Abstract: A low level, microprocessor based direct digital system controller includes power supply means for providing a source of regulated electrical power to the controller. A field programmable processor means transfers selected data base information to and receives status signals from a field interface means, digitally executes control and energy management algorithms respecting those signals in accordance with computer program routines selected from a library of mnemonically identified routines residing in the read only memory (ROM) portion of the processor means. The processor means responsively directs programmed data and digital command signals to the field interface means which periodically updates the data base of the processor means, analyzes and conditions signals received therein from the processor means and from remote data points and selectively controls the data points.

Abstract: Heating, ventilating and air conditioning control systems commonly use pneumatic actuators. A digital logic control has first and second output ports applied to control the actuator through dual channels, including an air supply channel and an air exhaust channel. Various sensed and related input signals are processed by the logic device and generate control signals at the control signal ports. Each channel includes an electrically controlled switch unit having an electrical operator and a pneumatic switch for controlling the flow to and from the pneumatic actuator. The switch may take the form of an electromagnetically actuated flow valve opening and closing a flow path from a supply or exhaust to the pneumatic actuator or, in the case of the supply channel, the form of a small electrically operated pump unit. The actuation of the actuator is controlled either on a time or frequency basis to set the actuator in the proper position.