The balance scale, which was the only kind of scale around for hundreds of years, had a fairly basic design. It consisted of a mounted beam with arms of equal length, and pans, or scales, suspended from the end of each arm. An object of unknown weight was placed in one pan while standard weights were added to the unknown pan. The user would place weights in the pan opposite the item being weighed until the two pans were level. Then the user would calculate the weight of the object in question by counting how many weights he had placed in the opposite pan. Although the balance scale was the primary scale used all around the world for many years, today we have other types of scales to choose from.

The spring scale was invented by Richard Salter in 1770. A spring scale works by measuring the amount of force an object exerts on a spring. This amount of force is directly proportionate to how much the object weighs. Spring scales, which are sometimes also called Newton meters, measure force in Newtons, but today’s scales often offer users readings that are already converted to weight in kilograms or pounds. Spring scales come in different forms. Some, like older bathroom scales, are flat and have internal scales. Others are hanging scales, meaning the object being weighed is suspended from a hook or pan that is on one end of a spring.

The digital scale is another, very popular type of scale that is used today. Digital scales are basically electronic versions of the spring scale. They work by measuring how much force is exerted by the weight of the object placed on the scale on a beam inside the scale. Digital scales are available in a many sizes that can accommodate objects that weigh anywhere from grams to tons. Some examples of these scales are food scales and modern weigh bridges, respectively.

The average person today most commonly uses digital scales and spring scales, and may encounter these weighing scales in a variety of places in their everyday life. For example, many people have digital or spring scales in their bathroom or in their kitchen. It is also very common for the average person to have to see either a digital or spring scale at their local grocery store or market. Today, digital scales for weighing meat and produce are built right into the checkout line.

The following is an overview of different types of small digital scales, listed approximately from highest to lowest resolution.

• High resolution scales

These types of scales are suited for laboratory use in universities.  Ideally, they should include a tare function for zeroing weighing vessels such as weighing paper or trays.  A standard feature is display capability for different weighing units, most commonly, ounces and grams.  The desired resolution for these scales is 1 mg, a requirement met by scales with maximum weighing capacities of 750 mg.  For pharmaceutical applications, the resolution should be 0.1 mg.

• Counting scales

Counting scales are useful for measuring quantities of items whose weights are consistent.  They often have a memory feature that stores the weight of as much as 450 different items, which eliminates the need to weigh a standard sample every time.  Fulfillment centers  use these scales for counting products quickly and accurately. Document control and business card supply companies often use them to count sheet paper and business cards. Utilizing counting scales for fulfillment purposes is advantageous to a business because it reduces quantity errors on product orders, which leads to greater client satisfaction.

• Rain gauge scales

The scale method of measuring precipitation is superior to standard graduated rain gauges in that the weight, rather than the volume of precipitation is measured.  This confers greater accuracy, since water tends to stick to the sides of standard rain gauges, resulting in under-estimates of actual precipitation.  Another advantage of using rain gauge scales is the option of using a meter that measures the amount of chemicals present in the precipitation, for the purposes of quantifying environmental pollutants.  These scales must be resistant to moisture, corrosion and extremes in temperature.

• Industrial bench scales

Bench scales have a display that is attached to the weighing platform by an electronic cord, and can be interfaced with a computer for advanced computing features and functions, including displaying and recording weight data.  A label, paper, and card printer may also be attached.  They are used in postal services, shipping and receiving centers, as well as the food and restaurant industry.

Aggregates are everywhere we look in the world around us. These materials, which are made up of an aggregate of different other materials, including various types of stones, clay, silt, and sand, include the asphalt that paves our roads, the concrete that is used for the foundations of our skyscrapers, or the cement that makes up the bricks of our homes. There is no single aggregate-each one is made differently for a different purpose. One aggregate that uses a certain mixture of stones, silt, and petroleum-based binding may have very different characteristics than one that uses another mixture of pebbles, clay, and a different binding. One aggregate may be more suitable for roads while another may be more suitable for sidewalks.

On any construction site, construction managers must ensure that the aggregate they are using, whether concrete or asphalt, meets the specifications necessary for the job. Therefore, at set intervals of time, the team must carry out a compositional analysis of the aggregate. The aggregate is poured into a sieve with large holes that will only block the largest pieces of stone from falling through. Following this, it is poured into sieves with consecutively smaller and smaller holes until each component of the aggregate is in its own sieve. Then, the sieves and their contents must be weighed with an electronic scale. The total percentage of each material is calculated and compared with the necessary standards.

It is necessary to measure the composition of each aggregate very accurately. This becomes particularly difficult when each component may weigh up to 100 pounds. A standard digital scale may only be able to weigh each component to .01 pounds, which is not precise enough. One scale company, Arlyn Scales, has developed ultra-precision electronic scales that use Surface Acoustic Wave (SAW) technology for aggregate testing. These industrial scales are rugged enough to withstand the force of aggregate components while being able to weigh each component to .001 pounds.

This data recording can be done by humans. However, this opens up the possibility of human error-the data may be recorded incorrectly. Sometimes, digital scales may be connected to a computer using a standard communication protocol such as RS-232. But if the computer is not in the vicinity of the scale, this introduces the issue of running long lengths of wire which is both expensive and time-consuming.

Scale manufacturers that offer the newest technologies, like Arlyn Scales, now make electronic scales with optional built-in Universal Serial Bus (USB) ports. Standard USB thumb drives can be plugged into these ports, and weight data from the industrial scale can be recorded on these memory devices. The digital scale can be programmed to automatically load the data on its screen onto the thumb drive at pre-set intervals such as every hour, every minute, or even several times a second. Or, an operator can press a button on the control panel of the scale to record the data at that point.

Once data has been stored onto the USB thumb drive, the device can be removed from the USB port of the electronic scale and the data can be imported into a database or spreadsheet program on any computer that has a USB port. This method of copying data from industrial scale to computer is very cheap, with 4 GB thumb drives costing as little as $10.

For all of these reasons, there are many rules and regulations pertaining to the management of hazardous wastes. Some of these simply define what materials and items are deemed to be hazardous and which are not. Others outline the methods required for physically handling hazardous materials. There are specifications for the types of clear and accurate documentation that must be maintained.

Much of this documentation is associated with the amounts of these materials. Generally, they must be weighed at all steps in the process. Clearly, it is important to know how much material is generated. That can be determined by using a good quality industrial scale. Depending on the amounts and type of hazardous waste, this could be a bench scale with resolution as high as 0.001 lb. If it is a liquid that is stored in a pail, tank or drum, then a drum scale would be considered. Cylinders of hazardous liquids and gasses are weighed on cylinder scales. Platform scales, floor scales and pallet scales are used to weigh larger containers, totes and larger tanks. The weight can be recorded by hand onto the proper form. Alternatively, Arlyn Scales offers computer interfaces for most of their electronic scales. Weights can now be automatically stored in a database file, or can be printed on labels and other types of forms. It is even possible to use a USB memory stick to log the weight information from these digital scales, along with the time and date of the weighing action. This is particularly useful for maintaining high quality records.

All types of liquids, powders, pellets, slurries and other materials are handled in a wide variety of different types of cans, buckets, pails, drums, tanks and other types of containers. Traditionally, these have been filled by hand. Liquids are often dispensed by a manually operated pump or gravity fed valve. Other types of materials may also be gravity fed, or filled by use of a conveyor or other type of device. In all of these cases, the accuracy of filling is dependent on the operator. Of course, it is also labor intensive, as the operator is needed at all times to monitor the filling process.

Industrial scales are perfect for monitoring the filling process. A bench scale is used to keep track of the weight during the filling process for smaller sized cans, pails and other containers. A drum scale will serve this purpose for drums and small tanks, whereas a platform scale or floor scale can handle larger dewars and larger tanks. While this will solve the accuracy issue, it still requires the filling operator to read the scale and control the filling process.

Arlyn Scales offers a programmable set-point controller for their entire line of bench scales, drum scales, platform scales and floor scales. This allows the filling operator to program the desired weight into the industrial scale. Electrical signals from the scale will control the filling device, shutting it off when the target weight is reached. While this minimizes the efforts required of the fill operator, there may still be some inaccuracies caused by latent delay in turning off pumps, and valves, and the material remaining in fill pipes or tubes.  This controller permits a second target value to be programmed, which can set the filling into a much slower trickle feed. Generally, this will be sufficient to obtain the desired target weights.

The weight values that are shown on the indicator of an industrial scale are of critical importance to the scale operator. A bench scale may be weighing small packages. Or a parts counting scale may be determining the number of parts in a container. Larger drum scales and platform scales may be determining the amount of liquid in a tank or dewar or drum. And large floor scales will be weighing totes, pallets and large tanks. Besides reading the weight information, the operator of the electronic scale can also perform certain control functions, such as applying a tare weight, zeroing the weight on the scale, and choosing the units of measurement, such as pounds or kilos.

While it is required and expected that all digital scales provide all of this functionality locally, it is often desired to be able to also perform all of these functions from another location. In these cases, the most common requirement is to read weight data and control the scale from a local computer. Arlyn Scales provides optional Remote Indicator software that can be operated from any Windows based computer. The electronic scale must be connected to the computer. Typically, this connection would be an industrial standard RS-232 communication line. Alternatively, the USB (Universal Serial Bus) connection may be used.

Now, the computer operator can read weight data directly on the computer screen. They can also save this data in some other computer format, including spreadsheets and databases. Furthermore, the industrial scale can also be controlled directly from the computer. If the scale must be switched from the Net mode to the Gross mode, or the weight of a container must be subtracted, this may be accomplished from the computer keyboard.

An industrial scale is a wonderful instrument for determining the weight of an item. Bench scales accurately weigh small items. Depending on the capacity of the digital scale, the readability of the weight can be as small as 0.0001 lb. Platform scales weigh larger packages and drums up to 1000 lb, whereas floor scales and pallet scales can accepts loads up to 20,000 lb. The accuracy of the electronic scale is dependent on the type of technology used. High quality industrial strain gage scales have an accuracy range of approximately 1/10 of 1%. If greater accuracy is required, alternate ultra precision scales, such as Arlyn Scales Surface Acoustic Wave technology can provide ten or even twenty times better accuracy.

But even an industrial scale with the best accuracy obtainable will not be of value within an industrial process if the user chooses not to use it because it is too difficult. Even if the electronic scale is being used, if the reading cannot be easily read, it is likely that inaccurate results will be obtained. Gross errors will occur if the front panel controls are confusing, potentially resulting in readings of kilograms where pounds are expected.

Good design practices can combine ease of use with excellent accuracy. For example, Arlyn Scales provides a combination of clearly marked front panel controls with a graphics, menu driven digital display. The user is guided through weighing operations by menu prompts which automatically scroll to the next operation. Furthermore, the very low profile of the industrial scales assist the scale operator in placing objects onto and off of the industrial scale platform. High quality stainless steel load cells protect the scale from damage caused by dropping items onto the scale platform, in addition to providing many years of trouble free use.

Digital scales manufacturers have had a choice of two prevalent technologies. The most common has been industrial scales that use one or more strain gage type load cells. Smaller bench scales and parts counting scales use a single load cell mounted in the center of the scale platform. Larger platform scales and floor scales use one load cell under each corner of the scale platform. Depending on the size of the scale platform, intermediate sized scales, such as cylinder scales and drum scales may use either a single load cell or four. The accuracy of this type of scale is quite good, often delivering error levels of only one tenth of one percent. Using modern electronics, some of the other error terms, such as temperature effects and non linearity, have been improved with smart algorithms. But there is still a limit of accuracy that cannot be exceeded.

The second technology is known as force restoration. Industrial scales using this method can achieve accuracy levels up to twenty times better than strain gage electronic scales. Unfortunately, the cost is generally two or three times higher.

Arlyn Scales has invented a third technology for precision scales called Surface Acoustic Wave scales. Semiconductor transducers provide digital weight values that are equal to force restoration, but at costs that are similar to strain gage digital scales. These precision scales are also much more rugged than the other technologies.