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Theory of Operation
This section describes the general overall operation of the 4338B and the operation of each
assembly.
Overall Measurement Theory
The 4338B measures the resistance of the Device Under Test (DUT) by measuring vector
voltage to current ratio. A vector is a value which consists of a magnitude and a phase. The
DUT resistance is the real part of vector impedance which is determined by the vector ratio
between the voltage across the DUT and the current
owing through the DUT.
In Figure 4-1, a DUT is connected in series with a signal source, voltmeter V, and ammeter A. If
the ammeter measures amperes when the source voltage is volts, the DUT's impedance
is expressed by:
The DUT resistance, R, is the real part of
format:
where, j is the imaginary unit and X is the reactance.
Note
For accurate and stable low-resistance-measurement, the 4338B employs an ac
voltage source, rather than a dc voltage source.
The 4338B essentially consists of a signal source, a vector voltmeter, and a vector current
meter.
v
Zx =
i
expressed in the complex real-imaginary number
Zx = R + jX
T roubleshooting
4-3
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