Datasheet

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last update
November 30, 2010
reference
smtutin
page
9/27
-5.0E-04
0.0E+00
5.0E-04
1.0E-03
1.5E-03
2.0E-03
2.5E-03
3.0E-03
3.5E-03
0.0E+00 2.0E+02 4.0E+02 6.0E+02 8.0E+02 1.0E+03 1.2E+03
Parasitic capacitance (pF)
Nonlinearity
Figure 5. The nonlinearity versus the parasitic capacitance C
p
The measurement range equals 0 -2 pF
5.5 Capacitive measurements with the UTI
The way UTI measures capacitance values is special. In general when a capacitor has to be measured the
capacitance of the cable is measured in parallel. See figure
Figure a) classical way of measuring capacitors, b) UTI way of measuring capacitors
In the classical way of measuring a capacitor, the cable capacitance is parallel to the capacitance to be
measured. To avoid this effect is not so easy and measuring small capacitance values in combination with
long cables is very hard. In the UTI this problem is solved by measuring the Cx in a four pole way, based on
charge transfer over the capacitor which is to be measured. The excitation of the capacitor comes from a
voltage
source. This means Cp1 is connected parallel to this voltage source and therefore not a part of the
measurement circuit. The transferred charge over Cx is absorbed by the virtual ground of a charge amplifier.
This means that the parasitic capacitance Cp2 is also short circuited. With this four-pole measurement
technique it is possible to measure capacitances as small as attoFarads (aF.) while the cable capacitances
may have value of up to several hundred’s of Pico Farads.
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