Data Acquisition Toolbox

The Sampling Rate

You control the rate at which an analog input subsystem converts analog data to digital data with the SampleRate property. SampleRate must be specified as samples per second. For example, to set the sampling rate for each channel of your National Instruments board to 100,000 samples per second (100 kHz)

• ai = analoginput('nidaq',1);
  addchannel(ai,0:1);
  set(ai,'SampleRate',100000)
  

Data acquisition boards typically have predefined sampling rates that you can set. If you specify a sampling rate that does not match one of these predefined values, there are two possibilities:

• If the rate is within the range of valid values, then the engine automatically selects a valid sampling rate. The rules governing this selection process are described in the SampleRate reference pages in Base Property Reference.
• If the rate is outside the range of valid values, then an error is returned.

Note    For some sound cards, you can set the sampling rate to any value between the minimum and maximum values defined by the hardware. You can enable this feature with the StandardSampleRates property. Refer to Device-Specific Property Reference, for more information.

For hardware that supports simultaneous sampling of channels (sound cards and Agilent Technologies devices), the maximum sampling rate for each channel is given by the maximum board rate. For scanning hardware (most National Instruments and Measurement Computing devices), the per-channel sampling rate is given by the maximum hardware rate divided by the number of channels contained by the device object.

After setting a value for SampleRate, you should find out the actual rate set by the engine.

• ActualRate = get(ai,'SampleRate');
  

Alternatively, you can use the setverify function, which sets a property value and returns the actual value set.

• ActualRate = setverify(ai,'SampleRate',100000);
  

You can find the range of valid sampling rates for your hardware with the propinfo function.

• ValidRates = propinfo(ai,'SampleRate');
  ValidRates.ConstraintValue
  ans =
    1.0e+005 *
      0.0000    2.0000
  

Configuring Analog Input Properties

Trigger Types