Linear variable displacement transducers

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. 5 Diagram example of a universal testing machine for bulk density testing during compression (from Thomson, 1997). LYDT, linear variable displacement transducer. 

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). 

Plots of sample temperature versus dimensional (or volume) changes enable the Tg to be obtained. The Tg is obtained from measurement of sudden changes in the slope of the expansion cnrve. In the thermo-mechanical analyser, a quartz probe closely monitors dimensional changes in the sample being studied. The position of this probe is continuously monitored by a high-sensitivity, linear variable displacement transducer. The transducer itself is temperature controlled to provide excellent... 

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). 

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...

Direct methods for measuring the strain that results from applying a field or vice versa, applying a strain, and measming the accumulated charge are ahim-dant. Interferometers, dilatometers, fiher-optic sensors, optical levers, linear variable displacement transducers, and optical methods are employed to evaluate the piezoelectric strain (converse effect) (69-72). The out-of-plane or thickness piezoelectric coefficient dss can he ascertained as a function of the driving field and frequency. The coefficient is measmed based on the equation... 

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. 

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