The modulation of the LED sensor

In 1970, it was discovered that LED has a long life better than the advantage that it can be a very fast switching speed, switching speed can be achieved KHz. The receiver amplifier to the modulation frequency modulation transmitter, then it is only the frequency of vibration of the optical signal in order to zoom.

We can be likened to the modulation wave transmission and reception of radio waves. The radio to a station, you can ignore the rest of the radio wave signal. Modulated LED emitter transmitter is similar to radio waves, the receiver is equivalent to the radio.

People often have a misconception: that because of the LED infrared light invisible to infrared light, infrared light energy then certainly very strong. Modulated optical sensors the size of the energy of the wavelength of light with the LED is no significant relationship. A small LED light emitted through modulation of energy only to become very high. A modulation of the sensor without the use of long focal length lens only by the mechanical shielding means so that the receiver can only receive light emitted by the transmitter in order to make the energy becomes high. In contrast, a modulated receiver can ignore the surrounding light, the light only on their own or with the same modulation frequency of light to make a response.

Unmodulated ambient light sensor to detect light or infrared radiation, such as fresh-baked red hot bottle, in this application if you use other sensors, may malfunction.

If a metal light emitted much stronger than the surrounding light, then it can be reliably detected around the light source to the receiver. Around the light receiver can also be used to detect the outdoor light.

But not to say that certainly through the modulation of the sensor from ambient light interference, when using the infrared thermometer in bright sunlight when there will be problems. For example, not through modulation of the photoelectric sensor, when it directly to the sun, it can function normally. We all know that there is amplification with a piece of glass will gather in the sun, when a piece of paper, can easily ignite the paper. Vision infrared thermometer sensor to replace the glass lens, replace the paper phototransistor, so that we can easily understand why the modulation of the receiver point to the sun when it does not work, which is around the light source so that it saturated.

Modulation of the LED to improve the design of optical sensors, increasing the detection distance, the angle of the beam expansion, the growing acceptance of the aim of this reliable and easy-to-beam. By 1980, non-modulated optical sensors and gradually withdrew from the stage of history.
Infrared LED beam is the most efficient, but also in the spectrum that best matches with the phototransistor beam.

However, some sensors need to distinguish between colors (such as color detection), which requires the use of visible light.
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In the early days, color sensors using incandescent light source, the use of photovoltaic receiver, until it was invented a highly efficient visible light LED. Now, most of the color sensors are used by the modulation of various colors of visible light LED emitters. The modulation of the sensor is often at the expense of response speed for a longer detection distance, detection distance is because it is a very important parameter. Unmodulated sensors can be used to detect small objects, or objects very fast action, speed of response required by these applications are very fast. But now, high-speed modulation sensors can also provide very fast response speed, to meet the most testing applications.