is called convergent beam mode.
A photosensitive sensor is used to convert light energy, also known as photons, into an electrical signal that can be read by a microcontroller or logic circuit. It is easy to use with a built-in potentiometer that can be turned to adjust the sensitivity, so it can detect even very faint ambient light.
There are several types of photosensors available to choose from depending on your Microwave sensor project requirements. The most common type of photosensor is the Light Dependent Resistor (LDR), commonly referred to as a light sensor or photoresistor. When exposed to light, the photoresistor changes its resistance from thousands of ohms in the dark to hundreds of ohms when illuminated. This happens because it becomes more conductive by creating electron – hole pairs at the material’s surface.
A second popular type of light sensor is the photodiode. Photodiodes are similar to photoresistors but offer faster response times. They are most useful in projects that require very quick light responses and they are also very sensitive to infrared. Another option is the phototransistor, which is basically a photodiode with added amplification and is very popular in applications that require long distances of detection. These sensors are often found in cameras, light meters and many other electronic devices including CD/DVD-ROM drives, TV remote controls, scanners, fax machines and copiers.
The illuminance (light intensity) of a surface can be measured by a photosensitive sensor. This can be useful for industrial applications such as machine vision in manufacturing where a certain amount of light is required for proper operation.
Light sensors are based on semiconductors such as the photoresistor and the photodiode, which use the working principle of the inner photoelectric effect to convert the light energy into electric currents. A photoresistor changes its electrical resistance as light hits it, with the resistance being lower when not illuminated and higher when fully illuminated.
Photodiodes are more complex than the photoresistor, as they actually change light into a flow of electron holes. This is what gives them their ability to detect a wide range of light intensities.
Both the photodiode and the photoresistor can be used to measure the illuminance of a surface by comparing its brightness against a pre-set photosensitive sensor value. To do this, they have two receiving elements: one for the target and another for the background. The output is activated when the reflected light at the receiver for the target is greater than that of the receiver for the background.
Photosensitive sensors are commonly available for purchase online and can be easily connected to various development boards, such as the Arduino. To get the specific illuminance value, an analog-to-digital conversion is needed through the ADS1115. This is done by connecting the AO output of the photosensitive sensor to the AIN output pins of ADS1115. The ADS1115, with its 16-bit precision, can provide a high level digital signal that can be read by the Arduino to determine the illuminance of the surface.
Contrast sensors use a light source that illuminates the area around the sensor. Then, the object or mark of interest is placed between the sensor and the light source to interrupt the light beam. The sensor detects this interruption and determines the difference between a strongly contrasting background and a barely contrasting background. If the contrast is not present, the output of the sensor remains off; otherwise, it turns on.
A variety of industrial applications require the detection of contrast markings on products, labels and packaging. These include printing lines, beverage and bottling lines, and paper and ceramics production machines. The most important factor in selecting a contrast sensor is to understand the specific characteristics of your process and mark or label. For example, glossy surfaces may require the sensor to be mounted at a slight angle to the surface to prevent interference from other reflective objects and colors, while matte surfaces diffuse the light more evenly so that positioning is not affected by surrounding materials.
The contrast of an object or mark is measured by comparing the reflected light from a taught reference value with a current target. The sensitivity settings of a photodetector allow the user to choose a desired teaching value for a mark or material. This allows the photosensitive sensor to evaluate its current condition based on these values and to determine if the result is within or outside of its set limits.
Photoelectric Sensors use a light transmitter (also known as an emitter) and a receiver to detect objects. The emitted light is transmitted to the receiver via lensed or fiberoptic light guides. When an object interrupts or reflects the emitted light, it changes the amount of light that falls on the receiver and triggers the sensor to change output. These sensors are not limited like Proximity Sensors to detecting metal objects, and can be used in environments where magnetic or ultrasonic sensing is impractical.
These sensors can also be used to detect orientation. By selecting the appropriate model, a user can configure the sensor to respond to the position of an object. This feature can be useful in many applications, such as a machine that must correctly orient and align bottle caps when it is capping a bottle.
Some models are equipped with an LED that illuminates the sensor when it is operating in a Light State or Dark State condition. This can help ensure that the sensor has been properly installed, and can indicate if the sensitivity is set correctly. Most of these sensors also come with a potentiometer to allow the sensitivity to be adjusted for different environments. This is especially helpful in industrial applications, where it is important for the sensors to work reliably and stably.