GEneral monitor flame detectors

Dear all,
Please help me in my below issue:
There is a new compression package is installed in my site eith fire detection system. Flame detectors at PLC is programed with limits as i see the analog value of it.and there are 3 limits of it LL=2.5 ma, H=12.5 ma and HH=19.5 ma.
This limits each make SD. My questions are:
1-Why vendor makes flame detector represented at PLC at analog values?
2-Why there are many points for shutdown? What are there stands for?

What is the complete catalog number of your detector?

On the flame monitors I have seen the analog output is used to provide status of the monitor with fixed analog values. (Start-up, ready, warning,alarm etc.)

The manual will provide the info.