Tektronix 372, User Manual

Page: 134 / 364

Measurement System
Reference
3Ć22
device is already grounded and may have an effect on measurement, or
noise may be introduced via a ground loop, measurement can be performed
by separating the measurement circuit from protective ground by removing
the shorting bar on the rear panel. This is called floating measurement.
The floating chassis should be connected to the protective ground unless a
floating measurement is made.
Protective Cover and Interlock System
The protective cover of the Test Fixture not only protects the operator from
high voltage or current, but also serves as a electrostatic shield to ensure
stable measurements.
The Test Fixture has an interlock mechanism so that, to ensure operator
safety, no measurement can be made with the cover open. This mechanism
can also be used to control the power from external equipment that has
been connected through the EXT connectors of the Test Fixture such as
power supply or signal generator, on or off.
DUT Connection and Kelvin Sense
The DUT is mounted to the 372 via the test adapter and the Test Fixture. The
circuit of the Test Fixture and the test adapter (A1101 TOĆ92/TOĆ72) are
shown in the Figure 3Ć4.
Each channel has three lines:FORCE, SENSE and GUARD:
H FORCE Line - An output line from either the LPU or the HPU. The
FORCE terminal is connected to the lead of the DUT via the test adapter
(see Figure 3Ć4).
H SENSE Line - A monitor input line from either the LPU or the HPU. The
SENSE terminal is connected to the lead of the DUT via the test adapter
(see Figure 3Ć4).
H GUARD Line - Prevents current leaking from the FORCE line to ground
when the potential is the same in both lines. Usually nothing is conĆ
nected to the GUARD terminal. However, stable measurement of very
small currents can be performed by connecting the GUARD line from
one of the channels to the metal package of the DUT or to the PLATE
pin terminal of the Test Adapter. The current in the GUARD line has no
effect on the measurement.
Test Fixture