German TELEMETRY sensor TELEMETRY model TELEMETRY price

TELEMETRY sensors are devices that convert magnetic signals into electrical signals. By utilizing the transformation relationship between magnetic quantities and other physical quantities, with the magnetic field as a medium, they can also convert signals of other non-electrical physical quantities into electrical signals. There are two driving methods: one is driven by a permanent magnet, and the other is driven by an electromagnetic coil. The former is mostly used for detection; for example, if a moving part is made of a magnet, it will attract and emit a signal once it approaches the magnetic induction sensor. The latter is mostly used for control; if the electromagnetic coil is energized, the contacts will attract. Using magnetic induction sensors to replace limit switches that rely on collision contact can improve system reliability and service life; therefore, they are often used in programmable logic controllers (PLCs) as signaling devices for position arrival.

TELEMETRY 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 part of the grating measuring 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, 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 structural characteristics and application scenarios.

TELEMETRY sensor principle

The essence of a grating displacement sensor is to measure position using the grating pitch as a standard ruler. High-resolution linear encoder 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 inclination angle, Moiré fringes are generated in the 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, its grating pitch is 0.02mm. If four-fold subdivision is adopted, 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 usually employed. 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.

TELEMETRY sensor usage precautions

When plugging and unplugging the connector of the linear encoder sensor and the digital readout unit, ensure the power is switched 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 strip, taking care not to splash it 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 (50%) to keep 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 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 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 chrome layer and the surface of the linear encoder scale, which would degrade its quality.

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