Emergency Shutdown System Transmitters Failure Mode

U

Thread Starter

Utz

Hi there,

I am wondering, what would be the best configuration in the ESD (Emergency Shutdown System) for the transmitters which giving BAD reading... like for example, transmitters at LL will trip something, what if this transmitters went to open circuit, which means 0 mA, which is below LL setting, will it trip the particular valve... or there is some configuration like it will retain the last reading?
 
H
That's one of the reasons for 4-20mA, or 1-5VDC signals, if you have a break in the circuit the signal goes 'below zero' indicating a fault.

Also, in my experience, I have seen major problems with setting a transmitter to 'Fault at last reading', no one knows its faulted until something bigger breaks.
 
a safety transmitter in case of self-fault should go to a predetermined value eg for LL to under 4mA like <3.5mA so than it can be diagnosed as faulty. Of course that is in the dangerous detected case.

The loop must trip.
An open circuit 0mA must trip also.

A short circuit eg >21.5mA must trip also. this is important because the process could go LL and the reading would be stuck at >max range.
This only leaves the dangerous undetected fault, eg a stuck transmitter value at normal reading, which you can't do much, except go for an 1oo2 (safety) or 2oo3 (safety and availability) voting configuration IF needed for the loop.
 
Top