A group of Points on an Acoustic Surface containing measurements from an identified noise source. Sources are used for Source Ranking of acoustic data. Source names are entered in the Acoustic Source column in the Traces or Shapes spreadsheet. Acoustic shapes from one Source can be displayed in animation on a structure model in ME'scope.

**Acoustic Surface**

A special type of SubStructure represented by a grid of acoustic measurement Points. Each measurement Point has a surrounding area and surface normal. Acoustic Surfaces can be created with the Drawing Assistant in ME'scope.

**Active Graph**

Either the upper or lower graphics area on the left side of an Acquisition window. The upper graph always displays the time domain measurements acquired from the connected front end. The lower graph displays M#s that are calculated from the upper graph M#s. The upper or lower graph is made active by right clicking on it, or by executing Display | Active Graph in the Acquisition window.

**Active View**

One of the four Views in the Structure window graphics area. Drawing operations like Move, Rotate & Resize are performed in the active View. A View is made active by clicking on it, or by executing one of the Display | View commands. Double clicking on one of the Views in the Quad View will replace the Quad View with the single View.

**Added File**

Any Windows file can be added to (referenced by) an Project file (VTprj). Added Files are not saved in the Project (VTprj). When an Added File is opened in ME'scope, it will open in the application program window that can display the contents of that file.

**Animation Frame**

Animation is created by displaying still pictures (frames) in rapid succession in a Structure window. There are three idfferent types of animation; sweep, sinusoidal dwell and static dwell. The Animate | Step commands can be used to pause the animation and step through the animation frames.

**Animation Source**

Any Data Block, Shape Table, or Acquisition window that is open in the Work Area is an Animation Source. The currently connected Animation Source is displayed in the Animation Source list on the Toolbar in the Structure window. During animation, data from each M# in the current Animation Source is animated using the Animation equations for each Point on the structure model.

**Auto spectrum**

An Auto Spectrum is calculated by multiplying the Fourier spectrum of a signal by its complex conjugate. The Auto spectrum has magnitude only. Its phase is zero. An Auto spectrum can have either Linear (RMS) units or Power (MS) units. Linear or Power engineering units are chosen in the Linear Power column in the Traces spreadsheet.

One of the three types of cursors in a Data Block or Acquisition window. It is displayed as two vertical lines on each M#. Click & drag inside the band to move the Band cursor. Click & drag outside the band to move the nearest edge of the Band cursor.

**Bitmap**

A copy of the pixels used to draw the graphics in a window. Bitmaps are used in all Copy to Clipboard and Print commands that operate on graphics.

**Block Size**

The number of samples of data in each M# of a Data Block or Acquisition window. The current Block Size can be viewed and edited in the File | Data Block Properties dialog box. Increasing the Block Size appends zero valued samples to each M#. Decreasing the Block Size removes samples from the higher frequency or time values of each M#.

Any Point that is referenced in the Center Point column of the Points spreadsheet in a Structure window. A Point that references a Center Point is called a Radial Point. If a Center Point has a Machine Rotation Animation equation, all Radial Points that reference the Center Point will exhibit rotational motion about the Center Point during animation. Center Points are also created to make a SubStructure rotate during animation. Rotation occurs about the Z-axis of a Center Point. To make a SubStructure rotate during animation, a non-zero speed must be entered in the RPM column, and Yes selected in the Rotation column of the SubStructures spreadsheet.

**Closely Coupled Modes**

Two or more modes that appear as a single peak in a frequency domain measurement. This occurs when two or more modes have frequencies and damping values such that their resonance curves sum together to form a single peak.

**CMIF**

CMIF is an acronym for Complex Mode Indicator Function. A peak in a CMIF curve indicates a resonance, or mode of vibration. Peaks on multiple CMIFs are used to indentify closely coupled modes and repeated roots.

**CoMAC**

CoMAC is an Acronym for Coordinate Modal Assurance Criterion. CoMAC indicates whether or not two shape components are co-linear for all (or selected) shapes in a Shape Table. If CoMAC > 0.9, the two shape components are co-linear. If CoMAC < 0.9, the two shape components are different.

**Comparison Animation**

During Compare animation, two shapes are animated on two strucutre models. Shapes from the selection in the Animation Source list are displayed on the left structure model, and shapes from the seelction in the Comparison Source list are displayed on the right. The structure model for animating shapes from the Comparison Source is chosen from a list on the Toolbar in the Structure window.

**Complex Shape**

A complex shape has shape components with phases other than 0 or 180 degrees. During animation, complex shapes will exhibit a \"traveling wave\" motion. Complex shape components can be normalized (to phases of 0 or 180 degrees) using the Animate | Normalize Shapes command in the Structure window or an Animation Source window.

**Contours**

Areas of equal shape magnitude above or below a surface during animation. Contour colors are displayed only on the surfaces of a structure model. Colors are selected in the Animation Source options box. Data Block M#s can also be displayed using color contours.

**Cross spectrum**

A cross-channel function that is calculated by multiplying the Fourier spectrum of a waveform by the complex conjugate of the Fourier spectrum of another waveform.

**Cross-channel Measurement**

A time or frequency domain measurement function that is calculated between two different simultaneously acquired signals. Examples are Transfer Functions, Impluse Response functions, Transmissibility's, Cross spectra, Cross Correlations, and ODS FRFs.

**Current Animation Source**

The Data Block, Shape Table, or Acquisition window that is currently used for animating shapes in a Structure window. The current Source file name is displayed in the Animation Source list on the Structure window Toolbar.

One or more measurements with a common time or frequency axis. Time domain measurements are real valued. Frequency domain measurements are complex valued. Each measurement has a unique measurement number (M#). M#s are displayed in the first column of the M#s spreadsheet in a Data Block window. M#s are used by the Animation equations at each Point for displaying M# data at the current cursor position.

**De-Convolution window**

A special window that is applied to Cross spectrum or ODS FRF measurements so that they can be curve fit using FRF-based curve fitting methods.

**DFT**

DFT is an acronym for Digital Fourier Transform. The FFT command transforms a uniformly sampled time waveform into its corresponding DFT. The inverse FFT command transforms a DFT back into its corresponding time waveform. If the time domain signal has N real samples, the DFT will have (N/2) complex samples.

**DOF**

DOF is an acronym for degree-of-freedom. A DOF includes a Point number & direction. If each measurement (M#) in a Data Block, Shape Table or Acquisition window has a DOF defined for it, the DOF can be used to create Animation equations by assigning M#s to matching Points & directions on the model in the connected Structure window. Each Point number should correspond to a numbered Point on the model. Each DOF direction should correspond to a Measurement Axis direction at the Point on the model. Scalar data has no direction associated with it.

**Drawing Assistant**

A set of tabs in a Structure window that are used for drawing and modifying structure models. The Drawing Assistant tabs are displayed above the SubStructure spreadsheet by executing Draw | Drawing Assistant.

**Drawing Object**

A Point, Line, Surface, or SubStructure on a structure model. Each Point is defined by its global X, Y, Z coordinates. Each Line is defined between two Points, each Surface Triangle between three Points, and each Surface Quad between four Points. Each SubStructure is a collection of Points, Lines, and Surfaces.

**Driving Point**

The point & direction on a structure where force is applied and response is also measured. In terms of its two DOFs, a driving point measurement has the same Roving & Reference DOFs.

**Driving Point Residue**

A modal Residue is the numerator term or the \"stength\" of a mode in an FRF measurement. A driving point Residue is obtained by curve fitting a driving point FRF.

EDS is an acronym for Engineering Data Shape. An EDS is used to describe any type of data measured from two or more points on a machine, structure, or acoustic surface. EDS data can be saved in a Shape Table along with ODS's and mode shapes.

**EMA**

EMA is an acronym for Experimental Modal Analysis. During an EMA, the test article is artificially excited with either an impactor, or using one or more shakers. The excitation force(s) and one or more responses caused by the force(s) are simultaneously measured, and a set of FRFs is calculated The FRFs are then curve fit to obtain experimental modal parameters for the test article.

**EMA Mode**

An EMA mode is obtained by curve fitting a set of experimentally derived FRFs. Each EMA mode has a frequency, a damping value, and a complex mode shape.

FEA is an acronym for Finite Element Analysis. FEA involves creating an FEA model by adding FEA elements (called FEA Objects in ME'scope) to a structure model. The FEA model can be solved for its FEA modes, and also used for other analyses in ME'scope.

**FEA Assistant**

A set of tabs in the Structure window that are used for drawing a structure model and adding FEA Objects to it. The FEA Assistant tabs are displayed above the SubStructure spreadsheet by executing FEA | FEA Assistant.

**FEA Model**

An FEA model is created in ME'scope by adding FEA Objects to a 3D model of a machine or structure. In ME'scope, this is called Experimental FEA because the same model used to display experimental mode shapes in animation can also be used to create an FEA model.

**FEA Modes**

FEA modes are the eigensolution of a set of FEA equations of motion derived from a structural FEA model. An eigensolution consists of an eigenvalue which is the frequency for each FEA mode, and an eigenvector which is its mode shape. FEA damping elements can also be added to the FEA model, and complex FEA modes with modal damping can be calculated.

**FEA Object**

FEA Objects are used by the SDM, Experimental FEA, and FEA Model Updating commands in ME'scope. FEA Objects are added between Points on a structure model. Their physical properties are defined in the FEA Properties window, and their material properties are defined in the FEA Materials window.

**FEA Rotations**

Mode shapes with FEA rotational components in them can be used in SDM and FEA calculations. FEA rotational components are displayed in animation by executing Animate | Animate Using | FEA Rotations.

**FFT**

FFT is an acronym for Fast Fourier Transform. The FFT algorithm transforms a uniformly sampled time domain signal into its corresponding Digital Fourier Transform (DFT). The Inverse FFT transforms the DFT back into its original time domain signal. The FFT in ME'scope transfroms any number of samples, not just powers of 2.

**Fixed DOF**

Each Point & direction (DOF) on a test structure model can be Measured, Interpolated, or Fixed. To display shapes in animation, each measurement (M#) in a connected Animation Source is assigned to a Measured DOF of the structure model. All Fixed DOFs do not move during animation. A DOF where no measurement was made is called an Interpolated DOF. During shape animation, the shape component of each Interpolated DOF is calculated from neighboring Measured and Fixed DOFs.

**Fourier spectrum**

A Fourier spectrum is also called the Discrete Fourier Transform, or DFT.

**Frequency Response Function (FRF)**

A Frequency Response Function is a cross-channel frequency domain function that defines the dynamic properties of a structure between an excitation Force and the Response caused by that force. An FRF is defined as the ratio (Response DFT / Force DFT). The FRF is a special case of a Transfer Function, where the response is the numerator (Output) and the force is the denominator (Input).

**FRF**

An FRF (Frequency Response Function) is a cross-channel frequency domain function that defines the dynamic properties of a structure between an excitation Force and the Response caused by that force. An FRF is defined as the ratio (Response DFT / Force DFT). The FRF is a special case of a Transfer Function, where the response is the numerator (Output) and the force is the denominator (Input).

The average of the minimum & maximum coordinates of all Points used by a Drawing Object, FEA Object, or structure model.

**Global Curve Fitting**

Global curve fitting processes multiple FRFs in a Data Block to obtain a global frequency & damping estimate for each mode in a frequency span or cursor band of interest.

**Group**

M#s in a Data Block or Shape Table can be grouped together by giving them a common name in the Group column of the M#s spreadsheet. During shape animation, if the Animate | Animating Using | Groups command is checked, each Group of M#s is scaled separately so that data from two or more Groups can be displayed together.

These designations are used by the MIMO commands, and by the Acquisition window for calculating cross channel functions. In order to calculate an FRF, each excitation force must be designated as an Input and each response as an Output. These choices are made in the Input Output column of the M#s spreadsheet in a Data Block or the Channels spreadsheet in an Acquisition window, When Both is chosen, the waveform will be used as both an Input and an Output in MIMO calculations.

**Interpolated DOF**

Each Point & direction (DOF) on a test structure model can be Measured, Interpolated, or Fixed. To display shapes in animation, each measurement (M#) in a connected Animation Source is assigned to a Measured DOF of the structure model. All Fixed DOFs do not move during animation. A DOF where no measurement was made is called an Interpolated DOF. During shape animation, the shape component of each Interpolated DOF is calculated from neighboring Measured and Fixed DOFs.

A Line cursor is one of the three types of Data Block or Acquisition window cursors. It is represented by a vertical line on each M# graph. The Line cursor is moved by clicking & dragging it one the graph. When it is displayed, clicking on a graph will place the Line cursor at the mouse pointer position.

**Line Object**

A Line Object is displayed as a straight line between two Points on a structure model. Lines are displayed by executing Display Objects | Lines | Show Lines. All Line properties are displayed in the Objects spreadsheet by executing Edit | Current Type | Lines.

**Local Curve Fitting**

Local curve fitting extracts modal frequency & damping estimates from each FRF in a Data Block.

M# is an abbreviation for Measurement Number. Each measurement function in a Data Block or Acquisition window has a unique M#. Also, each shape component in a Shape Table window has a unique M#. Each M# in the connected Animation Source must be Assigned to a DOF of the structure model in order to display shapes from the Source in animation. Each un-measured DOF on the model is animated by creating an M# Interpolation using nearby Measured and Fixed DOFs.

**M# Links**

Each Point & direction (DOF) on a test structure model can be Measured, Interpolated, or Fixed. To display shapes in animation, each measurement (M#) in a connected Animation Source must be linked to a Measured DOF of the structure model. All Fixed DOFs do not move during animation. A DOF where no measurement was made is called an Interpolated DOF. During shape animation, the shape component of each Interpolated DOF is calculated from neighboring Measured and Fixed DOFs.

**M# Matrix**

A M# Matrix is a Data Block where the Roving DOF of each M# designates the row, and the Reference DOF designates the column of the M# in the M# matrix. M# matrices can be added, subtracted, multiplied, divided and inverted using commands in ME'scope.

**MAC**

MAC is an Acronym for Modal Assurance Criterion. MAC indicates whether or not two shapes are co-linear (lie together on the same straight line). If MAC =1 the shapes are co-linear. If MAC > 0.90, the shapes are simlar. If MAC < 0.90 the shapes are different.

**Machine Rotation Data**

One of the kinds of shape data that can be displayed in animation on a structure model. To display it in anmation, Machine Rotation data must be assigned to a Center Point, in the local Z-direction of the Center Point. During animation, all of the Radial Points that reference a Center Point are animated with rotation about the Center Point in the local Z direction.

**Measured DOF**

Each Point & direction (DOF) on a test structure model can be Measured, Interpolated, or Fixed. To display shapes in animation, each measurement (M#) in a connected Animation Source is assigned to a Measured DOF of the structure model. All Fixed DOFs do not move during animation. A DOF where no measurement was made is called an Interpolated DOF. During shape animation, the shape component of each Interpolated DOF is calculated from neighboring Measured and Fixed DOFs.

**Measurement**

A measurement is a series of time domain or frequency domain samples stored in a Data Block or Acquisition window. Each measurement has a unique Measurement number (M#). Each shape component in a Shape Table is also called a measurement, and each component has a unique M#.

**Measurement Axes**

Each Point on a structure model has three Measurement (or local) Axes. Measurement Axes define the directions in which measurements were made at the Point. Measurement Axes are displayed using the .

**Measurement Set**

A Measurement Set is all of the time waveform data that was simultaneously acquired together. Simultaneous acquisition is done with a multi-channel acquisition front end. Measurement Sets are defined in an Acquisition window. Cross-channel measurements are calculated using data from the same Measurement Set. The Measurement Set number is appended to the DOFs of all acquired time waveforms or calculated measurement functions.

**Meshing**

Meshing subdivides selected Lines, Surfaces, FEA Objects, and SubStructures on a structure model into more Objects. If a SubStructure is meshed, all of its Lines, Surfaces, and FEA Objects are meshed. The commands in the Draw | Mesh menu are used for meshing.

**MIMO model**

A MIMO model is a Multiple Input Multiple Output frequency domain matrix model containing a vector of Inputs, a matrix of Transfer functions and a vector of Outputs. The MIMO model is an equation where the Transfer function matrix is post-multiplied by the vector of Input DFTs to obtain the vector of Output DFTs. Inputs, Outputs & Transfer functions can be calculated using different forms of the MIMO model equation.

**MMIF**

MMIF is an acronym for Multivariate Mode Indicator Function. Each peak in an MMIF is an indication of a resonance or mode of vibration. Peaks in multiple MMIFs will indicate closely coupled modes and repeated roots.

**Modal Model**

A Modal Model is a set of mode shapes that have been scaled so that they preserve the dynamic properties of a structure. Two types of modal models are used in ME'scope, Residue mode shapes and Unit Modal Mass (UMM) mode shapes. Residue mode shapes are obtained by curve fitting a set of calibrated FRFs. UMM mode shapes are obtained by re-scaling a set of Residue mode shapes. Modal models are used for SDM calculations, FEA Model Updating, FRF synthesis, and MIMO calculations.

**Modal Participation Factor**

Modal participation factors quantify how each mode shape contributes to the overall structural response of a structure. Modal participation factors of a set of mode shapes in a set of ODS's is displayed by executing Display | Participation in a Shape Table window.

**Mode Indicator Function**

A mode indicator function is used in the first step of curev fitting for counting resonance peaks (or modes) in a set of FRFs. The number of modes counted is then used for estimating modal frequency & damping using the Polynomial method in the second curve fitting step.

**Mode Shape**

Modes are used to characterize resonant vibration in structures. Each mode has a natural frequency, damping value, and a mode shape. The mode shape is a standing wave deformation of the structure at its natural (resonant or modal) frequency. An ODS is a summation of contributions fof all of the mode shapes of the modes being excited in a structure.

**mooZ**

mooZ is the reverse of a Zoom operation in a Structure, Data Block, or Acquisition window. It restores the full display of the structure model in a Structure window, or the display of all of the M# data in a Data Block or Acquisition window.

**MPC**

MPC is an Acronym for Modal Phase Colinearity. The MPC has values between 0 & 1. If MPC = 1, all of the components of a shape lie on a straight line in the complex plane. If MPC < 1, the components do not lie on a strraight line. Lightly damped structures normally have mode shapes with MPC's close to 1.

**Multiple Coherence**

Multiple Coherence is calculated whenever two or more excitation forces are simultaneously acquired along with responses caused by the forces. Multiple Coherence is a frequency domain function with values between 0 &1. It indicates how much all of the measured forces contribute to each measured response. If only one excitation force is used and measured, then Multiple Coherence is the same as Ordinary Coherence.

**Multiple Reference Test**

A Multiple Reference Test uses two or more fixed exciters, or two or more fixed response sensors during the test. The other sensors can be moved to different locations of the structure. This test is also called a MIMO test. Measurement functions in two or more columns (fixed exciters or Inputs), or two or more rows (fixed responses or Outputs) of the FRF matrix in a MIMO model are calculated from MIMO data.

A Nodal Line is a line of the surfaces of a structure model where all shape components are zero. The Nodal Lines of a normal mode shape or a normalized complex shape will not move during animation. The Nodal Lines of a complex shape can move during shape animation.

**Normal Mode**

A Normal mode has mode shapes with real valued mode shape components. If an FEA model has no damping in it, its FEA mode shapes will be Normal modes.

**Normalized Shape**

A Normalized Shape has shape components with phases of 0 or 180 degrees. During shape animation, a Normalized Shape will exhibit a \"standing wave\" motion, and its Nodal Lines will not move. Complex shapes can be normalized (have their phases rotated to 0 or 180 degrees) by executing Animate | Normalize Shapes in a Shape Table, Data Block, or Acquisition window.

An Octave band is a frequency band where the highest frequency is twice the lowest frequency. Acoustic measurements are often displayed using 1/1, 1/3, or 1/12 octave bands.

**ODS**

ODS is an acronym for Operating Deflection Shape. An ODS is the deformation of a structure at two or more locations and/or directions due to its own operational forces and/or other applied forces. A time domain ODS characterizes the structural deformation at a specific time. A frequency domain ODS characterizes the structural deformation at a specific frequency. An ODS is a summation of contributions of the mode shapes of all resonances being excited by the specific operating condition.

**ODS FRF**

An ODS FRF is a cross-channel frequency domain measurement that is calculated from operating (output only) data. An ODS FRF is created by combining the phase of the Cross spectrum between a Roving and a (fixed) Reference response with the Auto spectrum of the Roving response. ODS's can be displayed in animation directly from a set of ODS FRFs. Operating mode shapes can be extracted by curve fitting a set of ODS FRFs.

**OMA**

OMA is an acronym for Operational Modal Analysis. An OMA is performed when the excitation forces are not or cannot be measured, and hence FRFs cannot be calculated. Cross spectra or ODS FRFs are calculated instead of FRFs, and are curve fit to extract operating mode shapes.

**OMA Modes**

A set of OMA modes is obtained by using FRF-based curve fitting methods on a set of specially windowed Cross spectra or ODS FRFs. In ME'scope, a DeConvolution window is applied to a set of Cross spectra or ODS FRFs before curve fitting them.

**Operating Mode Shapes**

Another name for OMA modes.

**Order-Tracked ODS**

The ODS values at the running speed (first order) or one of the higher orders (second, third,... order) of a rotating machine. An Auto or Cross spectrum, or an ODS FRF of an operating machine will typically have a peak at each of its orders.

**Orthogonal Polynomial**

Orthogonal Polynomial is a least squared error curve fitting method for estimating modal parameters from a set of FRFs. Modal frequency & damping estimates are obtained either with a Global version or a Local version of this curve fitting method.

**Orthogonal Views**

The Quad View in a Structure window displays four Views of the structure model, a 3D View and three orthogonal 2D Views (X View, Y View, and Z View). A single View is obtained by double-clicking on one of the four Views in the Quad View.

Partial Coherence is calculated when two or more excitation forces are simultaneously acquired along with responses caused by the multiple forces. Partial Coherence is a frequency domain function with values between 0 &1. It indicates how much each one of the multiple forces contributes to a measured response. For each response, there is a separate Partial Coherence for each of the forces measured.

**Peak Cursor**

A Peak cursor is one of the three Data Block or Acquisition window cursors. A Peak cursor is displayed on each graph as a band with two vertical lines and a red dot indicating the peak in the band. Click & drag inside the band to move both edges of the peak cursor band. Click & drag outside the band to move the nearest edge of the band.

**Periodic Signal**

The FFT assumes that the waveform to be transforming is periodic in its transform window (the samples used by the FFT). Waveforms that are completely contained within the transform window satisfy this criterion. Cyclical waveforms that complete an integer number of cycles within the transform window also satisfy this criterion. If a time waveform is not periodic in its window, its DFT will have \"leakage\" (or distortion) in it.

**Photo Realistic Model**

A Photo Realistic Model is a structure model that has digital photographs attached to its surfaces. A Photo Realistic Model is created using third party software, and is then importing into ME'scope using the .OBJ file format.

**Point Matching**

Point Matching is the process of aligned an EMA with an FEa model, and re-numbering Points on an EMA model which coincide geometrically with Points on an FEA model. Point matching is part of the Experimental FEA option to ME'scope.

**Point Object**

A Point Object is a point on a structure model. Points are used as end points for defining all other Objects in the Structure window. Each Point has three global coordinates (X,Y,Z). Each Point has its own Animation equations that are used to animate the Point with shape data from the connected Animation Source (Data Block, Shape Table or Acquisition window). Point properties are displayed in the Objects spreadsheet by executing Edit | Current Type | Points.

**Pole**

A pole is another name for the frequency & damping pair of a mode of vibration.

**Pole Plot**

A graph of the poles of modes of vibration. Modal frequency is plotted on the horizontal axis and modal damping is plotted on the vertical axis of a Pole plot. A curve fitting Stability diagram can be displayed as a Pole plot, and a Pole plot can be displayed from a Shape Table by executing Display | Poles.

**Project**

All work in ME'scope is done with data contained in a Project file. A Project file can contain one or more Structure, Data Block, Shape Table, Acquisition, Program, Report, or Added files. Only one Project file can be open at a time. All of the names of the data files in the currently open Project are displayed in the top (or left) pane of the Project Flyout panel.

**PSD**

PSD is an acronym for Power Spectral Density. A PSD is calculated by dividing an Auto spectrum by its frequency resolution (the increment between frequency lines). PSD units are typically (g^2/Hz) or (g/(Hz^1/2))

A Quad View of a structure model consists of four Views (X View, Y View, Z View & 3D View). The Quad View is obtained by double-clicking on a single View. Double-clicking on one of the single Views in a Quad View will display only that View.

A Radial Point is any Point that contains a Point number in the Center Point column of the Points spreadsheet. If a SubStructure has one or more Center Points, Rotation is set to Yes, and RPM is non-zero in the SubStructure Object spreadsheet, all Radial Points will rotate about their Center Points during animation. Also, if a Center Point has a Machine Rotation Animation equation defined for it, then all Radial Points will be animated with rigid body rotatation about the Center Point during animation.

**Reference DOF**

A Reference DOF is the sensor that remained fixed when multi-channel data was acquired for calculating a set of cross-channel measurements. All cross-channel measurements have both a Roving and a Reference DOF. In a cross-channel DOF, the Reference DOF follows the colon and the Roving DOF preseeds it. A cross-channel DOF is listed in the DOFs column of the M#s spreadhsheet, .

**Repeated Roots**

Two or more modes with the same modal frequency but different mode shapes are called a Repeated Root. Repeated Roots can occur in geometrically symmetric structures such as disks, cylinders, square plates and cubes.

**Residue**

A Residue is one of the three modal parameters (frequency & damping are the other two) obtained during FRF-based curve fitting. A Residue is the numerator term in the partial fraction expansion of the FRFcurve fitting model. A Residue is also referred to as the \"strength\" of the mode. Residue units are the FRF engineering units multiplied by Hz (or radians per second). Typical Residue units are g's/N-sec.

**Residue Mode Shapes**

After curve fitting, when the modal parameters are saved into a Shape Table, each mode shape is called a Residue mode shape. Residue mode shapes can be scaled into UMM mode shapes if the Driving Point Residues are present in the Shape Table. Residue mode shapes can be used to synthesize an FRF bwtween each Roving & Reference DOF pair of the Residue mode shapes.

**Roving DOF**

The Roving DOF is the sensor that changes location or direction while multi-channel data is being acquired to calculate a set of cross-channel measurements. Each cross-channel measurement has both a Roving DOF and a Reference DOF. In a DOFs column of the M#s spreadsheet, the Roving DOF preceeds the colon and the Reference DOF follows the colon.

The Sampling Window is the block of time domain samples used by the FFT to calculate a DFT. The Sampling Window is also called the Transform window. To create certain properties in its corresponding spectrum, a special time domain windowing function (Hanning, Flat Top, Exponential, etc.) is often applied to the samples in the Sampling Window prior to transforming them into the DFT.

**Scalar Data**

Scalar data is a kind of shape component data that has no direction associated with it. Examples of Scalar data are Sound Pressure Level (SPL), Sound Power, temperature, and pressure. Scalar data is animated on a structure model using color contours on surfaces.

**SDI**

SDI is an Acronym for the Shape Difference Indicator. SDI indicates whether or not two shapes have shape components with the same values in them. SDI values range between 0 & 1. If SDI =1.0 the shapes have identical shape components. If SDI < 1.0 the shapes have different shape components.

**SDM**

SDM is an acronym for Structural Dynamics Modification. SDM is an algorithm that uses the modes of an unmodified structure together with FEA Objects that model structural modifications, and calculates the modes of the modified structure. SDM is very fast and provides useful results even when a modal model has only a few modes in it.

**Shape**

A Shape consists of two or more measured or calculated values at Poitn & directions on a structure or acoustic surface. Specific types of shapes are an Operating Deflection Shape (ODS), mode shape, acoustic shape, and Engineering Data Shape (EDS). Shape components can be Translational, Rotational, or Scalar. For correct shape animation, all shape components must have correct magnitude & phase values relative to one another.

**Shape Interpolation**

During animation, shape components for each Point & direction (DOF) on the structure can be Measured, Fixed or Interpolated. A Fixed DOF will not move during animation. DOFs where no measurements were made are called Interpolated DOFs. During animation, the shape components of Interpolated DOFs are calculated from neighboring Measured and Fixed DOFs. Measured DOFs are created by Assigning each M# in an Animation Source to a DOF of the structure model

**Shape Table file**

A Shape Table is a file for storing shapes. A shape is a spatial description of data measured or calculated for two or more Points & directions on a structure or Acoustic surface. Shapes can be imported from an external source, saved from an Animation Source, saved from the Structure window during animation, or created by saving modal parameter estimates into a Shape Table.

**Sine Dwell**

Sine Dwell in one of the three types of shape animation in a Structure window. During Sine Dwell animation, the displayed shape is animated by multiplying it by sine wave values as a unit circle is tranversed in equal increments from 0 to 360 degrees. .

**Single Reference Test**

A Single Reference test uses a single fixed exciter or a single fixed response sensor during the test. If the exciter is fixed, the Roving DOF of the roving response sensor define the components of the ODS's or mode shapes obtained from the measurements. If a fixed response sensor is used, the Roving DOFs of the roving exciter define the components of the ODS's or mode shapes.

**Single-channel measurement**

A Single-channel measurement is calculated using data acquired from a single acquisition channel. Examples are a Fourier spectrum, Auto spectrum, or Auto Correlation function. If Fourier spectra are calculated from simultaneously acquired time waveforms, they can be curve ft to obtain EMA mode shapes. Auto spectra can also be curve fit, but the EMA mode shapes will not have phases in them because the Auto spectra have no phases.

**SPL**

SPL is an acronym for Sound Pressure Level. An SPL is a measure of the RMS sound pressure relative to a reference value. It is measured in logarithmic units of decibels (dB) above a standard reference level. A common reference level used is 20 μPa RMS, which is considered the threshold of human hearing.

**Stability Diagram**

A Stabiliy Diagram is enabled with the Multi-Reference Modal Analysis option in ME'scope. It is a graph of modal frequency & damping estimates for multiple curve fitting model sizes, from 1 to a Maximum Model Size. All estimates that lie within user-specified tolerance limits are grouped into Stable Pole Groups. The average value of the poles in each Stable Group can be added to the Modal Parameters spreadsheet and used in the third curve fitting step, Residue estimation.

**Stationary Dwell**

Stationary Dwell is one of the three types of shape animation in a Structure window. During stationary dwell animation, each shape is displayed without any modulation. Stationary Dwell is most often used for displaying acoustic shapes using contour colors on surfaces.

**Structure file**

A Structure file contains the drawing Objects used to define a 3D model of a test structure. The structure model is used for displaying shapes in animation. Points, Lines & Surfaces are used for defining 3D structure models. FEA Objects can also be added between Points on the model. FEA Objects are used by commands in the SDM and Experimental FEA options of ME'scope.

**Structure Model**

A Structure Model is used for displaying operating deflection shapes (ODS's), mode shapes, acoustic shapes or engineering data shapes in animation. A \"stick model\" consists of multiple Points connected by Lines. A \"surface model\" has triangular or quad surfaces added between Points. A \"texture model\" has textures defined for its surfaces. A \"photo realistic model\" has digital photographs attached to its surfaces.

**Substructure**

A Substructure is a collection of Points, Lines, Surfaces, and FEA Objects. Substructures can be selected, moved, cut, copied & pasted like the other drawing Objects. Substructure properties are displayed in the Substructures spreadsheet. The Drawing Assistant is used to create structure models by added Substructures from the Substructure Library to the model. The FEA Assistant is used to add FEA Objects to a structure model.

**Substructure Library**

The Substructure Library is a special Project file containing pre-defined structure models. The Drawing Assistant is used to add Substructures from the Library to a structure model. Any structure model can be saving into the Substructure Library by executing File | Save In Substructure Library in the Structure window.

**Surface Quad**

A Surface Quad is a drawing Object that defines a surface between four Points on a structure model. Surfaces are used for hidden line displays, surface fills, surface textures, photo realistic models, and color contour displays. Surface Quad properties are displayed in the Objects spreadsheet by executing Edit | Current Type | Surface Quads.

**Surface Triangle**

A Surface Triangle is a drawing Object that defines a surface between three Points on a structure model. Surfaces are used for hidden line displays, surface fills, surface textures, photo realistic models, and color contour displays. Surface Triangle properties are displayed in the Objects spreadsheet by executing Edit | Current Type | Surface Triangles.

**Sweep Animation**

Sweep Animation is one of the three types of shape animation in a Structure window. During Sweep animation from a Data Block or Acquisition window, the cursor is moved through the graph from left to right, and the data at each cursor position is displayed as a shape on the model. During Sweep animation from a Shape Table, each shape is displayed in succession using Dwell Animation and the number of dwell cycles from the Animation tab in the File | Shape Table Options box.

A Tool Tip is a brief description of each button (or Tool) on a Toolbar. If Help | Show Tool Tips is checked, a Tool Tip will be displayed when the mouse pointer is hovered over a Tool.

**Transfer Function**

A Transfer function is a cross-channel frequency domain function that defines the dynamic properties between an Output from and an Input to a structure or machine. A Transfer function is defined as the ratio (Output Fourier spectrum / Input Fourier spectrum). An FRF is a special case of a Transfer Function where the Input is an excitaton force, and the Output is the response caused by the excitation force.

**Transform Window**

The Transform window is a block of time or frequency domain samples. A Transform window of time domain samples is transformed by the FFT to their corresponding DFT. Likewise, a Transform window of frequency domain samples is transformed by the Inverse FFT to their corresponding time waveform.

**Translational Data**

Translational data is one of the kinds of shape data that can be displayed in animation on a structure modal. Examples are vibration and acoustic intensity. Each Translational measurement has a direction associated with it. Measurement directions are defined by the Measurement Axes at each Point on the structure model. Up to three Translational measurements can be defined at each Point.

**Transmissibility (TRN)**

A Transmissibility is a cross-channel frequency domain measurement typically calculated from operating or output-only data. Transmissibility is defined as the ratio (Output Fourier spectrum / Input Fourier spectrum). Operating mode shapes can be obtained by saving the cursor values at a resonant frequency in a set of Transmissibility's. A set of ODS FRFs can be obtained by multiplying a single reference set of Transmissibility's by a reference Auto spectrum.

UFF is an acronym for Universal File Format. UFF is a disk file format used for exchanging data between different structural testing & analysis systems. Structure models, mode shapes, ODS's, and time or frequency domain measurements can be imported & exported using UFF files. Typical UFF file name extensions are .UFF, .UNV and .ASC.

**UMM Mode Shapes**

UMM mode shapes are mode shapes that have been scaled to preserve the mass & stiffness properties of a structure. A set of UMM mode shapes is also called a modal model. UMM mode shapes are used for FRF Synthesis, MIMO modeling & simulation, SDM, and FEA Modal Updating in ME'scope.

Zooming enlarges the display of the model in a Structure window, or the graphics along the X-axis in a Data Block or Acquisition window. A Zoom is initiated by executing Display | Zoom, or by clicking in the graphics area and spinning the mouse wheel.