Functional safety quantifies the probability of a failure on demand (pdf) of safety instrumentation. Consequently the manufacturers of safety – relevant instruments use high quality components to get this probability down to very low values. Gas detectors for instance, are operating in the „low demand“ mode. For these a pdf from 10-2 to 10-3 is low enough to achieve SIL Level 2. (SIL = Safety Integrity Level)
A low probability of failure is no warranty, that the failure does not occur just the other day.
Statox 560 is a stationary gas detector for toxic gases. An unnoticed failure of such a detector may cause serious danger or even death for the personnel working in a plant which is handling toxic gases. Therefore the Compur engineers did not only shape it to comply with SIL 2 standard, but also created a self test feature which checks the entire unit for proper function with gas.
In programmable time intervals a gas generator inside the sensor head is activated. Electrochemically it produces a small amount of the target gas and introduces it to the sensor with a micro pump. Now sensor must respond to the test gas within a certain time interval. Then the generator is switched off, the sensor is purged and the sensor head goes back into the measuring mode. The whole procedure takes only 2 minutes.
In case the sensor fails to respond within the specified time, the sensor head communicates “system failure” or “maintenance request” to the control room – depending on which part is out of specification.
This way the user can 100 % sure to have a functioning gas detector in the field, without even leaving the control room. Against this background it is reasonable to expand the maintenance intervals. Long term the Statox 560 is an excellent investment, saving the instrument people precious time. An economic investment too even when the initial investment is a little bit higher compared to the competitors.
Compur Monitors shows a prototype. The series production will start towards end of this year.