User Manual

2400 Series SourceMeter
®
User’s Manual Digital I/O Port, Output Enable, & Output Configuration 13-11
GUARD
With this output-off state, the current source is selected and set to 0A. Voltage
compliance is set to 0.5% full scale of the present voltage range. This output-off
state should be used when performing 6-wire guarded ohms measurements or for
any other load that uses an active source.
NOTE When changing the output-off state with the output off, the selected
output-off state will be entered immediately.
On power-up, the SourceMeter will momentarily be in the HIGH IMPED-
ANCE output-off state before going to the selected power-on output-off
state.
If an Over-Temperature condition or an output enable line violation
occurs, the SourceMeter will go into the HIGH IMPEDANCE output-off
state.
Output-off states and inductive loads
The output-off state you select for inductive loads depends on how much energy
the inductor holds. The NORMAL output-off state is not recommended as it lowers
the compliance setting. The ZERO or possibly GUARD state are better suited, as
ZERO does not change the compliance setting and the GUARD output-off state
would change the voltage source to a current source with a voltage compliance.
The GUARD state is typically used only for guarded ohms measurements.
To protect the unit from inductive energy, the application may require a spark gap
across the INPUT HI and LO terminals. The SourceMeter does not have internal
spark gap
protection, as some leakage current (nA) is associated with the protection circuits.