Sensors are a type of pump control that monitors levels or flow rates. For example, a flow sensor can effectuate pump operation (via relay controller or programmable logic controller - PLC) in the event of reduced flow or a flow stoppage. Similarly, a level sensor can trigger activation of the pump when the liquid reaches a certain level. An optical sensor uses optical refraction to determine if water is present, thereby enabling it to catch the smallest of leaks. Optical sensors can be used in in containment tanks, sumps, and pipes, and between the walls of double-wall tanks. For more on pump control and parts, see our pump control boxes and pump parts.