IWT4 - Frequently Asked Questions

Is IWT available worldwide?
IWT4 is manufactured by Interfleet in Sweden and shipped, trucked or flown to clients the world over. We have extensive international experience in the field of instrumented wheelsets.

How do I know that IWT4 is robust?
IWT4 has been heavily scrutinised by both internal and external parties. External review has been by an Independent assessor appointed by the German Railway Authority, EBA. This has been an exhaustive process. Testing has been carried out on a number of vehicles, EMU's, Freight Wagons and a Locomotive. Roller rig testing has also been undertaken. The system itself is CE marked, and undergone EMC testing, climate chamber testing, and even environmental testing to a military specification.

What quantities can IWT4 measure?
IWT4 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 non calibrated signal. IWT4 can also output the lateral position of the contact patch, in other words, the lateral position of where the tread is meeting the rail. Lastly IWT4 can also output an accurate value for the rotational speed of each wheel. In theory IWT4 can measure any load case that causes a significant strain in the wheel, the condition is that this load case needs to be simulated in a calibration process. One such particular load case is the spin moment and we are currently considering ways to calibrate for this.

Can all wheelsets be used by IWT4?
Nearly! IWT4 relies 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 measureable, hence these can't be used. IWT4 has not been tested on wheels with elastomeric elements, such as Light Rail Vehicles, hence it remains to be proven if we can instrument such wheelsets. IWT can be used on powered (locomotive or multiple-unit) and braked wheelsets, with the limitations on braked axles detailed below.

Can IWT4 be used on braked wheelsets?
IWT4 can be operated with axle-mounted disc brakes, or during regenerative braking from the propulsion system. IWT4 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.

Is there a difficulty in applying IWT to a narrow gauge locomotive powered axle with regards to constraint of space?
IWT4 is suitable for powered wheelset applications. In a narrow gauge locomotive application there is little room available for the power supply and radio equipment in its standard configuration. However Interfleet does have highly skilled instrument makers in-house, who are capable of manufacturing custom housings to meet most demands.

How long can IWT4 operate for if measuring continuously?
IWT4 is currently battery powered. Currently these batteries give a run time of approximately 11 hours and a battery change takes about 5 minutes. If longer run times are required Interfleet can adapt the system with larger capacity batteries or an inductive power supply.

How easy is IWT4 to use?
IWT4 is a highly complex item of instrumentation. As such, Interfleet's preference is that any test that requires IWT4 should be supported by Interfleet's test staff to ensure correct operation of the wheelset instrumentation and recording equipment. However if the client is likely to be a regular user of IWT4, Interfleet can supply equipment and training.

How often do the Instrumented Wheelsets require calibration?
After initial calibration of an IWT4 wheelset it is required that they are re-calibrated after they are reprofiled, and recommended that they are recalibrated every three years.

How long does it take to manufacture IWT4?
It currently takes about 12 weeks to instrument and calibrate an IWT4 wheelset, though we anticipate that this timescale will reduce in future. However, a vehicle's standard wheelset can be used directly with IWT4, removing the need for special wheel discs/axles to be manufactured, giving a significant reduction in total lead-time compared to other types of instrumented wheelsets.