An electronic process-controller

Up to the present time, process controllers have been pneumatic; the paper describes an electronically operated controller. Brief statements on the fundamental principles of process controlare given, and these lead to the mathematical equation which any process controller must solve. The basic principles of one method of converting the physical quantities to be measured into direct current are described; this method permits the use of a controller of a purely electronic type. The circuit arrangements of the controller which solves the fundamental equation are given in detail. The d.c. output from the controller is used to position the orthodox pneumatically operated process-control valve by means of an electro-pneumatic relay mounted on the valve. Some of the advantages claimed for the use of an electrical method as against others are listed. The method of operating the controller when installed on a plant is described, and details are given of an electronic process analogue used for testing the controller.