Sensing and Control

The Package

Locating the WPS in the pump housing of the dishwasher was a major factor contributing to the design team’s ability to integrate all four sensor functions into one package. The on-board processor also removed the sensory calculation workload from the host system processor. This array of sensors, coupled to the on-board RISC processor to manage sensor functions, forms a state-of-the-art, one-stop sensing module.

The sensor substrate consists of a _at printed circuit board, encapsulated within a transparent but liquid impermeable humiseal in such a way that the sensor probes are thermally, electrically, or magnetically exposed to the environment they need to sense. The same transparent material encapsulates the LED and photoreceptor diodes situated on top of the substrate. The package housing had to incorporate clear, highly polished surfaces to maximize the performance of the turbidity optics and accommodate the exposed conductivity probes while protecting the sensors, discrete components, and integrated circuits inside the package.

Located within the relatively calm but submerged environment of the dishwasher pump housing, the sensor cluster performs its job of sensing water conditions and feeding data to the fuzzy logic controller which, in turn, tells the dishwasher what to do. The output signal from the sensor cluster alerts the fuzzy controller to the current values of turbidity, conductivity, temperature, and spray arm rotation. The machine controller uses this information—in concert with other information such as frequency of door openings or time between loads—in a fuzzy control algorithm to determine how the machine will perform. The fuzzy controller, acting on precise knowledge of the wash water variables, tells the dishwasher how long a given cycle should run, whether or not to skip some cycles, and how much to heat the water.

By assembling multiple sensors into a cluster, with on-board processing to perform signal conditioning and convert sensory data to a form usable by the host system, we were able to produce a cost-efficient product that meets or exceeds the needs of the appliance maker.