The Anatomy Of A Modern Crane Scale

By Author: Karl Nowosielski
Total Articles: 4717
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Most of the strain gauges used are of the simples cantilever types and rely on four resistive elements that are bonded to the strain gauge surfaces in such a way that when weight is added to the platform two of the resistive elements are stressed (shortened by pushing) and two are strained (lengthened by pulling).

The four elements are arranged in a Wheatstone Bridge electrical circuit that provides an output signal proportional to the unknown weight. The next critical piece of the anatomy is called the display, but it is usually far more than just a display.

In order to amplify the error signal, scale it properly for calibration, correct for non-linearity’s, correct for temperature changes, accommodate the tare function, change from analog signal to digital value, a modern digital computer with memory is required.

In the case of the crane scale all of this functionality, plus a battery large enough to power the scale for at least one full shift, must be attached to the scale in such a way that it is not seen as a load by the strain gauge.

The display travels with the crane hook ...
... and can become quite elevated depending upon the load being weighed. This can make it difficult to read the weighing result on the scale or reach any of the controls, like the tare button. In order to alleviate this problem some manufacturers offer crane scales that feature a supplementary portable handheld controller that duplicates the controls and the weight display in the users hand (see www.torbalscales.com for an illustration of this feature).

These remote controllers are wireless devices and can allow the crane to operate at a distance from the handheld device. The fact that these scales are portable and battery operated means that they must be recharged periodically. Most of these scales will operate for at least 8 hours on a single recharge, and have recharging times that are about half that time.

All rechargeable batteries, however, have a finite life, usually expressed in terms of the number of recharge cycles that they can provide.

Modern batteries, including lead-acid types, are greatly improved in this area and provide meaningful service life if properly cared for.

The fact that these scales are often high capacity scales does not make them immune to overload problems and care must be taken to follow the manufacturers guidelines with regard to the scales overload capacity.

These scales are usually packaged in such a way as to make them impervious to harsh environments, like sealed front panels with membrane switches. The modern electronic digital crane scale has evolved rapidly and become a very useful factory tool.
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