Linear variable differential transformer LVDT

A TMA analyser will need to measure accurately both the temperature of the sample, and very small movements of a probe in contact with the surface of the sample. A typical analyser, as illustrated in Figure 11.20(a) and (b), uses a quartz probe containing a thermocouple for temperature measurement, and is coupled to the core of a linear variable differential transformer (LVDT). Small movements at the sample surface are transmitted to the core of the LVDT and converted into an electrical signal. In this way samples ranging from a few microns to centimetre thicknesses may be studied with sensitivity to movements of a few microns. For studying different mechanical properties the detailed construction of the probe will vary as is illustrated in Figure 11.20(c). 

Linear-variable-differential-transformer (LVDT) transducers, 20 652-653 Linear velocity, exponents of dimensions in absolute, gravitational, and engineering systems, 8 584t Lineatin, 24 473 Line-block coders, 7 691 Line-edge roughness (LER), 15 181 Line exposures, in photography, 19 209-210 Linen... 

An associated type of transducer is the Linear Variable Differential Transformer (LVDT) which is essentially a transformer with a single primary winding and two identical secondary windings wound on a tubular ferromagnetic former. The primary winding is energised by an a.c. source (see Fig. 6.13). 

FlO. 6.13. Linear variable differential transformer (LVDT) using C-type Bourdon tube as... 

A device which provides accurate position indication throughout the range of valve or control rod travel is a linear variable differential transformer (LVDT), illustrated in Figure 6. Unlike the potentiometer position indicator, no physical connection to the extension is required. 

The position can also be determined in a resistive or voltage mode. In the resistive mode, a current is sent to the center tap and to one of the end terminals, whereas the resulting voltage drop is measured by the transmitter. A potentiometer has an infinite resolution. Linearity for a precision rotary potentiometer can be as good as 0.25%. However, due to linkages and gears, the linearity for the entire assembly usually is about 0.5-1%. A linear variable differential transformer (LVDT) is mostly used in linear motion applications and also inside some pressure transmitters (Figure 3.131). 

The operating principle of an (linear variable differential transformer) LVDT-type sensor. 

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 ... 

Mechanical properties of the composite materials were tested by a hydraulic-driven MTS tensile tester manufactured by MTS Systems Corporation, Minneapolis, Minnesota. A strain-rate of 5x 10 5 s 1 was used. During deformation, the linear actuactor position was monitored and controlled by a linear variable differential transformer (LVDT), while strain was measured using MTS-brand axial and diametral strain-gauge extensometers. The axial extensometer serves to measure the tensile deformation in the direction of loading while the diametral extensometer serves to measure the compressive deformation at 90° to the loading axis due to Poisson s contraction. All tensile tests were performed at 23 °C and in accordance to ASTM D3518-76. 

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. 

The instruments have a furnace, and mostly a linear variable differential transformer (LVDT) to produce an electrical signal from a linear movement. An additional unit controls the force applied. Special attachments allow the same instrument to work in different modes such as elongation, compression, penetration, or tension. 

Tensile and compressive tests were performed at room temperature with a tensile testing machine (DY25, Adamel-Lhomargy). For the tensile tests, strain measurements were performed with an extensometer (EX-10) at a strain rate of 3.3 x 10-4 s-1, using ISO-60 standard specimens. Samples of dimension 20 x 12 x 6 mm were deformed in a compression cage between polished steel plates. The nominal strain was determined by averaging the results from two linear variable differential transformer (LVDT) transducers. The strain rate used was 8.3 x 10"4 s-1. 

Instrumentation - load cell, linearly variable differential transformer (LVDT), clip gage, etc. 

A widely used sensor in physiological research and clinical medicine is the linear variable differential transformer (LVDT). It is used to measure pressure, displacement and force (Reddy and Kesavan 1988). The LVDT is composed... 

Changes in the dimensions of a sample are detected by a mechanical, optical or electrical transducer although the transducer is usually a linear variable differential transformer (LVDT). The sample may be positioned either vertically or horizontally. The latter usually introduces friction between the sample and the support tube, which may be reduced to acceptable levels but never totally eliminated (l). Vertical dilatometers overcome the prob-... 

After calibration, a block-shear specimen was positioned in the profilometer. Two stepper motors, controlled by timed relays, were used to maneuver the specimen under the laser. Specimen position was measured by two linear variable differential transformers (LVDTs), one placed on each axis. A data acquisition system was configured to capture sensor outputs at the rate of 30 Hz. Initially the specimen was scanned across the non-bonded portion of the adherend (Fig. 5). About 1000 sensor readings were acquired for each profile (or about one reading per 25 pm). The specimen was then advanced 1 mm lengthwise and ain scanned across its width. This process was repeated up to 25 times to define a precise beam grid (Fig. 5) for scanning all specimens. 

FIGURE 2.1 Examples of displacement sensors (a) variable resistance sensor, (b) foil strain gauge, (c) linear variable differential transformer (LVDT), (d) parallel plate capacitive sensor, and (e) ultrasonic transit time-displacement sensor. 

With these requirements an automated multistation tester was built and controlled by an inexpensive microcomputer. Five samples were run simultaneously with linear variable differential transformers (LVDT s) monitoring the shear adhesion process to a resolution of better than 10 inches. Testing surface temperatures were measured and controlled to + 0.05°C. Via a data compression scheme, the entire event regardless of length of time can be represented by thirty data points or less. In this study, smooth stainless steel surfaces were used. The schematic diagram for the apparatus is presented in Fig. 2. 

Uniaxial tension tests were performed at room temperature at a constant strain rate (50 pm/mn). The load was measured using a 500 N load cell. The minicomposite elongation was measured using two-parallel linear-variable differential transformer (LVDT) extensometers that were attached to the grips. Extensometers were located on each side of specimens, in order to control specimen alignment. 

Measurement of Length by a Linearly Variable Differential Transformer, LVDT... 

---