Pneumatic Interfaces; Over Pressure Protection - Fluke 6270A Service Manual

Pneumatic Interfaces

All PMMs use the same pneumatic interface. See Figure 2.
PMM Pneumatic Interface
Reference port

Test port

Alignment bushing


Over Pressure Protection

Relief Valves - The main chassis contains two relief valves:
•
A 3500 psi relief valve that protects the pressure supply input.
•
A 120 psi relief valve on the exhaust port that limits exhaust port blockage.
Each PMM contains an overpressure protection device (resettable pressure
release valve). These valves are set to protect the module's internal sensor. For
PM600, the relief valves are typically set to 10 % to 15 % over the module FS.
The PM200 are set higher based on how the sensors are scaled.
The chassis design prevents hazardous conditions that result from improper
connection of supply and accidental pressure over-range.
The main firmware has a user-settable autovent function to vent the system if
pressure is greater than autovent level.
All solenoids in the chassis are normally closed. In a power-off condition, all
pressure is trapped in the system to avoid rapid pressure changes. Remove the
pressure supply to reduce pressure in the entire system. The pressure in the
system is reduced to approximately 150 psi as pressure decreases through the
reversed-biased solenoids.




Figure 2. Pneumatic Interface
Pressure Controller/Calibrator
PCM Pneumatic Interface
Supply port
Guide bushing, threaded rods
Test port
Reference port
Theory of Operation
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