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Torsional Vibration

Prime Photonics has performed extensive research in the field of torsional vibration and torque measurement.  Prime Photonics has built several advanced prototype instruments which optically measure the twist and speed of a rotating shaft.

The ultimate goal is to measure torsional vibration and torque through a completely non-contact system with no hardware attached to the shaft.  This sensor capable of measuring a bare shaft is called TVS™.  An intermediate sensor which relied on labels applied to the shaft, called TVS+™, was built and evaluated to prove the concept and help with the development of the final product.

We are currently looking for partners interested in these sensors to complete the development and bring the TVS™ instrument to market.

TVS™ Sensor: Measuring Torsional Vibration (Twist) and Speed of Bare Shafts

The prototype instrument measuring bare shafts, simply called TVS™, is a next-generation sensor which does not require any hardware or any markings on the shaft. 

Torsional Vibration Measurement System

Picture Above: Shaft Measurement Using TVS™ (center); TVS™ instrumentation (bottom right); TVS™ probe (top left)

TVS™ is an optical sensor which uses the unique optical reflective pattern of the shaft based on surface imperfections.  This optical fingerprint is tracked over time.  This sensor collects speed and twist (torsional vibration) data in real-time. 

To measure shaft speed, the system times the passage of each shaft section very accurately during each revolution.  Any change in speed is detected as a non-uniform time of passage of the shaft.  

To measure torsional vibration, the system accurately measures changes in speed and twist angle between the two probes.  

  • For extremely stiff shafts, measuring changes in speed is the only way to detect a torsional vibration.  This can be done with a single label and a single optical probe.
  • Measurement of dynamic twist, i.e. changes in twist around a mean value, allows measurement of both frequency and amplitude of torsional vibration.  

Additionally when there is no axial displacement of the shaft, the instrument measures static twist - i.e. twist averaged over a period of time - which is directly proportional to torque.  The more separation between the two sensors, the more accurate and sensitive the twist measurement.

At the moment TVS™ can measure up to +/- 5 degrees of twist with an update frequency of once per revolution.  Additional research is required to achieve the goal of measuring twist 16 times per revolutions, which allows detection of torsional frequencies up to 8x shaft speed.  TVS™ could also measure torque if there is no axial shift of the shaft.

TVS™ Components

The TVS™ system consists of two optical probes and an instrumentation box for collecting and processing data in near real-time.  The instrumentation box can output data of interest to a third party system via an analog or digital interface.  Alternatively, a remote computer with a secondary application GUI can be provided for viewing and recording data.

A complete system requires two optical probes mounted at opposite ends of the rotating member or shaft.  It is important that the surface the probe is mounted to is not subject to vibrations from the rotating member as vibrations can create noise in the optical signal and reduce the accuracy of torsional vibration measurements. Proper probe angle and alignment during installation is critical to accurate measurement.

Probe fixtures are typically mounted to a nearby rigid structure or shroud using threaded fasteners or magnetic mounts.  The mounts have simple rotating probe alignment cams that allow for rapid installation and alignment.  The probes can be provided with optical leads ranging from 1 m to 100 m, and are connected to the instrumentation box via common bayonet style optical connectors.

The instrumentation box supplies eye-safe laser light to the optical probes, converts the reflected optical signal to a digital signal, processes the digital data in near real-time, and produces an analog or digital output to host.  The host can be a third party system typical of industrial automation or a simple computer with host Graphical User Interface that plots and records data typical of a laboratory environment.

Data Output

The instrumentation box can output data of interest to a third party system via an analog or digital interface.  Alternatively, a remote computer with a secondary application GUI can be provided for viewing and recording data.  The system outputs the data in digital format (USB) and analog format (-5V/+5V voltage via BNC connectors or 4-20 mA current output via twisted pairs).  All analog outputs are configurable via software.


  • Have a hot application? No problem. Optical sensors have the best performance and longevity in environments with ambient temperatures of -40°F to 1100°F (-40°C to 600°C).  The default probes are not rated for high temperatures, please ask the sales team for our high temperature probes.
  • Contaminants in the environment such as grease can cause degradation of the optical signal over time.  For environments with significant contamination, an enclosure protecting the labels and the probes is recommended.
  • Vibration of the probe mount can cause reduced accuracy.  Therefore, it is preferred to secure the probe mounts to a rigid portion of the surrounding structure.
  • Hazardous area: the optical probes are intrinsically safe and can be used in any hazardous environment.  Very long optical leads can be built (300 meters / 1,000 feet) for locating the electronics outside of the ATEX zone.  For applications requiring the electronics to be located inside the hazardous area, air-purged enclosures are available upon request.


An Intermediate Step: affixing labels to the shaft

Prime Photonics has demonstrated good performance when attaching striped labels to the shaft and pointing optical probes to the labels.  Prime Photonics built a prototype instrument named TVS+ which used precision labels applied to both ends of the shaft and tracked the pattern of the labels over time.  TVS+™ measured torsional vibration, speed, twist, and axial displacement of shafts.  It tracked up to +/- 180 degrees of shaft twist.  Providing that the coupling exhibited sufficient twist, torque through the shaft could be calculated.  The TVS+™ system also measured axial displacement by tracking special markings on the label.

Torsional Vibration Measurement System

Picture Above: TVS+™ Torsional Vibration Measurement System

The following 2-minute video demonstrates the capabilities of the TVS+™ instrument on a small test rig. The rig represents a coupling instrumented with the TVS+™ labels on both ends.


TVS™ Software

TVS™ software is used for configuration of the analog output and verification of data.

TVS Plus Software

Picture Above: TVS™ Software Displaying Speed (top), static twist (middle), and axial displacement (bottom) from a TVS+™ instrument

Each analog output can be configured via software.  The user can select which data each channel will output, and scale the output of each channel.



The typical application for TVS+ is to instrument turbomachinery couplings and rotating shafts.  A few applications include pumps, compressors, rock crushers, turbines, synchronous motors and variable frequency drives (VFD) in a variety of industries from mining to power generation and oil & gas.

TVS plus torsional vibration sensorThe TVS™ and TVS+™ systems accurately measure speed and torsional vibration in rotating machinery.  They can be used for temporary measurement or for permanent installation.  Additionally, our sensors measure twist and the TVS+™ product also measure axial displacement of the coupling.


Using TVS™ to Measure Speed and Torsional Vibration

Torsional vibration and speed measurements can be achieved several ways, but the greatest advantages of our optical system approach are:

  • Non-Contact, No Hardware In-Line:  The entire system is stationary.  The sensor does not need to make contact with the shaft in order to give high accuracy measurement.  Rotating systems are sensitive to balance and loading conditions, by opting for a non-contact sensor you avoid these potential risks.  It eliminates the need for precision alignment that sealed systems or in-line systems require.  It eliminates the need for telemetry or slip rings that strain gauges require.  It also eliminates the weak point created in a drivetrain by an in-line system such as a torque cell, dynamometer, or torque meter.
  • Ease of installation:  Align the probes in front of the shaft and start collecting data.  Our TVS™ optical sensor does not require any marking or change to the shaft.  This makes it ideal for collecting data on existing installations.
  • Portability: The instrument can be used as a quick troubleshooting tool or permanently installed to the machinery for condition monitoring of torsional vibration.  The system is compact and fits in a hard case for ease of transportation.
  • Intrinsically safe: Optical systems are intrinsically safe and immune to electromagnetic interference.  The optical probes can be located in any ATEX zone.  Long optical leads allow the instrumentation to be located remotely, away from the hazardous area.  Instrumentation can also be enclosed in an ATEX rated enclosure.
  • No Power or Torque Limitation: the same sensor works for shafts of any size, any material, with any level of torque and power.  No more sizing of the system for each individual application.


Torsional Vibration Measurement

Torsional vibration measurements help you avoid downtime and surprises.

Torsional vibration is the angular vibration of a shaft about its axis of rotation.  It can be induced by variations in shaft load, unbalance, bearing degradation, or other undesirable characteristics of the drivetrain.

For example, Variable Frequency Drives (VFD) are notorious for generating torsional vibration in the coupled shaft.  More generally, the dynamic behavior of the whole drivetrain consisting of the driving force (turbine, VFD or other motor), the coupling shaft, and the driven load (such as compressor, alternator, or pump) generates torsional vibrations at given speed and acceleration conditions.

Other phenomena such as fluctuations in the available electrical power can also generate swings which induce torsional vibration.

Torsional vibration frequency is assessed by measuring variations in shaft speed at high resolution.  This can be performed in a single plane with a single sensor; however, a 2-plane, 2-sensor arrangement will give more accurate data, allowing differentiation between synchronous speed changes and actual torsional vibration.

Torsional vibration amplitude is determined by measuring the twist angle between two locations on the shaft.  This requires a dual-plane, dual-probe sensor.  Knowledge of amplitude is a critical factor in determining if a torsional vibration poses a high cycle or low cycle fatigue problem or if the vibration is benign for the sizing of the shaft.

Torsional vibration is usually not monitored continuously, resulting in unplanned failure.  Common failures happen in the coupling shaft. Both disc couplings and diaphragm couplings have experienced torsional failures.  Failures in other components, although not as frequent, also happen.

Torsional vibration measurements help identify issues in rotating equipment in lieu of scheduled maintenance intervals or prior to catastrophic failure.  Foreknowledge of a problem before failure and avoiding premature maintenance, results in less down-time and lower maintenance costs.

Torsional vibration on a piece of equipment can occur as a transient phenomenon during ramp up or ramp down while crossing specific speeds and frequencies of rotation.  It is essential for the operator to know where the torsional vibration frequencies are, to determine a safe range of operation and to avoid running for prolonged durations at damaging speeds.


Accurate shaft speed measurement

Hold your system accountable to the speed limits.  Speed measurement helps you ensure that your system is operating as intended.  Speed is critical in a variety of applications across industries.

  • In power generation speed changes can lead to fluctuations in frequency of the AC power produced.
  • In films and paper manufacturing variations in roller speed can lead to inconsistent product dimensions and scrap.
  • In automotive and industrial environments variation in speed can be an identifier of unbalance in the system.

Taking accurate real time speed measurements can allow you to automate system shut down before failure, identify out of tolerance product, and account for variation in your manufacturing system.  Our TVS™ system accurately measures speed and speed variation of your rotating assembly. 


More Information

For more information about the TVS™ prototype systems please fill out the form below.

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