Integrated Electronic Piezoelectric Excitation (IEPE)

If you attach an IEPE accelerometer or microphone to an AI channel that requires excitation from a device such as a DSA device, NI 9230, NI 9231, NI 9232, NI 9234 or an NI 9250, you must enable the IEPE excitation circuitry for that channel to generate the required current. IEPE signal conditioning can be independently configured on a per-channel basis.

To enable the IEPE current source on your device, use the Channel attribute/property AI.Excit.Val to specify a current in amperes. Some devices allow multiple excitation current values such as 0.004 A and 0.01 A. Other devices allow only a single value such as 0.004 A. A value of 0 A disables the IEPE excitation. Refer to the device documentation for details on your device.

Note

• You cannot enable IEPE excitation on DSA devices when the terminal configuration is differential. The exception is NI 9218 which has optional IEPE excitation and supports a differential terminal configuration.
• Changing the IEPE excitation level may cause transient voltages to appear in the signal. NI-DAQmx does not implement a delay to allow the signal to settle. Therefore, after changing the IEPE level and committing this change to the hardware with the Start function/VI or the Control Task function/VI, you might add a software delay to allow the signal to settle before proceeding with your application.

A DC offset is generated equal to the product of the excitation current and sensor impedance when IEPE signal conditioning is enabled. To remove the unwanted offset, you should enable AC coupling. Using DC coupling with IEPE excitation enabled is appropriate only if the offset does not exceed the voltage range of the channel.