Keithley 2701 User Manual

E-2 Measurement Considerations Model 2701 User’s Manual
Measurement considerations
Low-level voltage measurements made using the Model 2701 can be adversely affected by
various types of noise or other unwanted signals that can make it very difficult to obtain
accurate voltage readings. Some of the phenomena that can cause unwanted noise include
thermoelectric effects (thermocouple action), source resistance noise, magnetic fields, and
radio frequency interference. The following paragraphs discuss the most important of
these effects and ways to minimize them.
NOTE For comprehensive information on low-level measurements, see the “Low Level
Measurements” handbook, which is available from Keithley.
Thermoelectric potentials
Thermoelectric potentials (thermal EMFs) are small electric potentials generated by
differences in temperature at the junction of dissimilar metals. The following paragraphs
discuss how such thermals are generated and ways to minimize their effects.
Thermoelectric coefficients
As shown in Table E-1, the magnitude of thermal EMFs generated depends on the
particular materials involved. Best results are obtained with clean copper-to-copper
connections as indicated in the table.
Table E-1
Material thermoelectric coefficients
Material Thermoelectric potential
Copper-Copper
Copper-Silver
Copper-Gold
Copper-Cadmium/Tin
Copper-Lead/Tin
Copper-Kovar
Copper-Silicon
Copper-Copper Oxide
0.2µV/°C
0.3µV/°C
0.3µV/°C
0.3µV/°C
1–3µV/°C
40µV/°C
400µV/°C
1000µV/°C

Keithley 2701 Specifications

General

Max Voltage	300 V
Max Current	3 A
Frequency Range	3 Hz to 500 kHz
Frequency Accuracy	0.01%
Weight	3.6 kg
Measurement Functions	Frequency, Temperature
Interface	IEEE-488 (GPIB), RS-232
DC Voltage Range	300 V
DC Current Range	3 A
AC Voltage Range	300V
AC Current Range	1 μA to 3 A
Resistance Accuracy	0.01%
Channels	10
Dimensions	213mm x 88mm x 370mm