What is an appropriate calibration weight for a 4 ton weigh scale

Discussion in 'ISO 17025 - Calibration and Test Laboratories' started by Talha Siddique, Aug 14, 2020.

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1. Talha SiddiqueMember

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Hi,

Hope you are doing well. I am an industrial engineer form Pakistan. I work as a production engineer. My question is:

1) What amount of calibration weight is necessary to calibrate a weigh scale with a maximum capacity of 4 ton?

2) Are there any relevant industry standards for this?

I am being told that i would need at least 1 ton of calibrated weights but that would be too expensive and impractical to carry out

I would be extremely thankful for a response

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2. Andy NicholsModeratorStaff Member

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Welcome! What are you weighing and what accuracy/tolerance specification are you comparing the weight to? Do you need 4 tons +/- 0.5 tons, for example?

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3. Talha SiddiqueMember

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We weigh paper reels, which typically weight around 1200 kg to 2000 kg. Our tolerance is +/- 2 kg.

4. Andy NicholsModeratorStaff Member

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Who is interested in the actual weight? Customers? Your management? Do you sell by weight or by length of paper?

5. Eric TwinameWell-Known Member

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Paper rolls are by pound...I work in paper and plastic films these days.

My question would be the reliability of your tare weight (reel, core and wrap)...
The folks I work with have more than 2Kg uncertainty in tare...so a weighing tolerance of 2Kg is down in the noise...

For clarity...I see more than 2Kg uncertainty in what the core and reel weigh, not uncertainty in the gage...and you can't know the core weight until all the film is gone...by which time it's all moot.

6. Talha SiddiqueMember

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The management is interested. We want to reconcile the input weight with the output. That's why we have installed weigh scales at both input and output. We sell with respect to packets to be produced from a reel.
So after having installed a weigh scale, now i am confused about the appropriate amount of calibrated weights required for calibration of the weigh scale

7. Talha SiddiqueMember

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Basically we are weighing every thing. Gross weight of reel at input and weight of every single piece of output as well. But we are not able to reconcile perfectly due to the least count.
Anyways, do you have any standards regarding the appropriate amount of calibrations weights for calibrating a 4 ton weigh scale?

8. Jennifer KirleyModeratorStaff Member

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Good day Talha, welcome to QFO!

Based on the cost of weights I would suggest a service to perform a calibration of this type. Are there any such services in your area?

You did not state what type of scale this is, or the increments of its reporting (one kg?)

Is it a platform scale? A rail car scale? Methods to calibrate each would vary, but we can expect the range of your load weight to be covered in the calibration, and for discrimination to be less than your tolerance (some say 10:1, while others say 4:1 is enough) in order to confirm your scales are reporting results that you need.

9. Eric TwinameWell-Known Member

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You aren't going to like this answer, just so you know...

You are weighing things because management is interested...no other reason (though it's a good reason).
There is no "standard" for doing this.
There is what works and what doesn't work in the scale range you desire...and Jen's comment and question regarding calibration are right toward this.
The appropriate amount of accuracy required (what makes calibration "pass" or "fail" is up to accuracy of data desired/demanded).

The more accurate you demand your scale to be, the more it will cost...so it becomes a cost/benefit decision by management (whose money it will be).
How accurate do they want, and how much cash are they willing to put out to get it?

10. Talha SiddiqueMember

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Sorry for the late response.
The problem is that we are converting paper reels in to sheets. Since the grammage (GSM) varies in paper products, we almost never get the same output (in weight) as the input (in weight), even if we weigh every thing.
Personally speaking, it is quite frustrating since it is extremely unproductive to weigh every thing. But we are willing to accept a difference of maximum 2 kg between input and output, given that the weight of the reel is around 2000 kg

11. Talha SiddiqueMember

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It is a platform scale. The trouble with covering the entire range of the load weight in calibration is that it would be too costly. Is there any other way out?

12. Andy NicholsModeratorStaff Member

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Too costly - compared to? If you have little/low/no risk of a weighing issue affecting your customers, why not simply use three weights? 2000kg and then (-2kg) 1998kg and (+2kg) 2002kg? This would not be a calibration but would verify that you can meet the limits. Either have someone come, who has the necessary weights or buy them and have them checked for accuracy. You can simply drop them on the scales when you think it's necessary.

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Do you have a copy of Handbook 44? It provides guidance for large weight scales.

14. Talha SiddiqueMember

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