A piezo-optic measuring transducer is disclosed herein and an accelerometer, a pressure gauge, a dynamometer, and a thermometer based thereon.The piezo-optic measuring transducer comprises two polarization-optical channels. Each of these channels includes the following components arranged in series downstream the luminous flux produced by a light source: a polarizer, an elastic element which is common to both channels and sensitive to stress variations therein caused by a variation in the measurand, an analyzer, and a photocell. Both channels are provided with a means for varying the intensity of the luminous flux incident upon one of the photocells which intensity variation is opposite in polarity to that in the luminous flux incident upon the other photocell.
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Both photocells are arranged in a differential relationship with the difference in the electrical signals produced thereby being representative of the measurand. An accelerometer, a pressure gauge, a dynamometer, and a thermometer can be provided on the basis of said transducer. What is claimed is:1. The present invention relates to primary measuring transducers wherein a mechanical stress variation in an elastic element caused by a variation in the measurand, such as pressure, acceleration, force or temperature, is converted into an electrical parameter, and more particularly the invention relates to piezo-optic measuring transducers and to accelerometers, pressure gauges, dynamometers, and thermometers based thereon.Known in the art are measuring transducers in which a stress variation in the elastic element thereof causes a variation in a respective electrical parameter.
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These are, for example, tensoresistive (strain) transducers wherein a mechanical stress variation in the elastic element thereof brings about a variation in the electrical resistance of the tensoresistors (strain gauges) rigidly coupled therewith.By virtue of their simplicity and tiny size, these transducers have found wide application in technology and scientific research. However, tensoresistive transducers fail to provide for sufficiently high outputs in response to insignificant deformations of their elastic elements, which results in limited frequency response characteristics in dynamic measurements, as well as in more complicated amplifying and recording means in static measurements. This is due to the fact that the change in the resistance of the strain gauge, caused by a variation in the mesurand, is relatively small, hence the low level of the output signal which, regardless of the configuration of the tensoresistive (strain) transducer is in the same ratio to the supply voltage as the strain gauge resistance variation to its initial resistance.Magnetoelastic measuring transducers are much more sensitive and produce a stronger output signal. A typical transducer of this kind comprises an elastic element made from a ferromagnetic material, which forms part of the magnetic circuit of the electrical system, the magnetic circuit including one or more coils. As the elastic element is under stress, the current through the coils of the magnetic circuit changes proportionally to the change in the measurand.Since the magnetic and mechanical properties of the known ferromagnetic materials suitable for making elastic elements are not adequate enough, the field of applicatikon of such transducers is limited. They are mostly used as industrial transducers for measuring large-scale values.Low-scale forces, pressures, accelerations, etc.
Are normally measured by means of piezotransistor measuring transducers exhibiting high sensitivity and miniature size.The elastic (sensitive) element of such transducers is made from a ceramic or single-crystal material possessing piezoelectric properties, hence, when it is subjected to mechanical stress, an electric charge appears across its faces. Being advantageous in many respects, these transducers are used extensively. However, due to the fact that their amplitude-frequency response lacks uniformity in the low-frequency band, these transducers cannot be used for studying processes the spectra whereof have low-frequency components. For the same reason, they should be calibrated by dynamic methods, with involves a number of engineering problems. Piezoelectric transducers have a low-power output. This is one of the reasons for the poor noise-proof characteristics of the measuring system, which affects the accuracy of measurement.Noted for improved noise-proof characteristics are transducers in which the measurand is converted into an output frequency variation. Such transducers include a vibrating member (i.e.
Working PrincipleThe vibrations are measured with a tightly focused laser beam of a Michelson interferometer, thus employing the same measurement principle as the. The recorded displacements at each pixel can be analysed in the time or frequency domain. In addition, the instrument is equipped with a lock-in amplifier which allows for the direct imaging of bending modes without the need for data post-processing.The scanning of the measurement laser over the sample is performed by a 3D SmarAct positioning system that makes it possible to image structures with sizes from just a few µm up to 20 mm. Because closed loop piezo positioners with nm resolution are used, the positioning of the laser beam is highly reproducible.In order to excite the sample, vibrations can be either induced by the advanced piezo-based shaker stage or directly with an electrical signal that is generated by the PICOSCALE Vibrometer.A unique feature of the PICOSCALE Vibrometer is that the interferometer laser beam is used simultaneously to record a microscopy image of the sample. This microscopy image is thus intrinsically aligned with the vibration measurements and a separate microscope imaging system is not required. SpecificationsFor each of the of the PICOSCALE vibrometer, a detailed specification sheet is available at the download section.
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Vibration MeasurementsVibration Resolution 1 pm.
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January 2023
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