The QB2X implements external feedback and is often used to pilot dome loaded regulators like Burling Valve's BD-Series. 
The project aim was to take the previous breadboard development of a High Pressure Proportional Valve that started in 2008, further develop all aspects of this design and then build an Electronic Pressure Regulation sub-system and take it through extensive development and Engineering Model testing with a range of commonly used spacecraft propellants. The BVISF is internally potted and able to directly control hazardous media such as natural gas. [CDATA[// >
600mg/s Xenon at EoL, >600mg/s Helium at EoL. Regulation accuracy of <0.05 bar (mechanical regulation is typically >0.2 bar). It can be assembled to an air piloted regulator for high flow, higher pressures and various media control. Upon successful completion of the CDR the Electronic Pressure Regulator is ready to undergo full qualification. It can be assembled to an air piloted regulator for high flow, higher pressure and various media. The gold plated Xenon heater can be seen on the left. Intrinsically Safe Electronic Pressure Regulator.