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each Arb output change. It also includes voltage and current slew changes, so that the timer is
restarted throughout the entire slew time.
Current Limit starts the over-current delay timer by any transition of the output into current limit.
The delay can be programmed from 0 to 0.255 seconds. You can specify if the OCP delay timer is
started by any transition of the output into current limit, or only at the end of a settings change in
voltage, current, or output state.
Front Panel Menu Reference
Select Protect\OCP
Enter a delay value. Then press Select.
By default, the delay timer will be started by an output
"Settings Change".
Check "CC Transition" to start the delay timer by ANY
output transition into CL mode.
Factors that influence how long the output settings or load change may last include: difference
between old output value and new output value, the current limit setting, and the load capacitance in
voltage priority mode or load inductance in current priority mode. The delay required must be
determined empirically; the output programming-response time characteristics may be used as
guidelines.
Also note that the time it takes the output to go into current limit (CL) varies - depending on the
magnitude of the over-current condition compared to the current limit setting. For example, if the
over-current is only slightly greater than the current limit setting, it may take several tens of
milliseconds for the output to set the CC status bit. If the over-current is significantly greater than the
current limit setting, it may only take a few hundred microseconds or less for the output to set the CL
status bit. To determine when the output will shut down, you must add the time it takes for the CL
status bit to the over-current protection delay time. If the over-current persists beyond the sum of both
time intervals, the output will shut down.
In primary/secondary operation, current sharing during fast load current transitions could lead to false
protection tripping if OCP is programmed independently on each unit. It is recommended that OCP is
only programmed for the primary unit. The primary/secondary OCP is implemented by the primary
unit's firmware polling the status of each secondary unit. Note however, that this may result in delay
timing to be off by a factor of up to 0.5 seconds.
Output Watchdog Timer
When enabled, the output watchdog timer causes the output to go into protection mode if there is no
SCPI I/O activity on the remote interfaces (USB, LAN, GPIB) within the user-specified time period. Note
that the watchdog timer function is NOT reset by activity on the front panel – the output will still shut
down after the time period has elapsed.
Keysight RP7900 Series Operating and Service Guide
4 Using the Regenerative Power System
SCPI Command
To specify a 10 millisecond delay:
CURR:PROT:DEL 0.01
To start the delay timer by an output settings change:
CURR:PROT:DEL:STAR SCH
To start the delay timer by ANY output transition into CL
mode:
CURR:PROT:DEL:STAR CCTR
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