CIRCUIT THEORY
Introduction
The purpose of this section is to describe the theory of operation of each of the measuring circuits available with this
instrument. Simplified individual schematic diagrams accompany each of the circuit descriptions.
DC Voltage Measurement
Figure 4 shows that portion of the 565/555 meter circuit used for DC voltage measurements. Contacts 7-10 of
OUTPUT-AC-DC function switch S2 are closed in this mode. Jacks J3 ( - COMMON) and J4 (+) are used to measure
all voltage ranges except 5KV. In this case jacks J3 and J5 (D. C. 5000 V.) are used. Deck C of RANGE switch S1 is
used to select the resistance that must be placed in series with meter M1 so that the meter will provide the proper
reading for the selected range scale. The rotor of S1C is connected to the rotor of S1D, so the selected resistor is placed
in series with M1 through S1D-4. The following contacts of SIC represent the six available voltage ranges: 4 -
1KV/SKV; 5 - 250V; 6 - 50V; 7 - 10V; 8 - 2.5V; 12 - 0.25V.
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