Two parallel gold plated bars are fused to the sensor’s ceramic beams. This creates a capacitor. The gap between the plates is only a few “mils” (thousands of an inch) thick. This capaci- tor is then connected into an electrical circuit to form an Inductive Capacitance Oscillator. With no load applied the oscillation frequency is approximately 10 megahertz.

As load is applied, the capacitor gap is slightly reduced (or, in some cases, opened) by an amount imperceptible to the naked eye. The capacitance changes with changes in the gap,and the oscillation frequency in the circuit also changes. From no load to full load (equal to scale capacity), the frequency changes by 2-3 megahertz, an amount proportional to the weight on the scale.

The scale’s microprocessor counts the oscillations in the circuit and converts the signal to weight units, making any necessary corrections for environmental factors such as temperature, linearizes the output, digitally fi lters the result to dampen out vibration, and reports the weight to the display and to the RS232 drive. Because the Setra scale’s microprocessor can detect changes of one cycle, the Setra scales’s “internal Resolution” (IR) can be as high as 1 in 2 or 3 million, although other factors sometimes reduce the resolution to 1 in a million or lower.