E-10
Measurement Considerations
Model 2701 User’s Manual
Meter loading
Loading of the voltage source by the Model 2701 becomes a consideration for high source
resistance values. As the source resistance increases, the error caused by meter loading
increases.
Figure E-5 shows the method used to determine the percent error due to meter loading.
The voltage source, V
S
, has a source resistance, R
S
, while the input resistance of the
Model 2701 is R
I
and the voltage measured by the nanovoltmeter is V
M
.
Figure E-5
Meter loading
The voltage actually measured by the meter is attenuated by the voltage divider action of
R
S
and R
I
, and it can be calculated as follows:
This relationship can be modified to directly compute for percent error:
From the above equation, it is obvious that the input resistance of the Model 2701 must be
at least 999 times the value of source resistance if loading error is to be kept to within
0.1%.
V
M
Measured
Voltage
R
S
R
I
V
S
Source
Voltage
+
–
V
M
V
S
R
L
R
I
R
S
+
-------------------
=
Percent error
100R
S
R
I
R
S
+
-------------------
=
2701-900-01.book Page 10 Wednesday, August 3, 2011 9:43 AM
Summary of Contents for 2701
Page 344: ...12 CommonCommands 2701 900 01 book Page 1 Wednesday August 3 2011 9 43 AM...
Page 366: ...15 SCPIReferenceTables 2701 900 01 book Page 1 Wednesday August 3 2011 9 43 AM...
Page 393: ...A Specifications 2701 900 01 book Page 1 Wednesday August 3 2011 9 43 AM...
Page 399: ...B Model7700ConnectionGuide 2701 900 01 book Page 1 Wednesday August 3 2011 9 43 AM...
Page 410: ...C StatusandErrorMessages 2701 900 01 book Page 1 Wednesday August 3 2011 9 43 AM...
Page 417: ...D SignalProcessing SequenceandDataFlow 2701 900 01 book Page 1 Wednesday August 3 2011 9 43 AM...
Page 430: ...E MeasurementConsiderations 2701 900 01 book Page 1 Wednesday August 3 2011 9 43 AM...
Page 450: ...G KE2700InstrumentDriver Examples 2701 900 01 book Page 1 Wednesday August 3 2011 9 43 AM...