Model 8010 High Power Device Test Fixture User's Manual
Section 3: Working with devices and instruments
8010-900-01 Rev. C / March 2017
3-13
The guard terminal is useful for maintaining low-leakage measurements if you are using the
customized test board or if you are monitoring the test through the access port on the rear of the
cover.
The driven guard is always enabled and provides a buffered voltage that is at the same level as the
HI (or sense HI for remote sense) voltage. This allows you to monitor the output of the SourceMeter
instrument (SMU) without disturbing the DUT. For example, you can monitor the SMU with an
oscilloscope probe routed through the Model 8010 access port.
The purpose of guarding is to eliminate the effects of leakage current (and capacitance) that can exist
between high and low. In the absence of a driven guard, leakage in the external test circuit could be
high enough to adversely affect the SourceMeter instrument performance.
Leakage current can occur through parasitic or nonparasitic leakage paths. An example of parasitic
resistance is the leakage path across the insulator in a coaxial or triaxial cable. An example of
nonparasitic resistance is the leakage path through a resistor that is connected in parallel to the DUT.
Guard is typically used to drive the guard shields of cables and test fixtures. Guard is extended to a
test fixture from the cable guard shield. Inside the test fixture, the guard can be connected to a guard
plate or shield that surrounds the DUT. Note that the 8010-DTB and 8010-DTB-220 device test
boards do not have guard plates or shields. However, you can use the 8010-CTB customizable test
board to build custom connections that completely guard the connections all the way to the device
terminals.
To prevent injury or death, a safety shield must be used to prevent physical contact with a
guard plate or guard shield that is at a hazardous potential (>30 V RMS or 42.4 V peak). This
safety shield must completely enclose the guard plate or shield and must be connected to
safety earth ground. The next figure shows the metal case of a text fixture being used as a
safety shield. The cover of the Model 8010 serves as the safety shield.
