Interactive Alignment

LabVIEW SignalExpress

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Interactive Alignment

Aligns two plots so you can compare them. You can align the Test signal in signal with the Ref. signal in signal manually by dragging and/or expanding the Test plot on the graph or by using algorithms to automatically align steps, pulses, or periodic parameters.

Details

Parameter	Description
Input Signals	Displays the two signals to align.
Autoscale Y(x)	Adjusts the vertical scale to reflect the data from the input signals.
Comparison Result Signal	Displays the comparison signal that results from the operation you specified with Operation in the Resampling and Comparison Setup section of the Resampling page.
Autoscale Comparison Signal	Adjusts the vertical scale to reflect the result of the operation on the two aligned signals.
Autoscale x	Adjusts the time scale to reflect the data to display.
Input/Output	Contains the following options: Ref. signal in—Specifies the reference input signal. Test signal in—Specifies the test input signal to align with the reference signal. Export aligned signals—Exports the Ref. signal in and Test signal in signals to the Project View. The Interactive Alignment step resamples the Test signal in to match the Ref. signal in timing parameters. Export x-offset result—Exports the x-offset value the Geometry Parameters section of the Alignment page displays to the Project View. Export y-offset result—Exports the y-offset value the Geometry Parameters section of the Alignment page displays to the Project View. Export x-gain result—Exports the x-gain value the Geometry Parameters section of the Alignment page displays to the Project View. Export y-gain result—Exports the y-gain value the Geometry Parameters section of the Alignment page displays to the Project View.
Alignment	Contains the following options: Geometry Parameters—Contains the following options: x-offset—Sets or returns the time shift (offset) of the alignment operation. y-offset—Sets or returns the amplitude offset of the alignment operation. x-gain—Sets or returns the time stretch (gain) of the alignment operation. y-gain—Sets or returns the amplitude gain of the alignment operation. Ignore x0—Forces the timestamp value of the test signal to equal the timestamp value of the reference signal. Allow x-offset—Allows manual time shift (offset) of the test signal. Allow y-offset—Allows manual amplitude offset of the test signal. Allow x-gain—Allows manual time stretch (gain) of the test signal. Allow y-gain—Allows manual amplitude gain of the test signal. Alignment Conditions—Contains the following options: Mode—Specifies the mode Interactive Alignment uses to align the signals. You can select from the following options: Manual—Allows manual alignment of the test signal. Auto-Impulse—Selects an automatic alignment algorithm based on the assumption that the signals include a positive or negative impulse pattern. Auto-Step—Selects an automatic alignment algorithm based on the assumption that the signals include a rising or falling step pattern. Auto-Periodic—Selects an automatic alignment algorithm based on the assumption that the signals are periodic. Invert signal—Inverts the input test signal. Criterion—Specifies the following alignment criterion: Align Base and Peak—Aligns the two impulses to align the base and peak levels and to align the peak positions in time. Align 50-50%—Aligns the two impulses to superpose their respective 50% rising and falling edge points. Align Edge to User Levels—Aligns the rising or the falling edge of the impulses to superpose the Low level (%) and High level (%) points. Align Impulse to User Levels—Aligns the two impulses to superpose the points the Rising level (%) and Falling level (%) specify on both plots respectively. Step criterion: Align Low, High and User—Aligns the two steps so the low levels (0%) and high levels (100%) are aligned and the points on the edges Mid level (%) specifies are superposed. Align 10% and 90%—Aligns the two steps so the 10% and 90% points on the rising or the falling edges are superposed. Align to User Levels—Aligns the two steps so the points Low level (%) and High level (%) specify on the rising or the falling edges are superposed. Periodic criterion: Align Freq, Phase and p-p—Aligns the two periodic signals so the fundamental tones are superposed. Falling edge—Specifies to perform the edge alignment operation on the rising or falling edge of the impulses or steps. Level A—Contains the following options: Low level (%)—Specifies the level of a signal point to use as the low reference in an edge alignment operation. The unit is a percentage of the amplitude of the impulse or the step to align. The default is 10. Rising level (%)—Specifies the level of the rising edge points to superpose in an impulse alignment operation. The default is 50. Mid level (%)—Specifies the level of a signal point to use as the medium reference in a step alignment operation. The unit is a percentage of the impulse or the step to align. The default is 50%. Level B—Contains the following options: High level (%)—Specifies the level of a signal point to use as the high reference in an edge alignment operation. The unit is a percentage of the amplitude of the impulse or the step to align. The default is 90. Falling level (%)—Specifies the level of the falling edge points to superpose in an impulse alignment operation. The default is 50.
Resampling	Contains the following options: Resampling and Comparison Setup—Contains the following options: Interpolation type—Contains the following options: Coerce—Sets each output sample value to equal the input sample value that is closest to it in time. Linear—Sets each output sample value to be a linear interpolation between the two input samples that are closest to it in time. Spline—Uses the spline interpolation algorithm to compute the resampled values. Filter based—Uses an interpolation method based on the convolution of the signal with a finite impulse response (FIR) filter. Operation—Specifies to add, subtract, multiply, or divide the signals after alignment. The Resulting Signal graph displays the result of the operation. The default is Subtract. FIR Filter Specification—Contains the following options: Normalized bandwidth—The normalized cut-off frequency of the FIR filter to use. The default is 0.4000. Alias rejection (dB)—The minimum stopband attenuation of the FIR filter to use. The default is 80 dB.

Interactive Alignment Details

Moving the Test plot

You can drag the Test plot to move it. When you release the mouse button, the graph performs an autoscale operation to optimize the viewing of the plots unless you remove the checkmarks from the Autoscale checkboxes. LabVIEW SignalExpress does not update the lower graph that displays the Comparison Result Signal when you drag the Test plot, but it performs a new comparison operation as soon as you release the mouse button.

A small cross on the upper graph called the Anchor point marks the location where you last released the mouse. To move the Anchor point position, click on the new location.

Expanding the Test plot

You also can expand the Test plot in both directions, corresponding to a gain/attenuation of the signal amplitude in the vertical direction and a time expansion/compression in the horizontal direction. To expand the plot, press the <Alt> key, click the graph, and drag it. The expansion keeps the position of the Anchor point unchanged; and the mouse position point in the plane at the start of the expansion follows the mouse move.

Locking Move or Expansion

You can prevent unwanted moves and/or expansions in specific directions by removing the checkmark from the corresponding Allow x-gain, Allow y-gain, Allow x-offset, or Allow y-offset checkbox. Notice that preventing certain moves or expansion conflicts with the actual position of the Anchor point and results in slightly different expansion behaviors.

Alignment Evaluation

You can evaluate the alignment on the lower graph that displays the Comparison Result Signal. This signal displays the result of an arithmetic operation you can specify LabVIEW SignalExpress to perform on the two aligned signals. The default is Subtract.

Exporting Alignment Results

You can export the alignment information using the following checkboxes on the Input/Output page:

Export aligned signals
Export x-offset result
Export y-offset result
Export x-gain result
Export y-gain result

Resampling the Test signal

To align the Test signal in with the Ref. signal in, you must resample the signal so you can perform a sample by sample arithmetic operation like subtraction. The resampling process ensures that LabVIEW SignalExpress samples the aligned waveforms at the same rate and in phase. You can select different resampling options on the Resampling page.

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