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A new testing method is now available for the TDR sensors VEGAFLEX (guided microwave) and the radar sensors VEGAPULS. It allows the `recurring function test` for SIL applications to be carried out without influencing the ongoing process.
Safety instrumented systems (SIS) that operate in `low demand mode` require regular function checks. The safety indices of the components (sensor, logic and actuator) determine the inspection interval. As a rule, the sensor must be dismounted or contacted by the medium in order to verify the function in such applications. This is a procedure which usually cannot be carried out during ongoing production. Moreover, this way of testing is usually very cost-intensive and filling a process vessel up to the overfill alarm level to verify the sensor function also involves risks.
The function test via keystroke on the vibrating level switches VEGASWING, VEGAVIB and VEGAWAVE is already well known. A test cycle is started by simply pressing a button on the VEGATOR 636 signal conditioning instrument or briefly interrupting the cable connection. The scope of the test fulfils the requirements of both WHG (Water Resource Act) and functional safety (SIL) as a periodic test and can be performed during an ongoing production process.
For VEGAFLEX sensors, which operate according to the guided microwave principle, and VEGAPULS radar sensors of the plics® family a testing method is now available that allows the “recurring function test” for SIL applications to be conducted without disturbing the ongoing process. The plant operator can thus minimise the large amount of work otherwise required for testing, e.g. raising the product level to physically contact the sensors or even dismounting the sensors, and avoid the production loss or standstill caused by such tests.
This quick and simple function test considerably reduces the time and costs involved.