Table of Contents
,
Model 3476A
SECTION IV
THEORY
OF
OPERATION
4-1. INTRODUCTION.
4-2. This section contains the theory of operation for the
Model 3476A Multimeter. Included are simplified block
diagrams and descriptions of the function of each block.
4-3. Simplified Block Diagram Description ( Figure 4-1).
4-4. Signal Conditioning. The signal conditioning block
consist of the input terminals, overload protection fuses
and functional switching. Overload protection fuses provide
protection to the Multimeter circuitry during ac or dc amps
measurements and during ohms measurements.
4-5. Ohms Current Source. The ohms current source pro-
vides current for ohms measurements.
4-6. Input Amplifier. The input amplifier provides input
range switching for all five Multimeter functions. This is
accomplished by using FET switches to select different gain
Section IV
levels for the input amplifier. The FET switches are control-
led by the Logic Controller.
4-7. AC Converter. The AC Converter is an average re-
sponding detector used in ac voltage and ac current meas-
urements. The output of the AC Converter is a dc voltage
equal to the rms value of the ac input voltage. In the ac
current mode, the input voltage to the converter is the ac
voltage drop across the 1 ohm current shunt ( R45).
4-8. Integrator, Polarity/Zero Detector, Logic Control and
Display. The Model 3476A uses the dual slope integration
technique. The Integrator coupled with the Polarity/Zero
Detector and the Logic Controller converts the signal from
the conditioning circuits to a digital representation of the
input measurement. This digital representation is viewed on
the 3476A Display.
4-9. Power Supply. The Power Supply is a double regula-
ted dc supply which provides + 6 V dc, - 4 V dc and + 1 V
dc.
Figure 4-1. Simplified Block Diagram.
4-1/4-2
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