LVDT

Linear-Variable-Differential-Transformer and Reluctive Pressure Transducers. In ahnear-vatiable-differential-transformer (LVDT) pressure transducer, the pressure to be measured is fed to a Bourdon tube or diaphragm. The motion of this element is transferred to the... 

Fig. 39. Schematic of the TA Instmments model 2940 thermomechanical analyzer. LVDT = linear variable differential transducer.

Figure 6.18 Micro Force Balance (A) stage, (B) and (C) micromanipulators, (D) objective, (E) temperature controller device, (F) flexible blade, (G) travelling platform, (FT) travel piezo adjuster, (/) and (L) LVDT after Pratola etal., 2000)...

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... 

Using the dilatometer technique, a small sample of powder (about 1 -2 grams) is heated at constant rate in the apparatus depicted schematically in Fig. 43. Dilatation of the sample is measured by a linear voltage transducer (LVDT) contraction of the sample indicates particle-particle surface flattening and defines the minimum softening point ox sintering temperature, Ts. In... 

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... 

THREE AXIAL LVDT S PARALLEL TRACES INDICATE UNIFORM SPECIMEN SEPARATION... 

LVDT—linear variable differential transformer, A/D—analogue to digital, VDU—visual... 

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... 

Bourdon tube) is reflected in the position of the ferromagnetic core of the LVDT and is thus a function of the difference between the input and output voltages measured in terms of phase shift and amplitude ratio (see Section 7.8.4). 

Commercial LVDTs have a full range stroke from 0.1 to 80 mm with a sensitivity of about 25 to 1250 V/m depending upon the frequency of excitation and size of stroke. 

Fig. 6.35. Buoyancy meter with totally immersed float and LVDT sensing-element...

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-... 

Figure 7.13 Electric field induced macroscopic strain measurements of tetragonal and rhombohedral co-doped pzt using lvdt...

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 extension valve shaft, or control rod, is made of a metal suitable for acting as the movable core of a transformer. Moving the extension between the primary and secondary windings of a transformer causes the inductance between the two windings to vary, thereby varying the output voltage proportional to the position of the valve or control rod extension. Figure 6 illustrates a valve whose position is indicated by an LVDT. If the open and shut position is all that is desired, two small secondary coils could be utilized at each end of the extension s travel. 

LVDTs are extremely reliable. As a rule, failures are limited to rare electrical faults which cause erratic or erroneous indications. An open primary winding will cause the indication to fail to some predetermined value equal to zero differential voltage. This normally corresponds to mid-stroke of the valve. A failure of either secondary winding will cause the output to indicate either full open or full closed. 

As described above, position detection devices provide a method to determine the position of a valve or control rod. The four types of position indicators discussed were limit switches, reed switches, potentiometer valve position indicators, and LVDTs (Figure 7). Reed and limit switches act as ON/OFF indicators to provide open and closed indications and control functions. Reed switches can also be used to provide coarse, incremental position indication. 

Potentiometer and LVDT position indicators provide accurate indication of valve and rod position throughout their travel. In some applications, LVDTs can be used to indicate open and closed positions when small secondary windings are used at either end of the valve stem stroke. 

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. 

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