Overload Detection

DSA devices support overload detection in both the analog domain (pre-digitization) and digital domain (post-digitization). An analog overrange can occur independently from a digital overrange, and vice versa. For example, an IEPE accelerometer might have a resonant frequency that, when stimulated, can produce an overrange in the analog signal. However, because the delta-sigma technology of the ADC uses very sharp anti-aliasing filters, the overrange is not passed into the digitized signal. Conversely, a sharp transient on the analog side might not overrange, but the step response of the delta-sigma anti-aliasing filters might result in clipping in the digital data.

Some DSA devices support both analog and digital overload detection, while others support only digital overload detection. Consult your device documentation for more information on the overload detection capabilities for your device.

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

OverloadChansExist reads the overload condition from the device and caches it in the driver. It also resets the overload condition of the device after it is read. Subsequent reads of OverloadedChans attribute/property will read the overloaded channel information cached in the driver from the previous OverloadChansExist query.

Note  NI-DAQmx returns all data whether or not an overload occurs. If your application requires overload checking, it is recommended that you read the overload attributes/properties after each call to Read. Your program should discard questionable data or return a flag when the driver reports an overload.