Comtech EF Data SMS-7000, Installation And Operation Manual

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Theory of Operation SMS-7000 Modem Protection Switch
4–4 Rev. 3
4.1.4 Monitors
Three connectors provide switch status and fault information on the rear of the SCU
chassis (refer to Table 4-2).
Table 4-2. SCU Chassis Connectors
Switch Faults
J3 System, Equipment, and Stored Faults 9-pin D
Online Status
J6 Indicates whether prime modulators are on or offline 25-pin D
J5 Indicates whether prime demodulators are on or offline 25-pin D
Each set of fault output pins is isolated from internal switch electronics through single-
pole and double-throw relays. The three contacts of each relay are provided to the user
for direct application of visual and audio indicators. Relay contacts will support 1 mA of
continuous current at up to 30 VDC.
Normally open (NO) pins are connected to common (COM) for non-faulted indications
and online conditions. There is, however, one exception: the switch “COMMON
EQUIPMENT” fault has the normally closed (NC) contact connected to the common
(COM) for a no-fault condition (relay normally energized). This ensures that a fault is
indicated in the event of switch power loss.