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Definitions:
• MXA
– MACS/D Controller/Signal Processor
• ADC
– Analog to Digital Converter
• DSP
– Digital Signal Processor
• DAC
– Digital to Analog Converter
• CDA
– Coil Driver Amplifier
For MACS/D active compensation system installations, Operational Volume (OV) is defined as the space contained
within the orthogonal coil sets. Protected Volume (PV) is defined as the volume within the OV meeting the specified
site magnetic field reduction coefficient.
As illustrated schematically in the block diagram of
Figure 2
, cancellation of unwanted environmental magnetic
field variations is achieved by applying the canonic principle of negative feedback separately for each orthogonal
axis. Salient characteristics of the wideband negative feedback approach employed in the MACS/D system are
simultaneous compensation of all interference frequency spectra appearing within the MACS/D system’s passband
(approximately 1mHz – 500 Hz configured with standard probe, extended high-frequency options available) and
constant attenuation coefficient for any interference spectra within the system passband. Constant attenuation
applies, regardless of spectral amplitude, for the wide range of signal amplitudes within the system’s dynamic range,
which is approximately 6 orders of magnitude.
ACR capability of the MACS/D system is implemented within the main feedback loop as part of the DSP firmware;
ACR permits setting an over- or under-compensating ratiometric offset to counteract Intervening Medium (IM) and/or
gradient effects. Although implemented within the system primary negative feedback loop, the supplementary ACR
signal processing does not significantly affect MACS/D fundamental closed-loop operation or characteristics.
Figure 2. MACS/D Active Compensation System Functional Configuration, illustrating single axis of 3
identical axes
