Sensor Protection White Paper Sensor Protection Protecting sensors simply and securely Sensors are used everywhere in the world. Whether they are battery driven or powered from the grid, it is important to have suitable protection for electronics. For this purpose, SCHURTER offers such SMD fuses for primary and secondary protection. These fuses stand out due to their compact design, low power dissipation and a tight time tolerance for tripping. Smart meters provide one of many applications for sensors (Source: shutterstock) Secondary protection Many sensors are fed with power independent of the power grid. Instead, they have either a battery or get the required energy from an autonomous system, for example a solar system. In order to function in such autonomous systems, sensors must meet equally high requirements, which among other things, include maintenance requirements and the desired service life. Accordingly, battery operated devices should consume as little power as possible so as to achieve a long, maintenance-free operating time. Further, effective overcurrent protection is essential for providing the necessary protection of sensitive components in case of a malfunction. Among the safety-related technical aspects are a short, precise response time and high reliability in both low and high temperatures ­ of course over the entire service life of the sensor. A compact form factor and a good price/ performance ratio are additional key criteria. Smoke detector reliability and long life are important properties (Source: shutterstock) Because batteries in autonomous systems have very high power density, a short circuit can be all it takes to start a fire. To prevent damage to electronics and the environment, overcurrent protection is thus indispensible. This can be implemented both with an active solution as well as with a simple fuse. Here fuses offer clear advantages: compared to active solutions they are more reliable and take up less space. In addition, the latestgeneration fuses are convincing because of very low power dissipation and precise tripping characteristics. The USx line from SCHURTER — low-loss and precise acting In order to meet the requirements of sensor protection in an optimal way, SCHURTER developed the USx line for overcurrent protection in secondary circuits. The USx line consists of six types (see Table 1) in various SMD sizes from 0402 to 1206 and with rated currents from 50 mA to 25 A. Considerable breaking capacity as large as 600 A at rated voltages of up to 125 VAC/VDC make the chip fuses in the USx line unique in the market. The partially gold-plated contacts also have a positive impact on usability, storage life and the electrical qualities of USx fuses. The special design of these chip fuses also results in a low voltage drop. For example, it is only 87 mV for the 0.2 A design of the USFF Circuit Protection 1206 at rated voltage. For the 1 A version of the USF 0402, the voltage drop at rated voltage is a low 65 mV, a feature which no other product on the market claims. A further aspect that makes the USx line special is the tripping time. For the USFF 1206 and for a tenfold rated current, the UL 248-14 standard prescribes a tripping time between 0.1 and 1 millisecond; the SCHURTER fuse reacts with a typical tripping time as short as 0.5 milliseconds with a tolerance band of from 0.4 to 0.6 milliseconds (see figure 1). These performance characteristics also do not change even under high pulsed loads such as those that can arise in an environment with electronically commuted motors. 10000 Sensors of various types help monitor and control processes. They relieve people of tasks, particularly in dangerous environments, and simplify work processes. Often sensors are equipped with a sort of "intelligence" in the form of electronics that process the sensor signal. Further, many sensors have a communications interface so they can transfer data over a network to a central computer. The application range of sensors is equally large and continues to grow: smoke alarms, motion detectors, temperature sensors, humidity sensors, level detectors, smart meters as well as flow and volume metering are just a few of the application areas, whereby this list could continue indefinitely. Figure 1: Precise trigger time window of the USFF 1206 (160 mA) compared with the UL 248-14

Sensor Protection White Paper schurter.com/downloads www.schurter.com/downloads Primary protection Sensor applications can in some cases be attached to the power grid. This applies especially for those with more intelligence. Examples include smart power meters that are used in a "smart grid". In places where sensors are connected to the power grid, they need primary protection that can handle short circuits and grid spikes such as those that can arise from a lightning strike close to the equipment. Here, too, fuses are very well suited for protecting sensors. They offer the same advantages as...