Displacement transducer

Eddy-current proximity probes are primarily used as displacement transducers. Eddy probes generate an eddy-current field, which is absorbed by a conducting material at a rate proportional to the distance between the probe and the surface. They are often used to sense shaft motion relative to a bearing (by mounting them within the bearing itself) or to measure thrust... 

Asif, S.A.S., Wahl, K.J. and Colton, R.J., Nanoindentation and contact stiffness measurement using force modulation with a capacitive load-displacement transducer. Rev. Sci. Instrum., 70, 2408-2413 (1999). 

Displacement is the actual change in distance or position of an object relative to a reference point and is usually expressed in units of mils, 0.001 inch. For example, displacement is the actual radial or axial movement of the shaft in relation to the normal centerline usually using the machine housing as the stationary reference. Vibration data, such as shaft displacement measurements acquired using a proximity probe or displacement transducer, should always be expressed in terms of mils peak-to-peak. 

Technically, peak-to-peak values should be used in conjunction with actual shaft-displacement data, which are measured with a proximity or displacement transducer. Peak-to-peak terms should not be used for vibration data acquired using either relative vibration data from bearing caps or when using a velocity or acceleration transducer. The only exception is when vibration levels must be compared to vibration-severity charts based on peak-to-peak values. 

Most generators have relatively soft support structures. Therefore, they require shaft vibration monitoring measurement points in addition to standard casing measurement points. This requires the addition of permanently mounted proximity, or displacement, transducers that can measure actual shaft movement. 

Permanently mounted displacement probes will provide the most accurate data on machines with a low rotor weight, relative to the casing and support structure. Turbines, large process compressors, and other plant equipment should have displacement transducers permanently mounted at key measurement locations to acquire data for the program. 

Data are generated by placing a test specimen between the two flat, parallel faces of a testing machine and then moving these faces together at a specified rate (ASTM D 695). A displacement transducer may be used to measure the compression of the specimen, while a load cell measures the compressive force exerted by the specimen on the testing machine. Stress and strain are computed from the measured compression load, and these are plotted as a compressive stress-versus-strain curve for the material at the temperature and strain rate employed for the test. 

Mehta and Augsburger [68] later reported the mounting of a linear variable displacement transducer (LVDT) on the previously instrumented Zanasi LZ-64 machine [54] to allow the measurement of piston... 

In addition to imaging applications, the sensitivity of the STM may be implemented as a displacement transducer. For example, the small dis-... 

The displacement of the center part of the cover glass is continuously monitored by a displacement transducer. The actual measurements were performed using a modified thermo-mechanical system (TMS), a Perkin Elmer TMS-2 apparatus. 

Free end displacement by optical displacement transducers. Input from shaker electrical measurements E M E M... 

Electrical output transducers exist in many forms and consist simply of elastic elements coupled with suitable displacement transducers such as capacitance, inductance and reluctance pick-ups, certain types of strain gauge, piezoelectric elements, potentiometers and eddy current probes. A selection of these is described in the following paragraphs. 

Elastic elements such as diaphragms and capsules are used as sensing elements in combination with different displacement transducers (e.g. inductive, potentiometric, etc.) for low/medium vacuum measurements down to about 1 torr. Elastic elements have been employed in conjunction with capacitive transducers for the measurement of pressures as low as 10 5 torr. 

The deformation of the sample and the electrical potential difference over the sample were measured. The electrical potential difference between both electrodes were amplified by a Unicam 9460 amplifier (Unicam, USA). During the experiments, the displacement of the piston was recorded via a linear variable displacement transducer (LVDT, Schaevitz, USA). The data acquisition sampling was 0.5 Hz. A vibrator was attached to the set-up in order to overcome the sticking of the piston to the wall. This device vibrated intermittently at 50 Hz during 1 second. The vibration started 0.5 second after the data-acquisition. Lateral forces on the piston were minimised by allowing free lateral motion of the measuring chamber floating on a silicon oil film. Further-... 

The operation of proximity sensors can be based on a wide range of principles, including capacitance, induction, Hall and magnetic effects variable reluctance, linear variable differential transformer (LVDT), variable resistor mechanical and electromechanical limit switches optical, photoelectric, or fiber-optic sensors laser-based distance, dimension, or thickness sensors air gap sensors ultrasonic and displacement transducers. Their detection ranges vary from micrometers to meters, and their applications include the measurement of position, displacement, proximity, or operational limits in controlling moving components of valves and dampers. Either linear or angular position can be measured ... 

The Advantages of Digital Displacement Transducers Over LVDT s, Anter Laboratories, Inc., Unitherm Division, Pittsburgh, PA (1992). 

CAL-41S Calibrator, Linear and Angular Displacement Transducers, Catalog 101, Lucas Schaevitz, Pennsauken, NJ, p. 30 (1990). 

The first measurement of upper punch displacement was performed in the mid-1950s by Higuchi and co-workers [62, 71] with the aid of inductive displacement transducers. By the same instrumentation the movement of the lower punch can be visualized. Inductive transducers are mounted parallel to the punch and thus give information on punch position. Alternatively touchless measurement of displacement is possible. It is important that the transducers be positioned most closely to the punch in order to minimize the influence of machine deformation. 

The specimen deflection was recorded during the test using a displacement transducer connected to the load-points. 

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