Germany AST GMBH sensor AST GMBH model AST GMBH price

AST GMBH sensor is a sensor that measures the air flow drawn into the engine. For electronically controlled gasoline injection engines, in order to obtain the optimal mixture concentration under various operating conditions, it is necessary to accurately measure the amount of air drawn into the engine at every instant, using this as the main basis for the ECU to calculate (control) the fuel injection quantity. If the air flow sensor or wiring fails, the ECU will not receive the correct intake air signal, preventing normal control of the fuel injection quantity, which will cause the mixture to be too rich or too lean, resulting in abnormal engine operation.

AST GMBH sensor structure

It consists of two parts: the scale grating and the grating readhead. The figure on the right shows the structure of the linear encoder 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. Grating readheads come in many structural forms; based on their structural characteristics and application scenarios, they are classified as direct-receiving readheads (also known as silicon photovoltaic cell readheads, mirror-image readheads, beam-splitter readheads, or metal grating reflective readheads).

AST GMBH sensor principle

The essence of a grating displacement sensor is to use the grating pitch as a standard ruler for measurement. 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 adopt electronic subdivision methods. When two gratings overlap with a slight angle, Moiré fringes are generated in a direction roughly perpendicular to the grating lines. As the grating moves, the Moiré fringes also move up and down. 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 certain intervals can achieve electronic subdivision and direction discrimination functions. For example, for a grating scale with 50 line pairs/mm, its grating pitch is 0.02mm. If four-fold subdivision is adopted, counting pulses with a resolution of 5μm can be obtained, which has reached a very high precision in general industrial measurement and control. Since displacement is a vector, both its magnitude and direction must be detected, so 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 usually used. The 4 photoelectric signals obtained from 4 photosensitive devices are sent to the input terminals of 2 differential amplifiers respectively. The two signals output from the differential amplifier have a phase difference of π/2. To obtain direction discrimination and counting pulses, these two signals need to be shaped, first shaping them into square waves with a duty cycle of 1:1. Then, by discriminating and comparing the phase of the square waves, the movement direction of the grating scale can be obtained. By counting the square wave pulses, the displacement and speed of the grating scale can be obtained.

AST GMBH sensor usage precautions

When plugging or unplugging the connector between the linear encoder 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 linear encoder sensor. Regularly check whether the mounting and connection screws are loose. To extend the service life of the dust-proof sealing strip, apply a thin, even layer of silicone oil to the strip, taking care not to splash it onto the engraved surface of the glass grating. To ensure reliable operation of the linear encoder sensor, clean and wipe the scale surface and the index grating surface at regular intervals using an ethanol mixture (50%) to keep the glass grating scale surface clean. The linear encoder sensor must be protected from severe vibration and impact to avoid damaging the scale; if the scale breaks, the sensor will fail. Do not disassemble the linear encoder sensor yourself, and never arbitrarily change the relative gap between the main scale and the secondary scale. Doing so may compromise the sensor's accuracy and cause relative friction between the main and secondary scales, damaging the chrome layer and thus the grating lines, which renders the scale unusable. Take care to prevent oil and water contamination of the scale surface, as this can disrupt the grating line pattern and cause measurement errors. Avoid operating the linear encoder sensor in environments with severe corrosive effects to prevent corrosion of the chrome layer and the scale surface, which would degrade the quality of the scale.

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