Multifunction DAQ
Simultaneously AI and AO
Hello Jason,
The buffer overwrite error (-200279) you are seeing is caused by the fact that the analog input task in your program is not reading data from the buffer fast enough to prevent the buffer from filling up with data and overwritting existing samples. You can monitor the amount of data sitting in the buffer at any given time using the Available Samples Per Channel property of the DAQmx Read Property Node.
As for the size of the buffer used, the DAQmx driver chooses this automatically depending on the sampling rate you specify. You can manually override this and specify a larger buffer using the DAQmx Configure Input Buffer.vi.
In my experience, just increasing the buffer size only delays the time until an overwrite error occurs. I find it better to decrease the sampling rate and/or increase the number of samples to read until you find a set of options where the number of available samples per channel stays fairly constant.
I hope this helps,
Travis G.
Applications Engineering
National Instruments
www.ni.com/support
The buffer overwrite error (-200279) you are seeing is caused by the fact that the analog input task in your program is not reading data from the buffer fast enough to prevent the buffer from filling up with data and overwritting existing samples. You can monitor the amount of data sitting in the buffer at any given time using the Available Samples Per Channel property of the DAQmx Read Property Node.
As for the size of the buffer used, the DAQmx driver chooses this automatically depending on the sampling rate you specify. You can manually override this and specify a larger buffer using the DAQmx Configure Input Buffer.vi.
In my experience, just increasing the buffer size only delays the time until an overwrite error occurs. I find it better to decrease the sampling rate and/or increase the number of samples to read until you find a set of options where the number of available samples per channel stays fairly constant.
I hope this helps,
Travis G.
Applications Engineering
National Instruments
www.ni.com/support
Message Edited by Travis G. on 09-18-2006 11:49 AM
Hello Jason,
The sampling info input to the Basic Function Generator.vi used within that example allows you to specify how the data points of the waveform are created within LabVIEW. You can specify how many data points are created and the spacing between those points with the Fs (sampling frequency in samples per second) and #s (number of samples in the waveform) inputs to that function. The Basic Function Generator.vi will output a waveform data type, which consists of three components:
1. The array of data points to be generated.
2. T0 - the inital time of the first data point.
3. dt - the spacing between the data points in the waveform.
However, when you actually generate that data using DAQ hardware, those data points will be generated at the rate you specify with the rate input of the DAQmx Timing VI. If you want to just use the timing information contained within the waveform data type, select the Use Waveform instance of the DAQmx Timing VI instead of the Sample Clock instance. This way, you can just wire the waveform data into the DAQmx Timing VI and the driver figures out the rate based on the timing information contained within.
Regards,
Travis G.
Applications Engineering
National Instruments
www.ni.com/support
The sampling info input to the Basic Function Generator.vi used within that example allows you to specify how the data points of the waveform are created within LabVIEW. You can specify how many data points are created and the spacing between those points with the Fs (sampling frequency in samples per second) and #s (number of samples in the waveform) inputs to that function. The Basic Function Generator.vi will output a waveform data type, which consists of three components:
1. The array of data points to be generated.
2. T0 - the inital time of the first data point.
3. dt - the spacing between the data points in the waveform.
However, when you actually generate that data using DAQ hardware, those data points will be generated at the rate you specify with the rate input of the DAQmx Timing VI. If you want to just use the timing information contained within the waveform data type, select the Use Waveform instance of the DAQmx Timing VI instead of the Sample Clock instance. This way, you can just wire the waveform data into the DAQmx Timing VI and the driver figures out the rate based on the timing information contained within.
Regards,
Travis G.
Applications Engineering
National Instruments
www.ni.com/support
Message Edited by Travis G. on 09-19-2006 02:07 PM
