We know you know how to operate and maintain balances and scales, but the biggest challenge when shopping around is deciphering the jargon. Mettler Toledo has a great resource for understanding the technical terms, and here is a practical breakdown of the relevant specifications:
Serial tags on balances often show a d, or division, value. Also referred to as the readability of the balance, it represents the smallest measurement that the balance can detect. A balance with a readability of 1 g will only show measurements in increments of whole grams, a readability of 1 mg will show measurements in increments of milligrams, and so on.
This value loosely determines the price of the balance. If you divide the maximum load (or capacity) of the balance by the d value, you get the number of individual measurements (or divisions) that the balance can weigh. For example, a balance with a maximum capacity of 4000 g and a d value of 1 g has 4000 divisions. A balance with a maximum capacity of 120 g and a d value of 1 mg (.001 g) has 120,000 divisions. For that reason, the balance with the lower d value is generally more expensive than the balance with the higher capacity.
Dual- and multi-range readability
If you need a specific readability for all your measurements, look out for dual- and multi-range balances. This means that the d value of the balance will change depending on the load. For instance, compare a balance with a readability of 0.1 g to a dual-range balance with readabilities of 0.1 g and 1 mg. Both balances can measure 0.5 g, but the dual-range balance offers greater specificity at that value by producing a reading of 500 mg and detecting variations within a milligram. For masses over a certain size specified by the manufacturer, the dual-range balance will go back to a readability of 0.1 g.
Additional performance metrics
User manuals might include other specifications such as linearity, stability, sensitivity, and repeatability. Mettler’s guide provides formal definitions for these terms, but all you really need to know when you’re shopping is that the values are usually quantified as a standard deviation or the maximum limit of deviation. Minimal deviation indicates that the balance will have consistent, high-quality performance over a wide range of operating conditions. In our experience, they are commonly expressed like “Linearity = 0.007 g at 20 g.” For the manuals and data sheets that don’t follow these conventions, just look for the smallest values to get the most reliable readings.
If your company makes their business by selling their product by weight, you may need to find legal-for-trade balances or scales. Legal-for-trade means the balance meets or exceeds the requirements needed for that industry. That being said, most analytical laboratories will not need to worry about this because they are not using their balances commercially.
Most commercial brands will provide an NTEP certificate of conformance, a document showing their balance’s adherence to the standards set by the National Conference on Weights and Measures. Therefore, even if you are in a regulated industry, you most likely won’t have to be concerned about these standards, and regular calibration will be enough to ensure consistent and quality weighing. If the balance doesn’t have that documentation, you can make an appointment with a lab supported by the NCWM to obtain the certificate.
What else do you look for in scales and balances? Tell us in the comments below!
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