HP 34970A User Manual page 53

Chapter 3 System Overview
Data Acquisition System Overview
The HP 34970A Data Acquisition / Switch Unit
As shown below, the logic circuitry for the HP 34970A is divided into
two sections: earth-referenced and floating. These two sections are
isolated from each other in order to maintain measurement accuracy
and repeatability (for more information on ground loops, see page 341).
External Trigger
OUT
IN
Alarms Control
HP-IB
To Computer
RS-232
AC Power
The earth-referenced and floating circuitry communicate with each
other via an optically-isolated data link. The earth-referenced section
communicates with the floating section to provide PC connectivity.
The instrument is shipped with both an HP-IB ( IEEE -488) interface
and an RS-232 interface. Only one interface can be enabled at a time.
The earth-referenced section also provides four hardware alarm outputs
and external trigger lines. You can use the alarm output lines to trigger
external alarm lights, sirens, or send a TTL pulse to your control system.
The floating section contains the main system processor and controls all
of the basic functionality of the instrument. This is where the instrument
communicates with the plug-in modules, scans the keyboard, controls the
front-panel display, and controls the internal DMM . The floating section
also performs Mx+B scaling, monitors alarm conditions, converts
transducer measurements to engineering units, time stamps scanned
measurements, and stores data in non-volatile memory.
Floating
Logic
Earth
Referenced
Logic
= Optical Isolators
Optional
Internal
DMM
Digital Analog Bus
Bus
100
Plug-In
200
Slots
300
53
3