Electronic Analytical Balance: a Coil Current in Place of Weights (Akers et al., 1977)

The equal-arm balance with its weights replaced by electricity. The pan sits on a coil in the gap of a permanent magnet. A load pushes it down; capacitor rings sense the smallest movement, and a servo drives just enough current through the coil to lift it back to its rest position. That current is the weight. Result: a balance that reads the weight in grams or ounces on a digital display, with no weights to handle, and tare by its circuit. Source: C. B. Akers and others (Arbor Laboratories), US Patent 4,034,819 (1977). Unknown: the resolution, capacity, magnet type, materials and sizes; the circuits are given as blocks only. Picture: patent drawing.