Measurement Input
The HP 34970A allows you to combine a DMM (either internal or external)
with multiplexer channels to create a scan. During a scan, the instrument
connects the
DMM to the configured multiplexer channels one at a time
and makes a measurement on each channel.
Any channel that can be “read” by the instrument can also be included
in a scan. This includes any combination of temperature, voltage,
resistance, current, frequency, or period measurements on multiplexer
channels. A scan can also include a read of a digital port or a read of the
totalizer count on the multifunction module.
The Internal DMM
A transducer or sensor converts a physical quantity being measured
into an electrical signal which can be measured by the internal
DMM.
To make these measurements, the internal
DMM incorporates the
following functions:
• Temperature (thermocouple, RTD, and thermistor)
• Voltage (dc and ac up to 300V)
• Resistance (2-wire and 4-wire up to 100 MΩ)
• Current (dc and ac up to 1A)
• Frequency and Period (up to 300 kHz)
The internal
DMM provides a universal input front-end for measuring
a variety of transducer types without the need for additional external
signal conditioning. The internal
DMM includes signal conditioning,
amplification (or attenuation), and a high resolution (up to 22 bits)
analog-to-digital converter. A simplified diagram of the internal
DMM is
shown below.
= Optical Isolators
Analog
Input
Signal
Signal
Conditioning
Amp
Main
Processor
To / From
Earth
Referenced
Section
Analog to
Digital
Converter
Chapter 3 System Overview
Measurement Input
60
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