Hi!
Well, I work in what you may consider one of the "last bastion" career fields for component level troubleshooting, though I don't often have failures that require it.
I am an Control Instrumentation/Analyzer Technician for a Refinery/Chemical Plant complex.
There are basically 4 common specializations in my field. I'll offer quick job descriptions for each, and elaborate on what I do specifically.
Control Instrumentation:
Instrument Techs troubleshoot, calibrate, and repair "feedback loops" which monitor and react to changes in temperature, pressure, level, and flow in plant operating systems, such as furnaces, reactors, vessels, pumps, and compressors. Often this is a 4-20 mA signal from a local sensor (thermocouple/differential pressure cell) and/or transmitter. 4 mA is calibrated to zero in the range of the actuator (control valve) and 20 mA is calibrated to the span. Digitalized loops are of course replacing analog loops but both are common. Not particularly fun work, very repetitive.
Field Analyzers:
Analyzer Techs troubleshoot, calibrate, and repair equipment that monitors "analytical variables" in an operating system. This has more to do with chemistry than the physical properties that Instruments deal with. The most common analyzer is the Gas Chromatograph (GC), which is designed to seperate the molecular components of a liquid/gas chemical compound by molecular weight and quantify the volume of each component. With hydrocarbons it ranges from lighter methane or butane to complex molecules like cyclohexane etc. These analyzers capture product in the stream with valve sampling systems and pass them through a tiny capillary tube in a temperature controlled oven, carried by an inert gas such as helium. A detector, usually flame ionization, measures the volume of each species of molecule by burning them in a hydrogen flame and measuring the change in conductivity of the detector from the ionized byproduct (ie heavier volume equals higher detector conductivity) Being that pressure, temperature, and flow are precisely controlled, molecules passing through the analyzer "elute" through the capillary at a predictable rate, lighter molecules first, heaviest last. Thus, by calibrating against pure reference standards, we know our analyzers produce reliable data.
Lab Analyzers:
****This ius what I DO specifically, and is probably the most rewarding job of all. I work in a LABORATORY where hundreds of specialized benchtop analyzers are employed to test a much wider variety of properties. There are only three of us lab guys in the entire plant. GCs are used, but we also have viscometers, spectrometers (x-ray, UV, IR, visable, mass spec), flash analyzers, titrators, etc. as well as more specialized types of testers. Each analyzer is unique in its design and function and employs robotics, analog and digital signal processing, as well as electromechanical, pneumatic and hydraulic controls.
Usually, it is more efficient to perform board-level repairs with this equipment, but often my company retains equipment many years past its factory-supported lifespan. I have some 20+ year old instruments, and when a board fails a replacement can't be purchased. Also, when schematics are available (which is less and less common), and when operating schedules demand it, it is sometimes more feasable to attempt a board level repair than wait for parts to be shipped. Thats where I step in
The other classification in my field is Digital Technician, which is a group of Techs who, I believe, work on computer-related systems in the plant. I never recieved any training in this specialty, so I'm not 100% certain what it entails. I don't think it has much to do with software, though...more hardware related, probably the various computers and servers located in plant control rooms...swapping boards, drivers, and cards when they act up.
OK, that was a LONG post but maybe it sparks an interest in someone looking for a career.