National Instruments NI 4050 Diode Measurements

Chapter 2 NI4050 Operation

In the extended ohms range, the NI4050 adds a 1 MΩ resistor in parallel

with the test resistor, and then calculates the value of the resistor being

tested. The test current for the 200 Ω, 2.0 kΩ, and 20 kΩ ranges is 100 µA.

The test current for the 200 kΩ, 2 MΩ, and 200 MΩ ranges is 1 µA.

Many traditional multimeters can take continuity measurements, which test

for the presence or absence of continuity between the two test probes.

These measurements are simply resistance measurements, where the

resistance between the two probes is measured and compared to a set value.

You can perform continuity measurements on a circuit by setting the

NI4 050 to the 200 Ω range and comparing the measured value to some low

resistance value, typically 10 Ω. If the measured value is less than 10 Ω,

there is continuity between the test probes.

Diode Measurements

To properly measure the forward voltage of a diode, make sure that the

diode is not connected to any other circuits. The NI4050 biases the diode

with a current of 100 µA and measures the resulting voltage drop, as

illustrated in Figure2-5. Diode measurements are made with a fixed range

of 2.0 V.

Note Different multimeters use different currents to excite the diode. This may result in

different readings for the same diode.

Figure 2-5. Circuit for Diode Measurements

Iex

Vsense

–

Vdiode

Vsense = Vdiode

–

Iex

Input

VΩ