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  1. #1
    Site Team Second Chance's Avatar
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    CAT scale resolution and accuracy

    Reading a question posted on a non-Grand Design forum got me to wondering, so I contacted the CAT scale company to ask about resolution (the smallest possible change of a quantity which can be reliably measured by a sensor) and accuracy of CAT scales. I received a very prompt reply from them and thought some might be interested:

    "The variance of our scales is established in the National Institute of Standards and Technology Handbook 44 Table 6. Class IIIL scales are allowed one division, or a 20 pound variance off zero for each 10,000 pounds of weight applied.

    Most calibration tests preformed by either the State Weights and Measures or a licensed scale service company will use a minimum of 20,000 of certified test weights. In the case of a 20,000 pound test, anything beyond a 40 pound error in reading would be a failed test.

    In the case of CAT Scale, all of our scales are calibrated at least four times per year by a licensed service company and we require the calibration to be adjusted to zero error."

    So... with my 25,020 lb. combined weight, that number could be up to 50 lbs. off either way.

    Rob
    Last edited by Second Chance; 05-30-2020 at 12:34 PM.
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  2. #2
    Rolling Along jim1521's Avatar
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    Thanks Rob. I knew it was +/- 20 lbs, but didn’t know it was per 10,000 lbs.
    2016 Grand Design Reflection 313RLTS
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    Quote Originally Posted by Second Chance View Post
    Reading a question posted on a non-Grand Design forum got me to wondering, so I contacted the CAT scale company to ask about resolution (the smallest possible change of a quantity which can be reliably measured by a sensor) and accuracy of CAT scales. I received a very prompt reply from them and thought some might be interested:

    "The variance of our scales is established in the National Institute of Standards and Technology Handbook 44 Table 6. Class IIIL scales are allowed one division, or a 20 pound variance off zero for each 10,000 pounds of weight applied.

    Most calibration tests preformed by either the State Weights and Measures or a licensed scale service company will use a minimum of 20,000 of certified test weights. In the case of a 20,000 pound test, anything beyond a 40 pound error in reading would be a failed test.

    In the case of CAT Scale, all of our scales are calibrated at least four times per year by a licensed service company and we require the calibration to be adjusted to zero error."

    So... with my 25,020 lb. combined weight, that number could be up to 50 lbs. off either way.

    Rob
    Thanks Rob
    I had wondered about the accuracy.
    THAT'S ACCURATE
    Bob A.
    Bob & Alice
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  4. #4
    Seasoned Camper SteveTN's Avatar
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    Interesting - more accurate than I expected
    Steve and Peggy
    Based in beautiful East Tennessee
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    Quote Originally Posted by Second Chance View Post
    Reading a question posted on a non-Grand Design forum got me to wondering, so I contacted the CAT scale company to ask about resolution (the smallest possible change of a quantity which can be reliably measured by a sensor) and accuracy of CAT scales. I received a very prompt reply from them and thought some might be interested:

    "The variance of our scales is established in the National Institute of Standards and Technology Handbook 44 Table 6. Class IIIL scales are allowed one division, or a 20 pound variance off zero for each 10,000 pounds of weight applied.

    Most calibration tests preformed by either the State Weights and Measures or a licensed scale service company will use a minimum of 20,000 of certified test weights. In the case of a 20,000 pound test, anything beyond a 40 pound error in reading would be a failed test.

    In the case of CAT Scale, all of our scales are calibrated at least four times per year by a licensed service company and we require the calibration to be adjusted to zero error."

    So... with my 25,020 lb. combined weight, that number could be up to 50 lbs. off either way.

    Rob
    Good info Rob. I too knew about the plus/minus 20 but didn't know about the @10,000 lbs part. Thanks for posting
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  6. #6
    Big Traveler Wicked ace's Avatar
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    I spent the majority of my working life doing instrumentation. Calibration was a large aspect of it. In most instances, even in pharmaceutical and nuclear power industries the accepted tolerance is 1/2 of 1 percent of scale (.005). What they told you is .002 tolerance, pretty tight. I suppose they do that because the scales are used as tare. Meaning the printed ticket they issue can be used as confirmation of weight for payment. Whenever things got into revenue the more attention and detail paid to the measuring / metering device.
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  7. #7
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    If 20 or 40 pounds is going to make a difference you're probably already overloaded.
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  8. #8
    Left The Driveway
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    I know I'm late to this discussion, but notwithstanding what "CAT" states as their accuracy, I'm having a hard time believing it with my actual experience. Since purchasing our 2019 397TH, I have meticulously entered the weight of everything that goes into the rig - using a scale or whatever weight has been assigned per the package, invoice, on line etc. This goes for food, clothes, tools, miscellaneous, whatever. I normally dump all my FW, grey and black tanks prior weighing and have full diesel. I have weighed the rig (and truck) numerous times and get an average of about 400 lbs of "extra" (unaccounted for) weight in the rig. I can easily understand 100 or 200 due to potential human error but 400 seemed off. Eventually, I simply added the extra 400 lbs to my spreadsheet as a hidden default weight coming from "somewhere" (original GD UVW?). However, I then bought an electric golf cart and about 400 lbs of other junk and added it to the rig. My new weight should have been about 1400 lbs more than before (everything else being equal - included the hidden 400). Well the hidden 400 lbs is now around 800 lbs. I now have 800 lbs of weight I cannot account for. And by the way - if I go to get a "second opinion" at another CAT scale - the result may be another 300-400 lbs heavier. The GD UVW may be the culprit for the extra 400 lbs originally, but an extra 400 lbs after I add 1400 lbs? Eventually going to find an alternative way/Company to measure the rig. There's a "Penske" scales about 200 miles north of us - will try them.

  9. #9
    Site Team xrated's Avatar
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    Quote Originally Posted by Second Chance View Post
    Reading a question posted on a non-Grand Design forum got me to wondering, so I contacted the CAT scale company to ask about resolution (the smallest possible change of a quantity which can be reliably measured by a sensor) and accuracy of CAT scales. I received a very prompt reply from them and thought some might be interested:

    "The variance of our scales is established in the National Institute of Standards and Technology Handbook 44 Table 6. Class IIIL scales are allowed one division, or a 20 pound variance off zero for each 10,000 pounds of weight applied.

    Most calibration tests preformed by either the State Weights and Measures or a licensed scale service company will use a minimum of 20,000 of certified test weights. In the case of a 20,000 pound test, anything beyond a 40 pound error in reading would be a failed test.

    In the case of CAT Scale, all of our scales are calibrated at least four times per year by a licensed service company and we require the calibration to be adjusted to zero error."

    So... with my 25,020 lb. combined weight, that number could be up to 50 lbs. off either way.

    Rob
    I too had always heard it was +/- 20 lbs, but was not aware that was for 10,000 lbs. That comes out to .002......good enough for a town this size.
    2016 F350 CrewCab Dually
    2018 Momentum 394M...Heavily Modded!
    2023 Suzuki GSX-S1000 GT+
    Excessive Payload is a Wonderful Thing

    "If it ain't fast....It ain't Fun"

  10. #10
    Seasoned Camper
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    Quote Originally Posted by CaptDan View Post
    I know I'm late to this discussion, but notwithstanding what "CAT" states as their accuracy, I'm having a hard time believing it with my actual experience. Since purchasing our 2019 397TH, I have meticulously entered the weight of everything that goes into the rig - using a scale or whatever weight has been assigned per the package, invoice, on line etc. This goes for food, clothes, tools, miscellaneous, whatever. I normally dump all my FW, grey and black tanks prior weighing and have full diesel. I have weighed the rig (and truck) numerous times and get an average of about 400 lbs of "extra" (unaccounted for) weight in the rig. I can easily understand 100 or 200 due to potential human error but 400 seemed off. Eventually, I simply added the extra 400 lbs to my spreadsheet as a hidden default weight coming from "somewhere" (original GD UVW?). However, I then bought an electric golf cart and about 400 lbs of other junk and added it to the rig. My new weight should have been about 1400 lbs more than before (everything else being equal - included the hidden 400). Well the hidden 400 lbs is now around 800 lbs. I now have 800 lbs of weight I cannot account for. And by the way - if I go to get a "second opinion" at another CAT scale - the result may be another 300-400 lbs heavier. The GD UVW may be the culprit for the extra 400 lbs originally, but an extra 400 lbs after I add 1400 lbs? Eventually going to find an alternative way/Company to measure the rig. There's a "Penske" scales about 200 miles north of us - will try them.
    The Grand Design ULV was completely dry, no battery, no propane tanks or propane, and no residual water in the tanks. When I replaced the valve on my gray tank, I was very surprised by the amount of water remaining, even after it was drained "nose up". I spent a good bit of time "squeegieing" as much out as I could but also noticed that the laundry detergent seemed to make it semi-coagulate. There are going to be many other "little" things that will add to that total.
    Jerry & Kelly Powell
    Zebulon, NC
    2020 Solitude 390RK-R :target:

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