I need to measure the torque applied to a varying load. The torque levels are low 1-20 gm cms. Would like to resolve 0.1 gm cms. It needs to be settable. A continuous measure would be best but I could at a pinch settle for a limit detection.
The rotation is supplied by a small geared electric motor, running at around 500 rpm, which is speed controlled by a microprocessor.
The best I can come up with is to mount the motor body in some bearings with stops to limit the rotation to a few degrees, balance it, and use a spring with an adjuster to exert torque on the motor. I could then use an opto switch to determine when the motor has rotated, overcoming the spring force.
The other thought I had was to use a low speed motor in bearings with a pot attached to measure the motor rotation against a spring with a gearbox to supply the load. this would increase the amount of torque to be measured at the motor end though the accuracy of the final output would be affected by the gearbox losses.
Any ideas most appreciated.