MUONS: Zero-Field - IOC for Field Strength

[davidkeymer]

A magnetometer outputs three analogue voltages (one for each axis of the magnetic field - Longitudinal, Transverse and Vertical) which are fed into an A-D converter on a NI-cDAQ. These voltages should be converted to field strengths to be used in the calibration routine implemented in #4839.

Acceptance criteria:

1. An IOC to read raw voltages from the cDAQ and convert them to magnetic field strengths using configurable calibration values (offsets).
2. A PV for the raw field strength (in units of mG(?)) for each of the three axes.
3. A PV for each of the three corrected field strengths (in units of mG(?)). Details of correction routine given on wiki page here
4. A PV for the magnitude of the corrected field, based on the following equation:
   Magnitude = sqrt(corrected_X_field^2 + corrected_Y_field^2 + corrected_z_field^2) (this value is used to determine whether or not the field is stable in the auto-feedback routine).
5. The PVs should enter alarm state if the magnetometer is overloaded. (This state is read by the auto-feedback routine IOC and processing is temporarily disabled accordingly.)

Notes:

1. An NI-cDAQ has already been communicated with as part of the Muon Separator project described in Muon Front End: Monitor Separator #3072

[Alistair-McGann-Tessella]

Pull Requests:

EPICS
IOC
Support
IOC tests
GUI
DBUnitChecker

Docs:
https://github.com/ISISComputingGroup/ibex_developers_manual/wiki/Zero-Field-Magnetometer-IOC