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I-8
Delta, Pulse Delta, and Differential Conductance
Delta calculation example
Assume you wish to measure the voltage across a 1Ω DUT using a constant +10mA cur-
rent source and a voltmeter. Ideally, the measured voltage would be 10mV (V = I x R).
However, due to a 10µV thermal EMF in the test leads, the voltmeter actually reads
10.01mV (0.1% error due to EMF).
The error contributed by EMF can be eliminate by using Delta. Assume the square wave
output of the Model 622x is set to 10mA (high) and -10mA (low) and the following Model
2182/2182A measurement conversions (A/Ds) are made for the first Delta cycle.
A/D A = 10.01mV
A/D B = -9.99mV
A/D C = 10.01mV
The first Delta reading is calculated as follows:
Delta
=
The 10mV Delta reading effectively cancelled the 10µV EMF to provide a more accurate
measurement.
Measurement units
The fundamental measurement for Delta is voltage (Volts; V). However, the voltage read-
ing can converted into a conductance (Siemens; S), resistance (Ohms; W), or power
(Watts; W) reading by the Model 622x.
A 2B
–
+
C
-------------------------- -
=
•
(
1 –
4
–
– (
10.01mV 2 9.99mV
-------------------------------------------------------------------------------------- -
40mV
------------- -
=
4
=
10mV
0
)
˙ mV
)
+
10.01
4
•
1
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