2223A Oxygen Transmitter Functional Safety Manual
02223006A / Revision 0
7
3 SAFETY
INSTRUCTIONS
3.1
Boundary of safety system
The following aspects of the 2223A Oxygen Transmitter are considered to be within the
boundary of the safety system covered in this manual:
•
Paramagnetic
cell
•
All signal processing and support functions. This includes optional pressure
compensation and flow alarm when fitted and enabled.
•
mA
output
•
“Fault”
relay
•
External analog inputs
•
External flow sensor inputs
The following are considered to be outside of the safety boundary and are not covered in
this manual:
•
Communications interface to Control Unit
•
“Maintenance required” and “Service in Progress” relays
•
Digital
inputs
3.2 Safety
function
The safety function of the 2223A Oxygen Transmitter is the measurement of oxygen
concentration in a sample stream. The dangerous failure is the failure to indicate this
oxygen concentration to the performance stated in the product’s literature.
3.3 Installation
The 2223A Oxygen Transmitter must be installed as detailed in the Installation Manual.
To ensure that the safety instrumented system can respond to detected failures in the
transmitter, the equipment to which the mA output is connected must treat a current of 0mA
as a fault indication.
The fault relay can provide an additional method of notifying fault conditions. However, its
use in safety instrumented systems as the only method of fault indication is not
recommended as it results in a small decrease in the safe failure fraction. If the fault relay is
used then connections should be made to the contacts that are normally open when de-
energised.