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All dynamic signal acquisition (DSA) devices and some data acquisition (DAQ) devices with anti-aliasing filters or other filter protection have an input filter delay for which you might need to compensate. When acquiring a tachometer signal with an analog data acquisition channel, you do not have to compensate for the input filter delay. The vibration, sound, and tachometer acquisition channels use the same anti-aliasing filter, and the vibration, sound, and tachometer signals therefore contain the same delay. A counter device does not have an anti-aliasing filter that delays the signal. If you acquire the tachometer signal with a counter device, you must compensate for the input filter delay in the vibration or sound acquisition channel. Use the OAT Build Digital Tacho Info VI to compensate for the acquisition channel input filter delay.

For the NI?46x, NI?47x, and NI 449x series DSA devices, and for the NI 9229, NI 9233, NI 9234, and NI 9239 C Series devices, the OAT Build Digital Tacho Info VI computes the phase delay automatically. For other types of DAQ devices, you must specify the appropriate device information to perform the compensation. You can find the group delay information for individual DAQ devices in the device specifications.