4 34410A/11A/L4411A User’s Guide
Protection Limits
The Agilent 34410A/11A and L4411A Digital
Multimeters provide protection circuitry to
prevent damage to the instrument and to
protect against the danger of electric shock,
provided the Protection Limits are not
exceeded. To ensure safe operation of the
instrument, do not exceed the Protection
Limits shown on the front and rear panel,
and defined below:
Note: The front-panel terminals are shown
above. The rear-panel terminals are identi-
cal. The Front/Rear switch selects the ter-
minal set to be used. Do not operate this
switch while signals are present on the
front or rear terminals. The current-protec-
tion fuse is on the rear panel.
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 at
left) 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.
As is implied by the above limits, the Protec-
tion Limit for the HI input terminal is a maxi-
mum of 1500 Vpk relative to ground.
Current Input Terminal. The current input
("I") terminal has a Protection Limit of 3A
(rms) maximum current flowing from the LO
input terminal. This is Protection Limit "C"
in the figure. Note that the current input ter-
minal will be at approximately the same
voltage as the LO terminal.
Note: The current-protection circuitry
includes a fuse on the rear panel. To main-
tain protection, 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 and tempera-
ture measurements ("
Ω 4W"). The Protec-
tion Limit is 200 Vpk for all of the terminal
pairings ("D" in the figure):
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 10 V in normal
operation.
IEC Measurement Category II
Overvoltage Protection
To protect against the danger of electric
shock, the Agilent 34410A/11A and L4411A
Digital Multimeters provide overvoltage pro-
tection 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 34410A/11A and L4411A
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 34410A/11A
and L4411A may not be used with its HI and
LO inputs connected to mains in perma-
nently installed electrical devices such as
the main circuit-breaker panel, sub-panel
disconnect boxes, or permanently wired
motors. Such devices and circuits are sub-
ject to overvoltages that may exceed the
protection limits of the 34410A/11A and
L4411A.
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 Agilent 34410A/11A and
L4411A are designed to safely withstand
occasional transient overvoltages up to
2500 Vpk. Do not use this equipment to
measure circuits where transient overvol-
tages could exceed this level.
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