How to Suppress Background Suppression in a Photosensitive Sensor
Photosensitive sensors are everywhere – they open garage doors, turn on sink faucets with a wave of the hand and even detect winning cars at race events. They operate on a simple principle: Light hits the sensor and causes its current to flow.
The two most popular types of light sensors are Photodiode and Phototransistor. Both are PN-junction semiconductor devices.
Background Suppression
Background suppression is one of the most important factors in determining how well your photosensitive sensor performs. It’s what allows a sensor to differentiate between an object and its surroundings, especially when the objects are close together or have similar colors or textures. If a sensor is sensitive to both the object and its background, it can be difficult for it to distinguish between them, which results in poor performance and false triggers.
The background suppression feature in a photoelectric sensor is designed to eliminate the impact of ambient light on the sensor’s performance by reducing the amount of light transmitted from the lens to the sensing element. The result is that the photosensitive sensor can better discern the difference between a light-emitting object and its surrounding background. This provides a much more accurate and reliable operation, allowing it to be used in applications where the object is very dark or has a low contrast with its surrounding environment.
Foreground suppression, on the other hand, is more effective when the object has a high reflectivity. This mode of detection uses the same concept as background suppression, but it is less sensitive to ambient light and enables the sensor to detect objects with very low reflectivity, such as products on a reflective conveyor belt.
There are two ways to implement background suppression: mechanical or electronic. Mechanical types have an adjustment screw that you can use to calibrate the sensor by moving it in or out, adjusting the point where it will recognise an object. They can also be programmed to recognise an object by using Microwave sensor a button, which is useful when you need to change the sensor’s behaviour to suit different production lines or environments.
In comparison, an electronic sensor with a built-in position sensor, like the one in our SS-SP series, has no mechanical parts and adjusts through a potentiometer. It can also be switched Normally Open or Normally Closed, depending on your requirements.
Another benefit of background suppression is that it is far less affected by the color of an object. If you look at a red mark printed on white paper stock through a green filter, for example, the mark will appear very dark or even unreadable to your human eyes. However, a diffused mode photoelectric sensor with background suppression will still be able to see the mark, despite the fact that it looks dark to the sensor’s light-sensitive receiver. This is because the sensor can be programmed to only respond to signals that fall within the range of its set sensing distance plane, which is defined by the geometric relation between the sending and receiving elements.
Diffused Mode Sensing
The way an object reflects light directly affects the distance at which it can be reliably sensed. When selecting a photoelectric sensor, the surface texture and reflectivity of the objects to photosensitive sensor be detected should be taken into account. For instance, matte surfaces do not reflect light as well as shiny ones. Likewise, glossy or metallic objects have more reflective properties and can therefore be detected further away than less-reflective ones.
A sensor’s operating mode plays a vital role in how its performance can be maximized. For example, an opposed-mode (through beam) sensor requires a reflector to function, while diffuse mode sensors have the transmitter and receiver housed in the same unit. This enables the device to easily detect transparent objects, since the light that hits the surface of the object will be diffused and returned to the sensor in different directions.
The reflected light is then evaluated by the sensor and, depending on the intensity of this light, an output switch is activated or not. For example, a light-emitting diode is often used to detect transparent objects by measuring the voltage generated when the light passes through the material. If the light is interrupted, a change in the measured voltage occurs and an output switch can be activated.
Diffuse-mode photoelectric sensors allow for easy installation, because the transmitter and receiver are housed in one unit and do not require a reflector. They can also operate at short sensing distances and feature a wide sensitivity range, making them ideal for applications where space is limited or when a reflector-type sensor cannot be fitted.
Using diffuse-mode sensors with a clear glass lens can greatly enhance the device’s performance by improving the amount of light that is reflected back to the receiver. Many of these sensors come with collimating lenses, which increase their sensing ranges, as well.
Another important factor to consider when selecting a photoelectric sensor is its response time. This is the time it takes for the sensor to respond to a change in light levels and switch its output. A sensor with a faster response time is useful in situations where a large number of input events occur at high rates and must be resolved quickly.
Regular maintenance of a photoelectric sensor is critical for optimal performance. Performing regular visual inspections of the sensor for physical damage and loose connections can help prevent failure over time. Cleaning the sensor lens and transmitter/receiver components on a routine basis can help maintain optimum performance as well. For instance, dust build-up on a sensor lens can cause the device to lose excess gain and no longer detect a signal from a passing opaque object.
