Digital measurement of human proximity to electrical power circuit by a novel amplitude-shift-keying radio-frequency receiver

An electrical injury protection system is being developed to protect electrical workers from electrical injury and electrocution by human proximity and electrical contact sensing. Proximity is monitored by the insertion loss of a radiofrequency (RF) transmission between the power circuit and the human body. The system continuously transmits low power amplitude-shift-keying (ASK) RF waves from the power circuit to the surrounding area. An RF receiver attached to the human body measures the magnitude of incoming ASK RF waves which is inversely related to the proximity of the human body to the power circuit. A novel digital ASK demodulation method is used to conduct digital measurements of the incoming ASK RF wave magnitude efficiently. The RF receiver converts the incoming ASK signals to sawtooth-like enveloped ASK RF signals. A digital ASK demodulator demodulates the converted RF signal and digitizes the sawtooth-like envelopes into a square wave with the pulse width directly related to the magnitude of the incoming ASK RF signal. Human proximity and electrical contact are digitally detected by counting the width of the demodulated pulses. The current consumption of the prototype receiver is only 9 μA, which is 1600 times less than that for a conventional ASK magnitude detector.