Why Are Balances Different Prices?

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Why Are Balances Different Prices?

The Internet has enabled many customers to easily view competing pricing for items. This is a great for good old fashioned competition, which is part of what this country was built on!

However, in the world of weighing, sometimes it is not that simple. Just because the capacity (how much the scale or balance will weigh) and readability ( the smallest division of capacity that the balance will display) are similar, doesn’t mean that weighing results will be the same from balance to balance.

Many factors influence the weighing machine.

Construction

Plastic is cheap and efficient  but will allow the build-up of static, (static electicity can and does damage electrical components, such as keypads and can also affect your weighing results as static will cause metal parts to be attracted to one another creating) Plastic is sometimes subject to breakage and can be damaged by chemicals. It is also not a stable material when stress (weight) is applied. No weighing device likes movement of the support structure, no matter how small that movemant. This is why many of the more expensive balances have a cast aluminum or steel structure, to not only provide a stable platform, but to guard against static electricity effects and to provide longevity.

Repeatability Specification

Just like a gas pump, your balance reads a series of numbers, supposed to be in sync with the amount of fuel dispensed, or in the case of a balance, how much weight is applied. Just because the device reads to a division (smallest number displayed) doesn’t mean that it is accurate to that number. Your gas pump is controlled and tested by your local weights and measures department, you balance will more likely not be.

All balances have a specification showing how close they come to absolute accuracy. You will see the following specifications.

Repeatability

This describes how a balance will react when a known weight is applied (usually a weight is applied 10 times to verify this specification) showing the variation in results as ±. For instance a balance reading 300 g x 0.001 g (a milligram balance) might show a repeatability figure of ± 0.003 g. This shows that the balance will repeat over the 10 weight applications, to ± 0.003 g. For example, with 20 g, readings may appear as so:

19.997 g

19.998 g

19.998 g

20.000 g

20.003 g

20.002 g

20.002 g

19.998 g

19.999 g

19.999 g

This balance is actually in specification for a ± 0.003 g repeatability. If the balance has a closer repeatability specification, say ± 0.002 g, then it would be out of specification.

The better the balance, generally the more you pay for the balance, the tighter the specifications and the closer the balance is liable to meet said specification. Here it might be useful to look at the difference between real diamonds and paste jewelry. Both look the same from a distance, but close up the diamond sparkles, but the paste jewelry looks dull. It is important to use the right tool for the job. We sell many different levels of balances, but to really get the best result for your money, it is important to purchase the correct level of balance. Depending on your application, you may need a tight tolerance or you may need something not so exact. Please be careful to understand that these little ± signs are very important. Readability, that is what value the balance reads in is only half the story. How accurately it reads is contained in those pesky ± signs.

Linearity

All balances have a linearity specification, again described as ±.

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 below are exaggerated to provide clarity).

F1 - perfect-linearity-graph

Figure 1

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.

F2 - area-linearity-graph

F3 - acc-linearity-graph
F4 - uunac-linearity-graph

Figure 2

Hysteresis

Hysteresis describes how the effect of the weighing mechanism may affect the result of a weighing machine, during applying increased weight and then decreasing the weight. As the weight applied increases, the balance may read correctly “up” the range, but when you begin to remove weight, the displayed result does not return to the correct reading for the weight that is left on the platter. Many lower cost balances will weigh correctly on the way up, but suffer inaccuracies on the way down. If this error does not worry you, then perhaps you will be able to pay a little less for your balance, but if not, then this could be a serious issue for you.

Functionality

Many of the cheaper balances are able to weigh effectively, especially if weighing is not done many times per minute, but these balances will not do much more for you than weigh. If you want applications capability or connectivity in a meaningful way, then the higher end balances will be more likely to fit your needs.

Cost

So, the issue of cost of a balance is complex, but the main thing to remember is that just because a balance reads to 1 gram or 0.01 g doesn’t necessarily mean the answer you will get is correct. The more money you spend on the balance, the better your results will be.

That is not really a surprise is it?

Intelligent Weighing Technology offer balances from the highest price down to reasonably low cost. Every balance we sell is value for money and how much you spend is probably in proportion to the importance of the job

By | 2014-12-26T16:11:40+00:00 December 26th, 2014|Laboratory Balances, Scales and Balances|Comments Off on Why Are Balances Different Prices?

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