Reed Sensors Monitor Pressure in Fire Extinguishers REED RELAYS REED SENSORS REED SWITCHES Introduction Fire extinguishers are usually under high pressure. When called upon in an emergency situation they must expel their contents rapidly and over as long a distance as possible. If the pressure drops off while its sitting in its idle period, which could be several months or several years, then when its called upon to put out a fire, it comes up with nothing to expel. Obviously in this emergency situation, loss of life or severe burns could be the outcome. MEDER designers working closely with gauge manufactures have come up with a very clever solution. Figure 1. MK17-X-3 Sensor physical layout Features • Magnet and Reed Sensor are isolated and have no physical contact by typically having the magnet mounted to the gauge needle under the dial and the Reed Sensor is mounted strategically on a tiny PCB such that the magnetic field of magnet will be sensed as the gauge dial rotates indicating a changing reduced pressure. • The reed switch used in the Reed Sensors is hermetically sealed and is therefore not sensitive to its surrounding environment. Figure 2. At normal pressure the magnet is a distance away from the sensor which is in it's normally open contact state drawing no battery power. • The magnet is not affected by high and low temperature environments. • Tens of millions of reliable operations • Surface mounting and through hole mounting • Contacts dynamically tested Applications • Ideal for sensing the rotation of a gauge dial in a fire extinguisher. • Ideal for applications sensing any gauge rotation in a host of different applications. Figure 3. Pressure drops causing the spring with attached magnet to move into proximity with the reed sensor causing the contacts to close and signal an audible alert. Reed Sensors are are the Choice for monitoring the pressure in fire extinguishers All too many times fire extinguishers sit for many years and are not checked for pressure status. And of course when called upon to put out a fire, there is no pressure to expel the material necessary to put out the fire. Since this is a real safety issue and lives are at stake if the pressure fails, it’s very important to alert the user if there is a reduction in pressure in the extinguisher. The problem here is that most fire extinguishers sit on a wall with no connection to any power source. So using electronic circuitry can not be used unless powered by batteries. MEDER’s use of reed sensors to solve this problem aptly applies. Reed sensors do not use any power. MEDER electronic Application MEDER electronic AG | Germany | tel.: +49(0)7731/8399-0 | Email: [email protected] MEDER electronic Inc. | USA | tel.: +1 508.295.0771 | Email: [email protected] Page 1 of 3 www.meder.com Reed Sensors Monitor Pressure in Fire Extinguishers REED RELAYS REED SENSORS REED SWITCHES Specifications Operate specs Min Max Units Must close distance 5 25 mm Must open distance 5 25 mm Hysteresis Load Characteristics Switching voltage Switching current Carry current Contact rating Static Contact Contact resistance Dynamic contact resistance Breakdown voltage Operate time Release time Operate Temp (MK15) Storage Temp (MK15) Typical 50% Min Max Units 200 0.5 1.5 10 150 200 320 0.5 0.1 -20 120 -35 130 Volts Amps Amps Watts mΩ mΩ Volts msec msec °C °C The gauge has a small magnet welded to the spring of the pressure gauge. The gauge needle sits on one side of the pressure indicating plate while the magnet is on its underside. Just below the magnet is a small circular PCB which houses a reed sensor positioned such that when the gauge needle reaches a certain low pressure point, the reed sensors energizes. Once the reed sensor energizes an alarm is sounded indicating a low pressure situation. Here the marshalling of the pressure is carried on by the movement of the spring, which in turn moves the magnet, which in turn moves its magnetic field close enough to the reed sensor to activate it; and finally the alarm is activated. This allows the user to either have the fire extinguisher recharged or seek a new one. Because MEDER’s sensors use hermetically sealed reed switches that are further packaged in strong high strength plastic, they can be subject to various environments without any loss of reliability. The reed sensor is an excellent choice because it can operate reliably over a wide temperature range, and represents an economical way to carry out the sensing function. MEDER’s sensors are packaged for surface mounting as well as through hole mounting. Surface Mount Series Series MK15 MK16 MK17 MK22 MK23MK23-35 MK23MK23-66 MK23MK23-87 MK23MK23-80 Dimensions mm W 2.5 H 2.5 L 19.50 W 2.3 H 2.3 L 15.60 W 2.1 H 2.1 L 9.61 W 2.7 H 2.3 L 15.60 W 2.2 H 1.95 L 15.75 W 2.2 H 2.7 L 19.60 W 2.0 H 2.1 L 15.60 W 2.0 H 2.1 L 13.0 Illustration inches 0.098 0.098 0.768 0.091 0.091 0.614 0.083 0.083 0.378 0.106 0.091 0.614 0.087 0.077 0.620 0.087 0.106 0.772 0.079 0.083 0.614 0.079 0.083 0.512 MEDER electronic Application MEDER electronic AG | Germany | tel.: +49(0)7731/8399-0 | Email: [email protected] MEDER electronic Inc. | USA | tel.: +1 508.295.0771 | Email: [email protected] Page 2 of 3 www.meder.com Reed Sensors Monitor Pressure in Fire Extinguishers REED RELAYS REED SENSORS REED SWITCHES Through Hole Series Series MK06MK06-4 MK06MK06-5 MK06MK06-6 MK06MK06-7 Dimensions mm W 3.3 H 3.3 L 12.06 W 2.8 H 3.2 L 14.30 W 3.3 H 4.2 L 17.24 W 3.3 H 4.2 L 19.78 Illustration inches 0.130 0.130 0.475 0.110 0.126 0.563 0.130 0.165 0.679 0.130 0.165 0.779 **Consult ** our factory for your specific design requirements. MEDER electronic Application MEDER electronic AG | Germany | tel.: +49(0)7731/8399-0 | Email: [email protected] MEDER electronic Inc. | USA | tel.: +1 508.295.0771 | Email: [email protected] Page 3 of 3 www.meder.com