Wind Effect on Truck Scales

[lindbls]

I'm working with four above ground, low profile truck scales (bottom of the scales 7-18 are inches above grade). Wind effects cause fluctuations on the readings up to 600 lbs, both positive and negative, with or without traffic on the scale. Fluctuations occur regardless of wind direction. The scale company already provided some dampening of the scales to limit the fluctuations. This helped, but did not solve the problem. A large wind wall was constructed at one scale but is questionable whether it helped.

Any other suggestions? Blocking wind from beneath the scales would be easiest to construct. But, how much of the fluctuations are due to wind OVER the scales? How to quantify this with any reasonable accuracy?

I suspect this problem is not unique and has been resolved successfully somewhere...

 

[KRSServices]

Are you sure the problem is due to the effects of wind? It may be the scale itself. Does the reading flucuate all the time (windy or not)? Does the scale utilize a telemetry (or similar) cabling from the scale to the readout? Try this as a test.

Load the scale with a truck and semi-trailer and measure the flucuations in the readings. Next load with a flatbed (empty) and measure the flucuations. Thirdly, load with a passenger vehicle and again measure the flucuations. If they are relatively equal, the telemetry cabling, or readout device may be faulty. The scale pickup(s) could also be faulty. I would be interested to see whether the scale flucuations were different between the semi-trailer than with the flatbed.


KRS Services

http://www.krs-services.com

 

[lindbls]

Thanks for the response. The scale readings fluctuate with or without traffic on the scale when the wind is blowing. The magnitude of the fluctuations increase with increased wind speed. If there is little to no wind, the readings do not fluctuate at all, regardless of traffic.

We've seen fluctuations regardless of the size of vehicle, from passenger cars to loaded garbage trucks.

The scale company has dampened the scales as much as possible and they indicated there is nothing else they can do.

 

[IRstuff]

Is the measurement supposed to be that accurate? Why isn't it averaged over some period of time?

From a pure measurement statistics perspective, if the measurement falls with the error bounds of the measurement, it should be deemed correct to the extent possible.

TTFN

 

[ACtrafficengr]

It sounds like you are getting aerodynamic pressure effects on the scale surface, possibly caused by turbulence. Sort of a miniature Tacoma Narrows Bridge. Perhaps instead of a wall blocking the wind, you need to raise the grade on both sides of the scales to allow smoother airflow over them.

But then again, what do I know? I'm a traffic engineer. I'd cross-post your question to an aerodynamic engineering forum.

 

[KRSServices]

I'm assuming the scale is used to measure overloads, and therefore it has to be accurate. That number, depending on the DOT, could mean the difference between a "have a nice day" to getting an overload ticket. If it is beign used to determine haul loads (ie. from a gravel pit in a contract situation) it will be a contentious issue as a payment item or cost the owner money due to inaccuracies. Either way, a scale reading should not flucuate because the sole purpose or intention of the scale is compromised.

KRS Services

http://www.krs-services.com

 

[IRstuff]

But what is the allowable tolerance in the measurement of the overweight?

TTFN

 

[KRSServices]

I won't really matter. Lets say the limit before a ticket is 1000 lbs. If the scale is fluctuating +/- 600 and the reading is 1,500 lbs...yet the actual wieght is 100 lbs under. THe trucker gets the ticket. Another example, if a gravel hauler is being paid by the ton mile, and same as above, his actual weight is 25 tons, yet the scale measures 25.3 (600 lbs), he gets paid more than his haul is worth.

The scale should read accurate without flucuation.

KRS Services

http://www.krs-services.com

 

[cvg]

I hope the scale company is bonded or has guaranteed the scales. They should not be accepted if they don't function properly.

 

[dicksewerrat]

Call a few DOT's. they operate truck scales on the freeway system. They should be able to answer all your questions. Or some grain elevators, they pay by the ton.

 

[lindbls]

It sounds like this issue isn't as common as I suspected.

The acceptable tolerance is +/- 20 pounds. The scales are used to weigh both commercial and private vehicles at a landfill. When the fluctuations are several hundred pounds, a small, light private vehicle can weigh more when leaving landfill than when they arrived full of garbage (according to the scale reading). A few have even asked for a refund.

The DOT scales I've checked with are all below ground scales and have not had a problem. Other landfills I've contacted haven't had the probem either.

Lacking any other info, it seems most practical to install a wind curtain to keep wind from blowing below the scales as a pilot test. Trying to quantify the wind effects for both over and under the scales seems like an educated guess at best.

 

[KRSServices]

I'm not so certain that the wind is the chief constituent of the flucuations. There are hundreds of above grade scales, mobile and fixed, in use for applications such as landfills and gravel pits (hauling). This is the first I have heard of the wind having such a dramatic effect on a scale's readings. Before incurring the expense of constructing a windscreen, I would exhaust the options of having the manufacturer provide warranty to repair/replace whatever is defective on that scale. From what I have ascertained to date, it may be a balance of convenience for the manufacturer to assert the wind as a factor rather than a possible defect.

Just my observations and opinion after speaking with a few owner's of scales.

KRS Services

http://www.krs-services.com