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What Does Linearity Mean in a Balance or Scale?

2/14/2014

6 Comments

 

Original blog re-posted from Intelligent Weighing Technologies
Can be found here:


**Click to follow link**

“I often see linearity quoted as part of a balance or scale specification, but what does it mean to me?”



Balances and scales are very precise instruments and like all instruments, they perform within stated parameters. Other examples of these parameters will be dealt with in other sections, but for now we will concentrate on Linearity.

Basically, linearity is a deviation (or no deviation) from a straight line. If we draw a graph with weight at one side and displayed value on the other, a purely linear balance would show a straight 45° line from the zero point, right up to full capacity. Each time the load increases, the displayed value increases at the exact same rate, thus giving the straight line. See Fig. 1. (Please note that the errors in the graphs used below are exaggerated to provide clarity).

Picture
Balances and scales are very precise instruments and like all instruments, they perform within stated parameters. Other examples of these parameters will be dealt with in other sections, but for now we will concentrate on Linearity.

Basically, linearity is a deviation (or no deviation) from a straight line. If we draw a graph with weight at one side and displayed value on the other, a purely linear balance would show a straight 45° line from the zero point, right up to full capacity. Each time the load increases, the displayed value increases at the exact same rate, thus giving the straight line. See Fig. 1. (Please note that the errors in the graphs used below are exaggerated to provide clarity).

Picture
In Fig. 2. We see an example of the allowed linearity of an analytical balance of 200 g with an allowable linearity of ± 0.0002 g. This example shows the error allowed around the “perfect” linearity. The green shaded area represents the permissible error allowed.
Picture
In Fig. 3. We show the typical linearity of a 200 g balance, with a slight positive error (0.0001 g) below 100 g and a slight negative error over 100 g of 0.0002 g. This balance is just within specification.
Picture
In Fig. 4. We see a balance that is just outside the tolerance allowed, as the curve of the displayed value exceeds the ±0.0002 g permissible error.
Picture
Manufacturers and scale dealers have the ability to correct errors in linearization by adjusting the balance with test weights at regular intervals of the capacity. This is not calibration, that can be performed with a single weight, provided of course that the balance has been correctly linearized. Linearization should not be attempted without specialist knowledge and the correct test weights.

Richard Sharpe - Author
Intelligent Weighing Systems

6 Comments
Laxmikant R Katekhaye
11/2/2014 01:09:39 am

Sir, we have the balance of capacity 220 gm with resolution 0.0001gm. We want to calculate the linearity, please guide

Reply
Richard Bertrand link
11/2/2014 11:32:36 pm

Mr. Katekhaye,

To determine linearity a calibration procedure must be done to check multiple points across the span (220 g) of the scale. If the scale performs within the tolerance specified in either the quality manual of your company, Handbook 44 if in the U.S., or to the manufacturer of the scales service manual (whichever document supersedes the others) then you must go no further.

Some scales allow for a linearity calibration, in which usually up to 5 data points can be calibrated into the span calibration function which can eliminate some non-linearity issues seen in scales. This function usually only comes with very expensive "bran" name scales and is not found on the value based products on the market.

If you require service of your equipment, all the above can be performed in our South Florida Calibration Laboratory. Please visit our contact page and I would be happy to help you with any questions you might have.

Reply
Global Lab Supply link
3/23/2019 02:25:54 am

I have read your post it's very informative and helpful too for readers .Thanks for sharing your knowledgeable content with us and keep updating us with such great informative post.Keep writing.

Reply
Chris Pederson link
12/17/2020 11:43:58 am

I'm glad to know that balances and scales are precise instruments. I can only imagine how annoying it would be if they weren't. I'll see if I can find one though before I move to make sure my truck doesn't weigh too much.

Reply
SUMO Digital Scale link
2/2/2021 02:16:54 am

<a href="https://shovaonline.com">SUMO Digital Scale</a> is undoubtedly one of the best Digital Scale manufacturer. There diverse range of digital scales to fulfill every customers’ requirements and criteria. SUMO’s laboratory balances have best accuracy. These scales are ranging from 320gm to 5000gm having the accuracies of 1mg to 10mg respectively. Calibration is done very accurately in own factory by experts. To know more details please call or visit our website.
Website: https://shovaonline.com
Phone: +8801730041752

Reply
Mariam W link
7/18/2021 05:20:48 am

Interesting read

Reply



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