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Excitation Fault Detection

Last Modified: April 18, 2018

Two NI-DAQmx Read attributes/properties allow you to check for excitation faults. The first is ExcitFaultChansExist. This attribute/property returns a Boolean of true if one or more channels experience an excitation fault condition. The second is ExcitFaultChans. This attribute/property returns an array of strings indicating which channels (if any) experienced an excitation fault condition. You must query the ExcitFaultChansExist attribute/property before querying the ExcitFaultChans attribute/property.

ExcitFaultChansExist reads the excitation fault condition from the device and stores it in NI-DAQmx. Subsequent reads of ExcitFaultChans will read the excitation fault channel information stored in NI-DAQmx from the previous ExcitFaultChansExist query.

NI-DAQmx returns all data regardless of whether an excitation fault happens. If your application needs excitation fault checking, you should read the excitation fault attributes/properties after each call to read. Your program should discard questionable data or return a flag when NI-DAQmx reports an excitation fault.

The NI 9218 can detect if there is an overcurrent fault between Ex+ and Ex- pins of either channel for either the strain mode case or the powered sensor measurement case. When the NI 9218 is configured for powered sensor measurement, which requires a +12 V excitation, it can also detect the absence of the required 9-30 V external power supply connected to the Vsup terminal. Both of these types of faults are reported as excitation faults.

The PXIe-4340 can detect if there is an overcurrent fault between the Ex+ and Ex- pins of any channel. This fault occurs when a voltage source is connected to the Ex+ and Ex- pins of any channel, or the load impedance is too low (excessive current). Ensure that only the primary winding of an LVDT/RVDT sensor is connected to the Ex+ and Ex- pins of any channel on this module.

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