2-22
Voltage and Temperature Measurements
Low-level considerations
For sensitive measurements, external considerations beyond the Model 2182 affect accuracy.
Effects not noticeable when working with higher voltages are significant in nanovolt signals.
The Model 2182 reads only the signal received at its input; therefore, it is important that this
signal be properly transmitted from the source. Two principal factors that can corrupt
measurements are thermal EMFs and noise induced by AC interference.
NOTE
More detailed information on thermal EMFs and other factors that affect low-level
measurements are explained in
. Also, for comprehensive information on
low-level measurements, see the “Low level measurements” handbook, which is
available from Keithley.
Thermal EMFs
Thermal EMFs (thermoelectric potentials) are generated by thermal differences between the
junctions of dissimilar metals. These voltages can be large compared to the signal that the
Model 2182 is trying to measure. Thermal EMFs can cause the following conditions:
•
Instability or zero offset that is above acceptable levels.
•
The reading is sensitive to (and responds to) temperature changes. This effect can be
demonstrated by touching the circuit, by placing a heat source near the circuit, or by a
regular pattern of instability (corresponding to changes in sunlight or the activation of
heating and air conditioning systems).
To minimize thermal EMFs, use clean copper-to-copper connections wherever possible in the
test circuit. See “
” for details on connection techniques and cleaning.
Widely varying temperatures within the circuit can also create thermal EMFs. Therefore,
maintain constant temperatures to minimize these thermal EMFs. A shielded enclosure around
the circuit under test also helps by minimizing air currents.
The REL (Relative) control can be used to null out constant offset voltage. The basic
procedure to use REL is found in “
Measuring voltage and temperature
,” and details on Relative
are provided in
Noise
AC voltages that are extremely large compared with the DC signal to be measured may be
induced into the input of the Model 2182 and corrupt the measurement. AC interference can
cause the Model 2182 to behave in one or more of the following ways:
•
Unexpected offset voltages
•
Inconsistent readings between ranges
•
Sudden shifts in a reading
To minimize AC pick-up, keep the test circuit source and the Model 2182 away from strong
AC magnetic sources. The voltage induced due to magnetic flux is proportional to the area of the
loop formed by the input leads. Therefore, minimize the loop area of the input leads and connect
each signal at only one point.
Shielding also helps minimize AC interference. The metal shield should enclose the test
circuit and be connected to Channel 1 LO or to the chassis ground screw on the rear panel.
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...