B747skipper From , joined Dec 1969, posts, RR: Reply 2, posted (10 years 4 weeks 8 hours ago) and read 2112 times:
Cher Cricri -
This probe is called "Pt-2" and measures the ambient pressure of the air in the inlet area of the engine... It works in concert with a probe, or probes which you would find in the exhaust of that engine, called "Pt-7" which measure the pressure in the turbine discharge area...
These probes are tied to a "power gage" for the engine, called EPR, exhaust pressure ratio, a primary means to set power (takeoff or cruise) on many jet engines...
In example, if the pressure is 1.50 measured at Pt-5 and the pressure at Pt-2 is 1.0, the EPR gage would indicate "1.5"...