LIPS(linear inductive position sensor)is used for measuring the position over a range from 1 mm to 1.5 m. It typically relies on variations that occur in the self inductance of coils as a rod of magnetic material slides in or out of them. The rod, or target, shown below is connected to a moving object by a plastic or other non-inductive link.
This circuit is a bridge circuit, which has the two sections of the coil in two of the arms and it has 2 capacitors in the other two arms. To keep the bridge resonating the bridge is fed with a 1 MHz signal. The degree of amplitude of the alternating signal at vOUT largely relies on the relative self inductance
of the two sections of the coil. The target is conductive (normally aluminium) but not magnetic, so that the alternating field of the coil tends to induce eddy currents in it. These have the effect on the inductance of the coils, by varying their amounts and values, depending on what fraction of the target is within each of the coils. The output is sampled at the same stage in each cycle to provide with a DC signal. The DC voltage is associated to the position of the target and to the position of the object to which the target is coupled. Primary interface of this sensor is an integrated circuit that is running on a 5-V supply. The output typically ranges from 0 V to 5 V as the target is moved over its full range. As in our prior examples, variations in the measure have been converted to variations in a voltage which can be measured, displayed, or recorded in different manners.
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