HP 34970A The HP 34970A Data Acquisition / Switch Unit

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-referencedand 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

Optional

3

IN

Alarms

Control

Floating

Internal

Earth

Logic

DMM

HP-IB

Referenced

To Computer

Logic

Digital

Analog Bus

RS-232

Bus

100

AC Power

Plug-In

= Optical Isolators

200

Slots

300

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.

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