Open Sense Leads; Over-Voltage Protection Considerations - Keysight Technologies N6705C Operating And Service Manual

2 Installation
Connect the sense leads as close to the load as possible. Do NOT bundle the sense wire-pair together
with the load leads; keep the load wires and sense wires separate. The sense leads carry only a few
milliamperes of current and can be a lighter gauge than the load leads. However, any voltage drop in
the sense leads can degrade the voltage regulation of the instrument. Try to keep the sense lead
resistance less than about 0.5 Ω per lead (this requires 20 AWG or heavier for a 50 foot length).
Keysight Models N678xA SMU require remote sensing when using any of the High output bandwidth
modes discussed under Output Bandwidth. Also, these models have additional wiring restrictions as
discussed under Keysight N678xA SMU Wiring Requirements.
After turning the unit on, activate 4-wire remote voltage sensing by pressing the Settings key.
Navigate to and select Advanced. In the Sense dropdown list select 4-Wire.

Open Sense Leads

The sense leads are part of the output's feedback path. Connect them in such a way so that they do
not inadvertently become open circuited. The power analyzer includes protection resistors that
reduce the effect of open sense leads during 4-wire-sensing. If the sense leads open during operation,
the power analyzer returns to the local sensing mode, with the voltage at the output terminals
approximately 1% higher than the programmed value.

Over-Voltage Protection Considerations

You must take into account any voltage drop in the load leads when setting the over-voltage trip
point. This is because the OVP circuit senses at the output terminals and not at the sense terminals.
Due to the voltage drop in the load leads, the voltage sensed by the OVP circuit could be higher than
the voltage being regulated at the load.
OVP for Keysight N678xA SMU (local OVP)
For Keysight Models N678xA SMU only, the OVP circuit senses at the 4-wire sense terminals rather
than at the output terminals. This allows for more precise overvoltage monitoring directly at the load.
Since incorrect sense terminal wiring could defeat this feature, there is also a local OVP function.
Keysight N6705C Operating and Service Guide 63