German GROUP CENTRAL sensor, GROUP CENTRAL model, GROUP CENTRAL price

GROUP CENTRAL sensor is a sensor that measures the air flow drawn into the engine. For electronically controlled gasoline injection engines, 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 fuel injection, which will cause the mixture to be too rich or too lean, resulting in abnormal engine operation.

GROUP CENTRAL 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 part of the grating detection device is the grating readhead, which consists of a light source, condensing lens, index grating, photoelectric elements, and adjustment mechanisms. There are many structural forms of grating readheads, classified based on structural characteristics and application scenarios into direct-receiving readheads (also known as silicon photovoltaic cell readheads, mirror-image readheads, beam-splitter readheads, and metal grating reflective readheads).

GROUP CENTRAL 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 use 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 move up and down accordingly. This converts the measurement of grating pitch into the measurement of the number of Moiré fringes. Within one Moiré fringe width, placing 4 photoelectric devices at specific intervals enables electronic subdivision and direction determination. 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, which achieves high precision in general industrial measurement and control. Since displacement is a vector, both its magnitude and direction must be detected, requiring at least two photoelectric signals with different phases. 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 respectively. The two signals output from the differential amplifier have a phase difference of π/2. To obtain direction determination and counting pulses, these two signals need to be shaped, first into square waves with a duty cycle of 1:1. Then, by comparing the phase of the square waves, the movement direction of the grating scale can be determined. By counting the square wave pulses, the displacement and speed of the grating scale can be obtained.

GROUP CENTRAL sensor usage precautions

When plugging and unplugging the connector of the linear encoder sensor and the digital readout unit, ensure the power is turned off. Install an external protective cover whenever possible, and promptly remove 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 sealing strip, taking care not to let it splash onto the glass grating etched surface. To ensure reliable operation of the linear encoder sensor, periodically clean and wipe the linear encoder scale surface and the index grating surface with an ethanol mixture (each 50%), keeping the glass linear encoder scale surface clean. The linear encoder sensor must not be subjected to severe vibration or impact, as this may damage the linear encoder scale; if the scale fractures, the linear encoder sensor will fail. Do not disassemble the linear encoder sensor yourself, and never arbitrarily change the relative spacing between the main grating scale and the secondary grating scale. Doing so may compromise the accuracy of the linear encoder sensor and cause relative friction between the main and secondary grating scales, damaging the chrome layer and thus the grating lines, which renders the linear encoder scale unusable. Take care to prevent oil stains and water from contaminating the linear encoder scale surface, as this can disrupt the distribution of the grating lines and cause measurement errors. Avoid operating the linear encoder sensor in environments with severe corrosive effects, to prevent corrosion of the grating chrome layer and the linear encoder scale surface, which would degrade the quality of the linear encoder scale.

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