Acquire Signals from Charge Mode Sensors

Updated Aug 30, 2018

Reported In

Hardware

  • PXI Sound and Vibration Module
  • PXIe-4480
  • C Series Sound and Vibration Input Module

Issue Details

I have a charge mode piezoelectric sensor, and its sensitivity is specified in units of charge per engineering unit - such as in the case of a pC/g accelerometer. How can I acquire a signal from it using NI DSA hardware?

Solution

The PXIe-4480 supports the use of charge mode piezoelectric sensors without the need of any additional circuitry; for more information you can reference the PXIe-4480/4481 User Manual in the Related Links section below.

Other NI DSA devices are designed to function only with IEPE or ICP® sensors. These sensors contain both a piezoelectric element, as with charge mode sensors, and extra integrated electronics, namely an amplifier. This amplifier converts the high impedance charge signal from the piezoelectric crystal into a low impedance voltage signal that can be more easily digitized. As a result of adding active circuitry (i.e., the amplifier), the IEPE sensor will require excitation between 2-20 mA, which NI DSA cards are also capable of providing along the same coaxial cable as the measured signal. Thus, in order to acquire signals from a charge mode sensor, which lacks internal amplification, you will need to provide an external charge amplifier to convert the high impedance charge signal to a low impedance voltage signal. You can then measure the amplifier's output voltage signal with your NI DSA device. 

Consult the manufacturer of your sensor to select the appropriate external amplifier for your application. Depending on the type of amplifier, it may require 2-20 mA excitation, in which case NI DSA cards can be used to excite and read back from the amplifier over the same coaxial connection. If the amplifier requires some other type of excitation, then you will need to use a separate external power supply to excite the amplifier. Also, consult the specification sheet for your NI DSA device to ensure that, after amplification, your amplifier's output signal still falls within the DSA device's input range and compliance voltage specifications.

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