47
6 OPERATION
6.1 GENERAL COMMENTS
All MACS/D core systems are controlled by state machine logic contained in a Complex Programmable Logic Device
(CPLD). The CPLD monitors various system conditions, responds to user controls, displays status information, and
controls internal networks, based on the system operational state. The machine states are defined in the CPLD;
the sequence of machine states is defined in the DSP firmware (FW), which determines the current operating state
and what, if any, changes are to be made in the controller subsystem settings in response to changes in the system
operating conditions as determined by the MACS/D Digital Signal Processing (DSP) engine and Machine Control
Computer (MCC). Remote MACS/D system software and firmware upgrades can be downloaded to the DSP and
MCC at any time after installation. To preserve autonomous operational capability, the CPLD is field programmable
only. However, the MACS/D system operational states are normally not modified following installation so there is
generally no post-installation field requirement for CPLD reprogramming.
6.2 POWER-UP SEQUENCE
6.2.1 Baseline Acquisition:
Following the internal boot sequence when power is initially applied to the system or at any time when the RESET
pushbutton is pressed, the controller firmware enters a baseline acquisition sequence which rapidly determines
the environmental average magnetic field level and subsequently enters that level as the "zero interfering field"
(offset) value. The controller follows this procedure to minimize long-term system response to “D.C.” or constant-
field (primarily geomagnetic) conditions. In its normal OPERATE state, the system also adds or subtracts 1 least
significant bit (LSB) to the acquired baseline offset value at either a default fixed rate or a custom fixed rate
(selectable as a system configuration option) to constantly track the minimum average compensating magnetic
field.
If a RESET acquisition operation is initiated during an Operational Volume (OV) magnetic field offset event due
to external interference, the same periodic LSB steps insure that the correct minimum average environmental
magnetic field level is eventually attained. The time required for this equilibration process is dependent on the
offset value, and is determined by the system default offset recovery rate of approximately 0.19 nT (1.9 µG)
every 4 seconds for a 0.1 mV/µT system scale factor (19 nT every 4 seconds for a .01mV/µT system scale
factor). To illustrate, if a steel cabinet is moved in an adjoining room, inducing a 100 nT (1mG) change in the
MACS/D Protected Volume (PV), the system will initially compensate the field change, then adjust its acquired
baseline value to zero out the 100 nT offset over 500 LSB steps occurring every 4 seconds, for a total period of
approximately 33 minutes. At that point in time, the MACS/D system has adapted to the ambient field change and
the Coil Driver Amplifier (CDA) is no longer “fighting” the permanent offset in ambient magnetic field conditions.
6.2.2 Power/Level Trip and Reset:
A POWER Trip will occur, rebooting the system, if any MXA controller power supply is operating outside out of
specification, or an A.C. mains dropout occurs.
A
OVERLEVEL
Trip occurs if a programmed axial interfering magnetic field limit is exceeded (refer to
Section 4.4,
(49)
). Following a specified delay period, the CDA is switched off and a new baseline acquisition takes place. If
one or more of the axial fields remain above its Trip limit threshold after a specified number of retries (see table,
Appendix A.3
), the system controller proceeds to the
DISABLED-AR
(disabled by Automatic Reset) state. For
diagnostic purposes, the MACS/D controller displays DISABLED-AR or DISABLED-PB (disabled manually by the
pushbutton).
