User`s guide

Introduction to the 34980A 1
Agilent 34980A Mainframe User’s Guide 11
Measurement Input
The 34980A allows you to combine a DMM (either internal or external)
with multiplexer channels to create a scan. During a scan, the instrument
connects the internal 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 digital modules.
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 M)
• 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 block diagram of the internal
DMM is shown below.
Signal Conditioning, Ranging, and Amplification
Analog input signals are multiplexed into the internal DMM's
signal- conditioning section—typically comprising switching, ranging, and
amplification circuitry.
• If the input signal is a dc voltage, the signal conditioner is composed
of an attenuator for the higher input voltages and a dc amplifier for
the lower input voltages.
Analog
Input
Signal
Signal
Conditioning
Amp
Analog to
Digital
Converter
Main
Processor