An SDP protection can only be cleared by turning off the RP7900 unit, correcting the problem, andrebooting the RP7900 unit.The SDS has a watchdog timer that will also put it into a safe state if communicationwith the RP7900 unit is lost.Controlling the SDS Using Externally Wired ControlsThe SDS must still be connected to the RP7900 when being controlled externally.The external control lines described in this section must be wired to the appropriate connectors on theback of the SDS unit (see installation section). These external control lines provide an extra layer ofoperator safety, as they allow the SDS to be programmed externally of the RP7900 power supply.Customer-supplied Emergency Stop (ESTOP) SwitchIf an Emergency Stop safety switch is not being used, you must short RemoteInterface pin 1 to pin 2 and pin 3 to pin 4. If the pins are not shorted, there will be aSDP protection event - requiring power cycling.The ESTOP safety switch must be a dual-channel normally-closed switch that when pressed, puts theSDS in a latched, safe state that includes opening the main and sense relays and discharging the unitunder test. Pressing ESTOP is a latched safety state requiring the operator to reset the SDS to exit thesafe state. The ESTOP signals are located on the Remote Interface connector on the SDS rear panel.The opening sequence in response to an ESTOP event is as follows:1. Open the power relays2. Open the sense relays3. Disable the power supply output4. Discharge the UUT5. Remain in this latched safety state until the ESTOP event is removed and the RESET switch ispressedWhen the SDS is in ESTOP mode, the power supply indicates a status of Inhibit (INH). A SCPI querycan be used to determine the cause of the power supply inhibit.It is recommended to provide a reset switch for the operator to clear the SDS condition and turn theoutput back on (see Reset Switch).Customer-supplied Reset SwitchRESET is a momentary-contact, operator input switch used to manually reset the SDS and exit thelatched safety state. Once the ESTOP switches are closed or any other error condition is rectified, theoperator must press the RESET switch to use the system again. The RESET switch must be anKeysight RP7900 Series Operating and Service Guide 311Appendix A Keysight SD1000A Safety Disconnect System
