Table Of Contents

Fetch Measurement Multimode Function (Array » Single » Cluster) (G Dataflow)

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    Last Modified: March 3, 2017

    Obtains a waveform from the digitizer and returns the specified measurement array for a single channel and record as a cluster along with timing data.

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    session out

    Identifies a particular instrument session.

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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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    channels

    The channel from which to acquire data.

    Channel String Syntax

    You can input channels with the following options:
    • A single channel, such as 0
    • A list of channels, such as 0,1 or 3,2,1,0.
    • A range of channels, such as 0-7 or 0:7.
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    Note  

    The order of channels in a list is important. The data for each channel is returned in the order the channels occur in the list.

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    array measurement

    The measurement to add as a processing step.

    Name Value Description
    None 4000 No array measurement added as a processing step.
    Last Acq. Histogram 4001 Corresponds to the NISCOPE_VAL_LAST_ACQ_HISTOGRAM C or C++ command. In the last acquisition histogram method, a voltage histogram is created from the most recent acquisition. The limits of the histogram are set by the minimum and maximum voltages of the acquisition. NI-SCOPE then counts how many samples fall into each bin of the histogram.
    Multi Acq. Voltage Histogram 4004 Corresponds to the NISCOPE_VAL_MULTI_ACQ_VOLTAGE_HISTOGRAM C or C++ command. In this multi-acquisition histogram method, a voltage histogram is created from multiple acquisitions.
    Multi Acq. Time Histogram 4005 Corresponds to the NISCOPE_VAL_MULTI_ACQ_TIME_HISTOGRAM C or C++ command. In this multi-acquisition histogram method, a time-based histogram is created from multiple acquisitions.
    Multi Acq. Average 4016 Corresponds to the NISCOPE_VAL_MULTI_ACQ_AVERAGE C or C++ command. The first time this measurement is called after it is cleared, an array the same size as the input is initialized to the input waveform, and the initial x and x increment values of the waveform are set. Every subsequent call updates and returns the running average array without affecting the size of the array.
    Polynomial Interpolation 4011 Corresponds to the NISCOPE_VAL_POLYNOMIAL_INTERPOLATION C or C++ command. Polynomial interpolation allows over or undersampling a waveform using any order polynomial set by the Measurement Polynomial Interpolation Order property. For example, an order of 1 corresponds to linear interpolation.
    Array Integral 4006 Corresponds to the NISCOPE_VAL_ARRAY_INTEGRAL C or C++ command. In the array integral method, the waveform is integrated using Simpson's rule, fitting a parabola to every 3 points with the following equation:y[i] = (waveform[i] + 4 × waveform[i + 1] + waveform[i + 2]) × dt/3
    Derivative 4007 Corresponds to the NISCOPE_VAL_DERIVATIVE C or C++ command. The differences in the waveform are computed using the following formula:y[i] = (waveform[i+2] - waveform[i]) / (2 × dt), where dt is the time between two points.
    Inverse 4008 Corresponds to the NISCOPE_VAL_INVERSE C or C++ command. The inverse is computed using the following formula:y[i] = 1.0/waveform[i].If waveform[i] is zero, the inverse is zero.
    Multiply Channels 4012 Corresponds to the NISCOPE_VAL_MULTIPLY_CHANNELS C or C++ command. Multiplies the waveforms from two channels, where one channel is specified by channel of niScope Fetch Measurement, and the other channel is the Other Channel property. Any processing steps registered with niScope Add Waveform Processing are completed for the "other channel" before this measurement is taken.
    Add Channels 4013 Corresponds to the NISCOPE_VAL_ADD_CHANNELS C or C++ command. Adds the waveforms from two channels, where one channel is specified by channel of niScope Fetch Measurement, and the other channel is specified by the Other Channel property. Any processing steps registered with niScope Add Waveform Processing are completed for the other channel before this measurement is taken.
    Subtract Channels 4014 Corresponds to the NISCOPE_VAL_SUBTRACT_CHANNELS C or C++ command. The channel specified by the Other Channel property is subtracted from the channel specified by channel of niScope Fetch Measurement. Any processing steps registered with niScope Add Waveform Processing are completed for the other channel before this measurement is taken. The two channels used in the measurement must be different.
    Divide Channels 4015 Corresponds to the NISCOPE_VAL_DIVIDE_CHANNELS C or C++ command. The channel specified by the channel parameter of niScope Fetch Measurement is divided by the channel specified by Other Channel. Any processing steps registered with niScope Add Waveform Processing are completed for the other channel before this measurement is taken. The two channels used in this measurement must be different.
    Array Offset 4025 Corresponds to the NISCOPE_VAL_ARRAY_OFFSET C or C++ command. Adds the scalar value of the measurement array offset to every point in the waveform.
    Array Gain 4026 Corresponds to the NISCOPE_VAL_ARRAY_GAIN C or C++ command. Every point in the waveform is multiplied by the scalar value Array Gain.
    Hanning Window 4009 Applies a Hanning window to the waveform using the following equation:y[i] = 0.5 × waveform[i] × [1 - cos(w)]where w = (2Π)i/n and n = waveform size.The Hanning window is useful for analyzing transients longer than the time duration of the window, and also for general purpose applications.
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    Note  

    Hanning and Hamming windows are somewhat similar. However, in the time domain, the Hamming window does not get as close to zero near the edges as the Hanning window does.

    Flat Top Window 4010 Corresponds to the NISCOPE_VAL_FLAT_TOP_WINDOW C or C++ command. A Flat Top window is applied to the waveform using the following equation:y[i] = waveform[i] × (0.2810639 - 0.52088972cos(w) + 0.1980399cos(2w))where w = (2Π)i/n and n is the waveform size. The Flat Top window has the best amplitude accuracy of all the window functions. The increased amplitude accuracy is at the expense of frequency selectivity. The Flat Top window is most useful in accurately measuring the amplitude of single frequency components with little nearby spectral energy in the signal.
    Hamming Window 4020 Corresponds to the NISCOPE_VAL_HAMMING_WINDOW C or C++ command. A Hamming window is applied to the waveform using the following equation:y[i] = x[i] [0.54 - 0.46cos(w)]where w = (2Π)i/n and n = the number of elements in x.
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    Note  

    Hanning and Hamming windows are somewhat similar. However, in the time domain, the Hamming window does not get as close to zero near the edges as does the Hanning window.

    Triangle Window 4023 Corresponds to the NISCOPE_VAL_TRIANGLE_WINDOW C or C++ command. A triangular window is applied to the waveform using the following equation:y[i] = waveform[i] × (1 - |w|)where w = (2i - n)/n and n is the number of elements in the waveform.
    Blackman Window 4024 Corresponds to the NISCOPE_VALE_BLACKMAN_WINDOW C or C++ command. A Blackman window is applied to the waveform using the following equation:y[i] = waveform[i] × (0.42 - 0.50cos(w) + 0.08cos(2w))where w = (2Π)i/n and n is the number of elements in the waveform.
    FIR Windowed Filter 4021 Corresponds to the NISCOPE_VAL_WINDOWED_FIR_FILTER C or C++ command.Windowed FIR filters use the cutoff frequency as part of the design process, but the cutoff is specified before the windowing operation. For Windowed FIR filters of sufficient taps (more than 10 for a simple lowpass), the cutoff frequency has a magnitude near 0.5 (or 6 dB down). This magnitude varies slightly with the order and the window type.FIR filters are well-suited for applications that require phase information, because the phase response is always linear. This linearity prevents distortion of time-domain filtered data. The transient response of an FIR filter is a fixed number of points, filter taps -1, which are eliminated in the filtered waveform returned from this node.The number of taps in the filter (that is, the number of coefficients in the filter) is given by the Filter Taps property. This number must be odd for the highpass and bandstop filters. The window for the coefficients is set with the FIR Window property.
    Bessel IIR FIlter 4022 Corresponds to the NISCOPE_VAL_BESSEL_FILTER C or C++ command.The input waveform is filtered with a Bessel IIR algorithm. The type of the filter is specified by the Measurement Filter Type property as any of the following values: lowpass, highpass, bandpass, and bandstop.The order of the filter is specified by the Filter IIR Order property. Also, a number of points equal to the Percent Waveform Transient property divided by 100 times the input size are eliminated from the beginning of the filtered waveform so that the transient response of the filter does not affect further measurements.
    Butterworth IIR Filter 4017 Corresponds to the NISCOPE_VAL_BUTTERWORTH_FILTER C or C++ command.The input waveform is filtered with a Butterworth IIR algorithm. The input waveform is filtered with a Butterworth IIR algorithm. The type of the filter is specified by Filter Type as any of the following values: lowpass, highpass, bandpass, or bandstop.The order of the filter is specified by the Filter IIR Order property. Also, a number of points equal to the Percent Waveform Transient property divided by 100 times the input size are eliminated from the beginning of the filtered waveform so the transient response of the filter does not affect further measurements.
    Chebyshev IIR Filter 4018 Corresponds to the NISCOPE_VAL_CHEBYSHEV_FILTER C or C++ command. The input waveform is filtered with a Chebyshev IIR algorithm. The type of filter is specified by the Filter Type property as any of the following values:The Chebyshev filter allows you to specify the passband ripple and the Filter Ripple property in decibels. The order of the filter is specified by the Filter Order property. Also, a number of points equal to the Percent Waveform Transient property divided by 100 times the input size are eliminated from the beginning of the filtered waveform, so the transient response of the filter does not affect further measurements.
    FFT Phase Spectrum 4002 Corresponds to the NISCOPE_VAL_FFT_PHASE_SPECTRUM C or C++ command. The phase spectrum is calculated using a split-radix real FFT. If the number of acquired points is not a power of two, zeros are padded at the end of the waveform so it is the next higher power of two. The phase spectrum is unwrapped.
    FFT Amp. Spectrum (Volts RMS) 4003 Corresponds to the NISCOPE_VAL_FFT_AMP_SPECTRUM_VOLTS_RMS C or C++ command. The amplitude spectrum is calculated using a split-radix real FFT. If the number of acquired points is not a power of two, zeros are padded at the end of the waveform so it is the next highest power of two.
    FFT Amp. Spectrum (dB) 4019 Corresponds to the NISCOPE_VAL_FFT_AMP_SPECTRUM_DB C or C++ command.The amplitude spectrum is calculated using a split-radix real FFT. If the number of acquired points is not a power of two, zeros are padded at the end of the waveform so it is the next highest power of two. The FFT is scaled to decibels:dB[i] = 20.0 × log10 (Amplitude[i] / Peak Amplitude)
    FFT Amp. Spectrum (dB) 4019 Corresponds to the NISCOPE_VAL_FFT_AMP_SPECTRUM_db C or C++ command. The amplitude spectrum is calculated using a split-radix real FFT. If the number of acquired points is not a power of two, zeros are padded at the end of the waveform so it is the next highest power of two. The FFT is scaled to decibels:dB[i] = 20.0 × log10 (Amplitude[i] / Peak Amplitude)

    Default: None

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    timeout

    The time, in seconds, to wait for the data to be acquired.

    Alternate Uses

    Use 0 for this parameter to fetch whatever is currently available. Use -1 for this parameter to imply an infinite timeout.

    Default: 5

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    meas waveform size

    The maximum number of samples returned in the measurement waveform array for each waveform measurement.

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    Note  

    Use the Fetch Meas Num Samples property to set the number of samples to fetch when performing a measurement.

    Default: -1

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    session out

    Passes the instrument handle to the next node in the program. This parameter has the same value as session in.

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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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    meas waveform

    A single record for a single channel as a cluster for wiring to a graph, including the timing information.

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    relativeInitialX

    The time, in seconds, from the trigger to the first sample in the acquired waveform.

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    xIncrement

    The time, in seconds, between two samples in the acquired waveform.

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    measWfm

    A one-dimensional array of data for one waveform.

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    meas wfm info

    The timing and scaling information about the waveform.

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    actualSamples

    The actual number of samples in the acquired waveform.

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    Note  

    The number returned in actualSamples may be less than numSamples if the number you request is not available.

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    absoluteInitialX

    The timestamp, in seconds, of the first fetched sample. This timestamp is comparable between records and acquisitions; devices that do not support this parameter use 0 for this output.

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    relativeInitialX

    The time, in seconds, from the trigger to the first sample in the acquired waveform.

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    xIncrement

    The time, in seconds, between two samples in the acquired waveform.

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    offset

    The offset factor of the given channel. Use for scaling binary data with the following formula:voltage = binary data x gain factor + offset

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    gain

    The gain factor of the given channel.Use for scaling binary data with the following formula: voltage = binary data × gain factor + offset.

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    reserved1

    A reserved value. Do not use.

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    reserved2

    A reserved value. Do not use.

    Where This Node Can Run:

    Desktop OS: Windows

    FPGA: Not supported


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