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IviScope Fetch Waveform (G Dataflow)

Last Modified: October 24, 2017

Returns the waveform the oscilloscope acquires for the channel you specify. The waveform is from an acquisition that you initiate prior to calling this node.

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error out

Error information.

The node produces this output according to standard error behavior.

Standard Error Behavior

Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.

error in does not contain an error error in contains an error
If no error occurred before the node runs, the node begins execution normally.

If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.

If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.
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error in

Error conditions that occur before this node runs.

The node responds to this input according to standard error behavior.

Standard Error Behavior

Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.

error in does not contain an error error in contains an error
If no error occurred before the node runs, the node begins execution normally.

If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.

If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.

Default: No error

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x increment

Indicates the length of time between points in the Waveform Array. Units: seconds

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waveform array

Returns the waveform that the oscilloscope acquires. Units: volts

Configuring Interpolation

Testing a Waveform Value

You can test a waveform value for an invalid value condition by calling the IviScope Is Invalid Waveform Element node.

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initial x

Indicates the time of the first point in the Waveform Array. The time is relative to the trigger event. For example, if the oscilloscope acquires the first point in the Waveform Array 1 second before the trigger, this parameter returns the value -1.0. If the acquisition of the first point occurs at the same time as the trigger, this parameter returns the value 0.0. Units: seconds

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actual points

Indicates the number of points the node places in the Waveform Array parameter.

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waveform size

Value representing the expected size of the waveforms that the oscilloscope acquires. That value is greater than or equal to the minimum number of points you specify in the IviScope Configure Acquisition Record Node.

Determining Waveform Size

Default: 1000

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channel name ("CHANNEL1")

Pass the virtual channel name that you assign to the instrument in the Configuration Utility from which you want to fetch a waveform measurement.

Achieving Interchangeability

Using Virtual Channel Names

The virtual channel name should be sufficiently specific to the test system such that it is unlikely to conflict with a physical channel name. Virtual channel names are aliases for instrument-specific channel strings. The instrument-specific channel strings can differ from one instrument to another. Virtual channel names allow you to use and swap instruments without having to change the channel names in your source code. You assign a virtual channel name to an instrument-specific channel through the Configuration Utility. This control accepts virtual channel names you have assigned to the specific instrument you are using. It also accepts the instrument-specific channel names.

Default: CHANNEL1

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instrument handle out

The instrument handle that you obtain from the IviScope Initialize or IviScope Initialize With Options node. The handle identifies a particular instrument session.

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instrument handle

The instrument handle that you obtain from the IviScope Initialize or IviScope Initialize With Options node. The handle identifies a particular instrument session.

Initiating Acquisition prior to Calling IviScope Fetch Waveform

You use the IviScope Initiate Acquisition Node to start an acquisition on the channels that you enable with the IviScope Configure Channel Node. The oscilloscope acquires waveforms for the enabled channels concurrently. You use the IviScope Acquisition Status Node to determine when the acquisition is complete. You must call this node separately for each enabled channel to obtain the waveforms. You can call the IviScope Read Waveform Node instead of the IviScope Initiate Acquisition Node. The IviScope Read Waveform Node starts an acquisition on all enabled channels, waits for the acquisition to complete, and returns the waveform for the channel you specify. You call this node to obtain the waveforms for each of the remaining channels.

Waveform Array Parameter

After this node executes, each element in the Waveform Array parameter is either a voltage or a value indicating that the oscilloscope could not sample a voltage.

Configuring Interpolation

You configure the interpolation method the oscilloscope uses with the IviScope Configure Interpolation [I] Node. If you disable interpolation, the oscilloscope does not interpolate points in the waveform. If the oscilloscope cannot sample a value for a point in the waveform, the driver sets the corresponding element in the Waveform Array to an IEEE defined NaN (Not a Number) value and the node returns IVISCOPE_WARN_INVALID_WFM_ELEMENT (0x3FFA2001).

Testing a Waveform Value

You can test a waveform value for an invalid value condition by calling the IviScope Is Invalid Waveform Element Node.

Instrument Status and IviScope Fetch Waveform

The IviScope Fetch Waveform node does not check the instrument status. Typically, you call this node only in a sequence of calls to other low-level driver nodes. The sequence performs one operation. You use the low-level nodes to optimize one or more aspects of interaction with the instrument. If you want to check the instrument status, call the IviScope Error-Query Node at the conclusion of the sequence.

Configuring a Simulated Waveform

The class driver returns a simulated waveform when this node is called and the IviScope>>Inherent IVI Settings>>User Options>>Simulate property is set to TRUE and the IviScope>>Inherent IVI Settings>>User Options>>Use Specific Simulation property is set to FALSE. For information on how to configure a simulated waveform, refer to the online help manual.

Where This Node Can Run:

Desktop OS: Windows

FPGA: Not supported

Web Server: Not supported in VIs that run in a web application


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