Sherline Trailer Tongue Weight Scale accuracy

[Berdan]

The purpose of this thread is not to weigh (pun intended) the merits of using a tongue weight scale vs. going to a CAT scale. It is more to note my observations of calculation accuracy of measurement using a tongue weight scale.

Sherline notes that the accuracy of their scale is best in the mid range of the scale (mid 50% of range) and the implication is that you should buy a scale with a max range that will allow the result to be in this midrange. However this will not necessarily provide the best measurement accuracy.

The pressure gauges in the Sherline scales provide pretty good accuracy; 3% in the bottom and top 25% of the full scale range and 2% in the mid 50%. The percent accuracy is the percentage of the full scale range of the gauge.

For a 1000 pound scale 2% measurement uncertainty is +/- 20 pounds and for 3% is +/- 30 pounds. The mid-range for this gauge is 250 to 750 pounds.

For a 2000 pound scale 2% measurement uncertainty is +/- 40 pounds and for 3% is +/- 60 pounds. The mid-range for this gauge is 500 to 1500 pounds.

Now lets say, for instance, that you expect your tongue weight to be around 800 pounds, and that is what your scale measures. This measurement is outside the mid-range of the 1000 lb. gauge and inside the mid-range of the 2000 lb gauge. If you follow the guidance of Sherline, it might seem that you want to use the 2000 pound scale for better accuracy.

However the measurement uncertainty, outside of mid-range. in the 1000 lb. gauge is +/- 3% of full scale or +/- 30 lbs. If you use the 2000 lb. gauge the measurement uncertainty is 2% of full scale or +/- 40 lbs. in the mid-range.

So, all other factors being equal, in this instance the 1000 pound gauge should produce a more accurate measurement outside of mid-range versus a measurement within mid-range of a 2000 lb. gauge.

Generally you should pick the scale that will encompass the range of weights that you expect to measure.

[Customer1]

The thing I have learned about my Sherline is you should always take multiple readings. The scale is sensitive to being perfectly perpendicular to the load. If the scale is cocked a little off perpendicular it will cause stiction between the cylinder and piston and read low. Multiple measurements while adjusting the scale position will insure an accurate reading.

[Berdan]

I just jiggle the coupler around until it settles in to the highest weight. Not very scientific :-)

[German Shepherd Guy]

"Berdan I just jiggle the coupler around until it settles in to the highest weight. Not very scientific :-)"





I love it Berdan, after all the "scientific" in the original post.

[Berdan]

I love it Berdan, after all the "scientific" in the original post.
[/QUOTE]

Sometimes you're "scientific" and sometimes just "good nuff".

[JRTJH]

Originally Posted by Berdan

I love it Berdan, after all the "scientific" in the original post.

Sometimes you're "scientific" and sometimes just "good nuff".[/QUOTE]

And sometimes you're: The hitch ain't draggin' the ground, so we're good to go, get in the truck boys.....

[wrvond]

I packed my Sherline in high density foam inside a plastic case in the upright position, yet it somehow managed to leak out it's oil.
One thing I have determined is that using a bathroom scale with a a beam and fulcrum is just as accurate and much less expensive.