Keithley 6220 Reference Manual page 143

Model 6220/6221 Reference Manual
The (-1)
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 1Ω 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:
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
reading can converted into a conductance (Siemens; S), resistance (Ohms; Ω), or
power (Watts; W) reading. See
units".
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
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n
term in the Delta calculation is used for polarity reversal of every other
⎛ ⎞
A 2B – + C 0
• – ( )
--------------------------- -
= 1
⎝ ⎠
4
– (
⎛
10.01mV 2 9.99mV –
---------------------------------------------------------------------------------------------- -
=
⎝
4
⎛ ⎞
40mV
--------------- -
=
⎝ ⎠
4
= 10mV
Return to
Delta, Pulse Delta, and Differential Conductance 5-23
·
)
⎞
+ 10.01 mV
•
1
⎠
page 5-16 for details on selecting
Section 5 topics
"Measurement