Programmable electronic real-time load controller providing demand limit

Abstract

A programmable electronic real-time load controller includes: a plurality of load control circuits, each being adapted to be interconnected with a load; a hardware clock; and, a data processor, operating under control of a set of program instructions stored in a program memory thereof, for implementing real-time control by comparing real-time information from the hardware clock with a time schedule stored in an event memory, and accordingly establishing an on state or an off state for each load, the on state representing a desired load-on state for the associated load control circuit and the off state representing a desired load-off state for the associated load control circuit. In order that the controller may also implement demand limit control, the controller is provided with additional components including a sensor for measuring the actual rate of power consumption by the loads, a set point selector for selecting a set point representing a desired rate of power consumption, and an additional program memory storing a set of program instructions for demand limit control. The data processor is responsive to this set of program instructions to: obtain the actual power rate and the set point from the sensor and the set point selector, respectively; compare the actual power rate with the set point; and, for those loads in an on state under real-time control, vary the number of loads actually energized and de-energized so as to maintain the actual rate substantially equal to the set point. The additional components for demand limit control are preferably mounted on a printed circuit card adapted to be inserted into a housing of the controller and interconnected with the data processor therein.