Limit switches: Selection for safety

Abstract Limit switches are present throughout process control systems. Being classical components, their operation is taken for granted. However, an inappropriate choice may jeopardize the reliability and the safety of a production process. To achieve maximum safety and reliability, selection criteria for limit switches can be defined which go beyond simple operational criteria. This is possible mainly because of techniques and standards originating in Europe which deal with such things as positive opening of contacts, fail-safe condition and automatic monitoring.