Electronic scales? Accuracy

alvin l nunley

Premium User
I've never heard of an electronic measuring device that wasn't subject to the ambient conditions it was placed in.

Strain gauges (and springs) are sensitive to the ambient temperature of their surroundings. Bathroom scales (analog or digital) along with the most expensive corner weights measuring devices, as far as I know, are influenced by the ambient temperatures. I had to calibrate my go power dyno, which used a strain gauge, to the ambient temperature every time I used it. How can these expensive corner weight scales be any different? Do they have some sort of calibration procedure they use?
 

01ron

Member
Mine have a button to zero them. I let mine warm up for at least five minutes every time I use them and then hit the zero button.
 

sjona2011

Member
As with any measurement device, however precise, you are only comparing one measurement to the next. With corner scales, you simply zero them, then stand on each individual scale to make sure they're all reading the same weight before setting a kart on them. If you have one that's reading off, then it may need recalibrated to a known weight, or adjusted so it is reading the same weight as the rest. Temperature can affect the readings, as you've seen with the strain gauge on your dyno, but with corner weights, we only care about percentages, those will scale correctly with any fluctuation in readings of the scales. If ambient conditions are causing all the readings to be 2% off, your corner weights will differ, but percentages will remain the same. Aside from all that, even if the scales were calibrated poorly and are 1 or 2 lbs different from one another,for whatever given reason. Those percentage differences won't mean much considering whatever you scale the kart at is just a starting point to get you in the ballpark.
 

Kj26

Member
Aside from all that, even if the scales were calibrated poorly and are 1 or 2 lbs different from one another,for whatever given reason. Those percentage differences won't mean much considering whatever you scale the kart at is just a starting point to get you in the ballpark.
That's like the dumbest thing I have heard. If your off your adding unneeded weight and moving washers you shouldn't be or worse your coming up light at the track then needing to add weight.
 

sjona2011

Member
That's like the dumbest thing I have heard. If your off your adding unneeded weight and moving washers you shouldn't be or worse your coming up light at the track then needing to add weight.
if one of your scales is reading 1 lb high, thats going to equate to a couple tenths of a percent. if that .2% matters to you, then so be it. For me, its more than close enough considering im more than likely going to make changes at the track, and im sure as hell not scaling it after every change. As for total weight, yea it'll make a difference, but im betting most tracks arent going to let you use your own scales to weigh in, you're using theirs. so if the tracks scales are a couple lbs off of yours, you're gonna be adding/subtracting weight anyhow.
 

alvin l nunley

Premium User
Not to belabor the point but, I can understand a zero button. One more question, has anybody ever put a precisely known test weight on the scale. Any weight would do as long as it has been verified on a balance scale. That's what I did with my dyno. I wonder if any of the manufacturers have any specifications on environment where the scales are to be used.

The point I'm trying to make is; unlike a balance scale, Springs and/or strain gauges will read differently with changes in the ambient temperature. You push a button to zero out the electronic scales, and there's a little adjusting wheel on your bathroom scale to zero it out, what's the difference.

I know "go away Al, you bother us".
 

flattop1

Dawg 89
Too answer the original question .
Yes they can be calibrated .
Not by the consumer .
Unless your willing to open them up and start turning the variable resistors .
 
We scale outside 99% of the time and never see an issue with the temp from upwards of 100 with high humidity to around 50-60 with no humidity. Zero it, test it with a weight, and move on. Longacre and intercomp will recalibrate the scales if they are that out of whack.
 

alvin l nunley

Premium User
Too answer the original question .
Yes they can be calibrated .
Not by the consumer .
Unless your willing to open them up and start turning the variable resistors .
It would be interesting to know under what conditions the scales are tuned too. Is there a particular temperature and barometric pressure they use when calibrating the scales. I would think there would have to be some kind of a standard atmospheric condition.
 

flattop1

Dawg 89
I doubt there is a government mandated standard as they are not used for commodity sales too the commercial industry or consumer .
More interesting would be the percentage of tolerance .
Proprietary information no doubt .
We would have been out of the standard at 10* below at any rate . When coke syrup racing . Pitted in the barns at waterloo .
 

alvin l nunley

Premium User
I can't imagine this information being proprietary. You put the scale in a room with a controlled temperature. You put a certified 25 pound weight on the scale. The A to D (analog to digital) converter puts out a number, the computer is then told that number represents 25 pounds. I have experience doing this. How the scale differentiates between 25 pounds and 24 pounds is something the engineers would know. I'm kind of halfway aware of how an A/D converter works. The sensitivity of the converter, i.e. the number of discernible points between 24 pounds and 25 pounds, would be a function of the sensitivity of the device used. The more expensive the device the more sensitive it is, as a general rule. One device may only have 10 discernible points between 24 and 25, whereas a more expensive device might have 1000 points, or 10,000 points.
 

flattop1

Dawg 89
You may not feel it's proprietary .
The company may feel differently .
Even as a welder the company I worked for considered there techniques and methods proprietary . Same machines and rods/wire were avalible at the weld supply to anyone .
 

Pete_Muller

Moderator
If I'm not mistaken, good scales have at least 2 (and sometimes 4) strain gauges at each measurement point. They are oriented in a manner that -- simply stated -- one is "stretched" and one is "compressed" so that differences due to temperature (or other conditions) cancel each other.

PM
 

Dan Brown

Member
So if the kart is off a half pound when we get to the track, so what? The cheeseburger I ate in between heats weighs more than that, and we typically burn about 5 lbs of fuel every track session. On a hot day over the summer, at NYRC, I weighed myself in the morning and after the race event, I lost 8 lbs that day even though I drank 5-6 gatorades thruout the day. A few tenths up or down that a scale fluctuates means nothing in the long run, in my opinion.
 
It would be interesting to know under what conditions the scales are tuned too. Is there a particular temperature and barometric pressure they use when calibrating the scales. I would think there would have to be some kind of a standard atmospheric condition.
Call or e mail Longacre and ask them. They are the ones who would know.
 
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