Figure 11.1
(a)
(a) The LVDT with a movable core and three windings, and (b) the secondary volt-
(b)
are shown wired in series opposition. This gives zero output voltage, as shown in Figure 11.1(b), when the core is centrally positioned. An output voltage propor- tional to displacement is obtained for limited travel. These devices are not as cost-effective as potentiometers, but have the advantage of being noncontact. The outputs are electrically isolated, accurate, and have better longevity than potentiom- eters.
Figure 11.2(a) shows an alternative method of connecting the output windings of the LVDT using a special interfacing IC. A phase-sensitive detector is used to give a linear output with displacement, as shown in Figure 11.2(b). A variety of LVDTs is available, with linear ranges from ±1 mm to ±25 cm. The transfer function is nor- mally expressed in mV/mm.
Capacitive devices can be used to measure angular or linear displacement. The capacitance between two parallel plates is given by:
age Vs core displacement for the connections.
C = 8.85KA/d pF
Figure 11.1(a)(a) The LVDT with a movable core and three windings, and (b) the secondary volt-(b)are shown wired in series opposition. This gives zero output voltage, as shown in Figure 11.1(b), when the core is centrally positioned. An output voltage propor- tional to displacement is obtained for limited travel. These devices are not as cost-effective as potentiometers, but have the advantage of being noncontact. The outputs are electrically isolated, accurate, and have better longevity than potentiom- eters.Figure 11.2(a) shows an alternative method of connecting the output windings of the LVDT using a special interfacing IC. A phase-sensitive detector is used to give a linear output with displacement, as shown in Figure 11.2(b). A variety of LVDTs is available, with linear ranges from ±1 mm to ±25 cm. The transfer function is nor- mally expressed in mV/mm.Capacitive devices can be used to measure angular or linear displacement. The capacitance between two parallel plates is given by:age Vs core displacement for the connections.C = 8.85KA/d pF
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