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The measurement of the moisture content in a product can be very important in determining the value or quality of the product.  Measuring the moisture content in a product while the product is being manufactured can be a difficult and challenging thing to do.  Most moisture analysis is done by using a conventional laboratory scale that has been modified and has an oven mounted on the top of the scale.  The oven portion of the moisture analyzer is mounted over the weighing scale in such a way that it provides the heat to drive off the moisture without interfering with the weighing process for the sample.  This process is generally destructive as far as the sample is concerned and therefore does not lend itself to being inserted into a continuous production process.

Many people have scale applications that demand their scales be used in environments other than laboratories or indoor industrial sites with temperature control and 115 VAC outlets.  There are many outdoor applications with no shelter and no power outlets available.  There are many applications for use in motor vehicles and boats, where 12 VDC is the only power available.  Fortunately many of these applications only require the accuracy of an industrial scale using strain gauge technology to measure weight.  We tend to think of these as applications that require 1 part in 10,000 for accuracy (0.01%) to satisfy the user.  Modern strain gauge technology can do better than that, and many 0.005% scales are offered.

When we speak of the weight of an object we are referring to the maximum value of the force generated by that object when it is subjected to a gravitational field.  Gravitational fields have a definite direction toward what is known as the center of gravity.  The one of most interest to us is the earth’s gravitational center which is near the geometric center of the earth.  The earth’s gravitational pull may be viewed as being directed at this center in the earth.

When considering the acquisition of a precision scale, be it of the laboratory grade or the analytical grade, there are a few features that should be given serious consideration as they may bear heavily upon the utility of the scale for your purposes.
The most significant of these, to our mind at least, is Automatic Internal Calibration.  Scales with this feature calibrate themselves based upon a preset time schedule or a preset temperature change increment, but only when the scale is idle or the user agrees to the calibration.  The internal calibration weight must always be traceable back to a high accuracy secondary standard weight.  This feature can eliminate the need to redo projects where drift produces erroneous results.

There are many scale applications that require the user to make manual data entries into the scale.  In a prescription scale, if the drug name, part name or National Drug Code is not in the system, the scale user must enter these pieces of information by hand.  This process can be extremely frustrating, especially on scales where there is a limited number of keys on the scale’s keyboard.  Attempting to make alphanumeric keyboard entries on a scale that only has eight keys for information entry can be very time-consuming.  It also requires a fair amount of effort to learn and remember the sequences for character generation.  The closest analog would be writing words with the keys on a touch-tone telephone.

There are several different kinds of displays available to the scale purchaser.   This article will clarify the reasons for the two types of displays and what their most favorable characteristics are.  We will only consider LCD ( liquid crystal )displays, which make up the preponderance of analytical lab scale displays.

A force gauge can be thought of as an omnidirectional scale.  Unlike conventional scales, which only measure force in a vertical direction, force gauges can measure both positive and negative ( push or pull ) forces in any direction.  
    In order to accomplish this feat, the sensor of choice is the strain gauge.  While not the most accurate sensor in the world, it is quite capable of measuring both push and pull to the needed level of accuracy for industrial applications.  Also, the sensor is both small and light enough to fit comfortably in a hand-held measuring device.  Many force gauges allow the user to disable the internal strain gauge sensor and replace it with an external sensor.  An external sensor may have much higher capacity and/or measure torque rather than linear force.  These devices are almost always portable, and usually battery-powered.  In most cases the batteries are rechargeable.

Precision, Quality, and Reliability have been the hallmark of TORBAL products for over one hundred years. Our roots and our long history date back for over a century to when Christian Becker, Roeder-Springer, and the Torsion Balance Company pioneered the market for analytical balances and precision instruments.

When many people think of precision weighing they use terms like “Laboratory Balance” and “Laboratory Scale” to describe the same device.  The same applies to “Analytical Balance” and “Analytical Scale”. In weighing the term “balance” has historically meant a piece of weighing apparatus the allowed a user to determine the weight of an unknown object by balancing its weight against the sum of a series of known weights.  The characteristic of the balance which made it so extremely valuable was its high sensitivity to very small weight differences between objects on each of its two pans.  The equal arm balance with hanging pans has a long history and made early commerce and scientific endeavors possible.  Our modern symbol for justice is a blindfolded woman holding and equal arm balance with hanging pans in one hand and a sword in the other.

Modern force restoration scales, used in the analytical and laboratory scale markets, are quite similar in basic construction.  They are based upon the use of a Roberval structure which allows them to be top loading and eliminates the effects of end loading and side loading.  Roberval structures have been used in laboratory weighing for a long time. An illustration of an application can be seen on www.torbalscales.com/, where the first page of an early patent shows an equal arm top loading structure where taut bands are used in place of today’s flexures and individual weights are placed on a pan in place of the modern electromagnetic force motor.  The use of a parallelogram with flexures allowed weight to be placed directly on a pan above the whole structure, where previously hanging pans on equal arms had been the norm. 

Using a Crane Scale can be something of a pain if the controls and the display are an integral part of the scale that mounts on the crane hook.  The problem occurs if the load being weighed requires that the hook be far overhead in order to lift the load clear of the deck.  This makes reading the display difficult and can make operating any of the controls impossible.  Most operators handle the problem with some sort of a work around, like a ladder or platform.

Scales follow a fairly well defined hierarchy which is based upon their accuracy (linearity), and their resolution. For instance, an analytical scale usually presents a resolution of a part in one million (1:1,000,000) with a linearity of +/- 2 parts per million (+/-0.0002%).  These scales set the accuracy standards for scales produced in commercial quantities. On the other hand, the laboratory scale is still a high accuracy device with resolutions of one part per one hundred thousand (1:100,000) and linearity of +/-2 parts per one hundred thousand (+/-0.002%). These are the work horses of our research laboratories, our quality control laboratories, our gemstone businesses, our higher education labs, and many other applications requiring their kind of performance.