Biomedical Engineering Reference
In-Depth Information
FIGURE 2-22
Demodulation of LVDT output. (a) Circuit diagram. (b) Relationship between
displacement and output voltage.
FIGURE 2-23
Photograph of a
range of LVDTs.
(Courtesy of RDP
Electronics http://
www.rdpe.com/.)
LVDTs are also less sensitive to variations in temperature than the other linear encoders
discussed so far, but their main disadvantage is a limited frequency response. This is
determined by the inertial effects associated with the core's mass, the choice of excitation
frequency, and the bandwidth of the low-pass filter at the output (Alciatore and Histand,
2003).
Measurement of angles using the same principle is by means of a rotary variable
differential transformer (RVDT). In this case a rotary ferromagnetic core is used with
linear ranges of
40
◦
possible, with a nonlinearity error of about 1% (Fraden, 1996).
+
/
−
2.4.2.2 Inductosyns and Resolvers
Other inductive angle measurement systems include resolvers and inductosyns. Resolvers
resemble small motors and are essentially rotary transformers designed so that the
