A strain gauge balance suspension

A balance suspension is described in which the beam is supported by a flexible ligament. Out of balance loads result in bending of the ligament which is detected by a system of strain gauges. This use of strain gauges as a null detector gives greater accuracy than the normal weight transducer in which the full load has to be within the scale of the indicator. The suspension gives a balance which is easily made, is extremely robust mechanically and is resistant to corrosive atmospheres and temperature gradients. An expression for the sensitivity, defined as the ratio of signal voltage to out of balance load, is derived. The sensitivity is shown to be independent of load, which is limited by the mechanical strength of the suspension. The original model indicated an out of balance load of 0.1 g on a total load of 2 kg but a stronger beam and mounting would have given the sensitivity up to a load of the order of 100 kg.