Tandem Beamline Isolation (Fast Valve) System
Introduction
The Tandem Beamline Isolation System, historically referred to as the Fast Valve System, is now a PLC controlled vacuum valve interlock system. It is designed to quickly respond to vacuum failures by isolating the accelerator beamline sections and preventing the failure from propagating further. This system also interlocks with the Pelletron to shut down operation when vacuum faults are detected in the vacuum proximal to the accelerator tubes. Each of the six valves controlled has a corresponding valve control panel (VCP) which allows the valve to be configured for operation and/or maintenance activities. All user operation occurs through these valve control panels.
Photos
Master Control Panel
High Energy Valve Control Panel
Control Room Valve Status Display Panel
Functional Block Diagram
Rendered CAD graphic of VCP Front Panel
Operation
All operator actions are performed through the Valve Control Panel (VCP). Refer to the VCP front panel graphic for reference while reading this section. There are no operator actions available at the Master Control Panel (MCP).
The valve control panel is always located near the associated valve. The front panel is divided into three sections; LEFT, MIDDLE, and RIGHT. Note the small vertical lines marking these divisions. You may think of the MIDDLE section as representing the valve itself, and the LEFT and RIGHT sections as representing the vacuum sensors on the corresponding side of the valve.
Sensor Indication and Control
Take a look at the left side of the VCP. At the top, there is a green lamp that reads GOOD. When lit, the pressure in the beamline is below, or better than, the set point threshold. Below that, there is a red lamp that reads BAD. When lit, the pressure in the beamline is above, or worse than, the set point threshold. The GOOD and BAD lamps should never be lit at the same time, with one exception covered later. The lowest indicator on the LEFT side is colored yellow and reads IGNORE. This is both a lamp AND a momentary contact switch. This switch is used for maintenance activities. Pressing this switch will cause the system to IGNORE the sensor on the corresponding side. While that sensor is being ignored, the yellow lamp will flash at a 1 second rate to remind operators that this sensor is being ignored. The RIGHT side lamps and switches function identically for the sensor on that side of the valve.
 Notice : | On the VCP, LEFT and RIGHT refer to the sensor direction from the valve and have NO RELATIONSHIP to the idea of upstream and downstream beam reference. |
Valve Indication and Control
Recall that the MIDDLE section of the VCP can be thought of as representing the valve. There are two combination lamp/switch assemblies. The green one is labeled OPEN/ACK while the RED one is labeled SHUT. When the valve is open, the top lamp will be lit GREEN, and when the valve is shut, the lower lamp will be lit RED.
If the valve is SHUT, and you wish to OPEN the valve, then one of two conditions must be met:
- The vacuum on both the LEFT and RIGHT must be good, with the GREEN lamp lit or,
- Any sensor that does not indicate a good vacuum must be in the IGNORE mode.
If the valve is OPEN, and you wish to SHUT the valve, simply press the switch marked SHUT. Shutting the valve is NEVER impeded for any reason.
 Warning : | Placing a sensor in IGNORE mode will allow valve operation under any circumstance. If you are not confident that it is safe to do this, please contact staff. |
Fault Indication and Assessment
When a Tandem vacuum system fault occurs, one of the sensors will detect it and make a transition from GOOD to BAD. This transition is detected by the PLC and the system will enter fault mode. Most of the beamline isolation valves will immediately shut. The Tandem operator must then survey each vacuum station and determine the cause of the fault. Once the cause of the fault is identified, corrected, and the vacuum status restored, the valve may be reopened. Other valves in the system, with good vacuum on each side may be opened at any time after the system trips.
Occasionally, a transient condition may generate a fault. This occurs when a vacuum sensor makes a GODD to BAD transition, which trips the system, but then transitions from BAD to GOOD before an operator can identify the cause. In order to prevent this situation, the PLC is programmed to "remember" which station caused the fault. Should the offending sensor transition back to GOOD, the PLC will indicate that the vacuum is GOOD by lighting the green lamp, but will flash the red BAD lamp at a 0.5 sec rate to indicate which sensor caused the fault. When this occurs, before the valve can be opened, one must "acknowledge" the transient indicator by pressing the OPEN/ACK switch. This will stop the BAD lamp from flashing and reset the PLC transient tracking system. The valve may now be opened by the OPEN/ACK switch as usual.
If the fault occurs in the Tandem's High Energy or Low Energy vacuum station, the Pelletron Interlock will trip. This is automatically re-enabled after 1 minute if the vacuum in both of these stations are restored. Vacuum faults in other stations will not trip the Pelletron. Note that the IGNORE toggle will not permit Pelletron operation. The vacuum sensor MUST indicate GOOD vacuum in order for the Pelletron interlock to be satisfied. Bypassing the sensor with a prepared shorting connector is possible for emergency operation, but provides no protection whatsoever.