The output voltage is applied to the device under test
through the source impedance. The voltage across
the device is always less than or equal to the
output voltage. Source impedance values are
62.5
Ω
(R1), 1k
Ω
(R2) and 16 k
Ω
(R3).
The source impedance is selected as a function of the measurement
range. For most devices, including resistors, most capacitors and many
inductors, the 1.0 Vrms setting provide best result. For some inductors
and active devices, the 0.25 or 0.5 Vrms setting should be used.
Certain devices require a speci
fi
c test voltage, such
as Z5U ceramic capacitors (test voltage = 0.5 Vrms
for 25V parts and 1.0V for < 16V parts).
Note: Use the largest voltage possible for the best SNR and accuracy.
The ST5 provides three measurement ranges (R1-R3). Each of
the three ranges has the source impedance of approximately
the mid-scale impedance. The table below speci
fi
es the
impedance ranges for each of the measurement ranges.
Range
Source R
DUT Impedance
1
62.5
Ω
< 400
Ω
2
1 k
Ω
400
Ω
< < 4 k
Ω
3
16 k
Ω
> 4 k
Ω
Note:
Measurement ranges determine an impedance range (not
a value range), so the ranges for inductance and capacitance
depend upon the test frequency. In addition, the impedance
for capacitors is inversely proportional to its capacitance, so
larger capacitors are measured in lower impedance ranges.
During normal operations the unit automatically changes to the
optimal range for the DUT. There is a built-in hysteresis allowing to
avoid repeated range changes when a component is near a range
boundary. The auto-ranging function can be disabled by user.
Range holding is helpful if a number of parts with similar values are
being measured or a speci
fi
c measurement condition required.
5
