@Max: No. It is all pneumatic PID controller. Air is supplied at 15 to 30 psi. You can set P, I, D value for tunning the loop. I worked for Taylor Instruments Inc, Rochester and they manufactured them. As I understand, some organization currently do make them. They are very good for class I hazardous environment. Some pics for them:
Working at Atmel is a bit like being a kid in a candy store in terms of the weird and wonderful stuff I can steal, er, borrow to decorate my desk with. I started small... with a handful of colorful touch sensor boards nabbed from the 4th floor. I then pilfered an AVR man action hero from the creative lab (it is AMAZINGLY awesome and very hunky). Soon after I added a rather exotic looking AVR Dragon board to my collection, a couple of Arduino starter kits, some printouts of the infographics I've designed (on canvas they look super cool), some hexbugs... a half eaten bar of chocolate.
Still doesn't beat the electronic PCB shoe I used to have on my desk at EE Times... but oh well!
I don't know if I'v ever seen a pneumatic PID controller per se, but I guess that depends on what we're actually talking about -- do you mean an electronoc PIC controller that controls a pneumatic system -- or do you mean the entire controller implemented using pneumatic techniques?
I have my first big digit digital clock of 1981 still clocking at main entrance. I have all my Elektors and those projects stored in various boxes. I love pneumatic PID controllers and analog sample and hold.