ADCMT 12701A, Руководство по эксплуатации

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4-1
12701A Test Fixture Operation Manual
4.1
Driving Guard Function
4. Functional Description
4.1 Driving Guard Function
Figure 4-1 Driving Guard Function
(1) The measuring instrument such as 6245, 6246, 8240, 8340A and 8252 adopts the driving
guard (active guard) system that prevents the response from being slow or the apparent
insulation resistance from lowering due to the cable capacitance and the stray capacitance
between the HI and LO terminals when measuring voltage or high resistance with high
signal source impedance of 100M
Ω
or higher.
(2) The driving guard ignores the input cable capacitance Cx1 by driving the core wire of the
input cable and the inner shield at the same potential, and also ignores Cx2 because of low
impedance between the inner shield and the outer shield.
(3) The 12701A has a dual structure in which the chassis and the test box are insulated to
utilize the driving guard effectively. Consequently, the outer shield of the input cable can
be connected to the chassis, and the inner shield can be connected to the test box case via
the relay terminal DG.
(4) To use the driving guard function on the fixture, connect the DG terminal being used and
the TEST BOX GUARD terminal using the cable A01215-15.
Test box
Relay terminal Input cable