Measurement Considerations
C-9
Meter loading
Loading of the voltage source by the Model 2182 becomes a consideration for high source
resistance values. As the source resistance increases, the error caused by meter loading
increases.
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 2182 is
R
I
, and the voltage measured by the nanovoltmeter is V
M
.
Figure C-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 2182 must be at
least 999 times the value of source resistance if loading error is to be kept to within 0.1%.
V
S
Source
Voltage
+
–
R
S
R
I
V
M
Measured
Voltage
V
M
V
S
R
L
R
I
R
S
+
-------------------
=
Percent error
100R
S
R
I
R
S
+
-------------------
=
Summary of Contents for 2182
Page 1: ...www tek com keithley Model 2182 2182A Nanovoltmeter User s Manual 2182A 900 01 Rev B May 2017...
Page 18: ......
Page 22: ......
Page 23: ...1 Getting Started Getting Started...
Page 41: ...2 VoltageandTemperature Measurements Voltageand Temperature Measurements...
Page 68: ...2 28 Voltage and Temperature Measurements...
Page 69: ...3 Range Digits Rate andFilter Range Digits Rate andFilter...
Page 82: ...3 14 Range Digits Rate and Filter...
Page 83: ...4 Relative mX b and Percent Relative mX b andPercent...
Page 91: ...5 RatioandDelta Ratioand Delta...
Page 117: ...6 Buffer Buffer...
Page 123: ...7 Triggering Triggering...
Page 140: ...7 18 Triggering...
Page 141: ...8 Limits Limits...
Page 149: ...9 SteppingandScanning Steppingand Scanning...
Page 168: ...9 20 Stepping and Scanning...
Page 169: ...10 AnalogOutput Analog Output...
Page 175: ...11 RemoteOperation Remote Operation...
Page 205: ...12 CommonCommands Common Commands...
Page 221: ...13 SCPISignalOriented Measurement Commands SCPISignalOri entedMeasure ment Commands...
Page 225: ...14 SCPIReferenceTables SCPIRefer enceTables...
Page 239: ...15 AdditionalSCPI Commands Additional SCPICom mands...
Page 260: ...15 22 Additional SCPI Commands...
Page 261: ...A Specifications Specifications...
Page 263: ...B Statusand ErrorMessages StatusandError Messages...
Page 268: ...B 6 Status and Error Messages...
Page 269: ...C Measurement Considerations Measurement Consider ations...
Page 278: ...C 10 Measurement Considerations...
Page 279: ...D Model182Emulation Commands Model182 EmulationCom mands...
Page 284: ...D 6 Model 182 Emulation Commands...
Page 285: ...E Example Programs ExamplePro grams...
Page 293: ...F IEEE 488 BusOverview IEEE 488Bus Overview...
Page 307: ...G IEEE 488andSCPI ConformanceInformation IEEE 488and SCPIConform anceInforma tion...
Page 310: ...G 4 IEEE 488 and SCPI Conformance Information...
Page 311: ...H Measurement Queries Measurement Queries...
Page 316: ...H 6 Measurement Queries...
Page 317: ...I Delta PulseDelta and DifferentialConductance Delta Pulse Deltaand Dif ferentialCon ductance...