Keithley DAQ6510 User Manual

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In this section:

Introduction .............................................................................. 7-1

Equipment required .................................................................. 7-2

Device connections .................................................................. 7-3

Scanning resistors using 4-wire measurements ....................... 7-5

Introduction

This example application demonstrates how to use the DAQ6510 to accurately measure resistance

across multiple devices. To obtain the best results, the 4-wire (Kelvin) measurement method and

offset compensation are used for this test.

Typical resistance measurements made using the 2-wire method source current through the test

leads and the device under test (DUT). The voltage is measured, and the resistance is calculated.

It is difficult to obtain accurate 2-wire resistance measurements when the DUT is lower than 100 Ω.

Typical lead resistances lie in the range of 1 mΩ to 10 mΩ. When the 2-wire method is applied to low-

resistance measurements, there is a small but significant voltage drop across the resistance of each

test lead. The voltage measured by the instrument is not the same as the voltage directly across the

DUT.

The 4-wire method is preferred for low-resistance measurements. With this configuration, the test

current is sourced through the DUT using one set of test leads, while a second set of SENSE leads

measures the voltage across the DUT. The voltage-sensing leads are connected as close to the

device under test as possible to avoid including the resistance of the test leads in the measurement.

Thermoelectric voltages (EMFs) can seriously affect low-resistance measurement accuracy. The

DAQ6510 can apply the offset-compensated ohms method (OCOMP), which makes one normal

resistance measurement and one using the lowest current source setting to eliminate EMFs.

For this example, you will use resistors of different low values across multiple channels of a 7700

multiplexer module and examine how the 4-wire measurement method provides a more accurate

reading than the 2-wire method. Fixed measurement ranges are applied in order to optimize scanning

speed and OCOMP is applied to correct for any EMF effects.

For comprehensive information on 4-wire resistance measurements, thermoelectric EMFs, and offset

compensation methods, see the Low Level Measurements Handbook, available on tek.com/keithley

Section 7

Scanning resistors using 4W measurement

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General

Measurement Functions	DC Voltage, AC Voltage, DC Current, AC Current, Frequency, Temperature, Capacitance
Frequency Range	3 Hz to 300 kHz
Temperature Range	-200°C to 1820°C
Connectivity	USB, Ethernet, GPIB
Digit Display	6.5 digits
Channels	Up to 80 channels
Memory	Internal non-volatile memory for data storage
Power Supply	100 V to 240 V, 50 Hz to 60 Hz
Dimensions	213 mm x 297 mm x 88 mm (8.4 in x 11.7 in x 3.5 in)
Weight	3.6 kg