Counter Input >> General Properties >> More >> Advanced >> Data Transfer and Memory >> Number Of Possibly Invalid Samples

NI-DAQmx C Reference Help

Edition Date: January 2019

Part Number: 370471AM-01

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Data Type: uInt32
Description: Indicates the number of samples that the device might have overwritten before it could transfer them to the buffer.

On certain devices during finite buffered time measurements, it is not possible to detect if the counter overwrites a value it read before the device could transfer the sample to the buffer. This uncertainty is present only when Data Transfer Mechanism is DAQmx_Val_DMA and occurs as the acquisition nears completion.

Once the acquisition completes, it is impossible to tell if the status value on the counter indicates an overwrite as a result of a true overwrite, or because the counter detected another edge of the input signal after the acquisition completed but before the counter could disarm. As a result of this behavior, higher frequency input signals are more likely to increase the number of possibly invalid samples.

To decrease the number of possibly invalid samples, read more often from the buffer. Reading from the buffer forces a check on the hardware status and ensures all data is valid up to the present point in the buffer. By default, NI-DAQmx checks the validity of data every fourth of the buffer. If you do not perform a read until after the device acquires all data, the value of this property is one-fourth of the buffer size or zero.

The value this property indicates is valid only while the task is in the running state. The value of this property while the task is in any other state is zero.

Restrictions: Not Settable

You can get this property using:



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