What are Scale Test Cars used for? I’ve heard mention of them before on this forum, (and others) and am still none-the-wiser as to what their prupose is for[sigh].
I found a link to a website with pictures and a description of “Cars used to test railroad track sales”, but this hasn’t cleared matters up for me. As far as I can see from the pictures we in the UK have nothing similar to these.
It’s esentially a “known weight” that the RR can put on a scale so that they know if the scale is calibrated correctly.
ie - they know that the test car is 3.75 tons (ok, I’m making up a number here), but the scale reads it as 3.5 tons; so they have to recalibrate it to read 3.75 tons when the test car is on the scale.
A “scale” test car is used to check the accuracy and calibrate track scales. For simplicity sake, this is just a large scale with track on it for checking car or loco weight. The “test car” has a known weight and when placed on the track scale, the scale should read out that weight. Ken
Scales used for trade or commerce usually are required to be regularly tested for accuracy and recertified. Scale cars are used for this purpose on railroads. These are typically certified at a central location, usually against a government standard or from a standard derived from such a standard.
Then the scale cars are sent out to check the scales actually used on the railroad. In the past with single car railroading, these were usually on a siding, with some sort of bypass arranegment like a guantlet track so that there is no operation across the scale itself except when weighing is going on. Usally locos were not permitted on scales. Nowadays, there are electronic weigh-in-motion systems and such, so old time scale tracks are becoming an endangered species like many other aspects of railroading.
In American practice, the scale car was typically handled on the rear of trains. They don’t have an air brake system, because the wear of brake shoes in normal use would change the weight of the scale car and lead to inaccuracies. A hand brake is provided to hold the scale car in position. The scale car would be placed on the scale and then the scale would be recalibrated to the verified weight provided by it.
My guess is that foreign systems probably had a very similar process, although scale cars can come in different configurations. Seeing such a car was usually rare, except for once a year or at whatever interval recertification of scales was required, at any single location.
Scale cars can be used to add an extra twist to operation- the presence of a “traditional” two-axle scale test car on a train would usually require that it operate at a restricted top speed, say 25 miles per hour.
Scale test cars typically didn’t behave well at higher speeds due to their short wheelbase and lack of brakes.