Advantages of Capacitance Technology in Weighing

(originally written about the Gemscale 50 in Jan 1992, and updated in August of 1995, but is largely applicable to the new generation of DSP-based scales)

The design innovations and inventions engineered in Gemscale 50 have helped to meet the real needs of the professional gem dealer for a portable carat scale.

The challenge is developing Gemscale 50 presented itself in efficiency and size. Competitive scales on the market are larger and heavier. Even with plastic housings their weights range from 1.5 lbs to 5 lbs. including case and peripherals. The Strain Gauge technology of these scales is the major obstacle to reducing weight and size. These top-loading scales require a parallelogram linkage to prevent errors from off center loading (placing the weight other than in the exact center of the pan), limiting them to about a two inch minimum height and requiring costly manual adjustments in manufacturing.

Gemscale 50 relies on a new capacitance technology developed by its engineer and designer John Borchard. Portability and durability have been greatly improved by a new patented sensor. This sensor is a variable capacitor in which the gap between two parallel plates is measured. It is this sensor coupled with the custom micro-processor which corrects for off center loading and allows Gemscale 50 to be reduced to a weight of 1/2 lb., small enough to fit into a jacket pocket. This new technology is much more durable as there are no delicate hand adjustments to disturb in handling.

The patented draftshield of sturdy Lexan, hard coated to the hardness of glass to resist scratches, also acts as the scale's carrying case. With Gemscale 50, unlike its competitors, there is no need to pack and unpack the scale and peripherals (such as dust cover, draftshield, weighing pan, calibration weight and AC adaptor). As a case, the patented draftshield secures the calibration weight and weighing pan in the contoured body of the scale. This self-contained design precludes lost parts.

There is no AC adaptor necessary with this capacitance technology. The elimination of nearly all analog circuitry reduced power consumption from 1200 mW typical for Strain Gauge products, to 17 mW in this capacitance technology. This means that the expected battery life of a simple 9 volt is now over a year. This makes an AC adaptor unnecessary for Gemscale 50. Gemscale 50 is also equipped with automatic shut-off and simply will not allow bad weight readings due to low battery voltage.

The capacitance technology used in Gemscale 50 also greatly improves the ease and efficiency of operation. The microprocessor compensates for a slanted orientation during the turn-on calibration procedure. This eliminates time consuming foot leveling so necessary to get accurate calibrations and readings for Strain Gauge scales.

The capacitance technology has another advantage over strain gauge. This technology allows for a close fit between the cover and the weight sensor. There is virtually no gap for melee (small stones) to fall into. Beyond this there is a labyrinth design to further prevent any foreign matter from falling into the weighing mechanism.

In addition to the advantages that Gemscale 50's technology have afforded in size and durability, attention was paid to often over-looked details. Gemscale 50 is able to provide a larger weighing pan because unlike Strain Gauge placing a stone in the center of the pan is not critical for an accurate reading. Side placement has been adjusted for in the calibration program. The Gemscale 50 weighing pan has a 96% larger area than competitors.

The pan holds more than 50 carats of stones. Its ergonomically designed rim can be held by fingers or by stone tweezers. The pan features non-spill pouring angles. Also, the contoured area around the pan makes it easy to catch and pick up stones.

Ease of operation is also provided for with its one button operation. One finger releases the draftshield. One button turns the scale on, calibrates, tares and turns the scale off. The directions are so simple, the entire instructions fit on the back label. Simplicity of operation keeps weighing in a selling situation faster, more productive and more professional. There is nothing on the market like Gemscale 50.

Gemscale 50 was introduced in February 1991. Gemscale 100 was introduced in May of 1993.