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Alarm Sensor & Security Circuit Cookbook P2

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Tham khảo tài liệu 'alarm sensor & security circuit cookbook p2', kỹ thuật - công nghệ, điện - điện tử phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Hall-effect metal magnetic sensors 19 1 Cl 0.01-pF 25-V capacitor disk 1 DI LM329C zener diode National Semiconductor 1 QI LM395 transistor National Semiconductor 1 H Heater coil Hall-effect metal magnetic sensors The Hall-effect sensor can detect the pressure or absence of magnets or metal surfaces and can solve a number of measurement and alarm problems. We will illustrate some of these applications. Three different types of Hall-effect sensor are presented. Hall-effect sensors can be used for tilt switches counters proximity detectors metal detectors pressure sensors current sensors and gaussmeters. A basic low-cost Hall-effect sensor is the Sprague UGN3020T shown in Fig. 1-24. This sensor includes a Hall cell voltage regulator signal amplifier and Schmitt trigger. The circuit shown can protect instruments antiques or windows doors by placing a small magnet on the item you wish to protect. The sensor is then placed in close proximity to the magnet. When the magnet is moved past the sensor an output activates a relay. The sensor drives a 2N5812 transistor for an on-off type output. A DPST relay could be used to sound a local alarm or the circuit could be con- Fig. 1-24 Hall-effect switch. 20 Sensors and Detection Circuits nected to a central alarm panel. The same basic Hall sensor could be used for counting moving objects or as a wind-speed indicator. The diagram in Fig. 1-25 depicts an ac Hall switch that can control 115-V loads such as motors and lamps upon detecting the presence or absence of a magnet. The Sprague UGN3501T Hall sensor is more flexible because it provides an analog output. The 350IT Hall sensor is a single-ended output device which can sense small changes in a magnetic field. The 3501T includes a Hall cell linear amplifier emitter-follower output and a regulator. Fig. 1-25 Hall-effect ac switch. A ferrous metal detector shown in Fig. 1-26 can detect metal objects passing the sensor. A magnet is placed with its north pole facing the 3501T .