Temperature Transmitters

Curtis, the usual way of doing this would be to use something like a Rosemount 3144 Ex'd'-rated temperature transmitter (4-20mA out) in the field, wired back to a MTL ICC317 (or similar) dual-output trip amplifier in the safe area.

Hazardous area field connections cost money so it makes sense to locate the contact outputs where you need them, and not necessarily at the instrument itself. If you really do need the contacts in the field, you can mount the trip amplifier in an Ex'd' junction box somewhere close.

Cameron:-)

Cameron is right.

Walter.

Thanks guys. I'll tell you my project and maybe you can give me some ideas.

We have a steam superheater and we are finally joining the 21st century and putting in on our DCS. We have a stack tip temperature that we want to have an analog value coming into the DCS, but on a high temperature we want to shut down the heater. A manual furnace shutdown or a high stack temperature shutdown falls into the ESD catagory and will be controlled by our Triconex ESD PLC. So now I have one spot to measure temperature and want to send an analog value to the DCS (Bailey Infi 90) and will do some alarming in there, and then send a digital to the Triconex to shut the furnace down.

United Electric makes a 'One Series' type switch which is acutally a digital switch. The setpoint is programmed into it, and you can also buy them with a 4-20 mA output as well. They claim they're approved for Safety Systems use. I've never used one, buy have been curious to try one for a while. I'm not sure of how accurate and repeatable they are. I can't see them being as good as a Rosemount. I've seen it where the analog value has been brought into the DCS, gone through a Hi/Lo block and then a digital out goes to a PLC but to me that defeats the whole purpose of an SIS.

Anyway, that's why I'm asking about Tx's and switches. Anymore thoughts would be cool. Thanks

Curtis

Try

I'd be surprised if they don't have one