Multipath circuits for control and safety shutdown systems
Abstract
Multipath circuits for control and safety shutdown systems SAGE Publications, Inc.1981DOI: 10.1177/014233128100300207 A. Millar Area Instrument Engineer, Monsanto Ltd, Seal Sands, Middlesbrough, Cleveland This paper describes two types of electronic circuits. The fit of these provides a discrete output based on the rrtajarity status of three discrete inputs. This particular circuit design uses Zener diodes as part of the voting logic, and was developed to meet a specification incorporating a number of maintenance considerations. The circuit is part of an overall safety shutdown system. The second of these circuits provides an analogue output equal to the tniddle value of three analogue inputs. This circuit is referred to as an Analogue Mid Pin Selector (AMPS). It was developed for use in important control loops in which the process transmitters were triplicated. Both types of circuit have been successfully applied to the control of an industrial process. I troduction This paper is concerned with the instrument hardware developed to improve the safety and profitability of a chemical process. The purpose of the process is to produce a chemical used in the manufacture of textiles. In the process (Fig 1) two hydrocarbon feeds are mixed with air through a catalyst bed,