Sensors Products Page 15 Sensors Products

2017 Littelfuse, Inc. Specifications are subject to change without notice Littelfuse.com 15 Many types of security alarm systems use a reed switch/sensor attached to the frame of the door or window. The actuating magnet is attached to the moving door or window so that when it is opened, the reed sensor detects the moving magnet and opens/closes its electrical contacts-sending a signal to the alarm system. Similarly, reed switches can easily be mounted to circuit boards used in smoke or gas alarm systems. In portable systems, such as gas detectors, the reed switch is used to activate the system when the handheld detector or reader is placed in the docking station. In systems with smoke/gas detectors in fixed positions, the reed switch can be activated with a handheld magnetic wand to put the detector in test mode. Reed switches and reed sensors are effective solutions for many types of security and alarm sensor applications. Examples include detecting the door and window position, measuring the sump pump water level or activating the test mode of a smoke detector. Reed relays can be used to activate the alarm loop in active sensors like motion sensors and smoke detectors. SECURITY AND ALARM SYSTEMS- Door and Window Alarms Alarm Driver Power Circuit N S Magnet Reed Sensor Electronic Control Unit Figure 6-Door alarm system using a reed sensor No physical contact is required to operate the switch Zero power required for switch actuation Wide operating temperature range adequate for use in hot and cold temperatures Electrical contacts are within a hermetically sealed capsule that is immune to moisture, dust and dirt Overmolded sensors provide additional protection against mechanical stresses Low-cost alternative to mechanical switches MDSM-10 (10 mm reed switch) 59020 (Miniature firecracker) 59040 (Press-Fit Firecracker) 59140 (Miniature flange mount) 59170 (11 mm overmolded reed switch) HE3621A0510 (Miniature SIL reed relay) Similar Applications: Burglar systems, smoke alarms and gas detection systems Resistive reed ladder networks are used to measure the liquid level in a tank, which allows for a continuous output signal rather than discrete signals from single-point level sensors. This continuous level sensor produces a variable resistance or continuous current/voltage that is related to the position of the float/magnet assembly. As the liquid level changes, the relative float position follows, activating the reeds sequentially and producing the associated output voltage or resistance value. The typical spacing between reed switches is usually provided in 6.35 mm or 12.7 mm steps. Littelfuse supplies full assemblies that include stainless steel or plastic housings. Bare reed switches are also available. Level sensors incorporating reed switch and resistance technology are commonly used for measuring continuous liquid levels in the automotive, marine and industrial markets. The float, which contains a magnet, moves up or down over the sealed stem containing the reed switches/resistors. CONTINUOUS LEVEL SENSING- Industrial Tank Water Level S N S N Load + - DC24V Sensor Converter Float with Magnet R16 R15 R14 R13 R12 R11 R4 R3 R2 R3 R0 S16 S15 S14 S13 S12 S11 S4 S3 S2 S1 S0 White (Level Signal) Black (Ground) Blue (Thermistor Single) Empty Full R 5 R 4 R 3 R 2 R 1 Figure 7-Resistive reed ladder network for level sensing Continuous level output signal, not like a single-point level sensor Electrical contacts are within a hermetically sealed capsule that is immune to moisture, dust and dirt Sensor housing provides protection against mechanical stresses and vibration Reliable switching for millions of open/close operations Wide operating temperature range adequate for use in hot and cold temperatures MDSM-10 (10 mm reed switch) MDSM-4 (15 mm reed switch) Custom-designed level sensor assemblies Similar Applications: Fluid-level sensing for: urea in diesel trucks, fuel tanks, HVAC refrigerator tanks and condensate water tanks Features and Benefits: Suggested Products: Features and Benefits: Suggested Products: APPLICATIONS

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