Figure; Test Circuit Using Constant Current Source; Figure 5-1 Test Circuit Using Constant Current Source - Keithley 2182 User Manual

Figure 5-1

Test circuit using constant current source

HI
2182
1mA
V
CH 1
LO
A. Positive Current Source
HI
2182
1mA
V
CH 1
LO
B. Negative Current Source
Figure 5-1B shows what happens when the current is reversed. The measurement by the
Model 2182 still includes the 10µV of thermal EMF, but the voltage across the DUT is now
negative. Therefore, the Model 2182 will measure 90µV:
V = V + V
2182 THERM
= 10µV - 100µV
= –90µV
As demonstrated in Figure
the voltage across the DUT. However, if you take a simple average of the magnitudes of the two
readings (110µV and 90µV), the result is 100µV, which is the actual voltage drop across the
DUT. This is what the calculation for Delta does.
V
THERM
10µV
+
V = 100µV
DUT
DUT
0.1Ω
V = 10µV + 100µV
2182
–
= 110µV
V
THERM
10µV
–
V = –100µV
DUT
DUT
0.1Ω
V = 10µV – 100µV
2182
+
= –90µV
DUT
5-1, neither measurement by the Model 2182 accurately measured
Ratio and Delta 5-7