Metal detection and alarm systems

摘要: A metal detection alarm system detects the presence of an article a particular in given region by measuring disturbance two oscillating electromagnetic fields, one at from 5 to 20 kHz., other 16 Hz. and also magnetic field established D.C. pulses produced rate 0 per second. Receivers tuned respond fields produce different response when is present, change responses depending upon parameters article. The outputs receivers are compared with transmitted signals or logic circuit standard if least receiver indicate metal, actuated. Applied revolving doors, apparatus prevent person carrying firearm into bank building, entering aircraft, obtained. can be used conjunction conventional non-revolving doors windows. temperature controller utilizing resistance thermistor described. located base transistor which, turn, control which determines length applied gates thyristors silicon controlled rectifiers. time switching S.C.R.s pulse controls supply power heater.