Keithley 2182 User Manual

5-8 Ratio and Delta
To use the DC current-reversal technique, replace the constant current source with a bipolar
current source as shown in Figure 5-2. The current source will alternate between +1mA and
–1mA. When using Delta, the Model 2182 performs the first voltage measurement (V1t1) while
sourcing +1mA. The second voltage measurement (V1t2) is performed while sourcing –1mA:
NOTE When using the Model 2182 to perform Delta measurements, RATE must be set to
1 PLC or 5 PLC to optimize measurement performance. At 1 PLC or 5 PLC, Delta
measurements will cancel thermal EMFs to a <50nV level.
V1t1 = V
THERM
+ V
DUT
V1t2= V
THERM
– V
DUT
= 10µV + 100µV = 10µV – 100µV
= 110µV= –90µV
Delta is then calculated as follows:
Using Delta with a bipolar source effectively canceled the 10µV thermal EMF.
External triggering is required to control the timing between voltage measurements and
current source reversals. Trigger synchronization between the source and the Model 2182 is
explained in “Model 2182 and SourceMeter trigger synchronization” which follows the “Delta
measurement procedure using a SourceMeter.”
Figure 5-2
Delta measurement using bipolar source
Delta
V1t1 V1t2–
2
--------------------------------
110µV90µV–()–
2
----------------------------------------------
200µV
2
----------------- 100µV== ==
DUT
0.1Ω
V
THERM
V
10µV
HI
LO
+
–
2182
Delta
(CH 1)
SourceMeter
Source ±1mA
V
DUT
= 100µV
At +1mA:
V1t1 = 10µV + 100µV
= 110µV
At –1mA:
V1t2 = 10µV – 100µV
= –90µV
V
DELTA
=
V
DELTA
= V
DUT
= 100µV
V1t1 – V1t2
2
110µV – (–90µV)
2
=

Keithley 2182 Specifications

General

Brand	Keithley
Model	2182
Category	Measuring Instruments
Language	English