33
Signametrics
nce
s used for characterizing semiconductor part types. This function is designed to
display a semiconductor device’s forward or reverse voltage. The DMM measures diode voltage at a selected
current. The available source currents for diode I/V characterization include five DC current values; 100
η
A, 1
µ
A,
10
µ
A, 100
µ
A and 1 mA. The SMX2044 have an additional 10 mA range. The SMX2044 also has a variable
current source which can be used concurrently with DCV measurement (see “Source Current / Measure Voltage”).
This allows a variable current from 10
η
A to 12.5 mA. The maximum diode voltage compliance is approximately 4
V.
Applications include I/V characteristics of Diodes, LEDs, Low voltage Zener diodes, Band Gap devices, as well as
IC
testing and polarity checking. Typical current level uncertainty for diode measurements is 1%, and typical
voltage uncertainty is 0.02%.
4.7 Capacitance Measurement (SMX2044)
The SMX2044 measure capacitance using a differential charge slew method, where variable currents are utilized to
produce a dv/dt across the capacitor.
Use short high quality shielded probe cables with no more than 500 pF. With
the exception of the 10
η
F range, each of the ranges has a reading span from 5% of range to full scale. Capacitance
values less than 5% of the selected range indicate zero. Since some large value electrolytic capacitors have
significant inductance, as well as leakage and series resistance, the Autoranging function may not be practical.
Because Capacitance measurement is sensitive to noise, you should keep the measurement leads away from noise
sources such as computer monitors. For best measurement accuracy at low capacitance values, zero the DMM using
the ‘Relative’ while in the 10
η
F range. The effect of the cable quality and its total capacitance is significant
particularly on low value caps. For testing surface mount parts, use the optional Signametrics SMT Tweezer probes.
See Figure 4-9 for connection.
A special on board temperature sensor allows monitoring of the DMM’s internal temperature. This provides the
means to determine when to run the self-calibration function (S-Cal) for the DMM, as well as predicting the
performance of the DMM under different operating conditions. When used properly, this measurement can enha
the accuracy and stability of the DMM. It also allows monitoring of the chassis internal temperature, which is
important for checking other instruments.
4.6 Diode Characterization
The Diode measurement function i
Figure
4-9.
Measuring capacitors or inductors is best handled with shielded probe wires.
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