Chapter 2 NI4050 Operation
NI 4050 User Manual 2-8 www.ni.com
These additional errors are shown in AppendixA, Specifications . While the
NI4 050 is characterized and specified over the 20 Hz to 25 kHz frequency
range, measurements outside of this range can still be made with decreased
accuracy.
Resistance Measurements

2-Wire Resistance Measurements

The NI4050 measures 2-wire resistance by passing a current through the
device under test and reading the resulting voltage drop through the same
connections, as illustrated in Figure 2-4. The resistance value is then
computed using Ohm’s Law (R=V/I). To accurately measure the value of
aresistor, make sure the resistor is not connected to any other circu its.
Erroneous or misleading readings can result if the resistor you are
measuring is connected to external circuits that supply voltages or currents,
or to external circuits that change the effective resistance of that resistor.
Figure 2-4. Circuit for 2-Wire Resistance Measurements
Input Ranges
The NI4 050 has five basic input ranges for 2-wire resistance as well as an
extended range. The basic ranges are 200 Ω, 2.0 kΩ, 20 kΩ, 200 kΩ, and
2 MΩ. With the extended range, measurements up to at least 200 MΩ are
possible.
Runknown
+
–
Vsense Iex
Iex
Iex
Runknown = Vsense
Iex
Iex = 100 µA (200 Ω, 2 kΩ, 20 kΩ ranges)
1 µA (200 kΩ, 2 MΩ, 200 MΩ ranges)
HI
LO
Input
VΩ