Keithley 2182, Руководство пользователя, Страница: 110 / 339

5-20 Ratio and Delta
Superconductor Application #1 - fixed current
A typical test on a superconductor sample (DUT) is to vary the magnetic field (H) while
maintaining a fixed current (I) through the DUT. Such a test system is shown in Figure 5-6 . A
Keithley SourceMeter (Model 2400, 2410, or 2420) is used to source current through the DUT
and the Model 2182 measures the voltage across the DUT. Keep in mind that the I-Source of the
SourceMeter is a constant current source. Therefore, the current through the DUT will remain
constant as the resistance of the DUT increases.
Figure 5-6
Test circuit—Fixed I (Vary H)
After measuring the DUT voltage (V) at a series of increasing magnetic field values (H), you
can graph H vs. V. The example H-V curve in Figure 5-7 shows that the measured voltage across
the DUT remains at ~0V in low magnetic fields. This is the flat portion of the curve where the
DUT remains at 0
Ω . At some point, the voltage drop across the DUT will start increasing as the
magnetic field increases. The actual resistance of the DUT can be calculated at any magnetic
field point using Ohm’s law:
R = V/I
where: R is actual resistance of the DUT.
V is the measured voltage across the DUT.
I is the known current that flows through the DUT.
V
HI
LO
2182
CH 1
SourceMeter
Source
±
I
Thermal
EMFs
30´ Cables
DUT H
<4K
Cryostat