Using IWT leads to reduced costs and increased reliability, while streamlining the testing process

Instrumented wheelset technology IWT 5

A smarter, more flexible and highly reliable measurement technology

A smarter, more flexible and highly reliable measurement technology

Why is instrumented wheelset technology important?

An instrumented wheelset is a railway wheelset that is equipped with sensors to measure the dynamic contact forces at the wheel-rail interface. Historically they are primarily used to verify that new or substantially modified vehicles are not prone to derail and won’t cause unacceptable levels of rail wear or damageThe IWT5 technology installed on a train. to the infrastructure.

It is no challenge to calculate the forces arising from the static axle load. The forces resulting from the dynamic interaction between vehicle and track however are more difficult to determine. Using instrumented wheelsets, these forces can be measured directly and enable a better understanding of the dynamic interaction between a vehicle and the track.

The measurement and evaluation of forces between wheel and rail is a key element in the approval process for new and modified vehicles in Europe and many other regions. Depending on the region, different testing standards are required. Europe uses the standard EN14363 while the US standard is 49CFR-213. However, testing using IWS is also common elsewhere, like in China, Japan and India.

What sets IWT5 apart from other technologies?

TÜV SÜD is in a unique position as it holds the rights, and technical teams for two world leading IWS technologies, namely the IWT4 and PROSE IWS technologies. This enormous pool of experience has enabled the development of IWT5, a technology offering numerous advantages over traditional technology. Like its predecessor IWT4, TÜV SÜD’s fifth generation technology IWT5, utilises the vehicles existing wheelsets without any destructive modification. This means that no special testing wheels need to be manufactured, which results in simplified project logistics, compressed schedules, reduced risks and lower project costs.

IWT5 provides accurate measurement of dynamic contact forces between wheel and rail.The integration of PROSE’s instrumented wheelset technology allows IWT5 to provide an improved user interface alongside vastly improved connectivity options and backwards compatibility for legacy wheelsets.

While testing vehicles, vertical, lateral, and often longitudinal forces need to be measured. With IWT5, it is now possible to measure all forces simultaneously in all three directions. While vertical and lateral forces are important to evaluate vehicle dynamic performances and track condition, longitudinal forces are critical for rolling contact fatigue and wear.

IWT5 is set apart from other technologies by using a unique telemetry system. The fifth-generation telemetry system has increased performance and robustness while also using a ‘plug and play’ architecture that allows for extremely fast replacement if needed. Generally, a great benefit of using telemetry systems is, that the need for slip-ring devices is removed, therefore increasing reliability and simplifying the installation of the system. As IWT5 is using an inductive telemetry system specifically developed for the railway environment, it avoids electromagnetic interference issues that are normally characteristic of radio-based telemetric systems. IWT5 does not need additional batteries, as an advanced inductive power transmission system ensures IWT5 is powered up whenever the vehicle is.

What benefits does IWT5 offer you?

IWT5 will benefit you in various ways. The optimisations include:

  • A higher reliability due to a reduced number of parts
  • More flexibility due to multiple transmission and output options
  • Improved performance in switches

By acquiring and integrating the IWT4 and PROSE IWS technologies and teams, TÜV SÜD has assembled the leading experts in IWT. As a client you will benefit by receiving an unrivalled level of support.

The advantages of IWT5

Advantages of IWT5

Specifications of IWT5

IWT5 avoids structural integrity issues, as the wheels do not need to be machined. This removes the need for any additional periodic ultrasonic inspection of the instrumented wheelsets. The interface of IWT5 impresses with its updated Measuring Wheelset Computer (MWSC), which allows for an innovative and improved user experience. It offers various configuration and diagnostic options while being visual and intuitive, adding to the user experience.Backwards compatibility ensures support of existing instrumented wheelsets for the years to come

IWT5 opens the door to additional interfaces such as, TCP/IP, EtherCAT, CAN, digital interface to imc Cronos and HBK Quantum X, analogue voltage. Additional interfaces are available on demand.

IWT5 is backwards compatible, allowing legacy instrumented wheelsets to be used for decades to come. As further development of IWT4, IWT5 wheelsets can be calibrated while mounted in the vehicle, as a newly developed mobile calibration rig enables this to be undertaken efficiently and accurately

Track Condition Monitoring

It is important to regularly monitor the railway infrastructure. This allows to take timely action when track conditions degrade rapidly. Monitoring trends gives valuable information that could help planning long term maintenance.

IWT5 enables data driven optimisation at the wheel-rail interfaceModern track condition monitoring is not only based on the traditional geometric measurements, but also on the measurement of the wheel-rail forces as a reaction to track irregularities.

IWT5 is capable of measuring at high frequencies while using the vehicles original wheelset. The high frequencies make it possible to locate irregularities, both singular and periodical. Collecting this data enables TÜV SÜD to clearly identify, quantify and classify areas of degradation of the infrastructure. This is specifically important as parts of the tracks might include sections where track or wheel wear is high, corrugation has developed, or poorly performing switches or crossings can be identified.

Instrumented wheelsets cannot replace track geometry measurements, but they provide a direct measurement of the impact a particular set of geometry has on wheel-rail forces.

Friction MeasurementMeasurement of Wheel/Rail Forces

Friction at the wheel-rail interface is a critical parameter for an effective railway. By identifying areas of the network with low friction in real-time, operators could potentially drastically reduce wheel flats on their fleet. While the measurement of high friction gives operators the opportunity to actively manage lubrication regimes and drastically reduce wheel wear.

Technical capabilities of the instrumented wheelset technology IWT 5

  • Typical measurement uncertainty of vertical and lateral wheel-rail forces (Q, Y): Typically, better than 3 % at 20 Hz.
  • Measurement of longitudinal creepage forces (X): Currently measured and soon will be supplied as a fully calibrated signal.
  • Cut-off frequency for X: Typically, in excess of 10 Hz.
  • Measurement of contact point position: Typically, ± 2 mm accuracy is achievable. Accuracy is degraded during two-point contact conditions.
  • Handling of two-point contact: Creates equivalent, global values for the contact forces. The individual contact forces for each of the individual points of contact are not measured.
  • Temperature: -25 °C to +50 °C, may be increased after consideration of the specific application.
  • Special wheel disc design required: No special requirements. Nearly all wheelsets can be used.
  • Modification of the wheelset: No destructive modification of the wheelset is required, so the wheelsets fatigue life is preserved removing the need for additional ultrasonic inspections.
  • Signal and power transmission: Next generation IWT5 telemetry system for wireless signal/power transmission, no modification to the axle or wheel required, no batteries required.
  • Permitted test speed: 4 - 500 km/h. Lower test speeds are possible for special applications.
  • Traction/Braking forces: Traction and braking forces may be applied with the exception of tread brakes and wheel mounted disc brakes. Care should be taken in all cases to avoid wheel flats.
  • Output interfaces: Analogue connections BNC or D-Sub, EtherCAT, CAN, TCP/IP, digital interfaces to imc Cronos and HBK Quantum X. Other interfaces on customer demand.
  • Backward compatibility: P32 Telemetry System, PROSE IWSs, IWT4 Inductive Telemetry System
  • Calibration: Laboratory calibration with wheelset removed. Recalibration under the vehicle using the IWT5 mobile calibration rig. (Note: vehicle lift required)

As IWT5 uses the vehicles standard wheelset, geometry and hence wheelset characteristics vary between wheel types, the characteristics given above are typical values.

TÜV SÜD is your trusted Instrumented Wheelset partner

: IWT5 is the product of a 50 year tradition of developing Instrumented WheelsetsTÜV SÜD’s instrumented wheelset team has its roots in two technology streams, the Swedish IWT technology and the PROSE/Minden technology, and with over 50 years of development history it is at  the forefront of IW technology.

In 2019, TÜV SÜD took over the IWT4 instrumented wheelset technology and key personnel from SNC-Lavalin (Formerly Interfleet). From developing the first generation of instrumented wheelset technology in the 1950s, to: IWT5 is the product of a 50 year tradition of developing Instrumented Wheelsets optimising it on to IWT4 and IWT5, our experience and knowledge base is vast.

With the acquisition of PROSE Instrumented Wheelset technology in 2021, TÜV SÜD‘s IWS competence is unrivalled, enabling the provision of a cutting edge and field hardened technology and ability to deliver prompt and competent support.


Any questions left? Check our FAQ on IWT5

IWT5 - Instrumented Wheelsets - Frequently Asked Questions (FAQs)


  • Is IWT5 available worldwide?

    Yes, just as we currently do with our legacy instrumented wheelsets, IWT5 can be trucked or flown to clients the world over. We have extensive international experience in the field, to date our wheelsets have been used in Germany, The United States, Canada, Brazil, China, Austria, Switzerland, Poland, Czech Republic, Sweden, Finland, Norway.

  • How do I know that IWT5 is robust?

    IWT5 is based on our core Instrumented wheelset technologies IWT4 and the “Minden technology, improved by PROSE”, both have been heavily scrutinised by both internal and external parties. For example, an independent review has been undertaken by an independent assessor appointed by the German Railway Authority, EBA. Furthermore, the calibration of our technologies have been scrutinised by the independent bodies SWEDAC and SAS part of ISO17025 laboratory accreditations. Our experience in using instrumented wheelsets in demanding applications ranging from hot, humid, and dusty applications on iron ore cars in Brazil, through to harsh Nordic conditions on EMU’s and locomotives in Scandinavia ensures that IWT5 is a field hardened technology.

  • What quantities can IWT5 measure?

    IWT5 is able to measure vertical, lateral and longitudinal forces. At the present longitudinal forces are not easily calibrated in our calibration rig, so this quantity is provided as a scaled but non calibrated signal. IWT5 can also output the lateral position of the contact patch, in other words, the lateral position of where the tread is meeting the rail.

  • Can all wheelsets be used by IWT5?

    Nearly! Instrumented wheelsets rely on strain gauges to sense the deformation of the wheelset when a force is applied. Extremely small wheels with thick webs, will be so stiff that the deformation is not measurable, hence these can't be used. That said, we have produced over 150 wheelsets ranging from freight cars, heavy haul ore cars, EMU’s, DMU’s and locomotives and all have performed well.

  • Can IWT5 be used on braked wheelsets?

    IWT5 can be operated with axle-mounted disc brakes, or during regenerative/resistive braking from the propulsion system. IWT5 cannot be used with tread brakes (as the tread brake clamping forces will affect the strain measurements in the wheel and hence interpretation of the wheel-rail contact forces) nor wheel-mounted disc brakes (due to the risk of the discs damaging the wheel instrumentation). However, even if brakes are fitted it is recommended that the brakes be disabled to avoid the risk of wheel flats.

  • How long can IWT5 operate for if measuring continuously?

    Our latest version of IWT5 is powered by an inductive power transfer system. This is a contact free system, eliminating the need for slip ring devices and battery systems which would require regular maintenance. So, with the latest IWT5 system, as long as your vehicle is powered up then so is IWT5.

  • How easy is IWT5 to use?

    IWT5 is a highly complex item of instrumentation which should be used by measurement technicians with suitable training. Given the systems intuitive interface and architecture, with the right background and training then the IWT5 system is easy to use.

  • How often do the instrumented wheelsets require calibration?

    After initial calibration of an IWT5 wheelset it is required that they are re-calibrated after they are reprofiled and it is recommended that they are recalibrated every three years.



Do you have any further questions related to IWT5? If you would like to know more, please feel free to contact us.

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