Electronic Safety System for Table Saw

This article proposes a safety sensor for table saw, based on impedance measurement between two electrodes placed in front of blade. A multitone system is developed, acting as a selective barrier able to distinguish the proximity of a hand with respect to wood, both dry and wet. Due to conductivity of human body, the proximity of the hand introduces a shielding effect, causing a reduction in capacitive coupling between electrodes. On the contrary, wood cannot induce the same effect for all frequencies, even if it is wet. This results in achieving a very sensitive and cost-effective safety system, able to respond effectively to hazard situations. An electronic prototype, realized through digital synchronous detection of two tones at 10 kHz and 1 MHz, demonstrates the effectiveness of the proposed sensing technique. To better describe the working principles, a simple system simulator is studied, able to describe the experimental results. The proposed technique opens the way to a new generation of safety systems for table saw.