Selection and comparison of reed switches and Hall effect sensors

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Selection and comparison of reed switches and Hall effect sensors [Copy link]

Since the advent of the Hall Effect sensor, it has captured the imagination of designers, and solid-state devices are generally considered more reliable than electromechanical devices. However, when comparing reed switch sensor technology to Hall sensor technology, you can observe some noteworthy advantages of reed switch sensors. Reed Switch Sensor Technology In a reed sensor, the key component is the reed switch, which was invented by Western Electric in 1940. The other major components are the spring reed that opens or closes and the magnet or electromagnet. Over the past 60 years, reed switch development has seen several improvements that have made it more reliable, improving quality while reducing costs. Due to these dramatic improvements, reed switch switches have become the design choice in some demanding applications where quality, reliability, and safety are paramount. The most notable application for the quality and reliability of reed switch sensors is in automatic test equipment (ATE). In this equipment, the technology is state-of-the-art, and reed switches are used in reed relays, which are used as switches in test equipment for ICs, ASICs, silicon wafers, and printed test equipment. In these applications, there may be as many as 20,000 reed switch relays in a single test system. A relay failure rate is specified as 50ppm, so to meet this requirement, the quality level of the reed relay must be much better than the 50ppm requirement. To date, such quality levels are unheard of for an electromechanical device. Similarly, it also applies to some semiconductor devices. Once the initial operational quality test is completed, the reed relay needs to perform well throughout its life. In this regard, they have proven to outperform all other switching devices. This is because in many cases, ATE is running 24 hours a day, 7 days a week, and its cost is the main factor. Therefore, the operating life of the reed relay needs to be millions of times. Another example in favor of the reed relay is its use as an air bag sensor, where it has been tested over time in a severe safety application. Reed switch sensors are widely used in many demanding automotive safety devices (such as sensitive brake fluid level), many medical instrument applications, including cautery devices, pacemakers and other medical electronic devices. In these devices, the reed relay isolates small leakage currents. Comparison of Reed Switch Sensors and Hall Effect Sensors In both reed switch and hall effect sensor technologies, the size is shrinking. However, when comparing reed switch sensors to Hall effect sensors (see attached table), some advantages of reed switches can be seen: 1. Hall effect devices are generally low in price, but require expensive power circuits to power them. Their output signals are also low, and they also require amplifier circuits. The net result is that Hall effect sensors are more expensive than reed switch sensors. 2. Reed switch switches have excellent insulation from input to output and the insulation resistance of the switch is up to 10 ^15. The result is leakage current levels of 10 ^-15 A. On the other hand, Hall effect devices have sub-microampere leakage current levels. In medical electronic devices such as probes or pacemakers that are inserted into the human body, it is very important that these devices do not have any leakage current close to the heart. Microampere or sub-microampere currents can change the critical electrical activity of the heart. 3. Reed sensors are sealed, so they can work in almost any environment (such as being unaffected by humidity). 4. The contacts of the reed switch have extremely low on-resistance when conducting, with typical values as low as 50m, while Hall effect sensors may have hundreds of ohms. 5. Reed sensors can directly switch signals ranging from a few nanovolts to kilovolts, currents from femtoamperes to amperes, and frequencies from DC to 6GHz. The output range of Hall effect devices is very limited. 6. Reed sensors offer a wide range of magnetic sensitivity. 7. Reed sensors are insensitive to ESD, which can often damage Hall effect sensors. 8. Reed switch sensors can withstand very high voltages (minimum rating is 1000V). Hall effect devices require external circuits to be rated to 100V. 9. Reed switch sensors can withstand a typical 3-foot drop test, which is similar to the drop test of Hall effect sensors. 10. Because reed switch sensors have no wear components, low-level loads (less than 5V and lower at 10mA) can operate up to millions of times. This is comparable to the numbers of semiconductor micro-machined devices. 11. Reed switch sensors are not affected by the temperature environment, and the typical operating temperature range is from -50 ^. C to +150 ^. C, without special additional conditions, restrictions or fees. The operating temperature range of Hall effect sensors is limited. There are many great applications for reed switch products. Some reed switch relay manufacturers are excellent at designing for demanding applications and are first class in quality, reliability and safety.