Table Of Contents

IviScope Read Waveform Measurement [WM] (G Dataflow)

Last Modified: October 24, 2017

Initiates an acquisition on all channels that you enable with the IviScope Configure Channel Node. The node then waits for the acquisition to complete and returns the waveform measurement for the channel you specify.

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channel name

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

Achieving Interchangeability

Virtual Channel Names

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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measurement

Returns the measured value. Units: The units depend on the Measurement Function you select.

Measurement Functions

Rise Time seconds
Fall Time seconds
Frequency hertz
Period seconds
Voltage RMS volts
Voltage RMS (Cycle) volts
Voltage Max volts
Voltage Min volts
Voltage Vpp volts
Voltage High volts
Voltage Low volts
Voltage Avg. volts
Voltage Avg. (Cycle) volts
Width Negative seconds
Width Positive seconds
Duty Cycle Negative percent
Duty Cycle Positive percent
Amplitude volts
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measurement function

Pass the waveform measurement you want the oscilloscope to perform.

Defined Values

IVISCOPE_VAL_FALL_TIME Rise Time - The length of time for the first rising edge of the signal to rise from the low reference level to the high reference level.
IVISCOPE_VAL_FALL_TIME Fall Time - The length of time for the first falling edge of the signal to fall from the high reference level to the low reference level.
IVISCOPE_VAL_FREQUENCY Frequency - The frequency of one complete cycle in the waveform.
IVISCOPE_VAL_PERIOD Period - The length of time of one complete cycle in the waveform.
IVISCOPE_VAL_VOLTAGE_RMS Voltage RMS - The true Root Mean Square voltage of the entire waveform.
IVISCOPE_VAL_VOLTAGE_CYCLE_RMS Voltage RMS (Cycle) - The true Root Mean Square voltage over the first cycle in the waveform.
IVISCOPE_VAL_VOLTAGE_MAX Voltage Max - The maximum amplitude found in the entire waveform.
IVISCOPE_VAL_VOLTAGE_MIN Voltage Min - The minimum amplitude found in the entire waveform.
IVISCOPE_VAL_VOLTAGE_PEAK_TO_PEAK Voltage Vpp - The absolute difference between the Voltage Max and the Voltage Min.
IVISCOPE_VAL_VOLTAGE_HIGH Voltage High - The voltage that corresponds to 100% when you use 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 the most common value found above the middle of the waveform.
IVISCOPE_VAL_VOLTAGE_LOW Voltage Low - The voltage that corresponds to 0% when you use 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 the most common value found below the middle of the waveform.
IVISCOPE_VAL_VOLTAGE_AVERAGE Voltage Avg. - The arithmetic average amplitude of the entire waveform.
IVISCOPE_VAL_WIDTH_NEG Width Negative - The length of time between the mid reference level points of the first negative pulse in the waveform.
IVISCOPE_VAL_WIDTH_POS Width Positive - The length of time between the mid reference level points of the first positive pulse in the waveform.
IVISCOPE_VAL_AMPLITUDE Amplitude - The Voltage High less the Voltage Low in Volts over the entire waveform.
IVISCOPE_VAL_OVERSHOOT Overshoot - The relative waveform distortion which follows an edge transition. It is calculated using the following formula: - for the rising edge: OVERSHOOT = ((local maximum - Voltage High)/Amplitude)*100% where the local maximum is the maximum voltage of the signal in the first half of the time period that commences when the rising edge crosses the high reference level and concludes when the subsequent falling edge crosses the high reference level.

For the rising edge: OVERSHOOT = ((local maximum - Voltage High)/Amplitude)*100% where the local maximum is the maximum voltage of the signal in the first half of the time period that commences when the rising edge crosses the high reference level and concludes when the subsequent falling edge crosses the high reference level.

For the falling edge: OVERSHOOT = ((Voltage Low - local minimum)/Amplitude)*100% where the local minimum is the minimum value of the signal measured in the first half of the time period that commences when the falling edge crosses the low reference level and concludes when the subsequent rising edge crosses the low reference level. The instrument makes the measurement on the edge closest to the beginning of the waveform record.

Configuring Reference Levels

You must configure the appropriate reference levels before you call this function. You configure the low, mid, and high references either by calling the IviScope Configure Reference Levels Node or by setting the following properties: IviScope>>Waveform Measurement>>Measurement High Reference [WM] IviScope>>Waveform Measurement>>Measurement Low Reference [WM] IviScope>>Waveform Measurement>>Measurement Mid Reference [WM].

Default: IVISCOPE_VAL_RISE_TIME

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maximum time

Value indicating the maximum length of time in which to allow the read waveform operation to complete. Units: milliseconds.

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Note  

The Maximum Time parameter applies only to this node. It has no effect on other timeout parameters or properties.

IVISCOPE_ERROR_MAX_TIME_EXCEEDED Error

Defined Values

IVISCOPE_VAL_MAX_TIME_INFINITE (-1)
IVISCOPE_VAL_MAX_TIME_IMMEDIATE (0)

Default: 5000 (ms)

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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.

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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

IVISCOPE_ERROR_CHANNEL_NOT_ENABLED Error

If the channel you specify in the Channel Name parameter is not enabled for the acquisition, this node returns the IVISCOPE_ERROR_CHANNEL_NOT_ENABLED (0xBFFA2001) error.

IVISCOPE_ERROR_MAX_TIME_EXCEEDED Error

If the oscilloscope did not complete the acquisition within the time period you specify with the Maximum Time parameter, the node returns the IVISCOPE_ERROR_MAX_TIME_EXCEEDED (0xBFFA2003) error.

Obtaining Any Other Waveform Measurement

You call the IviScope Fetch Waveform Measurement [WM] Node to obtain any other waveform measurement on a specific channel without initiating another acquisition.

Configuring Reference Levels

You must configure the appropriate reference levels before you call this node. You configure the low, mid, and high references either by calling the IviScope Configure Reference Levels [WM] Node or by setting the following properties:
  • IviScope>>Waveform Measurement [WM]>> Measurement High Reference [WM]
  • IviScope>>Waveform Measurement [WM]>> Measurement Low Reference [WM]
  • IviScope>>Waveform Measurement [WM]>> Measurement Mid Reference [WM]

Interchangeability

This node performs interchangeability checking when the IviScope>>Inherent IVI Settings>>User Options>>Interchange Check property is set to TRUE. If the IviScope>>Inherent IVI Settings>>User Options>>Spy property is set to TRUE, you use the NI I/O Trace utility to view interchangeability warnings. You use the IviScope Get Next Interchange Warning Node to retrieve interchangeability warnings when the IviScope>>Inherent IVI Settings>>User Options>>Spy property is set to FALSE. For more information about interchangeability checking, refer to the help text for the IviScope>>Inherent IVI Settings>>User Options>>Interchange Check property.

Simulated Measurements

The class driver returns a simulated measurement 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 measurement, 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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