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SHT20 Datasheet(PDF) 5 Page - List of Unclassifed Manufacturers |
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5 / 14 page Datasheet SHT20 www.sensirion.com Version 4 – May 2014 5/14 recommended to further process the sensors within 1 year after date of delivery. It is of great importance to understand that a humidity sensor is not a normal electronic component and needs to be handled with care. Chemical vapors at high concentration in combination with long exposure times may offset the sensor reading. For this reason it is recommended to store the sensors in original packaging including the sealed ESD bag at following conditions: Temperature shall be in the range of 10°C – 50°C and humidity at 20 – 60%RH (sensors that are not stored in ESD bags). For sensors that have been removed from the original packaging we recommend to store them in ESD bags made of metal-in PE-HD12. In manufacturing and transport the sensors shall be prevented of high concentration of chemical solvents and long exposure times. Out-gassing of glues, adhesive tapes and stickers or out-gassing packaging material such as bubble foils, foams, etc. shall be avoided. Manufacturing area shall be well ventilated. For more detailed information please consult the document “Handling Instructions” or contact Sensirion. 2.3 Temperature Effects Relative humidity reading strongly depends on temperature. Therefore, it is essential to keep humidity sensors at the same temperature as the air of which the relative humidity is to be measured. In case of testing or qualification the reference sensor and test sensor must show equal temperature to allow for comparing humidity readings. If the sensor shares a PCB with electronic components that produce heat it should be mounted in a way that prevents heat transfer or keeps it as low as possible. Measures to reduce heat transfer can be ventilation, reduction of copper layers between the sensor and the rest of the PCB or milling a slit into the PCB around the sensor – see Figure 10. Furthermore, there are self-heating effects in case the measurement frequency is too high. To keep self heating below 0.1°C, SHT2x should not be active for more than 10% of the time – e.g. maximum two measurements per second at 12bit accuracy shall be made. 12 For example, 3M antistatic bag, product “1910” with zipper. Figure 10 Top view of example of mounted SHT2x with slits milled into PCB to minimize heat transfer. 2.4 Light The SHT2x is not light sensitive. Prolonged direct exposure to sunshine or strong UV radiation may age the sensor. 2.5 Materials Used for Sealing / Mounting Many materials absorb humidity and will act as a buffer increasing response times and hysteresis. Materials in the vicinity of the sensor must therefore be carefully chosen. Recommended materials are: Any metals, LCP, POM (Delrin), PTFE (Teflon), PEEK, PP, PB, PPS, PSU, PVDF, PVF. For sealing and gluing (use sparingly): Use high filled epoxy for electronic packaging (e.g. glob top, underfill), and Silicone. Out-gassing of these materials may also contaminate the sensor (see Section 2.2). Therefore try to add the sensor as a last manufacturing step to the assembly, store the assembly well ventilated after manufacturing or bake at >50°C for 24h to outgas contaminants before packing. 2.6 Wiring Considerations and Signal Integrity Carrying the SCL and SDA signal parallel and in close proximity (e.g. in wires) for more than 10cm may result in cross talk and loss of communication. This may be resolved by routing VDD and/or VSS between the two SDA signals and/or using shielded cables. Furthermore, slowing down SCL frequency will possibly improve signal integrity. Power supply pins (VDD, VSS) must be decoupled with a 100nF capacitor – see next Section. |
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