Dishwasher with controlled rotation of lower spray arm

A dishwasher for treating dishes according to at least one cycle of operation, comprising:

• a tub at least partially defining a treating chamber for receiving the dishes;
• a rotatable sprayer providing a spray of liquid into the treating chamber and defining a rotational path as the rotatable sprayer is rotated;
• a drive system operably coupled to the rotatable sprayer to effect movement of the rotatable sprayer;
• a liquid recirculation system defining a recirculation flow path and selectively recirculating the sprayed liquid from the treating chamber to the rotatable sprayer;
• a sump assembly mounted in a lower portion of the tub and including a sensor enclosure projecting upwardly from a bottom of the sump assembly and terminating in a tip near the rotational path;
• a first sensor element located within the sensor enclosure and configured to sense at least a portion of the rotatable sprayer during rotation of the rotatable sprayer and outputting a signal indicative of the rotatable sprayer being sensed;
• and
• a controller configured to receive output from the first sensor element and control the drive system and the liquid recirculation system to rotate the rotatable sprayer while selectively supplying liquid to the rotatable sprayer;
• wherein the first sensor element provided in the sump assembly is fluidly isolated from the treating chamber.