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Types of Balances and Scales

5/31/23

They weigh ingredients in recipes, check manufacturing tolerances, count bulk parts and ensure consistent product packaging. They measure micrograms of a reagent in the laboratory, tons of freight on a semi-trailer truck and everything in between. Scales and balances are important in so many kinds of work, and there are almost as many kinds of scales as there are jobs to do with them.

Bench Scales and Platform Scales

These general-purpose scales are used in a wide range of manufacturing and industrial environments. They sit on tabletops and work surfaces and facilitate bagging and packaging, among other tasks.

A standard bench scale has a display on the base of the unit beneath the weighing surface.

A platform bench scale has a display mounted above the weighing surface or on a remote indicator.

Counting bench scales can display a count of the number of parts in a sample by weighing it.

Precision and analytical bench scales display their measurements in smaller increments than standard bench scales. There are also precision and analytical lab scales for scientific applications.

Semi-micro bench scales display their measurements in even smaller increments than precision and analytical scales. There are also semi-micro lab scales for scientific applications. These scales include shielding to prevent air current from influencing weight measurements.

Beam balances are mechanical weighing instruments typically used for classroom instruction.

Food scales are bench scales with special features for use in food processing applications. For example, they may have easy-to-wash housings, infrared sensors to allow taring without pressing a button and modes like baker’s percentage, specific gravity and portion control check-weighing.

Floor Scales and Truck Scales

General-purpose floor scales are versatile scales used for weighing items at floor level without lifting them up to a work surface.

Truck scales are used for weighing semi-trailer freight trucks.

Hanging Scales

Hanging scales are used for weighing irregularly shaped loads that can’t easily sit on a flat scale. They’re also useful for weighing things when there’s no flat surface to place a scale on.

Digital hanging scales are available, but mechanical hanging scales are more common and are also known as spring scales. Dial spring scales have dials that display the weight, while linear spring scales have straight, vertical indicators.

Scales for Weighing Large Overhead Loads

Crane scales, crane dynamometers and load indicators are instruments for weighing large, suspended loads. Some units can weigh loads of up to 100,000 pounds or more.

Scales for Weighing People

There are many kinds of scales for weighing people in medical offices and at home:

Shipping and Receiving Scales

Shipping bench scales sit on counters and tables and can be used for estimating mailing costs or ordering postage.

Shipping floor scales are large, high-capacity scales that can be used to weigh loaded pallets, plastic and steel drums and other bulk cargo. 

Balance and Scale Terms

Accuracy is the ability of a scale to provide a result that's as close as possible to the actual value.

Precision, also known as repeatability, is the agreement between repeated measurements of the same quantity under the same conditions. A scale can be extremely precise without necessarily being accurate.

Readability is the smallest increment of the scale's readout. When a scale can be read in smaller increments (such as 0.01 g compared to 0.1 g), it's said to have higher readability.

Calibration is an adjustment that brings the scale output into line with a known calibration weight. Scales should periodically be checked for accuracy and calibrated as necessary.

Capacity is the heaviest load that can be measured on the instrument. Placing a weight on a scale that's significantly over its capacity may damage it.

Tare is the function that "zeros" the scale when there's weight already on it. It's usually used to remove the weight of the weighing container from the measurement. Most balances allow taring to 100% of capacity.

Frequently Asked Questions

Q: What's the difference between mass and weight?

Mass is a measure of the amount of matter in an object, while weight is a measure of gravity's effect on the matter in that object. So, an object floating in outer space would have the same mass as it has on Earth, while its weight would be dramatically different under those conditions. This distinction is important in some scientific and technological contexts, but in everyday applications and common language, weight and mass are used interchangeably.

Q: What is readability of a scale?

A: The smallest increment of a scale's readout is its readability. There are several ways of expressing readability.

 

Numerical Decimal Number of Decimal Places Fraction

0.1 g

1 place

1/10 g

0.01 g

2 places

1/100 g

0.001 g

3 places

1/1,000 g

0.0001 g

4 places

1/10,000 g

0.00001 g

5 places

1/100,000 g

Q: What's the difference between accuracy and precision?

A: An accurate scale delivers a measurement that's close to the true weight of the thing on the scale. A precise scale delivers measurements that are consistent when the same thing is weighed again and again. Precision is sometimes called repeatability. A scale can be precise without being accurate. Calibration can address problems with accuracy but not problems with precision.

Q: How often should calibrate my scale?

A: A lab scale should be calibrated at least once a year or per the manufacturer’s guidelines. It can be done using reference weight sets or by a calibration professional. 

Q: What kind of calibration reference weights should I use for my scale?

A: The choice of weights for calibrating a scale depends on the readability of the scale and the application you're using it for. Calibration weights are manufactured to different specifications:

ANSI/ASTM specifications are typically used for laboratory calibration. ASTM-E617-18 specifies 10 classes of weight standard, which are – in order of decreasing accuracy – 000, 00, 0, 1, 2, 3, 4, 5, 6 and 7. Reference weights used in the lab are typically Class 4 or lower. 

The NIST Class F specification was developed for the reference weights that state and local regulatory officials use to field test commercial scales. However, Class F reference weights aren't accurate enough to calibrate some newer commercial scales, and new Class F weights are no longer being put into service for this purpose by regulatory agencies. However, Class F calibration weights are still commonly used in warehouses and industrial settings. The accuracy of Class F weights is similar to that of ANSI/ASTM Class 6 reference weights.

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The information contained in this article is intended for general information purposes only and is based on information available as of the initial date of publication. No representation is made that the information or references are complete or remain current. This article is not a substitute for review of current applicable government regulations, industry standards, or other standards specific to your business and/or activities and should not be construed as legal advice or opinion. Readers with specific questions should refer to the applicable standards or consult with an attorney.