Rotational and Torsional Vibration Measurement and Analysis with DewesoftX

Course overview

This course provides a detailed guide to capturing and analyzing rotational and torsional vibrations using DewesoftX, ideal for drivetrain diagnostics in automotive, marine, and power-generation applications. You’ll begin by exploring vibration basics—how rotational speed variations and shaft twist affect equipment performance—and the physics of torsional systems (spring–mass–damper analogies).

Next, the training shows you how to enable the Torsional Vibration module, connect and configure two precise encoder or CDM sensors, and set parameters like gearbox ratio and angle offset. You’ll apply glitch and rotational DC filters, then derive output signals for rotational angle/velocity and torsional twist and speed differences.

Hands-on lessons include configuring the Counter Sensor Editor for custom sensors, using SuperCounter inputs for ultra-precise timing, and compensating for mounting errors and gear ratios. You’ll also learn how to export angle-aligned data and leverage the Order Tracking module for deeper harmonic and order analysis.

By the end, you’ll have the skills to diagnose vibration issues—like drivetrain resonance and coupling misalignment—with accurate measurements and advanced analytics, using DewesoftX’s integrated tools and synchronized data workflows.

Video overview

Vibrations are mechanical oscillations that occur around an equilibrium point. These oscillations can be either periodic or random.

Vibrations of mechanical devices in operation are typically unwanted. Such vibrations can be caused by imbalances in rotating parts, uneven friction, or the meshing of gear teeth. Unwanted vibrations can be minimized through proper design.

Any vibrating system can be decomposed into elementary parts:

• Spring (k): a means of storing potential energy

• Mass (m): a means of storing kinetic energy

• Damping (c): a means by which energy is gradually lost

Vibrations can be classified as:

• Free (after the initial disturbance, the system vibrates on its own) or forced (the system is subjected to an external force, often a repeating one)

• Damped or undamped

• Linear (all basic components of a vibration system—the spring, the mass, and the damper—behave linearly) or nonlinear (one or more components do not behave linearly)

• Deterministic (the excitation force or motion acting on the system is known at any given time) or random (the excitation cannot be predicted at any given time, e.g., wind velocity, road roughness, or ground motion during an earthquake)

When a system vibrates at its own natural frequency, it enters resonance—oscillating with the largest amplitude under the same excitation force.

Quantities used to describe vibrations include:

• Displacement (in [m])

• Velocity (in [m/s])

• Acceleration (in [m/s²])

These quantities are directly related: velocity is the derivative of displacement, and acceleration is the derivative of velocity.

Torsional vibration

Torsional vibrations are angular oscillations of an object, typically a shaft, along its axis of rotation. They are evaluated as variations in rotational speed within a cycle. RPM variations are usually induced by irregular driving torque or varying load conditions.

The level of torsional vibration is influenced by several parameters, including material properties and operating conditions such as temperature, load, and RPM.

Torsional vibrations are significant whenever power is transmitted through rotating shafts or couplings—for example, in automotive, truck, and bus drivelines, recreational vehicles, marine drivelines, or power-generation turbines.

The quantities used to describe torsional vibrations are:

• Angular position (in [rad] or [°])

• Angular velocity (in [rad/s], [°/s], or [RPM])

• Angular acceleration (in [rad/s²] or [°/s²])

All three quantities are directly related and can be obtained through integration and differentiation. The most common quantity used to measure torsional vibrations is angular velocity, often expressed as RPM.

The source of excitation is quantified by torque.

The system’s response is characterized by angular velocity and displacement, which describe the effect of the applied torque. Torque and angular velocity are closely linked:

Where T is the torque in [Nm], and Jz is the torsional constant or the polar moment of inertia in [m⁴].

This formulation is similar to Newton's law, which relates the force acting on a mass to the acceleration of that mass.

The torsional vibration software option in Dewesoft is used to provide a complete solution for monitoring and analyzing rotational/torsional vibrations in research, development, and optimization. With the compact form factor of Dewesoft instruments (e.g., SIRIUS, DEWE-43), it offers the perfect mobile solution for test engineers and consultants.

Torsional and rotational vibrations, along with the corresponding velocities, are calculated. The software can compensate for off-center sensor mounting and also account for gearbox ratios. Furthermore, Dewesoft provides advanced capabilities such as angle-domain visualization and data export.

When using Dewesoft to capture data from additional sources—such as video, CAN, or Ethernet—the data is perfectly synchronized within a single file. If the powerful integrated post-processing features of Dewesoft are not sufficient, the data can be exported into several different file formats.

In addition to torsional vibration analysis, the system can be expanded with the order tracking option, providing a more complete overview of the measurement situation.

System overview

Since torsional vibration measurements require extremely high accuracy, only precise counter sensors are supported. At least one encoder is required for rotational vibration, but typically two encoders are used for torsional vibration.

A variety of angular sensors are supported:

• Encoder

• CDM with zero pulse (Gear-tooth)

• Zebra tape sensor (with DS-TACHO4 and auto-gap detection)

• Sensor with missing teeth (e.g., 60-2)

For example, the CA-RIE sensor has a resolution down to 0.5° and is therefore less sensitive to vibrations, which could otherwise damage standard encoders over time.

Like many additional mathematical modules, torsional vibration is an optional feature in the standard Dewesoft package and must be enabled in the Math section.

Basic operating concept

The torsional vibration module in Dewesoft is one of several application modules that provide dedicated mathematics and specialized visual controls, such as angle-based XY diagrams.

The user interface of the torsional vibration module is divided into the following sections:

• Input: Define the counter channels for input (e.g., CNT 7, CNT 8).

  Counter Setup: Define the type of angle sensor (e.g., Encoder-512, CDM-360, etc.), and select the gear ratio if gearing is used.

  Filter Setup: The input filter is required to prevent glitches and spikes in the signal. The rotational DC filter should be set to remove the DC component from the RPMs. The filter must be configured to include all desired frequencies, but not set too low; otherwise, static DC deviations may appear in the output signal.

  Output Channels: Select which calculations should be performed (e.g., rotational velocity, torsional angle, etc.).

  Angle Offset: Compensate for constant angle offset, off-center mounting, or sensor errors.

  Output: Preview the output channels, and switch between them using the arrow buttons.

  Preview: View a preview of the torsional angle.

  Switch to View Channel List in the upper-right corner to display the list of calculated output channels.

here are some typical sensors predefined. However, if your sensor type is not listed, you can define a custom sensor in the Counter Sensor Editor. For the Torsional Vibration module, you can use different types of sensors:

• Encoder

• CDM with zero pulse (Geartooth)

• Zebra tape sensor (with DS-TACHO4 and auto-gap detection)

• Sensor with missing teeth (e.g., 60-2)

To configure, go to Options > Editors > Counter Sensor Editor.

First, click Add Sensor, then enter a name and configure all other required parameters. The available parameters will vary depending on the selected sensor. When finished, click Save & Exit.

The sensor will then be accessible from the dropdown menu in the Torsional Vibration module.

It is important to understand that the torsional vibration module can measure two distinct parameters: rotational vibration and torsional vibration.

Rotational vibration refers to the dynamic component of the rotational speed. When measuring the rotational speed of the shaft with high precision, significant deviations in speed can be observed in certain regions of the run-up. These deviations occur when angular vibration crosses the shaft’s angular natural frequency. Rotational vibration is calculated by removing the DC component of the rotational speed or rotation angle.

In the graph below, two curves are shown: the upper curve represents the RPM, while the lower curve displays the deviation in degrees, which corresponds to the rotation angle vibration. During coast-down, the maximum vibrations appear again at the same RPM values.

The graph illustrates the run-up and coast-down phases, where the static twist of the shaft is clearly visible. As the system passes through the natural frequency, the shaft’s angular vibration reaches its maximum.

Torsional vibration is the oscillation of angular motion (twist) that occurs in rotating parts such as gear trains, crankshafts, or clutches. To measure torsional vibration, two encoders are required, as the measurement is essentially the difference between the angles recorded by the two encoders. Torsional vibration analysis also captures the static twist of the shaft at higher RPMs.

Both torsional and rotational vibration can be measured using either an encoder (with a resolution of up to 3600 pulses per revolution) or a special sensor (e.g., CA-RIE-360/720). Although the special sensor has a lower resolution (up to 720 pulses per revolution), it is much less sensitive to vibrations that could otherwise damage standard encoders.

For our test setup, we use an electric motor (placed in the center) and two encoders. The encoder on the left is connected to the motor via a coupling, while the encoder on the right is connected with a spring to intentionally generate high vibrations.

Since we are currently only interested in rotational vibration, we will use only the encoder on the right side, which is connected with the spring. This encoder is connected to the Dewesoft instrument through a Counter input.

As mentioned earlier, there is no need to configure the analog or counter channel setup. Simply go to the Torsional Vibration module and select the First Sensor Input. For example, if the first sensor is connected to CNT 7, select it from the list. Then, define the sensor. If the sensor provides 1800 pulses per revolution, choose Encoder-1800. If the required sensor type has not yet been defined, it must first be created in the Counter Sensor Editor.

Next, set the Input Filter for the counters. This filter is required to prevent glitches and spikes in the digital encoder pulse signal. It can be adjusted from 100 ns to 5 µs, with the optimal value determined using the following equation:

Example: Suppose our machine is running at 3000 RPM and we are using an encoder with 512 pulses per revolution. If we insert these values into the equation above, we obtain the following result:

The rotational DC filter must be set to remove the DC component of the RPM signal. The filter should include all relevant frequencies, but not be set too low; otherwise, static DC deviations will appear in the output signal. The filter can be adjusted from 0.1 to 10 Hz. It is important to ensure that your lowest RPM is not filtered out.

A 10 Hz filter, for example, means that frequencies below 600 RPM will be suppressed.

Output channels

The output channels are:

• Rotational angle: The filtered angle value of vibration.

• Rotational velocity: The filtered velocity value of vibration.

• X-axis reference angle: The reference angle, always ranging from 0 to 360, which can be used as a reference for angle-based XY diagrams.

• Frequency: Expressed in RPM units.

When you switch to Measure mode, the calculated channels of the Torsional Vibration module are shown in the channel selector on the right side. The first step is usually to select the TV_Frequency channel and display it in either an analog/digital meter or a recorder.

The Sensor_1_angle is the reference angle and can be used for an angle-based display in the XY recorder. To set this up, add an XY recorder and first click on Sensor_1_angle (x-axis), then on RotAngle_1 (y-axis). Next, in the properties panel on the left side, set the recorder to Angle-based X-Y. Select, for example, two periods to be displayed. The XY recorder will now show the rotational angle of the current revolution. It functions like an oscilloscope but uses an angle reference instead of a time reference.

Vary the RPM, and as you approach the resonance frequency, the amplitude will reach its maximum.

In the next graph, the rotational velocity (the first derivative of the angle) is also added. According to theory, it is shifted by 90 degrees.

The next step is to measure the torsional vibration.

On the left side, there is an encoder with a rigid (coupled) connection to the motor, while on the right side, there is another encoder. Both encoders are connected to Dewesoft hardware through counter channels. The torsional vibrations of the metal spring in between are measured.

Add a Torsional Vibration module. In the setup, select both input channels. For example, choose CNT0 as the first channel and CNT1 as the second channel. Then define Sensor 1 and Sensor 2 by selecting the correct type from the dropdown menus on the right side. If a gearbox is present between the encoders, enter the Gearbox ratio, which is used to measure the torsion angle across the gearbox.

As explained in the rotational vibration section, you can apply an input filter to clean the signal from glitches. The rotational filter removes the DC offset from the difference signal.

The Input filter can be set within a range between 100 ns and 5 ms. The optimal setting is derived from the following equation:

We have the following Output channels:

• Torsional angle: The dynamic torsional angle, representing the angle difference between Sensor 1 and Sensor 2.

• Torsional velocity: The difference in angular velocity between Sensor 1 and Sensor 2.

• Sensor 1 rotational angle

• Sensor 2 rotational angle

• Sensor 1 rotational velocity

• Sensor 2 rotational velocity

• X-axis reference angle: A reference angle that always ranges from 0 to 360 and can be used as a reference in angle-based XY diagrams.

• Frequency: Measured in RPM.

In the Angle Offset section, you can see the angular difference between the two sensors. Click Zero to remove this static offset. The current average value of the signal will be subtracted. Then, click on the y-axis to auto-scale the signal.

Reference curve configuration

There is also an option to compensate for off-center mounting and unstable pulses from the encoder.

Centered mounting is very important. In the first picture (1), there is no issue—the disk is mounted perfectly. However, in real life, off-center mounting, as shown in the second picture (2), often occurs. Imagine drawing a red line on the disk at 0 degrees and a blue line at 90 degrees. When the disk is rotated, the sensor (black box) will count the pulses and, after a certain number, detect the 90-degree position. But if you look at the disk, it is actually far from 90 degrees!

Imagine the disk rotating: a constant sine wave will be generated in addition to the torsional vibrations. This can be compensated in Dewesoft using the Reference Curve. However, it is essential that the load is removed from the engine—it must be free-running. Otherwise, you may also cancel out the vibrations you actually want to analyze.

When the machine is running at idle speed with no significant torsional vibration, press the Set button.

The current curve is then recorded over one revolution as a reference. After this, the line becomes much flatter.

Now let’s perform the measurement. We have added an analog and a digital meter for frequency, a recorder for frequency, torsional angle, and torsional velocity, and we have also included an angle-based XY display for these parameters.

The run-up and run-down clearly show the static torsion angle as well as the region of the natural frequency, where high torsional vibration values occur.

To extract orders from torsional or rotational vibration, we need to add the Order Tracking module. For the frequency source, we must define the Torsional Vibration module. To do this, select the previously created module and then choose the Frequency channel within that module (if torsional vibration is being used).

Next, we need to define the Upper RPM limit and Lower RPM limit. These settings reserve memory for the waterfall FFT. The waterfall will be generated from the lower to the upper limit in steps of ΔRPM. In this case, we will have:

(3000−0)/50=60(3000 - 0) / 50 = 60(3000−0)/50=60 steps in the waterfall.

Finally, we extract the first three orders by entering 1; 2; 3 in the Harmonics field.

Now let’s perform some measurements. Since we already have the frequency and harmonic channels, we can add an XY display to visualize the orders. The OT_Frequency should be used as the x-reference (the first selected channel on the x-axis), while the RotAngle_1/Amplitude1, RotAngle_1/Amplitude2, and RotAngle_1/Amplitude3 orders should be used as the y-axis. Performing a run-down allows us to clearly observe the orders, where we can see a peak at 2422 RPM, previously detected in the recorder, corresponding to the first order of vibrations.

To visualize this even more effectively, we can add a 3D graph. This graph can only display matrix channels. Order tracking provides two of these — the Order Waterfall and the FFT Waterfall — both of which can be used as data sources. Once we start a run-up or run-down, the color representation shows the amplitude at specific frequencies and RPMs. It is important to carefully select the amplitude scale to ensure the graph is displayed clearly. To make smaller amplitude values visible, a logarithmic y-scale is recommended.

In addition, the amplitudes and phases (or even the real and imaginary components) of the orders can be plotted against frequency. For this, use an XY recorder, but set the graph type to Single x-axis to create a Bode plot. The first harmonic (green line) is clearly visible, with its maximum occurring around 2400 RPM, aligning well with the previous measurements. The phase shift further indicates the presence of resonance.

One of the standard measurements is to perform a run-up of the machine and then calculate the maximum amplitude from the FFT.

To do this, add an FFT analysis function from the Frequency Domain Analysis section in Math.

Next, select the input channel — for example, Torsion_angle — and set it to Amplitude, Overall, with the averaging type set to Peak.

Here is an example performed offline on a data file (although you can also perform it online during measurement). A section was selected in the recorder instrument (green line) to analyze only the run-up of the machine.

Next, a 2D graph was added (see instrument bar, red box), and the AmplFFT math channel was assigned.

For convenience, the Y-axis type can be set to logarithmic in the 2D graph properties (left panel).

You can either perform a standard export or simply click on the 2D instrument and use Options → Copy to Clipboard → "Widget data".

Exporting the data (e.g., pasting into Excel) produces the following result:

The angle-based display of measurement data is often very useful. In the XY recorder, assign the reference angle Sensor_1_angle to the x-axis, and then select one of the following views:

• Single x-axis: Displays all cycles layered over each other (persistence mode). This makes it easy to identify minimum and maximum values across cycles. The persistence can be adjusted using the Pretime limit in the properties.

• Angle-based XY: Displays only the current cycle, functioning like an oscilloscope.

Now, how can this cycle-based data be exported? Go to Math and add a Time-to-Vector transform.

With this powerful tool, Dewesoft arranges the input data (e.g., Torsion_angle) over Sensor_1_angle in a matrix by resampling the values to the angle base. You can also select the resolution; in this example, we use 1 degree.

The output data includes Actual, Average, Minimum, and Maximum values across all cycles.

To display matrix data, you need to use a different visual instrument: the 2D graph. From there, you can assign the ACT (Actual), MIN (Minimum), MAX (Maximum), or AVE (Average) channels generated by the Math function.

After storing a data file, go to the Export section and select only the three matrix channels (to ensure that the data is exported in the correct format).

In this example, we exported the data to Excel. Instead of a time axis, the export provides angle-based data.

If you copy the data into Excel, use the Paste Special... function. This allows you to transpose columns and rows automatically, so the angle is displayed from top to bottom instead of left to right.

Selective export:

To analyze a specific section of your data file in Dewesoft, use the Recorder instrument. Position both white cursors (I and II) and click between them. The calculation and export will then be performed only on the selected section.