Scales. Need advice

[Stan Pope]

This looks like a pocket scale. Could be difficult to read and or ballance the cars on the scale.

Look for a message thread about "weighing cars safely". There are some pix of a lightweight bridge so that the cars won't try to roll around. Bridge can be compesated by zeroing a 200g scale... weighs well less than an ounce!

Found it ... http://derbytalk.com/viewtopic.php?t=1729

[Jungle Jim]

In addition to the CS200's certified 200.0g calibration weight, I supply our district races with a couple of 5.000 oz "confirmation" weight for "quick checks" before sending someone off to trim their car's weight down.

And having a 5 oz. standard on hand also helps to quell all the naysayers about how accurate your scales are.

[TAL]

I'm going to give the scale offered by MaxV try. I just ordered it the other night. I like not having to keep up with two different standard weights, one for calibration (200.0 g) and one to put parents minds (and mine) at ease (5.00 oz). I'll let y'all know how it goes with that scale.

Well, unfortunately, I have nothing good to report on this scale. I tried to calibrate the scale with the 5.00 +/- 0.00021 oz weight, but when I put the weight back on the scale, it would read 4.98 oz. Scales USA sent me another scale and it had the same issue. It turns out that this scale has an accuracy of only +/- 0.03 oz, so that 5 oz "calibration weight" could display from 4.97 to 5.03 oz. I would have a hard time trying to explain that to a parent if we were trying to hold everyone to a 5.00 oz limit. In reality, how much of an impact would this measurement error have? Probably not much, but to me, if a scale displays to 0.01 oz, then a 5.00 +/- 0.00021 oz weight should display it as 5.00, not 4.97 and definitely not 5.03.

HELLO gp race man,, Might you be talking about the USA SCALE PW 5200.... Well actually the accuracy on that scale is 0.01 in ounces and the +/- 0.03 you talk about is stability accuracy which is the max it would be off if the scale has been tipped such as moved after calibrating the scale... If you calibrate the scale correctly and keep it on a stable place and keep it there it for us is a very very acurrate scale...
The PW 5200 also comes standard with a A/C cord and is also operational with a 9V battery ....So for about $48.00 to $49.00 dollars we find it to be a very great buy verses the other scales you talk about which is around $68.00 with an optional (extra) $12.00 A/C cord for a total of about $80.00..........

[gpraceman]

Might you be talking about the USA SCALE PW 5200....

That is the scale.

Well actually the accuracy on that scale is 0.01 in ounces and the +/- 0.03 you talk about is stability accuracy which is the max it would be off if the scale has been tipped such as moved after calibrating the scale...

It may display out to 0.01 ounces, but according to Scales USA, the accuracy is actually +/- 0.03 ounces. I was never able to get either scale that I tried to calibrate to 5.00 ounces. The calibration weight was 5.00 +/- 0.00021 oz but after calibration, the scale would never read 5.00 oz with this weight. To me, that was unacceptable. To Scales USA, that was acceptable for a low end scale.

[TAL]

Well I suppose we were one of the lucky ones then because ours scales out to 5.00 ounces on three different scales...
But yet the same scale showing 5.00 ounces will show different simply by placing the power cord under it (scale slightly tilted) ...
I find that the scale has to be on a stable level surface and calibrated and left in the same position for operation........
And double checking , while scale is reading 5.00 and we add a 1/4 ounce weight it then shows 5.25 .... And also if we add a 1.50 ounce weight to the 5.00 calibration weight it then shows 6.50.... Again this is with the scale calibrated correctly on a level firm surface and operated in the same position..... Since we've had these scales and weigh our cars out at 4.99, We have'nt been overweight at any race and were weighed in at 4.99 ( 4.9 ) on scales we never seen......

[gpraceman]

But yet the same scale showing 5.00 ounces will show different simply by placing the power cord under it (scale slightly tilted) ...
I find that the scale has to be on a stable level surface and calibrated and left in the same position for operation........

I am glad that you found some that work as we'd hope. The two that I tried did not. I was using a level surface and could not get the scales to read 5.00 after calibration.

[TAL]

Hey again gp race man.........
I to at first found the scale to be uncopperative and once we figured it out ,we really like this scale ...........
Just curious about one detail in the instructions of the calibration process ...........In step #4 it states put the 5.00 ounce weight on platform and wait for "OE" to appear on the display.........And then says end of calibration..........
Then #5 says turn the scale off . Calibration is completed ......
Where we made errors at first was we removed the weight before turning the scale off...... and it lead to what problems your describing (4.97 to 5.03 readings)......
BUT when we do steps #4 and #5 and leave the 5 ounce weight on the platform during shutting the scale down we have no problems with the scale calibrating to 5.00 ounces with the included 5 ounce calibrating weight .........

[gpraceman]

Just curious about one detail in the instructions of the calibration process ...........In step #4 it states put the 5.00 ounce weight on platform and wait for "OE" to appear on the display.........And then says end of calibration..........
Then #5 says turn the scale off . Calibration is completed ......
Where we made errors at first was we removed the weight before turning the scale off...... and it lead to what problems your describing (4.97 to 5.03 readings)......
BUT when we do steps #4 and #5 and leave the 5 ounce weight on the platform during shutting the scale down we have no problems with the scale calibrating to 5.00 ounces with the included 5 ounce calibrating weight .........

That is interesting. I did follow the calibration instructions as they were written. If that should be the procedure, then they really need to update their documentation.

Does the scale keep its calibration throughout the check-in period? At the end of check-in, can you put the calibration weight back on and get the scale to still say 5.00?

My main beef was that the scale would never indicate 5.00 after calibrated. There are some minor other things that I didn't like about the scale, like no tactile sense on the touch pad, but the calibration issue was the killer.

[TAL]

Absolutely the instructions need to be redone, because also on the instructions state for switching from grams to ounce to mash button 3 to 4 seconds and we found it works best on 5 seconds and it switches back and forth every time .........
As for keeping 5.00 reading at the race last week we scaled in 25 cars with in 30 minutes and it was reading 5.00 ......... But it pays to not leave it unattented due to it is a sensitive scale.......
It might not be the easyest scale in the world to work but for less than $50.00 it sure as heck beats a 1/8 inteval scale or a scale that weighs in tenths instead of hundreths...........

[gpraceman]

I just got the Acculab EC-211 scale at http://balance.balances.com/scales/20 with the 200 g calibration weight for $70 + S&H.

It was a breeze to calibrate and more importantly, when I stick the 5.00 +/- 0.00021 oz weight that I got from MaxV on it, low and behold it displays 5.000 oz It even has a lock on the bottom of the scale to prevent damage to the load cell when the scale is not in use. The buttons even give a good tactile sense that they have been pushed.

I just wish it didn't display out to 3 decimal places, but observing it I have not seen the last digit be anything other than a 0 or 5.

So far so good. We'll see how it performs when "battle tested" tomorrow night.

Note: If you buy from these guys and pay by PayPal, then all sales are final. If you don't like the scale you are stuck with it. If there is a problem, then you need to resolve that directly with the scale manufacturer. If you do not use PayPal, then you do have the option of returning the scale, but with a 20% restocking fee.

[PWD]

I purchased two of the Harbor Freight scales yesterday and love them. Small, portable and so far seem to be very accurate. Will see if they hold up.

[BigDozer66]

I went with the USA SCALE PW 5200 and I appreciate the hint on zeroing.

I will play with it and see if it works correctly.


Thanks,
Lynn

[SuperDave]

Any digital reading (of a continuous function) is +/- 1/2 count in the last place so a scale that measures only ounces and reads 5 could be measuring a 4.5 to 5.5 weight, assuming no other error sources (like offset and gain and linearity).

One of our suggested rules is:
2. Weight: 5.00 ounces or less, 4.90 or more will be accepted without further change. Three attempts to reach the correct weight range. then the committee does it. The official scale is official. (It's about the kids!)

1.00 gram = 28.35 ounces, so 5.00 grams = 141.75 ounces. Go to the bank and get new nickels. Each nickel weighs 5.00 grams (true, ask the US Treasury) so 28 nickels will be 140 grams and will pass, 29 nickels = 145 grams and will fail. Cheapest precision weight I've ever found. Then go back and read rule 2.

[BigDozer66]

I'm going to give the scale offered by MaxV try. I just ordered it the other night. I like not having to keep up with two different standard weights, one for calibration (200.0 g) and one to put parents minds (and mine) at ease (5.00 oz). I'll let y'all know how it goes with that scale.

Well, unfortunately, I have nothing good to report on this scale. I tried to calibrate the scale with the 5.00 +/- 0.00021 oz weight, but when I put the weight back on the scale, it would read 4.98 oz. Scales USA sent me another scale and it had the same issue. It turns out that this scale has an accuracy of only +/- 0.03 oz, so that 5 oz "calibration weight" could display from 4.97 to 5.03 oz. I would have a hard time trying to explain that to a parent if we were trying to hold everyone to a 5.00 oz limit. In reality, how much of an impact would this measurement error have? Probably not much, but to me, if a scale displays to 0.01 oz, then a 5.00 +/- 0.00021 oz weight should display it as 5.00, not 4.97 and definitely not 5.03.

The other things that I didn't like on this scale were the buttons and the operation of the scale. The buttons do not give any tactile sense that the button was pushed. They have to be pushed harder than expected to work. For calibration and changing from grams to ounces you have to push the On button for so many seconds but nothing happens until the button is released. I was rather expecting that after holding the button for the required time the scale would start the calibration procedure or do the change from grams to ounces. I could have lived with these things, but not the accuracy issue.

So, I am going to try some other scale and see if I fare any better. I contacted Precision Weighing Balances (http://www.scaleman.com) and tried asking a couple of questions but the guy was very rude. He continued talking to someone while I was trying to ask my questions, just tried to refer me to their website info, and then said "this isn't rocket science" and suggested I go somewhere else. Lovely customer service. Needless to say I will.

I seem to have a PW5200 that weighs the calibration weight at 4.98 ounces. Before and after calibration is the same thing. I will be 'playing' with it some more but so far I am not impressed with it.

Sure it is only $50.00 but I could have put that toward a more precision scale.

I don't like having to push the buttons hard to get it to respond when you should only have to press the button to get it to do it.

Unless something miraculous happens to it then it will not be the official scale when the PWD gets here.

Lynn

[SuperDave]

Perhaps this is going to cause more confusion but there are important differences between precision, accuracy and consistency that have a real bearing on what you are trying to do.

Precision = number of places. A scale that displays 5.00 AND has a next step of 5.01 (beware scales where the next step is 5.12), has a precision of 1/100th of an ounce (or more precisely 1 part in 500). Curiously, if you work the gram equivalent and switch the scale to grams it might have more or less precision. Precision has little to do with accuracy or consistency as detailed below.

Accuracy = does it match the worldwide standard. A perfect 5.00 ounce weight that always reads 5.51 shows a scale that is essentially equally precise but the scale's accuracy is off by roughly 10%.

Consistency = repeatability. If the perfect 5.00 ounce weight ALWAYS reads 5.51, then the scale is perfectly consistent and, with a little explanation, all that you need for Pinewood Derby. The rules presumably say not more than 5.00 ounces. Anyone with a truly 5.00 ounce car will pass the 5.51 'local' value, which can be easily verified. You don't really need a readout that matches NIST.

By the way, an equally acceptable alternative in the test and measurement world, given the numbers you quote from the manufacturer, is to simple accept 5.03 as a pass. This is an error that is less than 1 gram, less than 1% and perfectly defensible. Ask the 'little league dad' who complains to buy you a more precise AND accurate AND consistent scale. One of our suggestions on how to run the Pinewood Derby includes providing tee shirts for the officials that state, "The officials of this race are volunteers, before you criticize their actions, be prepared to take their place."