Model 6220/6221 Reference Manual
Delta, Pulse Delta, and Differential Conductance
5-23
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The (-1)
n
term in the Delta calculation is used for polarity reversal of every other
calculated Delta reading. This makes all calculated Delta readings in the test the
same polarity.
Delta calculation example
Assume you want to measure the voltage across a 1
Ω
DUT using a constant
+10mA current 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 volt-
meter 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 fol-
lowing 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:
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
reading can converted into a conductance (Siemens; S), resistance (Ohms;
Ω
), or
power (Watts; W) reading. See
for details on selecting “
With Ohms, Siemens or Watts measurement units selected, the reading is calcu-
lated as follows:
Ω
= V/I
S = I/V
W =I x V
Delta
A
2B
–
C
+
4
----------------------------
⎝
⎠
⎛
⎞
1
–
(
)
0
•
=
10.01mV
2
9.99mV
–
(
)
–
10.01
·
mV
+
4
-----------------------------------------------------------------------------------------------
⎝
⎠
⎛
⎞
1
•
=
40mV
4
----------------
⎝
⎠
⎛
⎞
=
10mV
=
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