Linear variable displacement transducers LVDTs

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... 

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-... 

FIG. 12 Shear tester. A constant normal load N is applied over the lid, acting like a piston. A motor moves the lower compartment, and a shear load cell measures the shear force necessary to maintain the upper compartment still. Two linear variable displacement transducers (LVDTs) measure the horizontal and vertical displacements in the cell. 

An old but still properly working Perkin Elmer IMS-1 was adapted to perform TSD/TMA experiments. The TMS-1 is schematically drawn in Figure 6.1 together with some of the important dimensions. The sample, between the probe and the quartz glass sample holder is placed in the furnace. The furnace temperature is programmed to increase linearly with the time. The thermal expansion of the sample is measured via the probe by the linear variable displacement transducer (LVDT). A thermocouple, placed as close as possible to the sample is giving the sample tenperature information. 

A schematic of a commercial TMA instrument is shown in Fig. 16.33. The instrument consists of a dimensionally stable (with ternperamre) sample holder and measuring probe, a programmable furnace, a linear variable displacement transducer (LVDT) to measure the change in length, a means of applying force (load) to the sample via the probe (core rod, push rod), and a temperature sensor (usually a thermocouple). 

Figure 5 Schematic illustraticm of the MASIF (measurement and anal5rsis of surface interaction forces) SFA. The upper surface is mounted on a piezo ceramic actuator that is used for changing the surface separation the hysteresis of the piezo expansion/ contraction cycle can be accounted for hy using a linear variable displacement transducer (LVDT). The lower surface is mounted on a bimorph force sensor. (From Ref. 26, with permission.)...

The cylindrical specimen is placed into the steel load frame of the testing device, similar to the one used in the indirect tensile test. The measurement of horizontal deformation can be carried out by load transducers (linear variable displacement transducers [LVDTs]), with an arrangement similar to Figure 7.2, or by strain gauges with extensometers (see Figure 7.3). 

Real-time measurement of the structural response was achieved by using an electronic data acquisition system. Several instruments were used to monitor the specimen behavior linear variable displacement transducers (LVDTs) to monitor the global deformed shape and the joint panel shear strain a potentiometer on tip beam to monitor the actual displacement imposed by the actuator to the specimen strain gauges on internal steel rebars to record their strains at ends of beam and columns and strain gauges on CFRP quadriaxial sheet along fibre directions to monitor FRP strains at joint panel. 

The earthquake engineering experimental facility at Northeastern University provides large-scale dynamic testing of soil samples under uniform cyclic or earthquake motions. It includes a shaking table (Fig. 21.2), a data acquisition card (NI-DAQ) and software (LabVIEW), a set of instmments including accelerometers (Crossbow, Ig, 2g, 5g, Fig. 21.3a), linear variable displacement transducers (LVDT, RDP DCTH400AG, Fig. 21.3b), miniature pore pressure transducers (GE Druck PDCR 81, Fig. 21.3c), and multiple bender element and bending disk measurement equipment for S and P wave measurements (Fig. 21.3c-e). 

Both the TMA and DMA apply force and measure the displacement that results from this stimulus. Most TMAs and DMAs currently in production use linear variable displacement transducers (LVDTs) to measure displacement. There is one exception, which is the TA Instruments 2980, or later variant Q800, which uses an optical displacement transducer instead. 

Fig. 21.3 Instruments used in Earthquake Engineering Experimental Eacility at Northeastern University (a) Crossbow Accelerometer (b) LVDT (Linear Variable Displacement Transducer) (c) GE Druck PDCRSlminiature pore pressure transducer (d) HP Eunction generator, power amplifier and Yokogawa Oscilloscope (e) Bender element (f) Bending disk...

On the other hand, there may be instances when seemingly unstable fractures are in fact valid stable fractures. The inability to adequately detect stable crack extension results in the appearance of an unstable test and the presumption of an invalid result. A variety of methods have been used to verify stability such as load-point displacement (LPD) as determined from the linear variable differential transducer (LVDT) used to control the test system actuator center-point displacement (CPD) as determined using an LVDT or capacitance extensometer placed in or near the flexure fixture a time record as generated with an XY recorder or strain as monitored with a strain gage centered about the crack plane on the compressive or back-face of the test specimen [12,13]. In addition, laser extensometers have also been used [14]. 

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 ... 

Linear variable differential transformer (LVDT, Fig. 2) is a device that produces voltage proportional to the position of a core rod inside a cylinder body. It measures displacement or a position of an object relative to some predefined zero location. On tablet presses, LVDTs are used to measure punch displacement and in-die thickness. They generally have very high precision and accuracy, but there are numerous practical concerns regarding improper mounting or maintenance of such transducers on tablet presses. 

Displacements of the test specimen relative to the table or relative displacements between parts of the specimen are monitored either with Celesco draw wire displacement transducers or with Linear Variable Differential Transformers (LVDT), whichever is most convenient... 

The displacement transducer shown in Fig. 5 is generally one of two types. A linear-variable differential transformer (LVDT) is effectively a transformer where the coupling to the secondary winding(s) is a function of the position of a movable magnetic core. A capacitive displacement transducer (CDT) is a capacitor where the... 

Figure 14.6. Schematic diagram of the three-point support flexural test h, sample thickness LVDT, Linear Variable Differential Transformer displacement transducer R = 46.75 mm [69]...

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