German Hagglunds sensors Hagglunds models Hagglunds prices

Hagglunds sensors are components that convert changes in non-electrical quantities (such as speed and pressure) into changes in electrical quantities. Depending on the non-electrical quantity being converted, they can be classified into pressure sensors, speed sensors, temperature sensors, etc., and serve as parts and accessories for measurement and control instruments and equipment.

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

Hagglunds sensor principle

The essence of a grating displacement sensor is to measure position 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 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 certain intervals enables electronic subdivision and direction judgment functions. For example, for a grating scale with 50 line pairs/mm, the grating pitch is 0.02mm. If four-fold subdivision is used, 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; 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 respectively. The two signals output from the differential amplifier have a phase difference of π/2. To obtain direction judgment 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.

Hagglunds 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. Add a protective cover whenever possible, and promptly clean chips and oil splashed onto the scale to strictly prevent any foreign matter from entering the grating scale sensor housing. Regularly check whether the installation screws are loose. To extend the life of the dust-proof sealing strip, apply a thin layer of silicone oil evenly on the sealing strip, taking care not to splash it onto the glass grating engraved 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 (each 50%) at regular intervals to keep the glass grating scale surface clean. Grating scale sensors are strictly prohibited from severe vibration or impact to avoid damaging the grating scale; if the grating scale breaks, the sensor will fail. Do not disassemble the grating scale sensor yourself, and never arbitrarily change the relative spacing between the main grating and the secondary grating. Otherwise, it may damage the precision of the grating scale sensor on one hand, and cause relative friction between the main and secondary gratings on the other, damaging the chromium layer and thus the grating lines, resulting in the scrapping of the grating scale. Prevent oil stains and water from contaminating the grating scale surface to avoid disrupting the distribution of grating lines and causing measurement errors. Grating scale sensors should avoid working in environments with severe corrosion to prevent corrosion of the grating chromium layer and the grating scale surface, which would degrade the quality of the grating scale.

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