4
HOW IT WORKS
ST evaluates impedance of a component by measuring the voltage
across the component and current through it. The complex ratio
of voltage to current is equal to the complex impedance. The unit’s
processor calculates various parameters that are displayed i.e. R, C or L.
Voltage across the component is generated by the test signal
source Vs. Both the amplitude and frequency of Vs can be set. The
voltage is applied to the device under test (DUT) through the source
resistance Rs. Current flows to the virtual ground of the current
amplifier AI, and through the current conversion resistor Ri. The
output of AI provides a signal proportional to the current, I*Ri.
Voltage across the DUT is measured by a separate signal path
(amplifier AU), thus providing a pseudo 4-wire Kelvin connection.
Voltage and current signals are processed by the A/D converter.
Obtained values are then corrected using calibration factors,
converted to impedance and sent to the display.
There are four selectable frequencies: 100Hz, 120Hz,
1.0kHz and 10kHz. The output frequency is accurate
to 50 ppm (0.005%). Frequencies are set in the menu
or by moving the Navigation Control UP.
There are three output voltage levels that can be selected: 0.5 Vrms
and 1.0 Vrms. The accuracy of the output voltage levels is 2 %.
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. The source impedance value is 100Ω .
DUT
AU
RS
VS
VOLTAGE SIGNAL
TO ADC
CURRENT SIGNAL
TO ADC
AL
RI
