Read Operation

The Read operation initiates and returns a measurement from an instrument. Read is a higher-level acquisition operation that encapsulates some of the details of using the Initiate and Fetch operations. If the Sample Count setting is greater than 1 and the Multi Point extension is enabled, the Read operation returns an array of values. Otherwise, the operation returns a single value.

The returned value is either the actual reading the Measurement Function setting defines, or a value that indicates that an over-range condition occurred.

If an over-range condition occurs, the reading parameter contains an IEEE-defined not a number (NaN) value. To test a value for the over-range condition, specify a status expression in the Set Status if Over-Range control. If a timeout occurs before the Read operation completes, the Set Status on Timeout control determines the step status .

The Read operation contains the following options:

• Data Type —Specifies whether the step expects a single value or array of values. The step coerces the data type of the Step.Result.Reading property to NI_IviSinglePoint or NI_IviWave , respectively.
• Measurement Destination —A variable or property, as the following table describes, to which the step assigns the measurement value.

  Value Type	Data Type of the Variable or Property
  Single values	Number or NI_IviSinglePoint
  Array of values	Array of Number or NI_IviWave

  The default configuration for the step specifies Step.Result.Reading as the destination. When you edit the step, the step automatically coerces the data type of the Step.Result.Reading property to NI_IviSinglePoint or NI_IviWave , based on the value of the Data Type control. If you do not specify Step.Result.Reading as the destination, TestStand copies the measurement value to the Step.Result.Reading.Data property at run time unless the Copy Data to Execution Results option is disabled.
• 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 DMM 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.
• 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, TestStand copies the measurement value stored in the property Step.Result.Reading.Data to the step result. When you disable this control, TestStand cannot include the measurement in a report or log the measurement to a database. For single-point measurements, this option is always enabled.