m+p Analyzer offers four different types of charts for specific data analysis needs:
- 2D Single chart
- 2D Multi-chart
- 3D Waterfall chart
- Colormap chart
In the first issue we will explain 2D chart functionalities including chart layout, online data display and basic analysis features.
Single and Multi-charts are the key tools to use when acquiring and reviewing measurement data. The single chart can display up to 256 traces in a single diagram and is continually updated during a measurement. The multi-chart tool is useful for a more structured display of data. Scaling may be applied to several charts at once and groups of traces can be displayed together in separate sub-charts. Similar to a webbrowser, all charts may be arranged freely on the working plane either side-by-side or as tabs.
Charts can be configured to show a secondary axis on the right hand side with independent scaling, which streamlines acquisition of data with different units, e.g. acceleration [g] and force [N]. Comparison of signals, such as phase difference between sine waves, can be done automatically online during the measurement.
Both the single and multi-charts are completely customizable. The size and color of titles, legends, annotations and the plot area can be tailored to the user’s preference. The grid and traces may be individually colored and styled.
The 2D chart capability is not limited to the display of time data. m+p Analyzer’s real-time FFT feature allows for online display of different metrics calculated from measurement data. This includes real-time spectra of windowed time signals, histograms, auto- and crosscorrelations, power spectral densities, auto- and crosspower spectra and frequency response functions.
The display type of the chart may be individually customized to fit the requirements of a given measurement type, e.g. a frequency response function. Common axis types such as real/imaginary, amplitude/phase, logarithmic/phase and dB (referenced)/phase plots are available with different types of scaling such as peak, peak-to-peak and rms.
m+p Analyzer offers four different types of charts for specific data analysis needs: 2D Single chart, 2D Multi-chart, 3D Waterfall chart and Colormap chart. The second article of our series „m+p Analyzer basics“ will focus on the advanced functionality of 2D charts.
The overview feature is useful when post-processing and reviewing large data sets. It allows to select a zoom region and pan this region in the overview field to get a close-up view of a subset of data.
To review the data values at specific time instances, vertical and horizontal cursors may be used. Besides the charts a display with useful metrics at the cursor location is displayed. Multiple cursors may be linked with the "band cursor" feature where slave cursors will move together with the master cursor at a given distance. Together with the "seek to peak" feature, extrema and their relative distances (in time or frequency) may be easily tracked and displayed in the chart legend.
2D charts offer specifically tailored cursors for the analysis of spectra (basically anything with a frequency axis). The harmonic cursor displays slave cursors at frequency locations of the 1st, 2nd, 3rd, ... harmonic based on the master cursor frequency. The sideband cursor displays slave cursors equally spaced to the left and right around the master cursor.
The tacho tool can be used to extract RPM values from a tacho signal or sine wave. It is a simple tool that is real-time capable in that it can be used at acquisition time. More advanced features "tacho spline fit" and "RPM extractor" are part of the m+p Analyzer "Rotate" toolbox and allow for more complex RPM extraction methods such as smoothing of the extracted RPM signal and extraction of RPM from vibration data. In the following example we will show the basic tacho tool which comes with the 2D chart. Suppose a sine sweep from 20 Hz to 100 Hz was recorded. We can now configure the tacho tool displaying the rotational speed, which - in the case of our sine sweep - yields an RPM range of 1200 to 6000 RPM. The result may either be shown as a cursor on the original data or shown as a new signal "RPM over time". In this example we use a sine sweep, yet any rectangular pulse train - which is typically measured by tachometers - is applicable.
Reference traces may be overlaid in the 2D chart to compare previously acquired results to the currently acquired data in real time. Besides showing recorded measurements as a reference, this feature is also useful to show, for example, upper and lower limits when measuring time signals such as forces. In the following example we show how to set up a previously acquired spectrum as a reference trace and perform several impulse response measurements which can then visually compared to the reference response. Tip: Reference traces may be added quickly by holding the "alt" key while dragging and dropping a measurement into the chart.
In the last issues of our series “m+p Analyzer Basics” we showed basic features of 2D charts such as formatting and positioning and more advanced features such as different types of cursors and reference traces. This issue is dedicated to data manipulation. The m+p Analyzer provides a rich set of data manipulations within packages like "modal analysis", "rotational analysis" and "acoustic analysis". Yet basic analysis features are included in the 2D charts which come with the standard licence and are available to all customers.
The 2D chart can be configured to perform basic calculations on the data it currently shows. These functions include integration and differentiation in time and frequency domain, octave spectra with A-, B-, C-weighting, orbit plots and many more. All calculations may be chained consecutively in arbitrary order and will be applied during run time. The following animation shows how acceleration data can be integrated to velocity or displacement during the time of measurement.
For an application example we will use our demonstrator for rotational analysis such as balancing and orbit analysis.
On the left journal we placed two accelerometers to measure vibrations in X- and Y-direction. Within the chart we can now integrate these accelerations twice to get the displacement and then setup an orbit plot. This will show us the movement of the journal in the X-Y-plane during the run-down of the demonstrator.
In a real world application, one is typically interested in time histories and spectra as well. In that case we would setup different charts showing the desired metrics. The following animation shows a typical setup and how to export and import such a setup for repeated use.
m+p Analyzer offers four different types of charts for specific data analysis needs, a 2D single chart, a 2D Multi-chart, a 3D Waterfall chart and a Colormap chart. In this issue we take a look at the 3D chart and its online capabilities.
The 3D chart displays a set of waveforms against a third axis such as time, frequency or RPM. Applicable waveforms include time histories, spectra, FRF, PSD and many more. Just like the 2D charts, the format and properties of the 3D chart can be easily edited and stored as a template, see also Issue 1: Basics of 2D Charts. The following animation shows different styles of the chart: Several spectra are recorded and shown in the waterfall chart during measurement. The user may easily switch between a waterfall and a colormap display by a double click on the chart. In this case we configured the waterfall chart to show a shaded surface, though several other styles are also available.
For the following example we recorded acceleration data of a rotating machine during run-up. We used m+p Analyzer (DSA-Pro license) and an m+p VibPilot acquisition front-end. In addition to the acceleration on the mount we recorded the RPM of the machine. The measurement was configured so that the 14.25 s of time data is automatically split into 57 blocks of 250 ms length. For each block a spectrum is calculated using a FFT algorithm and a Hanning window. The spectra are displayed in a colormap of frequency vs. time. As we also recorded the RPM of the machine, m+p Analyzer will automatically attribute every spectrum with the average RPM during the time of aquisition. Therefore we can easily generate a colormap of RPM vs. frequency, giving a clear indication of the machine’s rotating frequency and its harmonics (i.e. the orders). Exemplarily, a cursor is used to extract the amplitudes of the 1st order over the rotational speed.
This example shows a simple and quick way to analyze a rotating machinery in m+p Analyzer. For more advanced analysis the rotate package may be licensed, which offers advanced tacho acquisition, RPM and time based colormap generation and more sophisticated order tracking features. Contact us for more information about m+p Analyzer and its rotate capabilities.
The project browser is the core element of the m+p Analyzer when it comes to managing projects, measurement data and calculated results. In this issue of our series m+p Analyzer Basics we will go through various neat tips and tricks on how you can use the project browser to its full potential and to help you speed up your work and get the job done faster!
Figure 1 shows the two-pane layout of the project browser: By default, the "Measurement"-tab is selected and the left side contains a tree with different projects and their workspaces. The right pane shows contained measurements and their corresponding meta data. Switching the tab in the top will change this view to show all available geometries, setups, layouts or the recycle bin for the current (active) project.
Please note: The right pane will always show all measurements contained *below* the item that is selected in the left pane. I.e., when 'Project 1.sop5' is selected, measurements from all workspaces below ('Workspace 1' and 'Workspace 2') are shown on the right side - three in this case. But if a workspace is selected, only measurements from this workspace are shown, thus two measurements for 'Workspace 1' and one measurement for 'Workspace 2'.
Positioning: By default, the project browser is positioned on the bottom of the screen, but it may be docked to the top, left or right side as well.
Auto-hide during measurement: During a measurement the project browser is often not required and may be hidden once a measurement is started.
Custom columns: The columns headers on the right pane may be customized by the user through right-clicking any column header and choosing 'Select Columns...'. The user will be presented a list of all available properties and meta data applicable to the current project and may freely rename and use them as columns headers. (Learn more about measurement properties and meta data in our next newsletter issue.)
When dealing with larger amounts of measurements, the grouping and filtering options may come in handy. Grouping is done on the left pane and applies to workspaces: Within a workspace, the measurements may be grouped together e.g. by their function type (spectrum, time history, FRF, PSD, etc.), response or reference channel, measurement time or just their name.
Filtering is done on the right pane: For each column a filter may be applied to reduce amount of measurements shown. Right-clicking on a column header and selecting 'Filtering' shows a menu with automatically generated filters and a free field, which can be used like the windows search field. As shown in the example, one may select all measurements whose 'Name'-field contains an upper case 'S' by putting *S*. Similarly one could filter for measurements taken on a special time by putting a filter like '*-12-24' on the 'Measurement Time' column, showing only measurements taken on Christmas Eve.
Some general remarks:
The m+p Analyzer is all about measuring vibration data and providing traceable results that, even years later, can be reviewed and put into context. In this 6th issue, we will have a look at the data structure of the measurement object with its properties and metadata. You will learn how to work with metadata tags during measurement, in reviewing data sets and post-processing data.
At first glance, acquiring data is mainly about sampling a voltage signal - may it be acceleration, pressure, temperature, etc. - and saving those sample values to the hard drive. But that is merely what is required in a production setup: One might want to save not only time sampled data but spectra, PSDs, FRFs, octaves, etc. and while the actual sample values are the most important, properties associated to the measurement process such as sample rate, channel names, references, etc. need to be traceable as well. In m+p Analyzer, we solve this by having a data structure for the measurement that consists of three main parts: data, properties and metadata.
Many engineering tasks comprise repeated measurements of similar test specimen or measuring the same specimen in a slightly different test setup (ambient temperature, mounting, etc.). In these scenarios where repeated measurements need to be distinguishable, metadata and the auto-popup feature may come in handy. In fact, some of m+p Analyzer’s built-in measurement modes rely heavily on this feature, e.g. the shock capture which we will use as an example:
First open the “Configuration”, click on “Advanced” below and check “Meta-data”. Now you'll find a tab called "Meta-data". This tab allows the user to specify custom metadata tags suited for the given measurement task. It is specified by Name/Value pairs presented in a spread sheet. The Name field is how m+p Analyzer refers to a metadata, i.e. company, specimen no., operator and can later be used to filter data. The Value field is the actual content, which may be a text, a date or a predefined list of values. I.e. if only three specimens will be tested, one may specify a list and during the test campaign would just select the correct one from a dropdown menu instead of writing the name out every time.
The checkbox “Auto prompt metadata” enables the auto-popup feature, which will bring up a metadata screen when starting a measurement. The following example shows how to configure m+p Analyzer and enable the auto-popup metadata feature.
You can review and edit all data, properties and metadata of a measurement in the Measurements Editor. Select multiple measurements to block-edit several values of different measurements at once.
All metadata tags may be shown as column headers in the browser. The columns filters (see also Issue 5 in last Newsletter) can also be applied to metadata to filter for similar tagged measurements.
In this edition of our Newsletter series we will take a look at the throughput and post-processing features of the m+p Analyzer. We will show how to set up the m+p Analyzer for throughput recording and how to post-process the acquired data.
Throughput refers to the process of directly writing (streaming) acquired data onto the hard disk. m+p Analyzer provides many online processing options like FFT, FRF, PSD, Octave spectra, Order extraction and so on. We call that online because all metrics are computed while the measurement is running. After the measurement is done, the calculated data is stored in the .sop5 project file. See flowchart below.
Often, we only need to save these online processed data and subsequent analyses are performed on them. See for example an impact modal test: For modal extraction we would only save the measured FRF - the original time data is not required for modal model extraction. But in other cases, it may be useful to have the original data stream. In rotational analysis for example, when a run up of a machine is measured, it may not be obvious how to choose processing settings before we know the measurement result. In these cases, it is useful to just stream the data onto the PC and try different post-processing settings afterwards, based on the acquired data.
Thus, in post-processing, we can do just about everything we can do during measurement (except for changing sample rate). E.g. for our run up we could use post-processing to check if a different block size, overlap or order tracking algorithm improves our result - all without repeating the test itself!
See below how to set up a throughput and post-process it.
In this edition of our series m+p Analyzer Basics we will take a look at the reporting features of m+p Analyzer. We will show how to setup reporting, save and load templates and enable the quick report feature.
Configure Personalized Reports
The report features are intended to automatically place 2D charts, 3Dcharts as well as mode shapes in a .pdf or .docx document. A report may be defined to use all data available in a project or just the data from the currently selected workspace. Reporting templates for workspaces make it easy to generate reports very quickly: Just right click the workspace, select "Report (Workspace)" and the report is generated.
The reporting layout is pre-configured to display the most relevant information by default, but can be customized for your specific use. A wide range of configuration options are offered, most notably:
These are just a few of many options that allow for a custom-tailored report. The ability to save the reporting layout as a template for future projects is particularly convenient. A template file can be easily exported from m+p Analyzer and exchanged with colleagues or imported in new projects.
In this edition of our m+p Analyzer Basics series, we explain the basics of Operating Deflection Shapes.
Operating Deflection Shapes (sometimes called "Operational Deflection Shapes" or ODS) provide additional insight into vibration problems by visualizing the vibration pattern of a structure. In contrast to modal analysis, which can give similar insight, operating deflection shapes are extracted from measurement data acquired during real-world operation, hence the name "operating" deflection shapes. Typically, an ODS is presented in the frequency domain, as can be seen in this animation of a car frame at 16.4 Hz:
For a given frequency, the amplitudes and relative phases of all measurement points are extracted and applied to a geometry to visualize the deformation pattern. To clarify the process, let’s have a look at a very basic example. We consider only two points, where the phase of point 2 is referenced to point 1. The two spectra might look like this:
We can find three regions of interest marked by three cursors:
1. At the first cursor, we can see that both points show approximately the same amplitude and their phases are identical as well. The ODS from this configuration would look like this:
Both points move in phase with the same amplitude.
2. At the second cursor, the second point has significantly smaller amplitude than point 1. Also, a phase shift of 90° is observed. The ODS for this configuration looks like this:
The animation shows large movement of point 1 and the very small amplitude of point 2.
3. At the third cursor, both points again show the same amplitude but their phases are shifted by 180°. The ODS looks like this:
The phase shift of 180° means that the two points move in exact anti-phase to each other.
This example shows that an ODS is really just an animation of the amplitude and phase relations of the measured points. One might argue that it is quite easy to draw this information directly from the chart. This may be true for this simple example, but for more complex geometries like the car ODS above with many measurement points, it would be much more difficult.
Geometry: A geometry consisting of the locations of the measurement points on the structure is required. Typically, this means x-, y-, z-coordinates for each measurement point and defined connecting lines between these points. m+p Analyzer offers an easy to use Geometry editor for this task, which is sufficient for simple geometries. In case of more complex geometries the .stl file format (Standard Triangulation/Tesselation Language format) may be used to import geometries from a CAD software.
Phase referenced spectra: Because ODS requires phase information and "normal" spectra generally have random phase, additional treatment for phase referencing is required. Normally, this is done by choosing a reference sensor and referencing the phases of all sensors to it. This implies that the phase of the reference sensor becomes zero for all frequencies, as it is referenced to itself. Note: Data from the reference sensor and all other sensors needs to be acquired simultaneously! In m+p Analyzer, phase referenced spectra are calculated using auto- and crosspower spectra. For a given measurement point:
... the autopower spectrum results in the amplitude spectrum.
... the crosspower spectrum to the reference provides the phase referenced spectrum.
Steady state operation: Depending on how the data is acquired a steady state operation (or a least reproducible state) of the machine may be necessary. Generally, two approaches to data acquisition may be chosen:
1. Full sensor equipment with single measurement: This is a straightforward approach where sensors are applied to all desired locations. In a single run, data from all sensors is acquired simultaneously. The advantage of this approach is that it is quick as only one measurement run is required. However, this may require a large number of sensors and input channels on the front-end.
2. Partial sensor equipment with repeated measurements: With this approach, we can get all measurements done using as few as two sensors. One sensor - the reference sensor - remains at the same location for the entire test. The second sensor - the roving sensor – is successively moved to the remaining measurement locations and at each position a measurement is taken. While this approach requires less hardware, a steady state condition of the machine is required to make the individual measurements "compatible". This is because we "stitch" together measurements from different runs, and we need to make sure that the vibration pattern of the machine is identical for each run. The easiest way to achieve this, is to run the machine at constant RPM.
Are you interested in learning more about ODS measurement? Read the next issue of m+p Analyzer Basics, where we go through an example demonstrating how to measure and extract ODS using m+p Analyzer.
We measure the ODS of our rotating demo machine. It is made of a rectangular aluminum base plate onto which a motor and a rotating shaft are mounted (see picture). The goal is to measure the ODS of the foundation of the machine (the base plate) by measuring vibrations encountered during operation.
The first basic requirement for ODS animation is a geometry of the system under test. For the sake of simplicity, we only analyze the base plate of the demo machine. Eight measurement points on the base plate are defined and a basic geometry created in m+p Analyzer "Geometry Editor" (requires license AN-ODS/AN-eODS):
The partial sensor equipment method is used, with four accelerometers to measure the eight points on the base plate. We need three runs for all points: The reference sensor stays at position (1) the entire time. Three "roving" sensors measure positions 2, 3 and 4 in the first run, then 5, 6, 7 in the second run and finally only one sensor is required to get the measurement of the 8th position.
We first configure the sensors with their respective sensitivity and in our case we activate IEPE supply. Setting the first sensor to "excitation" (while all others are "response") will mark it as the reference sensor for phase referencing. We choose a sample rate of 2,048 Hz and a maximum frequency of 800 Hz in the spectra is sufficient. On the configuration save page we choose "ODS-FRF", which will give us phase referenced spectra. Note: These are "pseudo"-spectra. Because we use amplitude averaging, the actual spectrum doesn’t have useful phase information anymore. Behind the scenes, auto- and crosscorrelation functions are used to generate the "ODS-FRF" with meaningful amplitudes and referenced phases.
When we first started this experiment, we wanted to let the machine run at a fixed RPM and measure the vibrations on the base plate. We expected the motor to introduce enough "random" vibration to excite the bending modes. After setting up the machine, configuring m+p Analyzer and starting the first measurement we saw the following spectra:
This was not what we expected to see! Clearly there are many spikes in the spectrum, which don't seem to be structural vibrations. Closer inspection shows that all of these spikes are at integer multiples of 100 Hz (50 Hz being the power line frequency in Germany). It turns out that every time the motor is under load - meaning, it has to speed up the shaft, those spikes are present . So, we had to change plans: We sped up the shaft and turned off the motor to measure a run-down of the machine. The results look more promising:
While this is still not the most perfect spectrum, it will do for our purpose. This goes to show that even a simple demo machine may have its own quirks. Figuring out the best way to get data is part of the process and often solved with trial and error. There are two regions of interest in this spectrum. In the lower frequency range (~ 0 - 100 Hz), we see high vibrations due to the shaft rotation (~ 0 - 6000 RPM). The area is quite wide because we measured a run-down. Thus, all the different RPMs during operation are now found (smeared) in the spectrum. The second region from ~150 - 500 Hz is where we'll find the structural vibrations of the base plate.
With the measurements acquired by the previously described procedure, we can now start extracting the ODS using the m+p Analyzer "Operating Deflection Shape" wizard. The ODS wizard is a straight forward tool for ODS extraction. In three panes (left to right) we can see all valid measurements, a chart to select the frequency to which the ODS is extracted and the final ODS. Note: The ODS animation window also contains the frequency and an estimated damping ratio using half-power method.
As a final step, we can save the extracted ODS into the workspace. As an example, we extracted the deflection shapes for the first and second bending mode of the base plate at 153 Hz and 485 Hz:
Operating deflection shapes are a great tool to analyze the dynamic properties of a structure under operating conditions. They can help engineers to find and solve structural and acoustic problems. The procedure relies on the structures (machines) "self-generated" vibrations, thus the results are only valid for the given operating condition and only structural properties excited under the given condition are found. A different working condition (e.g. rotating speed) may result in different structural responses. A more general approach to analyze structural properties is modal analysis, which will be a topic in one of our next m+p Analyzer Basics issues.