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Frans_M_Everaerts_Isotachophoresis_378342.pdf

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CONDUCTIVITY DETECTION<br />

Fig.6.14. The d.c.-a.c. converter.<br />

100 kR<br />

10 Ma, although between 10 and 50 kR a fairly linear response can be obtained. With<br />

the converter, as shown in Fig.6.14, a maximal potential difference of 10 V can be<br />

measured between two points, which has a maximal common mode potential of 6 kV with<br />

respect to earth. The impedance between the two points, at the input of the circuit<br />

shown in Fig.6.14, is greater than 10l2 !d and the common mode impedance is greater<br />

than 10’’ R.<br />

The junction-field effect transistor (FET) is used as a source follower. This junction-<br />

FET is supplied by a battery, which eventually can be replaced with an electronic circuit,<br />

although it is used here in order to minimize both the leak current towards earth<br />

(discussed in section 6.6.4) and the parasitic capacitance towards earth. An advantage is<br />

that the supply current of the circuit given is very small (

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