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Appendix A Keysight SD1000A Safety Disconnect System
Normal Relay Open/Close Sequence
In normal operation, the RP7900 power supply directly controls the state of the SDS relays to prevent
hot-switching the DC relays. The following is the normal closing sequence of the SDS and the power
supply:
1. Close the power relays
2. Enable the power supply output
3. Up-program the power supply output
4. Close the sense relays
The following is the normal opening sequence of the SDS and power supply:
1. Disable the power supply output
2. Open the sense and power relays
You may choose to Lock the output relays of the SDS closed to improve the output response time for
applications that do not require a physical output disconnect during normal output on/off operation of
the RP7900 power supply (see OUTput:RELay:LOCK).
The following is the latched "safe" state of the SDS after a safety disconnect event has occurred:
1. Power relays are open
2. Sense relays are open
3. "Connected" light is off
4. Power supply output is disabled
5. Discharge relays are closed and are discharging the DUT
6. Auxiliary output is disabled
7. General purpose output is disabled
As part of the safety-disconnect sequence, the SDS will discharge the UUT terminals to a level under
40V within three seconds. This provides for an additional level of safety at the UUT. This is
accomplished by switching a 25 kΩ resistance for Option 500 and a 97.5 kΩ resistance for Option 950
across the output terminals of the SDS. In the unlikely event that UUT does not stop sourcing power,
the SDS resistors are sized to tolerate the power draw continuously.
System Disconnect Protection
The RP7900 power supply periodically checks the status of the SDS. If at power-on or at any other
time the SDS does not respond, the RP7900 will go into a latched System Disconnect Protection
(SDP). If the SDS status indicates a fault condition, the RP7900 will also go into a latched SDP
protection. Finally, latched protection will also occur if an external AC contactor is connected, but not
active when the SDS relays are instructed to close.
SYST:SDS:STAT?
A
query can be used to determine the cause of an SDP.
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Keysight RP7900 Series Operating and Service Guide
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