German SPM sensor SPM model SPM price

SPM 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 as pressure sensors, speed sensors, temperature sensors, etc., and serve as parts and accessories for measurement and control instruments and equipment.

SPM 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, condenser lens, index grating, photoelectric elements, and adjustment mechanisms. There are many structural forms of grating readheads, which are 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 reflection readheads.

SPM 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 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 determination. 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 amplifiers 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.

SPM sensor usage precautions

Power off before plugging or unplugging the connector between the linear encoder sensor and the digital readout. Install an external protective cover whenever possible, promptly remove chips and oil splashed onto the scale, and 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 scale and the secondary scale. Doing so may compromise the accuracy of the linear encoder sensor and may also cause relative friction between the main and secondary scales, damaging the chrome layer and thus the grating lines, which renders the linear encoder scale unusable. Take care to prevent oil contamination and water from polluting 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 chrome layer on the grating and the surface of the linear encoder scale, which would degrade the quality of the linear encoder scale.

Weidou Intelligent Technology specializes in selling German SPM sensors, SPM proximity sensors, SPM distance sensors, SPM vision sensors, SPM displacement sensors, SPM torque sensors, SPM speed sensors, SPM photoelectric sensors, SPM position sensors, SPM angle sensors, SPM tactile sensors, SPM temperature sensors, SPM pressure sensors, SPM flow sensors, SPM level sensors, SPM motion sensors, and SPM process sensors. Original imports from Germany. Welcome inquiries and orders from users.