Honeywell Experion MX Operator's Manual page 64

SCANNER SAFETY AND LOCAL CONTROLS
Scanner Heads (red: shutter open, radiation indicators active)
Fig. 56.
The green radiation lights are driven by a series electrical circuit that runs through all
green light indicators and radiation shutter microswitches in both heads and scanner user
panels. The lack of active components and software in this circuit allows for high reliability
of the shutter closed status indicators independent of EDAQ and LAN operation.
Proper operation of radiation indicator lights are monitored by feedback circuitry and
reported to the MSS and FC.
Table 14 lists and describes shutter status indicators.
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