The last section discussed elements of the mechanical assembly for IR proximity measurements. One of the key issues to consider when implementing the mechanical design is to reduce the optical coupling. In systems where there is a lot of reflection or optical coupling from everything else other than the object, it is difficult to detect the actual signal of interest. These other reflections create very large offsets much bigger than the objects reflection. This slide shows two different topologies: single port and dual port. The single port has a single transparent window for both the transmit and receive energy. From the internal lines it can be seen that the single port has high internal reflectance which will use up much of the dynamic range of the sensor. For this reason single port designs are not recommended. The single port design may be useful for short range, simple detection where the object’s reflection provides enough signal to be resolved. However, the sensing system requires higher resolution since the signal of interest is small compared to the unwanted internal reflections. The dual port design has separate windows for the transmit and receive energy and provides a barrier between the two paths thus reducing the optical reflections. For greater detection range, either use lenses or integrating pulses. Lenses can either be implemented on the transmitter or the receiver. The easiest option is to use an LED with an integrated lens. Integrating pulses is also called “averaging”. This can remove the sample-to-sample variation to lower the noise floor, and therefore, allow better range. Portless designs use no enclosure and allow the light to pass unobstructed. In portless designs there should still be high optical isolation to provide for increased dynamic range. In any of the cases outlined, the signal detection capability is dependent on the dynamic range of the system: the background IR vs. the reflected energy from the object. In the single port case the dynamic range is consumed by the internally reflected energy. In the dual port case the distance and the ambient IR energy eventually take up the dynamic range. As the object moves farther away from the sensor, the lower the reflected energy and the more influence the ambient IR has on the measurement.