HP 3457A - Page 169

8-6. Chassis Common Circuitry
The Chassis Common Circuitry consists-of digital circuits and associated power supplies. The main cir-
cuits are the Main Controller, HP-IB Input/Output, Front Panel Control and the Isolation Logic.
8-7. Main Controller
The Main Controller controls the HP 3457A’s measurement process, communicates with the Front Panel
and HP-IB 1/O, applies measurement corrections and performs math calculations. The Main Controller
circuitry consists of a microprocessor, program ROM’s, storage RAM’s and associated digital circuitry.
8-8. HP-IB I/O Circuitry
The HP-IB circuitry provides communication between the main controller and other instruments con-
nected to the HP-IB bus. The HP 3457A main controller receives HP-IB commands (Remote, Listen,
etc.) and control information (DCV, ACV, etc.) and sends measurement data through the HP-IB 1/O
circuitry.
HP-IB is Hewlett-Packard's implementation of IEEE Standard 488-1978, "Standard
Digital Interface for Programmable Instrumentation" and ANSI MC 1.1.
8-9. Front Panel Control
The Front Panel Control circuitry provides communication between the user and the Main Controller,
The Main Controller microprocessor receives control information through the front panel keyboard
and returns measurement information through the front panel display.
8-10. Floating Common Circuitry
The Floating Common Circuitry consists of Input Switching Circuitry, an Input Amplifier, an Ohms
Current Source, an AC to DC Converter, an Analog To Digital Converter, a Voltage Reference, an A/D
Controller, Isolation Logic Circuitry, and Power Supplies.
8-11. Input Switching
The Input Switching section is responsible for routing the input signal to the proper signal conditioning
and measurement circuitry, and connecting the Ohms Current Source when making resistance measure-
ments. The input switching is also used during Autocal and multimeter Self Test procedures to route
stimulus and measurement signals.
8-12. Input Amplifier
The
Input
Amplifier
scales
the
input
signal
to
maintain
a
0
to
10
volt
signal
to
the
input
of
the
Analog
to
Digital Converter
circuitry.
The
amplifier
also provides
isolation
between
the
device
being
measured
and
the
HP
3457A
measurement
circuitry.
8-13. Ohms Current Source
The Ohms Current Source supplies a known current through resistors being measured to provide a
proportional voltage which can be measured by the HP 3457A. The current source is also used as a
HP 3457A Multimeter
8-3