What is the detection principle of fiber optic sensors?
For fiber-optic sensors, if a through-beam fiber is used, it is a through-beam detection mode; if a direct-inversion fiber is used, it is a proximity detection mode. The ultrasonic sensor is divided into two types of detection modes: through-beam and proximity.
Proximity detection mode
The photoelectric and ultrasonic sensors in the near detection mode determine whether there is a test object by detecting the energy reflected from the test object. For example, when an ultrasonic sensor receives a sound wave reflected from the measured object, the measured object is detected. The transmitter and receiver of this sensor are assembled together on the same side of the sensor. In this detection mode, when the test object appears, it reflects a certain amount of light back to the sensor instead of blocking the light as in the through-beam detection mode. The photoelectric proximity detection mode is further divided into the following detection methods: direct-inversion, wide-beam, focused, fixed-area, and adjustable-area.
Among photoelectric sensors, the direct-reversal sensor is a common detection mode. In this way, the light emitted by the transmitter strikes the surface of the object at various angles, and the surface of the object also reflects the incident light at various angles, of which only a small part is reflected back to the receiver.
The direct detection mode has a relatively low utilization of light energy, because its receiver can only receive a small portion of reflected light. Like other proximity detection modes, the direct-transform type is also affected by the reflectance of the surface of the measured object. For a test object with a bright white surface, the detection distance of the sensor is longer than that of a dark surface.
Most direct-sensors are equipped with a lens to calibrate the emitted light, making it more focused, so as to get more reflected light. Although the addition of a lens can extend the detection distance, it is more difficult to detect very bright surfaces. At this time, the installation angle of the sensor becomes very important.
Because the very bright surface is like a mirror, the installation angle is slightly deviated, most of the reflected light is reflected away, and only a small part is reflected back to the receiver. If the surface of the object to be measured is parallel to the sensor's detection head, most direct-reflex sensors can receive the reflected light. However, if the test object is a round surface (such as a metal bucket) or the metal sheet / film being tested is subject to frequent flutter, the test will be unreliable.
Wide beam direct trans
In order to avoid the impact of light loss on the detection performance when detecting bright objects, especially when detecting at short distances, a wide-beam direct-reflection sensor can be used. Without a condenser lens, the detection distance will be shortened. The bright measured plane is parallel. This is its advantage.
For any proximity detection mode sensor, its detection distance is affected by the size and shape of the object being measured. Larger objects reflect more light energy than smaller objects.
In the 2.5mm detection distance, the detection performance of the wide-beam direct-reflection sensor is better than that of the general direct-reflection sensor. Therefore, if the sensor lens can be detected close to the object to be detected, the wide-beam direct-inversion sensor can reliably detect small objects such as fine sand or wires.
Another type of detection mode that can detect small objects is focusing. Most focusing sensors add a lens to the transmitter so that the emitted light is focused at a point in front of the lens, and the focus of the receiver lens is also here. This forms a small energy-concentrated detection area at a fixed distance.
The focus sensor has a high utilization rate of reflected light. It can reliably detect small objects and objects with very low reflectance that cannot be detected by general direct-reflection or wide-beam direct-reflection sensors.
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