The Hall C On-line gas mixing system exists in the gas shed located to the left of the counting house in the parking lot between the counting house and the accelerator service building. It provides two parallel flow-controlled gas streams from a common source. Flow rates, and gas mix can be controlled independently in each of the gas streams. The main component of the system is a single MKS 647 menu driven 4-channel controller that operates both of the parallel systems. Gas flow is controlled by 2259c proportional mass flow control valves. The 647 allows the Gas Calibration factor to be altered in software, allowing the user to change to a different gas without recalibration of the mass flow control valves.
A temperature controlled alcohol bubbler is provided for each gas stream. The alcohol level in each stream is maintained by a float valve fed from a reservoir outside the bubbler chiller. This allows the alcohol system to be refilled without opening the system to air. A sight glass on the side of the reservoir allows the level to be monitored. A by-pass loop around each alcohol system is provided should alcohol free gas be desired or if the alcohol system requires maintenance.
The 647 is factory upgradeable to 8 channels. The gas mixing system has been plumbed to provide 2 parallel 3 channel gas streams. In the original installation, the mass flow control valves for channels 5 and 6 (gas #3) were not installed.
To upgrade to 6 channel operation, 2 additional 2259c valves need to purchased and installed. The 647 needs to be returned to the factory for the upgrade to 8 channel operation
The system will support a remote monitor and remote control through a separate display port and an RS232 port on the back of the MKS 647 unit.
This system operates by measuring and controlling flow rate instead of pressure. This system will maintain a constant rate of flow regardless of pressure. It should not be used without appropriate pressure relief device such as relief bubblers and relief valves. It should not be connected to a closed vessel or system.
Warning: When using flow controlled systems such as this one, one must never introduce gas into a vessel without insuring that an outlet from the vessel is open. The gas will continue to flow at the flow rate set point until the gas reaches the pressure setting of the pressure device ie. the regulator or relief bubbler, or until the vessel fails.
The manual valves used in this system are numbered on their handles. Those numbers are referenced in this document and in Figure 2.23.
