The principle of common photoelectric speed sensors

commonPhotoelectric speed sensorThere are two types: direct and reflective. The direct input shaft is connected to the axis to be tested, and light is irradiated onto the photosensitive element through the perforated disk and gap plate. When the perforated disk rotates once, the number of times the photosensitive element receives light is equal to the number of openings on the disk. If the number of openings is m, the recording process time is t seconds, and the total number of pulses is N, then the speed is:

The reflective photoelectric sensor is shown in Figure 1-50. The front-end part adopts fiber optic packaging, which is suitable for measuring small objects, especially small rotating bodies. Due to the presence of light sources (LEDs), photosensitive elements (phototransistors), and amplifiers inside the sensor, it is designed to be small in size and easy to use. The light source is frequency modulated, so it has strong anti-interference ability and status display, which can be used by users to confirm the working status during measurement. The oscillation circuit is used to generate a modulation frequency to light up the light emitting diode of the light source. It adopts an unstable multi harmonic oscillation method, with an oscillation frequency of about 7kHz and a pulse width of about 25 μ s.

The pulse light emitted from the light source is reflected by the detected object and detected by the photoelectric transistor of the sensor

Accepted, then amplified to an appropriate level by an AC amplifier, detected and integrated, and converted into a DC voltage signal. Next is waveform shaping, which compares with a certain DC voltage. If it is higher than this value, the output is Hi, and if it is lower than this value, the output is Lo. The status indicator light is also the same. When the output is high level Hi, the LED lights up, and when the output is low level Lo, the LED does not light up, which is used for status confirmation.

The photoelectric speed sensor is used in conjunction with a counter, with a detection range of up to 10000r/min and an error of 1r/min.