German S PRODUCTS sensors, S PRODUCTS models, S PRODUCTS prices

S PRODUCTS sensor is a sensor that measures the air flow drawn into the engine. In electronically controlled gasoline injection engines, to achieve the optimal mixture concentration under various operating conditions, it is essential to accurately measure the amount of air drawn into the engine at every instant, using this as the primary basis for the ECU to calculate (control) the fuel injection quantity. If the air flow sensor or its wiring fails, the ECU will not receive the correct intake air signal, preventing normal control of fuel injection, which results in a mixture that is too rich or too lean, causing abnormal engine operation.

S PRODUCTS sensor structure

It consists of two parts: the scale grating and the grating readhead. The figure on the right shows the structure of the grating scale. The key component of the grating detection device is the grating readhead, which comprises a light source, condensing lens, index grating, photoelectric elements, and adjustment mechanisms. There are many structural forms of grating readheads, classified based on their structural characteristics and application scenarios into direct-reception readheads (also known as silicon photovoltaic cell readheads, mirror-image readheads, beam-splitter readheads, and metal grating reflective readheads).

S PRODUCTS sensor principle

The essence of a grating displacement sensor is to perform measurement by using the grating pitch as a standard ruler. High-resolution grating scales are generally expensive and difficult to manufacture. To improve system resolution, Moiré fringes need to be subdivided; grating scale sensor systems mostly employ electronic subdivision methods. When two gratings overlap with a slight inclination angle, Moiré fringes are generated in a direction roughly perpendicular to the grating lines. As the grating moves, the Moiré fringes move up and down accordingly. This converts the measurement of the grating pitch into the measurement of the number of Moiré fringes. Within the width of one Moiré fringe, placing 4 photoelectric devices at specific intervals enables electronic subdivision and direction discrimination. For example, for a grating scale with 50 line pairs/mm, the grating pitch is 0.02mm. With four-fold subdivision, counting pulses with a resolution of 5μm can be obtained, achieving high precision in general industrial measurement and control. Since displacement is a vector, both its magnitude and direction must be detected; therefore, at least two photoelectric signals with different phases are required. To eliminate common-mode interference, DC components, and even harmonics, differential amplifiers composed of low-drift operational amplifiers are typically used. The 4 photoelectric signals obtained from 4 photosensitive devices are sent to the input terminals of 2 differential amplifiers. The two signals output from the differential amplifiers have a phase difference of π/2. To obtain direction discrimination and counting pulses, these two signals must first be shaped into square waves with a duty cycle of 1:1. Then, by comparing the phases of the square waves, the movement direction of the grating scale can be determined. By counting the square wave pulses, the displacement and velocity of the grating scale can be obtained.

S PRODUCTS sensor usage precautions

When plugging or unplugging the connector between the grating scale sensor and the digital display unit, ensure the power is turned off. Install an external protective cover whenever possible, and promptly clean chips and oil splashed onto the scale to strictly prevent any foreign matter from entering the housing of the grating scale sensor. Regularly check whether the installation screws are loose. To extend the life of the dust-proof sealing strip, apply a thin, uniform layer of silicone oil to the strip, taking care not to splash it onto the glass grating etched surface. To ensure the reliability of the grating scale sensor, clean and wipe the grating scale surface and the index grating surface with an ethanol mixture (50%) at regular intervals to keep the glass grating scale surface clean. Grating scale sensors are strictly prohibited from being subjected to severe vibration or impact to avoid damaging the grating scale; if the grating scale breaks, the sensor becomes inoperative. Do not disassemble the grating scale sensor yourself, and never arbitrarily change the relative gap between the main grating and the secondary grating. Otherwise, it may damage the accuracy of the grating scale sensor and cause relative friction between the main and secondary gratings, damaging the chrome layer and thus the grating lines, leading to scrapping of the grating scale. Take care to prevent oil stains and water from contaminating the grating scale surface, as this can disrupt the distribution of grating lines and cause measurement errors. Grating scale sensors should avoid working in environments with severe corrosive effects to prevent corrosion of the grating chrome layer and the grating scale surface, which would compromise the quality of the grating scale.

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