3 ms·
Pneumatic signaling has been commonplace too... set points for valves, etc. can be sent by varying the (low) pressure in an air line to the valve itself. One d
by mschaef 9y ago
Pneumatic signaling has been commonplace too... set points for valves, etc. can be sent by varying the (low) pressure in an air line to the valve itself.
One downside to this is the case where there's condensation in the line and temperatures go below freezing. You can lose control thanks to the ice that forms. I remember this causing trouble with powerplants in the 90's during an ice storm in Houston (which is usually quite warm and humid, so they didn't think too much about icing.)
- zkms 9y agoYes, there's lots of building automation / HVAC stuff that uses pneumatic signalling/actuation (like the infamous T-4002 thermostat, look up images of it, you've probably seen it before!). Amusingly enough, lots of those pneumatic systems use 3-15 PSI signalling, which works the exact same way that 4-20 mA signalling works -- with a live zero so breaks in circuits can be detected!
- mschaef 9y agoEarly in my career, I did some work on what was essentially a Foundation Fieldbus to 4-20ma adapter. To get it to control our pneumatic valve for a demo, we wired it to a 4-20mA to 3-15PSI converter and then to the valve itself. It was a bit Rube Goldberge-esque, but it served our purpose well.