Subsystem Guidelines

To manage operation of NUSTAR DCS with a flexible set of sub-systems, and to keep the integration complexity at a manageable level, each NUSTAR DCS sub-system should follow the set of guidelines outlined here.

Sub-system State Machine

A finite state machine (FSM) should govern sub-system state transitions. This FSM should be implemented at least at the top level of each sub-system, and it may also be benefitial to implement a state machine at lower levels. The state machine consists of two sets. One set controls the desired sub-system state. The second set reflects the sub-system error state.

States

The main states for sub-systems defined in NUSTAR DCS are shown in the state diagram:

Off

The sub-system is powered off as much as possible. Some IOCs may be shut down as well, and will only be started in the ‘Standby’ state.

Standby

The sub-system is ready for switching on. Also, devices are configured as much as possible. The transition from ‘Off’ to ‘Standby’ may take a long time. Sub-systems should reach in ‘Standby’ state at least 24 hours before beam taking.

On

The sub-system is fully switched on and ready for beam. Transition of a sub-system from ‘Standby’ to ‘On’ should take less than 10 minutes for most sub-systems.

Safety

Some operations may require beam condidions that are harmful to parts of the sub-system. In this case, the sub-system should be operated in the ‘Safety’ state. Transition to and from the safety state should not take longer than a few minutes (better < 1 minute).

No error

Normal operation.

Error

In case of an unresolvable error condition in any of the ‘On’ states, a transition into the ‘Error’ state occurs. In this case operator intervention is necessary. The operator then decides which state should be used next.

Error recovery

For specific types of errors and error conditions, automatic recovery procedures may be implemented in the state machine. In this case, this recovery is attempted. If it fails, the sub-system goes into ‘Error’ state.