MERLIN Instrument Details - ISISComputingGroup/ibex_developers_manual GitHub Wiki

This page collects information that will be useful for the implementation of the IBEX control system on MERLIN.

Background & Timeline

Merlin is a high count rate, medium energy resolution, direct geometry chopper spectrometer on TS1 at ISIS. The MERLIN web page describes the background to the instrument.

Control System

MERLIN will migrate from the SECI control system to the IBEX control system.

MERLIN Equipment

The equipment listed below is used on MERLIN. Please add new information (e.g. new items of equipment, new notes, information about drivers, etc. to this table).

Manufacturer	Model	Type	Connection	Driver	Notes
ISIS	DAE 2	Detector Electronics	Ethernet		see DAE note
ISIS	TBD	T0 Chopper	TBD		see T0 Chopper note
ISIS	TBD	Disk Chopper	TBD		see Disk Chopper note
ISIS	TBD	Fermi Chopper	TBD		see Fermi Chopper note
ISIS	TBD	Fermi Chopper Lift	TBD		see Fermi Chopper Lift note
GALIL	DMC2280	Motion Controller	Ethernet	EPICS	see Galil note
???	???	1 x 4-blade jaws			see Jaws note
Pfeiffer	TPG300	ISIS Vacuum System	RS232	#216	see Pfeiffer note
Eurotherm	Temperature Controller	All models at ISIS	RS-232	EPICS	see Eurotherm note
McLennan	PM600	Motion Controller	RS-232	EPICS	see McLennan note
ISIS		Sample Changer	via McLennan		see Sample Changer note
ISIS		Collimator	via Galil		see Oscillating Radial Collimator note
Sumitomo	4K 100mm TL GM	Top-Loading Closed Cycle Refrigerator			see Sumitomo note
ILL?	Orange Cryostat	Cryogenic System	RS-232		see Orange Cryostat note
???	???	Heater	RS-232		controlled via Eurotherm
ISIS	RAL	Furnaces	N/A		controlled via Eurotherm
Neocera	LTC-21	Temperature Controller	RS-232	#1828	see Neocera note
McWhan	TIZR	Pressure Cell	N/A		controlled manually? see McWhan note

Note: DAE

Main Detector banks + several fixed monitors.

Note: MERLIN T0 Chopper

T0 chopper is generally operated in read-only mode (i.e. visiting scientists should never change its settings). T0 is an ISIS Mk2 chopper.

Note: MERLIN Disk Chopper

User needs the ability to change speed & phase settings. Also provide the ability to park the disc. Disk Chopper is an ISIS Mk2 chopper. At present, scientists often have to press a button on the chopper electronics crate before they can change the settings. It would be helpful if this was no longer the case (i.e. design IOC to eliminate this extra step, if possible). We believe this "button" is the local vs computer-control switch. If set to local, the chopper can only be controlled by the control panel on the crate. If set to computer-control, IBEX can control the chopper. Unfortunately, the chopper control system does not serve up the state of the local vs computer-control switch.

Note: MERLIN Fermi Chopper

The fermi chopper is a Jülich model (FZJ - Forschungszentrum Jülich) - custom built for ISIS (therefore unique, although very similar to models installed on MAPS and MARI). A copy of the communications manual (PDF) is here and the operating manual here. The control program will need to include various safety-critical condition monitoring routines (e.g. overspeed, bearing voltage out-of-range). There are some aspects of the control system which are specific to MERLIN and will need to be incorporated into the IOC. Ideally, they would be modular (e.g. macro, configuration file) so that the main program would be compatible between the three systems (MERLIN, MAPS, MARI). David Keymer wrote the original VIs, which are a useful reference. The Fermi chopper on MERLIN is primarily controlled via scripts. Scripts are used to calculate the frequency & phase, based on the energy (longer-term this calculation could be folded into IOC). The OPI should merely display the frequency & phase, not allow the user to change them. Current system exhibits odd behaviour at 600Hz - see if we can fix this when migrating to IBEX. Ideally, the Fermi Chopper should have a hierarchy of OPIs - at least, Simple UI (user) & Complex UI (manager). The current VI has too many details on it - instrument scientists would like to hide these. Talk with the instrument scientist about what is important when we design the IOC & OPI(s). The 600Hz issue occurs when resending the speed setpoint or "switch drive on and run" The fermi chopper originally exhibited strange behaviour (Ticket 2628) because the high and low words of the delay setpoint were being sent in the wrong order. The order should be the low word followed by the high word. The device appeared to "take" the setpoint and the setpoint readback was correct, but the actual delay readback would go towards another value instead.

Note: MERLIN Fermi Chopper Lift

A lift is used to raise/lower the Fermi chopper. Lowered means the Fermi chopper is in the beam; raised means it is out of the beam. It would be helpful if the lift can report its status to the IBEX GUI. Lift is controlled by a PLC, therefore IBEX can report status of lift by interrogating the PLC. IBEX will not be able to change the lift position - that will have to be done on the PLC control panel. Make/type of PLC - to be determined. Given the above, the requirement that "The Fermi chopper must not be operated (i.e. it must not be spinning) when it is in the raised position. Lift controls should not be accessible to the user." is automatically satisfied.

Note: Galil

Galils are used to drive the jaws.

Note: Jaws

Single 4-blade jaw-set. Jaws are driven by Galils. Apparently, the position of these jaws is reported via a potentiometer (rather than an encoder), which might also have implications for working with limit switches (as in, it won't be possible).

Note: Pfeiffer

Model TPG 300, used for vacuum system read-back. May actually be read back via PLC (same PLC that controls the Fermi Chopper Lift).

Note: Eurotherm

Three Eurotherms in use on MERLIN. Used to control temperature of all top-loading CCRs, Orange cryostats, heaters and furnaces.

Note: McLennan

One McLennan is used to control the rotating centre-stick, McLennan-Newport Rotation Stage
1. Typically used to rotate sample (about vertical axis) into position and hold for periods of several minutes to several hours before moving on to next measurement.
2. MERLIN scientists would also like to be able to oscillate the rotating centre-stick (i.e. slowly rotate back & forth between two fixed angles).
One McLennan is used to control the Sample Changer.

Note: Sample Changer

The Sample Changer is driven by a McLennan motor. It is similar (but not identical) to the sample changer used on IRIS.

Note: Oscillating Radial Collimator

The Oscillating Radial Collimator (presumably) is driven by a Galil motor controller. Oscillates at a fixed, low frequency - 0.2Hz. A similar system is used on LET. The mounting radius is 284.00 mm Note: 31-07-2017: The currently proposed design for the Oscillating Radial Collimator on MERLIN has been scrapped. A new design will be created. No need to progress this item until a new design is ready.

Note: Sumitomo

MERLIN has a dedicated SUMITOMO 4K 100mm TL GM CCR: CCR-62. Not directly computer-controlled - controlled via Eurotherm.

Note: Orange Cryostat

MERLIN will soon have a dedicated Orange Cryostat: models to be determined. Eurotherm controlled.

Note: Neocera

Neocera is used only occasionally. Neocera LTC-21 Manual

Note: McWhan

McWhan pressure cell. McWhan refers to the design of the cell (not to the manufacturer). Cell cannot be controlled directly from IBEX. It may be possible to report the current pressure via a device such as a Chell pressure transducer. See also General Clamped Cells and High Pressure Gas Cells.

MERLIN SECI Configs

MERLIN has a number of SECI configurations, which need to be migrated.

MERLIN Genie Scripts

The critical OpenGenie scripts, for initialisation and focussing, are in C:\\OG (duplicated, more or less, in C:\\scripts\OG)

MERLIN has a number of instrument specific Genie scripts. These need to be migrated to genie_python.

MERLIN Notes

Add any notes about special items of equipment, setup or conditions on MERLIN that might impact the deployment and configuration of IBEX.