Can't put a Band-Aid on a boomerang

摘要

While working for a company specializing in sensors, I received a board to test-a signal-conditioning module for a strain-gauge torque transducer that bolted directly to the hub of a drive motor. The board had been designed with size and cost reduction as key directives. The schematic showed that the input amplifier stage comprised a single operational amplifier acting as a current-input amplifier. The sensor comprised four 350Ω strain gauges acting as a Whetstone bridge, equivalent to driving the inputs with Thevenin sources with 175Ω source resistance. While the board was on the bench, everything seemed fine; manually applying torque corresponded to changes in the analog output signal.