Brake Fluid Level Sensor REED RELAYS REED SENSORS REED SWITCHES Introduction When applying one’s foot to the brake pedal, it is taken for granted that the braking mechanism will begin to slow or stop the vehicle. A hermetically sealed reed switch plays a key reliability role by monitoring that the brake fluid level is maintained at its proper level. Low brake fluid level could mean the loss of the vehicle braking system. Figure 1. KSS-BV50685 Sensor physical layout Features • Hermetically sealed • Dynamically tested contacts • Reliable switching • Accurate control of the open and closure points • Wide differential preventing on/off cycling Figure 2. Brake Fluid Level Sensor in the un-activated state with a full reservoir • Designed for under the hood environment • Ability to operate up to 150 C • Low cost • Housing vapor sealed • Different headers and sleeves available • Millions of hot switching operations • Use of PCB assembly preventing potential cracking with other assembly technologies • 10 year proven technology Applications • Sensing the fluid level in brake fluid reservoirs • Sensing fluid level in gasoline, oil and other liquid reservoirs • Air conditioner system condensate: detecting high water levels Figure 3. Brake Fluid Level Sensor activated disabling ABS and dash indicator lamp • Coolant overflow fluid system sensing MEDER’s Reliable Reed Approach To Brake Fluid Level Sensing Systems Designing a sensing system for under the hood of a vehicle presents difficult requirements. The sensor must operate at extreme temperatures that are as low as -40°C and as high as 125°C. This dirty environment is typically visited by oil, gasoline, brake fluid, salt water and a host of solid particulates. MEDER’S approach has been to use only the most reliable technology to insure quality operation and long reliability in the field for the life of the vehicle. 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 2 www.meder.com Brake Fluid Level Sensor REED RELAYS REED SENSORS REED SWITCHES Specifications (@ 20° 20°C) KSS Series Operate specs Min Max Units Must close distance 3.3 5.7 Must open distance 4.3 12.2 mm mm Hysteresis Load Characteristics Switching voltage Switching current Carry current Contact rating Static Contact resistance Dynamic contact resistance Breakdown voltage Operate time Release time Operate Temp Storage Temp Min Max Units 200 0.5 1.0 10 150 200 200 0.4 0.05 -40 125 -65 150 V Amps Amps Watts mΩ mΩ V msec msec °C °C Since this sensor requires some electrical circuitry, using a printed circuit board with plated thru solder holes guarantees reliable connections using an automated wave soldering system. Others have chosen welding technology which can guarantee a good connection, but can also damage the delicate hermetic seal of the reed switch with its high temperature point contact and its tough mechanical approach. This poses an even bigger problem in the field if a slight crack of the reed switch seal occurs during assembly, as it could take up to a year or more for enough gas and/or moisture to leak into the capsule to oxidize the contacts. Then if the brake fluid drops below acceptable limits the contacts would fail to close; therefore, not alerting the driver that a critical situation has developed. Figures 2 and 3 show the proper operating sequence. Also, part of our design criteria is to build sufficient hysteresis into the operation of the sensor. This insures once the sensor activates, it will not go on and off with every sway of the vehicle or bump in the road. Another critical element is the acknowledgement that during assembly problems can occur. MEDER tests all sensors 100% for all operating conditions, but in addition tests for dynamic contact resistance (DCR). Essentially this test is a guard against the many faults that can occur during assembly. If the reed contacts have any internal contaminations; or the reed capsule has been stressed or a slight crack has occurred, this DCR will detect these conditions and reject the sensor. This testing is all carried out in an automated testing system that is independent of any operator, and rejected parts are automatically placed in a lock box. MEDER’s design for manufacturing approach provides a long reliable life in the field. The header and sleeve shown in the dimensional diagram have several other potential options allowing different connectors to be used, as well as the ability to fit into several other types of brake fluid reservoirs. Consider some of the below level sensor options for similar brake fluid sensor applications. Liquid Level Series Series KSSKSS-BV50685 LS01 LS02 LS03 Dimensions mm W 17.0 Illustration inches 0.669 H 19.0 0.748 L W H L W H L 70.0 19 24 42 19 24 75 2.756 0.748 0.945 1.654 0.748 0.945 2.953 W 25 0.984 H 25 0.984 L 80 3.150 **Consult ** the factory for more options not listed above. 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 2 www.meder.com