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2.2.
2-2
MEASURING PRINCIPLE, Figs. 1, 2, 3
1. Reference measurement:
2. 0° voltage measurement:
The voltage at the CUT is measured.
The switching phase of the phase sensitive rectifier is O°.
3. 90° voltage measurement:
The voltage at the CUT is measured.
The switching phase of the phase sensitive rectifier is 90°.
4. 0° current measurement:
The current through the CUT is measured.
The switching phase of the phase sensitive rectifier is 0°.
The gain of the programmable amplifier is set to.x.1 and, as for voltage measurement,
increased to x1
with regard to the level detector. Next, if necessary, the conversion coefficient of the I/V converter
is increased from x1 to x10 (high at 309.30) and —as valid for our example with a 100 k& resistor—
the gain of the programmable amplifier is increased to x10 and set back to x1 after overrange detection.
An A/D conversion is performed.
For low-ohmic
components
a slightly different sequence
is performed:
If for voltage measurement
the gain was set to x1 or x10, the impedance is in any case very low, resulting in maximum current to
flow. The current measurement is performed at gain x.1 without trial for gain changing.
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