2470 High Voltage SourceMeter Instrument Reference Manual
Section 5: Source-measure considerations
2470-901-01 Rev. A /
May
2019
5-15
All measure connections should be considered to be hazardous.
The maximum floating (common mode) voltage for a source-measure unit (SMU) is ±250 V.
Exceeding this level may cause damage to the instrument and create a shock hazard.
Using an external source to float a SMU could create a shock hazard in the test circuit. A
shock hazard exists whenever >42 V
PEAK
is present in the test circuit. Appropriately rated
cables or insulators must be provided for all connections to prevent access to live parts.
When >42 V is present, the test circuit must be insulated for the voltage used or surrounded
by a metal safety shield that is connected to a known protective earth (safety ground) and
chassis ground; refer to
(on page 5-11).
Guarding
Use guarding to isolate impedance that you do not want to measure. Guarding is an effective way to
reduce the leakage current and capacitance that can exist between HI and LO. A guard is a low
impedance point in the circuit that is at nearly the same potential as the high impedance lead that is
being guarded. Use guarding when you are sourcing or measuring low current (less than 1
μA) or
when test circuit impedance is more than 1
GΩ. Also use guard in noisy environments.
The rear panel of the 2470 includes a current-limited (100 µA minimum) driven cable guard designed
to drive cable capacitance at the sense HI and force HI connections. This guard is always enabled
and provides a buffered voltage. For 2-wire measurements, guard is at the same level as the force HI
voltage. For 4-wire measurements, it is at the same level as the sense HI voltage.
To use the built-in guards of the 2470, you must use the rear-panel triaxial connections. There are no
guards available on the front panel.
Guard is at the same potential as output HI. Therefore, if hazardous voltages are present at
output HI, they are also present at the GUARD terminal. Failure to heed this warning may
result in personal injury or death due to electric shock.
