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software. This means that open coil detection will report open coils on the unused excitation
lines with sensors that use multiple channels and one excitation, such as synchros and resolvers.
Overcurrent Detection
The PXIe-4340 is protected against overcurrents and overvoltages on the excitation terminals.
If excessive current is detected at either of the excitation pins, a relay at the output disables the
excitation for approximately one second. This prevents damage to the module, but may cause
erroneous readings. Overcurrent conditions are reported to software.
Signal Acquisition Considerations
This section contains information about signal acquisition concepts, including operation modes,
delta-sigma converters, filtering, timing, triggering, and synchronization.
Excitation Verification
The TB-4340 provides excitation verification pins that are pulled to the excitation lines by
4.7 k
resistors. These terminals allow external gross checks for monitoring the excitation of
the PXIe-4340. The resistors prevent faults on the excitation verification pins from affecting
excitation, but reduce the accuracy of the voltage measured because the higher impedance is
more sensitive to loading from the verification instrument.
Demodulation
The PXIe-4340 digitizes oversampled data, which is digitally demodulated. The digital
demodulation process uses constant delay filters to extract the relative amplitudes and phases of
the voltages on the primary and secondary LVDT windings. The amplitudes are divided to
determine the ratiometric voltage and the phase is used to determine the sign. Small amplitude
signals can cause the phase detector to become noisy.
ADC
The PXIe-4340 ADCs use a conversion method known as delta-sigma modulation. This
approach involves oversampling the input signal and then decimating and filtering the resulting
data to achieve the desired sample rate. The PXIe-4340 supports rates of 1 S/s to 25.6 kS/s.
Operation Modes
The PXIe-4340 supports two modes of operation: Buffered Mode and Hardware-Timed Single
Point Mode. In a Buffered Mode acquisition, oversampled data is decimated to your requested
sample rate and digital filters are applied to filter out frequency content above the Nyquist
frequency. These digital filters introduce group delay and for some applications this may be
undesirable. For this reason, the PXIe-4340 also supports Hardware-Timed Single Point Mode
in which the oversampled data is only filtered in the demodulator to reduce the group delay.
