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<strong>HIMax</strong>AppendixAppendixIncreasing the SIL of Sensors and Actuators<strong>Safety</strong>-related <strong>HIMax</strong> controllers are used in safety applications up to SIL 3. This requiresthat the sensors and actuators (signalers and actuating elements) in use also achieve therequired SIL.In some cases, sensors or actuators may not be available for the requirements defined inthe application, such as process value, range of value, SIL, etc. If this is the case, proceedas follows:• For inputs: Use any of the available sensors that meet all of the requirements with theexception of the SIL value. Use enough of them such that their <strong>com</strong>bination provide aninput signal with the required SIL.• For outputs: Use any of the available actuators that meet all of the requirements with theexception of the SIL. Use enough of them such that their <strong>com</strong>bination affects theprocess with the required SIL.With inputs, associate the values of the individual sensors and their status information witha part of the user program such that a global variable with the required SIL results from this<strong>com</strong>bination.With outputs, distribute the value of a global variable among multiple outputs such that theprocess adopts the safe state if a fault occurs. Further, the <strong>com</strong>bination of actuators mustbe able to affect the process in the required manner (for example, the serial or parallelconnection of valves).For both inputs and outputs, design the system to have the required number of sensors andactuators for a given process variable until the greatest possible degree of safety isachieved for the process. SILence, the calculation tool manufactured by HIMA, can be usedto calculate the SIL.iThe use of multiple sensors and actuators for inputting or outputting a single signal asdescribed here is only intended as a means of increasing the SIL. Do not confuse this withthe use of redundant inputs or outputs for improving availability!For information on how to achieve the required SIL for sensors and actuators, see IEC61511-1, Section 11.4.HI 801 003 D Rev.2.0 Page 65 of 70
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