Controls

The target controls have been implemented with the EPICS control system and with hardware very similar to that employed by the accelerator. The basic control functions reside on a VME based single board computer. The graphical interfaces to the control system use a PC, and also require the Hall A Hewlett Packard, HP, computer for control (HAC) to be present as well.

All of the instrumentation for the target is downstairs in Hall A. Most of the equipment (in fact all of the 120 V AC equipment) is on an Uninterruptable Power Supply, UPS. The items whose power is not on UPS are:

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The scattering chamber vacuum pumps and the gas panel backing pump

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The target lifting mechanism

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The target circulation fans.

This is a 7 kVA zero switching time UPS which is dedicated to the target. The PC, HAC and the counting house target X-terminal are on Uninterruptable Power as well. The targets dedicated UPS provides 18 minutes of power at full load (or 50 min at one half load). The status of the UPS, online or offline, is read by the control system and after ten minutes the control system will initiate an orderly shut down of the targets.

The principal functions that the control system performs are:

Pressure Monitoring

The pressure at various places in the system is monitored and alarm states are generated if a transducer returns a value that is outside user defined limits. High pressures will cause the small orifice solenoid valve to open and cause an FSD.

Temperature Monitoring

The temperature of the target is read from resistors and vapor pressure bulbs and alarm states are activated when any temperature sensor returns a value outside the user defined limits. High temperatures will cause an FSD to occur.

Temperature Regulation

The control system allows the target temperature to be regulated. In the default operating scenario this regulation is performed by a stand alone temperature controller.

Solenoid Valve Control

The gas systems have a number of solenoid valves that must be switched.

J-T Valve Control

The flow of coolant through the heat exchangers is controlled by a set of J-T valves. These valves control the coolant helium flow through the three loop heat exchangers and the precool heat exchanger.

Circulation Fan Monitoring and Control

The fans which circulate the target fluid are monitored (current, voltage, frequency). The voltage supplied to the fans is adjustable and alarm states can be set on out of range frequency, voltage or current values.

Vacuum Monitoring

The scattering chamber vacuum is monitored by the control system. Unacceptable values will generate an FSD and close the upstream and downstream scattering chamber valves.

Target Lifter

The target lifting mechanism is controlled by the computer. This allows one to place the desired target in the beam.