High Integrity Safety Switches
High Integrity Safety Switches
(OP)
My application involves measuring the temperature in a furnace. I need to provide a hardwired High temperature safety switch to operate a deluge system. I was going to activate this stand-alone switch via a 4-20mA signal from a close coupled "puck" type transmitter wired to the K-Type.
I also want to provide operators with an indication of this temperature via their SCADA. Is it OK to loop the 4-20mA signal from the transmitter through a PLC AI card as well as the high integrity switch? It would seem to be OK as the switch is fail safe in case of signal loss but I am not sure whether a frozen PLC would corrupt the signal to the switch. While a separate temperature element would appear to be the logical solution, access to the furnace is very limited.
I look forward to comments from those with more experience than me, and if you can cite a standard or accepted text regarding this point that would be even better.
Thank you in advance
I also want to provide operators with an indication of this temperature via their SCADA. Is it OK to loop the 4-20mA signal from the transmitter through a PLC AI card as well as the high integrity switch? It would seem to be OK as the switch is fail safe in case of signal loss but I am not sure whether a frozen PLC would corrupt the signal to the switch. While a separate temperature element would appear to be the logical solution, access to the furnace is very limited.
I look forward to comments from those with more experience than me, and if you can cite a standard or accepted text regarding this point that would be even better.
Thank you in advance
TISM





RE: High Integrity Safety Switches
However, if this is saftey-related, it should really have a dedicated transmitter - actually probably at least two sensing methods - and fail-safe as you mention.
RE: High Integrity Safety Switches
Thanking you in advance,
TISM
RE: High Integrity Safety Switches
I'm not sure if I really understand the function on the valve you are referring to. I generally think of the block valve as a manual valve that generally must be physically locked OPEN in the US.
RE: High Integrity Safety Switches
Thanks for the reply. Sorry for the confusing nomenclature. I was using the customers term but the valve I referred to as the block valve is the solenoid valve on the high pressure fire protection system water line. I appreciate the lack of a universal standard but I would appreciate your comments on how you would do this if faced with the same situation.
Thanks,
TISM
RE: High Integrity Safety Switches
I would call your local fire marshall and just ask.
RE: High Integrity Safety Switches
You have been most helpful.
TISM