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IviDigitizer Fetch Multi Record Waveform Int16 [MRA] (G Dataflow)

Last Modified: October 24, 2017

Returns the (multi-record) waveform the digitizer acquired for the specified channel. The waveform is from a previously initiated acquisition.The acquired waveform records can be retrieved all together, or in chunks. You specify the first record and the number of consecutive records to fetch. Note that the record number is zero-based, and reset when you initiate a new acquisition, i.e. record 0 is the first record of the last acquisition. The Actual Records output indicates how many of the requested records have actually completed successfully. The Actual Points, First Valid Point, Initial X Offset, Initial X Time Seconds and Initial X Time Fraction ouputs have a value for each record, and therefore are arrays of size NumRecords. However, if the value of ActualRecords is smaller than the requested number of records, these arrays shall have only their first ActualRecords elements valid. If a NULL pointer is passed in for any of these parameters, the driver ignores it.

The value of First Valid Point is relative to the start of the waveform array, such that:

Sample i of record R = WaveformArray[FirstValidPoint[R]+i]

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Note  

You must use the IviDigitizer Initiate Acquisition node to start a multi-record (Num Record > 1) acquisition on the channels that the end-user configures with the IviDigitizer Configure Channel node. The digitizer acquires waveforms on the concurrently enabled channels. If the channel is not enabled for the acquisition, this node returns the channel not enabled error.

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You can use the IviDigitzer Acquisition Status node to determine when the acquisition is complete. You must call the IviDigitizer Fetch Multi Record Waveform Int16 node separately for each enabled channel to obtain the waveforms. Alternatively, you can use the IviDigitizer Wait For Acquisition Complete node to block the calling program until the acquisition is finished.

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After this node executes, each element in the Waveform Array output is an unscaled value directly from the digitizer's analog-to-digital converter (ADC).

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This node does not check the instrument status. Typically, the end-user calls this node only in a sequence of calls to other low-level driver nodes. The sequence performs one operation. The end-user uses the low-level nodes to optimize one or more aspects of interaction with the instrument. Call the IviDigitizer Error Query node at the conclusion of the sequence to check the instrument status.

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The data type of the returned waveform array is ViInt16.

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This node is part of the IviDigitizerMultiRecordAcquisition [MRA] extension group.

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Initial X Offset

The time in relation to the Trigger Event of the first point in the waveform in seconds. Negative values mean that the first point in the waveform array was acquired before the trigger event.

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Initial X Time Seconds

Specifies the seconds portion of the absolute time at which the first data point was acquired. Note that the actual time is the sum of Initial X Time Seconds and Initial X Time Fractionn. The time is specified as the sum of two values because a single double-precision floating-point number does not have sufficient range and resolution to specify the time.

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Initial X Time Fraction

Specifies the fractional portion of the absolute time at which the first data point was acquired. Note that the actual time is the sum of Initial X Time Seconds and Initial X Time Fraction. The time is specified as the sum of two values because a single double-precision floating-point number does not have sufficient range and resolution to specify the time.

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Waveform Array

Buffer into which the acquired waveform is stored. Notes: This array is always user allocated, and it must contain at least as many elements as the value you specify with theWaveform Array Size parameter.

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Actual Records

Indicates how many records in the acquisition completed successfully.

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Actual Points

Indicates how many data points were actually retrieved from the instrument for each completed record. This is an array of size at least Num of Records or a NULL pointer. For IVI-C, this array is always user allocated.

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First Valid Point

Indicates the index of the first valid data point in the output Data array for each completed record. This value will often be zero. However, some digitizer hardware designs transfer data most efficiently when the data is aligned with specific memory address boundaries. In those cases, the hardware may return a few invalid data points at the beginning of a record. This eliminates the need to shift the data during the transfer, ensuring maximum data transfer rates. This is an array of size at least Num of Records or a NULL pointer. For IVI-C, this array is always user allocated.

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X Increment

The time between points in the acquired waveform in seconds.

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Scale Factor

Scaling factor for the waveform data.

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Scale Offset

Scaling offset for the waveform data.

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Num of Points Per Record (256)

Specifies the number of data points to return. This number may be larger than the amount of data available. Use the Actual Points output to determine how many data points were returned. Default Value: 256

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Offset Within Record (0)

Specifies the start index within the record from which the data should be retrieved. While normally zero, this parameter allows users to retrieve partial records using non-zero values. Data that comes before the Offset Within Record index will not be retrieved. This is perhaps most useful when retrieving very large data records because it allows records to be retrieved in several smaller chunks. Default Value: 0

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Num of Records (256)

Specifies the number of consecutive records to read. If Num of Records is greater than 1, this input allows full or partial (if Offset Within Record and Num of Points Per Record are specified accordingly) data to be retrieved from multiple digitizer records in a single Fetch call. If Num of Records is less than or equal to zero, an error will be returned. Default Value: 256

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First Record (0)

Specifies the number of the first record to read. Default Value: 0

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Channel Name ("")

Specifies the name of the channel from which to retrieve the data. Users who want to achieve interchangeability should use a virtual channel name. The virtual channel name should be sufficiently specific to the test system such that it is unlikely to conflict with a physical channel name. Default Value: "" Note: You can specify the trace name as a string variable or as a literal enclosed in double quotes.

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Waveform Array Size (256)

Specifies the allocated size of the WaveformArray buffer, in number of data points. If this value is smaller than the total number of points to be retrieved, the driver will fill the waveform buffer as fully as possible and return the actual number of points retrieved in the Actual Points parameter. Default Value: 256

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instrument handle out

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

Default: None

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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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instrument handle

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

Default: None

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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