I know when I worked at a water utility, (not offshore, of course, and no chemicals except chlorine bleach, nothing hazardous) the telemetry shop did most of the instrumentation. They had a PM schedule, and calibrated and checked all instruments in the system over the year. They were also responsible for the RTU's and the radios to SCADA, and had a small department within their shop that did just that. I was an electrician, and we had to know instruments, naturally, especially on call outs where operations had lost a reading (level, flow, pressure, etc.) We wouldn't call telemetry at 2 am unless absolutely necessary.
Bottom line was it seemed to me to be very borr-ring. They didn't seem to do much of anything IMHO. We called them "twidgets". They didn't run conduit or pull their own wire, and if they had to work with anything over 24VDC, then that was a major concern to them.
If I had to go into a plant again or do anything other than mostly writing programs and doing my own start-ups, I would get back into electrical. I really liked trouble calls--interesting, challenging, rewarding. I really enjoy troubleshooting and fixing things. And although they're necessary, I hate PM's. Each to his own, I guess.