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VI 34450A User’s Guide

Protection Limits

The Agilent 34450A 5½ Digital Multimeter

provides protection circuitry to prevent

damage to the instrument and to protect

against the danger of electric shock, pro-

vided that the Protection Limits are not

exceeded. To ensure safe operation of the

instrument, do not exceed the Protection

Limits shown on the front panel, as defined

below:

Note: The front-panel terminals and current

protection fuse are shown above.

Input Terminal Protection

Limits

Protection Limits are defined for the input

terminals:

Main Input (HI and LO) Terminals. The HI

and LO input terminals are used for voltage,

resistance, capacitance, and diode test

measurements. Two Protection Limits are

defined for these terminals:

HI to LO Protection Limit. The Protection

Limit from HI to LO ("A" in the figure

above) is 1000 VDC or 750 VAC, which is

also the maximum voltage measurement.

This limit can also be expressed as

1000 Vpk maximum.

LO to Ground Protection Limit. The LO

input terminal can safely "float" a maxi-

mum of 500 Vpk relative to ground. This is

Protection Limit "B" in the figure.

Although not shown on the figure, the Pro-

tection Limit for the HI terminal is a maxi-

mum of 1000 Vpk relative to the ground.

Therefore, the sum of the “float” voltage

and the measured voltage must not exceed

1000 Vpk

Current Input Terminal. The current input

("I") terminal has a Protection Limit of

100 mA (rms) maximum current flowing

from the LO input terminal. This is Protec-

tion Limit "C" in the figure. Note that the

current input terminal will be at approxi-

mately the same voltage as the LO terminal.

Note: The current-protection circuitry

includes a fuse on the back panel. To main-

tain protection, replace this fuse only with a

fuse of the specified type and rating.

10 A Current Input Terminal. The 10 A cur-

rent input terminal has a Protection Limit of

10 A (rms) maximum current flowing from

the LO input terminal. This is Protection

Limit "D" in the figure. Note that the current

input terminal will be at approximately the

same voltage as the LO terminal.

Note: The current-protection circuitry

includes an internal fuse. To maintain pro-

tection, service-trained personnel should

replace this fuse only with a fuse of the

specified type and rating.

Sense Terminal Protection

Limits

The HI and LO sense terminals are used

only for four-wire resistance measurements

Ω 4W"). The Protection Limit is 200 Vpk

for all of the terminal pairings ("E" in the fig-

ure):

LO sense to LO input.

HI sense to LO input.

HI sense to LO sense.

Note: The 200 Vpk limit on the sense termi-

nals is the Protection Limit. Operational

voltages in resistance measurements are-

much lower - less than 5 V in normal opera-

tion.

IEC Measurement Category II

Overvoltage Protection

To protect against the danger of electric

shock, the Agilent 34450A 5½ Digital Multi-

meter provides overvoltage protection for

line-voltage mains connections meeting

both of the following conditions:

The HI and LO input terminals are con-

nected to the mains under Measurement

Category II conditions, defined below, and

The mains are limited to a maximum line

voltage of 300 VAC.

IEC Measurement Category II includes elec-

trical devices connected to mains at an out-

let on a branch circuit. Such devices include

most small appliances, test equipment, and

other devices that plug into a branch outlet

or socket. The 34450A may be used to make

measurements with the HI and LO inputs

connected to mains in such devices, or to

the branch outlet itself (up to 300 VAC).

However, the 34450A may not be used with

its HI and LO inputs connected to mains in

permanently installed electrical devices

such as the main circuit-breaker panel,

sub-panel disconnect boxes, or permanently

wired motors. Such devices and circuits are

subject to overvoltages that may exceed the

protection limits of the 34450A.

Note: Voltages above 300 VAC may be mea-

sured only in circuits that are isolated from

mains. However, transient overvoltages are

also present on circuits that are isolated

from mains. The 34450A is designed to

safely withstand occasional transient over-

voltages up to 2500 Vpk. Do not use this

multimeter to measure circuits where tran-

sient overvoltages could exceed this level.

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