**Variable Inductance Transducers**

Inductance is a measure that relates electrical flux to current . Inductance reactance is a measure of the inductive effect and can be expressed as:

X = 2p*f*L

where X is the inductive reactance in ohms, *f* is the frequency of the applied voltage in Hz and L is the inductance in henryâs.

The inductance of a circuit is influenced by a number of factors, including:

1) the number of turns in a coil

2) the coil size

3) the permeability of the flux path

As a result of a mechanical displacement the permeability of the flux path is altered and a resulting change in the inductance of the system occurs. Inductance is monitored through the resonant frequency of the inductance coils to an applied voltage. As inductance changes, the resonant frequency of the coils changes. Electronic circuits that convert frequency to voltage are used to gain a voltage output to inductive transducers.

Inductive transducers can be classified as follows:

1) Variable self inductance: single coil, two coil

2) Variable mutual inductance: simple two coil, three coil

3) Variable reluctance: moving iron, moving coil, moving magnet

The various arrangements of that lead to the above classifications are shown in Figures 7, 8 and 9.

Figure 7 Simple self inductance arrangement [4]

Figure 8 Two coil inductive pickup for an electronic micrometer [4]

Figure 9 A simple variable reluctance pickup [4]

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Support for the development of this module was provided by the National Science Foundation and The Cooper Union for the Advancement of Science and Art.

Please send questions or comments to Professor Ron Adrezin or Professor Daniel Raichel.