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Chapter 2
Using the Module
LVDTs are frequently used in applications where ruggedness, operation over large temperature
ranges, insensitivity to contamination, or long life are important considerations. They are
extremely reliable in harsh conditions.
An RVDT is the rotational version of an LVDT. The angular measurement range of typical
RVDTs is between ±30° and ±70°.
Resolvers are similar to RVDTs, but employ secondaries at right angles that produce two
simultaneous signal voltages proportional to the sine and cosine of the shaft angle. Thus,
resolvers can measure over 360° of rotation and do not need to pass through 0° before making
absolute position measurements, as is required by quadrature encoders.
LVDTs, RVDTs, and resolvers are advantageous in hostile operating environments. Resolvers
are often easier to use than RVDTs. All that is needed to convert measured voltages to degrees
is an arctangent function; there are no scaling considerations.
Synchros function similarly to resolvers, but have three secondaries (stators) that produce three
simultaneous signals proportional to the sine of the shaft position, each offset by 120°.
Therefore, synchros can measure over 360° of rotation with a unique combination of stator
voltages across the entire range.
Remote Sense
Remote sense continuously and automatically corrects for errors in excitation leads. Its use is
most critical in applications that employ long wires and/or small gauge wires, as these have
higher resistance. The resistance in the wires that connect the excitation voltage to the primary
winding causes a voltage drop, which is a source of gain error. The PXIe-4340 includes remote
sense to compensate for this gain error. Connect remote sense inputs of the PXIe-4340 to the
excitation voltage wires of the sensor as close to the sensor as possible. Refer to Figures 2-3
through 2-7.
Due to the unique digital demodulation employed on the PXIe-4340, remote sense can also be
used to sense the excitation of synchronized channels to measure accurate ratios across channels
for sensors with multiple secondaries, such as resolvers and synchros. Refer to the
sections for more information.
