Each Si7005 is factory-calibrated and interchangeable, facilitating production, rework and field servicing. Since the sensor element must be exposed to the environment (air), RH sensors are subject to damage and contamination, especially during PCB assembly. The sensor MUST be kept clean and undamaged. Adding protective tape before PCB assembly and removing it afterward is a common, but labor-intensive approach. The sensor continues to require protection over the life of the end product, requiring some kind of protective filter. Silicon Labs offers a unique, factory-installed cover that both protects the Si7005 during PCB assembly (solder reflow), but remains in place and acts as a filter throughout the life of the product. Moisture sensing polymers exhibit hysteresis and “memory” effects; they take time to reach equilibrium with their environment, particularly after being exposed to high or low humidity levels for long periods of time. Long exposures to high humidity can cause the sensor to accumulate a small, positive offset. This effect can be reduced by activating the on-chip heater at high humidity levels. This raises the temperature of the sensor by a few (4 – 5) degrees, reducing the absorption of moisture into the polyimide (while in this mode, the sensor measures dew-point, not relative humidity). This issue is not unique to Silicon Labs; it applies to virtually all RH sensors in one degree or another. To get the best performance, the humidity readings from the Si7005 must be temperature-compensated and linearized in host software. The computations are simple, using fixed coefficients that do not vary from unit-to-unit or lot-to-lot. The coefficients are published in the datasheet. Many RH sensors are bulky and/or rather delicate and not completely compatible with typical PCB assembly flows. The Si7005 works with typical SMT manufacturing flows.