Installation 2
Keysight N6700 User’s Guide
37
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 system includes protection resistors that reduce the effect of
open sense leads during remote-sensing operation. If the sense leads
open during operation, the power system 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.
Note that 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 backup local OVP function.
The local OVP function tracks the programmed OVP setting and trips if
the voltage at the + and - output terminals rises more than 1.5 V above
the programmed OVP setting. The local OVP also trips if the voltage at
the + and - output terminals exceeds 7.5 V on the 6 V range and 21.5 V
on the 20 V range.
Output Noise Considerations
Any noise picked up on the sense leads will appear at the output
terminals and may adversely affect CV load regulation. Twist the sense
leads or use a ribbon cable to minimize the pickup of external noise. In
extremely noisy environments it may be necessary to shield the sense
leads. Ground the shield at the power system end only; do not use the
shield as one of the sensing conductors.
The noise specifications documented in the Keysight N6700 Modular
Power System Family Specifications Guide apply at the output terminals
when using local sensing. However, voltage transients may be produced
at the load by noise induced in the leads or by load current transients
acting on the inductance and resistance of the load lead. If it is desirable
to keep voltage transient levels to a minimum, place an aluminum or
tantalum capacitor, with an approximate value of 10
µ
F per foot (30.5
cm) of load lead, right across the load.
