Series 3700 System Switch/Multimeter User's Manual
Section 6: Model 3750 Additional Information
3700S-900-01 Rev. C / July 2008
6-13
Output loading precautions
In addition to the maximum specified loads for the output voltage and current,
note several other precautions:
Excessive amounts of capacitance present on the voltage output nodes can
affect their normal behavior. For example, exceeding the specified output
capacitance for the voltage output can cause a stability problem and result
in a noisy output. The Model 3750 voltage output stage is compensated for
a significant amount of capacitance that far exceeds the normal expected
amount due to cables, circuits, and loads.
Another consideration for the voltage output is load current. Inevitable
resistance in the series path of the voltage output experiences a voltage
drop when current flows. At levels of 10 mA or more, this can be a
significant portion of the accuracy specification.
For example, only 0.1 Ohms of stray resistance causes 1 mV of error at
10 mA of load current.
To avoid this additional error, keep circuit loading to a minimum and use
short heavy connections where possible. For voltage drops that are
constant, programming additional voltage can help compensate.
For current outputs, excessive amounts of series resistance can also cause
a problem if the output voltage rises to near the compliance level. At
voltages above the specified compliance level, the output may experience
higher offsets and ultimately result in a clamped value.
Because both outputs are electrically isolated from earth potential, they can
float or be driven to some arbitrary reference point. Do not exceed the
maximum ratings stated for the card on any of the channels under all
operating conditions.