Teknis: WCM Normalization

Wheel Condition Monitor (WCM)

NORMALIZATION

The system normalizes all impact readings to the vehicle's fully loaded condition.

A nominal (good) wheel passing over the system reads zero whether it is loaded to 20 tonne or 3 tonne. A defect on that wheel may cause an impact reading of say, 100 kN but the track actually sees the load PLUS the 100 kN. As explained, the load can vary quite a bit and so without some normalization the impact reading will vary one pass to the next. The 100 kN defect in this example without normalization would record 130 kN empty (30 kN load + 100 kN impact) and 300 kN full (200 kN load + 100 kN impact).

One normalization scheme used in other systems is to use an 'Impact Factor'. This is impact force/static force. In this example this would yield 100/30 = 3.3 for the empty and 100/200 = 0.5.It does not work very well but serves some purposes. It is completely useless for trending wheel defects though.

What the Teknis WCM does is assume a fully loaded vehicle and adds the impact to that.

For a gross vehicle rating of 80 tonne the wheel force load is 10 tonne which is 100 kN force due to gravity.

A 100 kN impact then reports as 100 kN maximum load + 100 kN impact = 200 kN total force.

The maximum vehicle load cannot be measured as it goes over the site. It has to be looked up in tables. The WCM does measure the actual axle load if it has a weighbridge option installed but this is never used in impact calculation. Maximum load is determined as follows:

If tagged, look up vehicle class in a table and get total number of axles and maximum gross and calculate the maximum wheel load.
If not found or not tagged then look up maximum structure load in the WCM table for the site. Site maximums vary and so this is not the best method for multi-site traffic.

Although there are normalization functions for speed these are not normally applied above 80 km/h because for the bulk of wheel defects there is not a significant increase in defects with regards speed above 80 km/h. This is highly dependent on the defect shape and type but experience has shown that well over 95% of defects are speed independent (above 80km/h). Ovalities and out-of-round defects are highly speed variable below 80 km/hr. Significant variability starts to appear as the wheels slow down below 40 or 50 km/h.

A Traditional strain gauge based impact measurment and reporting. Cannot separate the forces.

B Teknis WCM impact normalization.

Impact forces are in a much more damaging frequency domain and have much sharper loading and unloading than normal rolling forces. They need to be isolated and quantified. The WCM isolates and reports all the measures shown in B above.