Uninterrupted Monitoring of Binary Ex i Signals in Applications Using Isolators
21 May 2008
New versions of the type 9170 switching repeater and the type 9175 digital output provide increased safety while transferring intrinsically safe binary signals: for the first time, they ensure complete, consistent error monitoring of every channel from the field to the control level despite an isolator inbetween.
The new modules, which complement R. STAHL's ISpac model range, allow users to detect cable errors between isolator and process control units and also to identify interferences in the field which are then reported to the control system via signal channel. Applications with safety-oriented signals according to IEC EN 61508 / 61518, for example emergency stops using magnetic valves, benefit especially from the reliable monitoring of the complete connection. Safety is increased for the operating staff and the plant, and the time spent on error detection is minimized. Therefore, the new modules are suitable for Ex i signals in zones 0 and 1 and, at the same time, for use in SIL 2-compliant signal circuits.
The 9170/x0-14-12 type switching repeater, which is available as a one- or two-channel version, emulates a Namur signal at its control system output. This allows users to distinguish between OFF signals and wire breaks on one side and ON signals and short circuits on the other side. The output features an additional NCC which opens in case of an error in the field, thereby reporting the detected cable error to the control system. An analysis of a separate error detection contact, which was required up to now, is no longer necessary. The type 9175/10-1x-12 digital outputs detect short circuits and wire breaks in the field. The standard models were already capable of reporting detected errors via separate contacts. The new models can now emulate errors detected in the field via an integrated contact in the isolator input for the digital control system output. The control unit’s error detection system can then directly identify the problem and display it for the user.
