Level switch as part 2oo3 voting

[helpyou]

Hi

Is it a good idea to use level switch as part of 2oo3 voting where the other two devices are transmitters.. in this case , if the switch fails, we will not know and we will end up having two devices (2oo2) configuration.. is this correct ? Can anyone add more comment from experience on this type of configuration please

Thank you

 

[TugboatEng]

I don't think it provides as high of a level of redundancy. A pair of transmitters can indicate trouble if the sensor values deviate. 3 transmitters will tell you which one is defective so that value can be ignored. A switch provides no indication of proper functionality other than a heart beat in some cases.

 

[Emad Abraham]

The 2oo3 Voting With diverse Devices is a very good idea to minimize common causes which affect the Safety integrity Level(SIL). however, the Switches are dummy and do not have any diagnostic coverage and can fail dangerous and can not be detected. by using all three transmitters you can implement deviation alarms and detect out-of-calibration transmitters by simple comparison as part of our design. you can use different transmitter manufactures as diverse devices by doing this you will minimize the common cause but you introduce complicity in the design and additional spare parts need to be maintained ad additional indirect cost.

 

[OpticControl]

First and foremost, yes you can use a limit switch in a voting scheme.
On the other hand, assuming that this is for a Safety Instrumented System (SIS), limits switches have a higher failure rate when compared with process transmitters.

With that in mind, perform the SIL calculation and determine if you met the SIL level required.