Plankton is a library that assists in building simulated hardware devices. Currently this repository contains a simulated neutron chopper as it will be present at ESS. Choppers at ESS are abstracted in such a way that all of them are exposed via the same interface, regardless of manufacturer. The behavior of this abstraction layer can be modelled as a finite state machine.

The docs-directory contains an fsm-file (created using the program qfsm) which describes the state machine. While this is still work in progress, it gives an idea of how the choppers are going to operate internally.

Install dependencies through the requirements.txt file:

$ pip install -r requirements.txt

Run the basic chopper simulation:

$ python simulation.py --device chopper --scenario default --protocol epics --parameters pv_prefix=SIM:

Observe available EPICS PVs in an automatically updating screen:

$ watch -n 1 caget SIM:STATE SIM:LAST_COMMAND SIM:SPEED SIM:SPEED:SP SIM:PHASE SIM:PHASE:SP SIM:PARKPOSITION SIM:PARKPOSITION:SP

The following series of caput-commands, executed from a different terminal, will move the chopper to the specified speed and phase:

$ caput SIM:COMMAND INTERLOCK
$ caput SIM:SPEED:SP 100.0
$ caput SIM:PHASE:SP 23.0
$ caput SIM:COMMAND START

It may take a while until the simulation reaches the phase_locked state.

The simulator is exposed to channel access, using the pcaspy-module. Depending on the level of simulation there may be different PVs available to control the simulated chopper. At a minimum, the following PVs will be exposed:

| PV | Description | Unit | Access | |---|---|---|---|---| | SPEED | Current rotation speed of the chopper disc. | Hz | Read | | PHASE | Current phase of the chopper disc. | Degree | Read | | PARKPOSITION | Current position of chopper disc if in parked state. | Degree | Read | | STATE | Enum for chopper state. | - | Read | | TDCE | Vector of TDC (top dead center) events in last accelerator pulse. | to be determined | Read | | SPEED:SP | Speed setpoint. | Hz | Read/Write | | PHASE:SP | Phase setpoint. | Degree | Read/Write | | PARKPOSITION:SP | Position to which the disc should rotate in parked state. | Degree | Read/Write | | DIRECTION | Enum for rotation direction (clockwise, counter clockwise). | - | Read/Write | | COMMAND | String field to accept commands. | - | Read/Write |

Possible values for STATE

• Resting*: The chopper disc is resting, the magnetic bearings are off.
• Levitating*: The chopper disc is in the process of being lifted up into stable levitation.
• Delevitating*: The chopper disc is in the process of being let down into the resting state.
• Accelerating: The chopper disc is accelerated to the speed setpoint.
• Phase locking: The chopper is trying to acquire a phase lock.
• Phase locked: Speed and phase are at the setpoints.
• Idle: The motor is off, the disc is rotating only via inertia.
• Parking: The chopper disc is in the process of rotating to the park position.
• Parked: The chopper disc is parked in the specified position.
• Stopping: The chopper disc is actively decelerated to speed 0.
• Stopped: The chopper disc is at speed 0.
• Error*: An error has occured (to be specified in more detail).

The states marked with a * are not implemented yet and are not present in choppers which work with mechanical bearings.

Possible values for COMMAND

• START: Speed and phase are adjusted to match the corresponding setpoints
• PHASE: Phase is adjusted to match the corresponding setpoint
• COAST: Switch off motor, but do not actively decelerate disc
• STOP: Go to velocity 0, disc remains levitated
• PARK: Go to velocity 0, disc remains levitated, is rotated to PARKEDANGLE:SP
• LEVITATE*: Levitate disc if it's not levitated
• DELEVITATE*: Delevitate disc if possible

The commands marked with a * are not implemented yet. There are however two additional commands, INTERLOCK and RELEASE. INTERLOCK takes the chopper from the initial init state to the stopped state, RELEASE does the opposite. This behavior will likely change soon.

In a separate repository there is an OPI-file for use with CS-Studio and two files that expose the simulated chopper as a setup in NICOS (see readme there).