Section 3: Series 3700A cards power usage Series 3700A Switch and Control Cards Reference Manual3-8 3700AS-909-01 Rev. B / December 2011Figure 2: Simplified interlock circuitEngaging hardware interlocksTo engage the hardware interlocks, you must provide a low-resistance path between the twoapplicable interlock pins as shown in the diagram. This path routes a 5 V power source to an onboardinterlock relay which in turn enables power to the backplane relays. If a 37xxA-ST accessory terminalboard is used, this low resistance path is provided to automatically engage the interlock circuit.NOTEDo not use the supplied 5 V power source for anything other than energizing the interlock relay. It isnot designed for external circuit use.Be sure to provide a low resistance path between the interlock pins for reliable operation. Significantresistance if present can cause the interlock circuit to fail to engage.Interlock statusSome switching cards have more than one interlock. At any time, the current status of each interlockcan be determined by using the appropriate slot[X].interlock.state remote ICL command.When the interlock status reports engaged, associated backplane relays are allowed to be energized.When the interlock status reports disengaged, associated backplane relays are prevented from beingenergized.Refer to the Series 3700A Reference manual (part number: 3700AS-901-01) for more information oninterlock related commands and details.
