Fetch Operation

Channels Tab

The Channels tab contains a list control with the default channels for the selected logical name. Use the Add and Remove buttons to add new channels and remove existing channels from the list. You can specify whether the oscilloscope acquires a waveform for the channel by enabling the channel in the list control.

The Channels tab for the Read operation also contains the following channel-specific options:

• Name —The name of the channel to read. The channel name must be a valid virtual channel name as the IVI configuration for the logical name being used defines.
• Waveform Type —The type of data to retrieve from the oscilloscope. Depending on this value, the returned data is a single value (for a measurement), a one-dimensional array (Waveform), or a two-dimensional array (Waveform Min Max).

  Supported Value	Description
  Amplitude (15)	High Voltage less the Low Voltage, in volts, over the entire waveform.
  Negative Duty Cycle (13)	Ratio of the Negative Width to the Period of an integer number of cycles in the waveform, expressed as a percentage.
  Positive Duty Cycle (14)	Ratio of the Positive Width to the Period of an integer number of cycles in the waveform, expressed as a percentage.
  Fall Time (1)	Length of time, in seconds, for a falling edge of the signal to fall from the high reference level to the low reference level.
  Frequency (2)	Frequency, in hertz, of one complete cycle in the waveform.
  Overshoot (18)	Relative waveform distortion that follows an edge transition.
  Period (3)	Length of time, in seconds, of one complete cycle in the waveform.
  Preshoot (19)	Relative waveform distortion that precedes an edge transition.
  Rise Time (0)	Length of time, in seconds, for a rising edge of the signal to rise from the low reference level to the high reference level.
  Average Voltage (10)	Arithmetic average, in volts, measured over the entire waveform.
  Cycle Average Voltage (17)	Arithmetic average, in volts, over an integer number of cycles in the waveform.
  Cycle Rms Voltage (16)	True root-mean-square (RMS) voltage over an integer number of cycles in the waveform.
  High Voltage (8)	Voltage that corresponds to 100% when using the reference levels. The oscilloscope calculates this value using either the min/max or histogram methods. The min/max method uses the maximum value found. The histogram method uses a common value found above the middle of the waveform.
  Low Voltage (9)	Voltage that corresponds to 0% when using the reference levels. The oscilloscope calculates this value using either the min/max or histogram methods. The min/max method uses the minimum value found. The histogram method uses a common value found below the middle of the waveform.
  Max Voltage (6)	Maximum amplitude, in volts, found in the entire waveform.
  Min Voltage (7)	Minimum amplitude, in volts, found in the entire waveform.
  Peak To Peak Voltage (5)	Absolute difference, in volts, between the Max Voltage and the Min Voltage.
  Rms Voltage (4)	True root-mean-square (RMS) voltage of the entire waveform.
  Negative Width (11)	Length of time, in seconds, between the mid-reference level points of a negative pulse in the waveform.
  Positive Width (12)	Length of time, in seconds, between the mid-reference level points of a positive pulse in the waveform.
  Waveform (-1)	Specifies that the Read or Fetch operation acquires a waveform with the current configuration. If specified, Read returns a one-dimensional array of points.
  Min/Max (-2)	Specifies that the Read or Fetch operation acquires a min-max waveform that is a two-dimensional array. This constant is valid only when Acquisition Type is set to Peak Detect or Envelope.

• Data Type —Specifies whether the step expects a single value, an array of values, or a wave pair. The step coerces the data type of the elements in the array property, Step.Result.Reading , to NI_IviSinglePoint , NI_IviWave , or NI_IviWavePair , respectively.
• Measurement Destination —A variable or property to which the step assigns the measurement value. For single values, the data type of the variable or property must be Number or NI_IviSinglePoint . For an array of values, the data type of the variable or property must be array of Number or NI_IviWave . For a wave pair, the data type of the variable or property must be a two-dimensional array of Number or NI_IviWavePair . The default configuration for the step specifies Step.Result.Reading as the destination. This property is an array of container where the size of the array is equal to the number of channels specified for the Read or Fetch operation. When you edit the step, the step automatically resizes the array and coerces the data type of each element of the array to NI_IviSinglePoint , NI_IviWave , or NI_IviWavePair , based on the value of the Data Type control for each channel. If you do not specify Step.Result.Reading as the destination, TestStand copies the measurement value to the Data subproperty in each array element at run time unless the Copy Data to Execution Results option is disabled.
• Set Status if Over-Range —The status for the step result when a timeout condition occurs. When you leave this control blank, the step does not check for an over-range condition.
• Copy Data to Execution Results —When you enable this option, the TestStand copies the measurement value stored in the property Step.Result.Reading.Data to the step result. When you enable this control, TestStand does not include the measurement in a report or log the measurement to a database. This setting is always enabled for single-point measurements.
• Timeout (mS) —The timeout, in milliseconds, for the operation. The Timeout setting applies to the length of time between initializing a call to Read and completing the data acquisition, not the time the instrument requires for computations or to transfer data across the instrumentation bus. To set an infinite timeout, set Timeout to -1 .
• Set Status on Timeout —The status for the step result when a timeout condition occurs. When you leave this control blank, the step ignores timeout conditions.