What is a scale test car? How does it work?

Question

I noticed a little rail car that was being pulled around the yard, after it uncupled from a long pull on a Mail #9 trailer train. The car was a scale test car. Why was it on a train right behind the three lead locomotives? How does it work, and what is it testing ?

Answer 1

Most scales are tested once a year.If it fails they fix it and then test it every six months til it proves it will stay accurate,then they put it back on a yearly schedule.

Answer 2

Dave is right.  It is a car of known weight and when calibrating scales, either standard scales or "coupled in motion" scales, it is used either standing, uncoupled or in a train moving over the scale, knowing how much it weighs will tell how much inaccuracy (if any) is in the scale being calibrated.

The reason why it was entrained on the head end is that these are extremely heavy cars, made all the more precarious owing to a shorter wheelbase.  Further back in the train it'd be like swinging a sock around with a rock in it.  It will dramatically alter the slack action and you do not want it on the rear.

It is the same for transporting locomotives "DIC" (dead in consist).  Here there are air concerns as well, but you don't want the 200 tons banging around back in the train.  Some older locomotives are moved "dead in train."  Usually smaller engines, like old switchers, lack a "dead engine" feature in the air box.  So, these needed to be entrained near the rear, because of air brake operation.  Being older and smaller, as a rule, they are near the weight of a standard loaded 140 ton car today.  So, it's just another freight car, in reality.

In addition, these older engines don't have a "coupler stop" that is used for road moves on engines like the SW1500.  Being switchers, the arc of the swing of the drawbar in the coupler pocket is much wider than what a road engine will allow.  The reason is simple in that industrial tracks usually come complete with super tight radii.  The extra swing is necessary.  The coupler stops restrict this movement, which would be extreme in road movements.  In addition, whenever possible, these locomotives will not be found as the trailing unit in the consist.

I am curious myself as to how often scales need to be calibrated.

Anybody know?

Answer 3

First for Skidderback. I know that the grain elevators are calibrated every six months. A State authorized agent meets us when we spot the scale car. He does the official certification. The time frame might be different for other types of scales though.

And second, to Ziggie. Many industries have scales. Especially when materials and goods are sold by weight. This would include corn, soy beans, wheat, ores, scrap iron, and even sugar. I sometimes do switching in an American Crystal Sugar plant. The sugar goes out at about 100 tons per car to Hostess, General Mills, Kellogg's, Little Debbie, and dozens of others.

Answer 4

That would be a known total weight, used to test and calibrate scales.

Many possibilities as to why it was behind the three engines, figger it wasn't that hard to pull, so probably it was convenient to sennd the test car with them. Could have been for testing tractive power, but I kind of doubt it.