Fluke 5500A, Service Manual

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5500A
Service Manual
2-4
2-2. Encoder Assembly (A2)
The Encoder assembly (A2) has its own microprocessor and is in communication with
the Main CPU (A9) on the Rear Panel through a serial link. Memory for the Encoder
assembly is contained in EPROM. The Encoder assembly handles the interface to the
Keyboard assembly (A1).
2-3. Synthesized Impedance Assembly (A5)
The Synthesized Impedance assembly (A5) generates variable resistance and capacitance
outputs. It uses discrete resistors and capacitors as references, with an amplifier in series.
Figure 2-2 is a block diagram of the synthesized resistance function. Figure 2-3 is a
block diagram of the synthesized capacitance function.
For resistance synthesis, there is a two-wire compensation circuit, an input amplifier,
two DACs (coarse and fine) with offset adjust, and an output LO buffer.
For capacitance synthesis, there is a two-wire compensation circuit, selectable
references, an input amplifier, two DACs (coarse and fine), and an output LO buffer.
+
_
DAC
SCOM
K
R
x
= (1 + K) • R
ref
NORMAL
HI
R
x
=
-1
SCOM
R
ref
NORMAL LO
om004f.eps
Figure 2-2. Synthesized Resistance Function