Turbidity sensing as a building block for smart appliances

The US Department of Energy standards for laundry and dishwashers are expected to be announced soon for appliances built after Jan. 1, 1999. To meet these high-efficiency targets, the OEM designers are searching for practical solutions to improve the efficiency of these appliances. The availability of turbidity sensing on appliances will provide design engineers with a way to determine how soiled a particular load of clothes or dishes may be so engineers can then create a control system that adapts the operation of the machine to save water, time, and energy, while providing superior cleaning performance. Because of this capability, the turbidity sensor is emerging as a key building block developing the next generation of energy-efficient "smart" appliances. This article is intended to provide some insight to the origin of turbidity sensing, improvements to the technology since its introduction, and its relative importance to the appliance industry today. Different turbidity sensor configurations are discussed, along with practical design issues the engineer will need to address.