HP 34970A The Internal DMM, Measurement Input, Measurement Input

Chapter 3 System Overview

Measurement InputMeasurement 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.

Analog			Analog to		To / From
	Signal	Amp		Main	Earth
Input			Digital		Referenced
	Conditioning			Processor
Signal			Converter		Section
					= Optical Isolators

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