CAT scale accuracy
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Mountain Pass
Joined: Apr 2021
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CAT scale accuracy
Has anyone had a problem with the accuracy of a CAT scale? I removed 135# from my camper since my last weigh in and put back 56# of water. My last weight was 9960# and today's weight was 9940#. I also had about the same amount of gas which was 1/2 tank. If you do the math I should be around 9881# which is off about 59#. So it just makes me wonder. Every thing else was exactly the same except for the gas which could have been a little more.
Hotshot
Joined: Jan 2010
Posts: 10,060
Likes: 491
From: Bristol, TN.
There is a small amount of wiggle room in terms of accuracy.
From the Internet - "According to the laws, scales must be accurate to 1/10 of 1% of the capacity of the scale. Back to that in a moment. Highways scales in most locations are either 200 or 300,000 pounds capacity. So multiply that capacity by the accuracy and it means the scale is only accurate within 200 lbs"
Plus trying to get exact with amounts of water and "about the same amount of gas" is tough. My thought would be human error plus a small bit on the part of the scale could throw things off a bit. There are multiple comments on the Internet reporting similar findings using CAT scales. Being designed to measure very large weighs, CAT scales are not intended to discriminate very small weights. Another quote about CAT scales used by truckers.
About scales - "must be good enough to satisfy commercial needs, but should not be subject to such stringent tolerance values as to make it unreasonably costly, complicated, or delicate." In other words it only has to be able to discriminate changes in weight that would cause truckers problems, hence the guarantee on the ticket. It is not accurate enough measure weight changes in people or groceries for example.
Steve
From the Internet - "According to the laws, scales must be accurate to 1/10 of 1% of the capacity of the scale. Back to that in a moment. Highways scales in most locations are either 200 or 300,000 pounds capacity. So multiply that capacity by the accuracy and it means the scale is only accurate within 200 lbs"
Plus trying to get exact with amounts of water and "about the same amount of gas" is tough. My thought would be human error plus a small bit on the part of the scale could throw things off a bit. There are multiple comments on the Internet reporting similar findings using CAT scales. Being designed to measure very large weighs, CAT scales are not intended to discriminate very small weights. Another quote about CAT scales used by truckers.
About scales - "must be good enough to satisfy commercial needs, but should not be subject to such stringent tolerance values as to make it unreasonably costly, complicated, or delicate." In other words it only has to be able to discriminate changes in weight that would cause truckers problems, hence the guarantee on the ticket. It is not accurate enough measure weight changes in people or groceries for example.
Steve
Hotshot
Joined: Jan 2010
Posts: 10,060
Likes: 491
From: Bristol, TN.
As long as you had the front wheels on one scale and the rear wheels on the other, it should make no difference. My interpretation of what I have read means you are expecting the scale to do something it is not designed to do and you are introducing possible changes by fuel estimates or water weight. The following is from a discussion about someone who asked about two different weighing with a trailer.
"This is a common misconception. Many people confuse accuracy with discrimination. By statute, a weighing device in a commercial application must be accurate within it's allowed error tolerance throughout it's range. But your trailer is small enough that it is conceivable that your trailer may have actually been up to 50 pounds lighter the second time but that difference is within the allowed error tolerance ...
generally +/- 0.1% of the applied weight, or possibly a total of two increments of discrimination, whichever is larger."
Search the Internet and you will find multiple discussions like this. Variations are common with all measuring devices, torque wrenches, multimeters, you name it.
Steve
"This is a common misconception. Many people confuse accuracy with discrimination. By statute, a weighing device in a commercial application must be accurate within it's allowed error tolerance throughout it's range. But your trailer is small enough that it is conceivable that your trailer may have actually been up to 50 pounds lighter the second time but that difference is within the allowed error tolerance ...
generally +/- 0.1% of the applied weight, or possibly a total of two increments of discrimination, whichever is larger."
Search the Internet and you will find multiple discussions like this. Variations are common with all measuring devices, torque wrenches, multimeters, you name it.
Steve
Tuned
Joined: Nov 2018
Posts: 398
Likes: 110
From: Southwest Montana & Idaho
Has anyone had a problem with the accuracy of a CAT scale? I removed 135# from my camper since my last weigh in and put back 56# of water. My last weight was 9960# and today's weight was 9940#. I also had about the same amount of gas which was 1/2 tank. If you do the math I should be around 9881# which is off about 59#. So it just makes me wonder. Every thing else was exactly the same except for the gas which could have been a little more.
There are some rental square scales we've been thinking about renting ($300) for a weekend to do some weights with our new NL 811 to see for starters if there are differences between the manufacturer and our numbers.
Hotshot
Joined: Jan 2010
Posts: 10,060
Likes: 491
From: Bristol, TN.
You will get differences depending on the tolerance to which the scale was built. The discrepancies being reported here are common and within acceptable design limits. This is all information available online.
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Senior User
Joined: Jul 2020
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Maybe it's just me, but I think in the grand scheme of things, in terms of trucks + campers, worrying about 100lbs or so isn't really worth concern. But if you're enjoying the challenge of weight shaving, enjoy.
Hell, as an former serious MTB'er from the 80's/90's, we were parsing grams...... drilling chainrings, derailleur cages, cutting excess seat post length..... LOL
Hell, as an former serious MTB'er from the 80's/90's, we were parsing grams...... drilling chainrings, derailleur cages, cutting excess seat post length..... LOL
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Tuned
Joined: Nov 2018
Posts: 398
Likes: 110
From: Southwest Montana & Idaho
Maybe it's just me, but I think in the grand scheme of things, in terms of trucks + campers, worrying about 100lbs or so isn't really worth concern. But if you're enjoying the challenge of weight shaving, enjoy.
Hell, as an former serious MTB'er from the 80's/90's, we were parsing grams...... drilling chainrings, derailleur cages, cutting excess seat post length..... LOL
Hell, as an former serious MTB'er from the 80's/90's, we were parsing grams...... drilling chainrings, derailleur cages, cutting excess seat post length..... LOL
Thread Starter
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Mountain Pass
Joined: Apr 2021
Posts: 115
Likes: 8
I did notice that my front axle weight was 20# more this time and nothing changed up there. My rear axle weight was 40# lower than last time. I admit I was enjoying playing the weight shaving game but just wanted more for my effort.
Lead Driver
Joined: Jul 2003
Posts: 9,353
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From: AKRON ohio
Every mini van on the road with a hitch carrier is overloaded, every contractor truck with a ladder rack and tool box is overloaded. I’ll never weigh mine so I can honestly say I had no idea I was overloaded
4wd Low
Joined: Aug 2020
Posts: 14
Likes: 11
Good article with an overview on CAT scales in Truck Camper Magazine
https://www.truckcampermagazine.com/...tch-challenge/
https://www.truckcampermagazine.com/...tch-challenge/