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Unlike most laboratory balances, which employ magnetic force restoration as a weight sensing technology, and unlike most counting scales which use strain gage load cell technology, Setra Systems uses a unique sensor of its own design. All Setra balances and scales use a ceramic variable capacitance load cell.

The design is very rugged and provides unsurpassed weighing accuracy at an affordable price. It consists of two parallel gold plated bars fused onto the ceramic load cell. The gap between these two electrodes is just a few thousands of an inch thick.

A small load applied to the scale pan causes the ceramic beams to bend, changing the gap across the two electrodes, thereby changing the capacitance across the gap. The electrodes are wired into an LC oscillating circuit. Frequency of oscillation in the circuit changes with changes in the capacitance of the load cell. From no load to full load (the rated scale/balance capacity) the frequency may change by as much as two million cycles per second. Because the on-board microprocessor can detect changes as small as one cycle per second, many balances have extremely high displayed resolution (e.g., 1 part in 500,000). For the same reason counting scales may have very high internal counting resolution (e.g., the model 2000C will resolve a weight change of l ppm).

This approach to measuring weight is unique and covered by several of the company's patents. The simplicity of the design is evident from the relatively small parts count, and reliability is enhanced by the lack of moving parts.

In 1987 the International Society for Weighing and Measurement presented Dr. S.Y Lee with its Technical Excellence Award in recognition of the fact that this new technology has benefited science and industry and has proven itself to be commercially viable. The company has dedicated itself to finding new and better ways to measure force, and the next generation of high accuracy scale and balance products is already under development within Setra's innovative R&D group.

   
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setra   159 Swanson Road, Boxborough, MA 01719-1304
Tel (978) 263-1400 · Toll Free (800) 257-3872
     
   

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