Input Terminal Measurement Limits
Measurement Limits are defined for the input terminals:
Main Input (HI and LO) Terminals. The HI and LO input terminals are used for voltage, resistance, frequency
(period), and diode test measurements. Two Measurement Limits are defined for these terminals:
l HI to LO Measurement Limit. The Measurement Limit from HI to LO (Input terminals) is 1000 VDC or 750
VAC, which is also the maximum voltage measurement. This limit can also be expressed as 1000 Vpk maximum.
l LO to Ground Measurement Limit. The LO input terminal can safely "float" a maximum of 500 Vpk relative to
ground, where ground is defined as the Protective Earth Conductor in the AC mains power cord connected to the
instrument.
As implied by the above limits, the Measurement Limit for the HI input terminal is a maximum of 1500 Vpk relative to
ground when LO is at its maximum of 500 Vpk relative to ground.
Current Input Terminal. The current input ("I") terminal has a Measurement Limit of 3 A or 10 A (DC or AC)
between the "I" terminal (3 A or 10 A) and the LO input terminal. Note that the current input terminals will always be
at approximately the same voltage as the LO terminal, unless a current protection fuse is open. The 10 A terminal is
only available on the 34461A.
Sense Terminal Measurement Limits
The HI and LO sense terminals are used for DCV ratio measurements and four-wire resistance and temperature
measurements. The Measurement Limit is 200 Vpk for all of the terminal pairings: LO sense to LO input, HI sense to
LO input, and HI sense to LO sense.
The 200 Vpk limit on the sense terminals is the Measurement Limit. Operational voltages in resistance
measurements are much lower – up to ± 12 V in normal operation.
IEC Measurement Category II
To protect against the danger of electric shock, the Agilent Truevolt Series DMM protects the user from AC mains power
overvoltage events. When measuring AC mains, the HI and LO input terminals may be connected to AC mains power
up to 300 VAC under Measurement Category II conditions as defined below.
IEC Measurement Category II includes electrical devices connected to AC mains power at an outlet on a branch circuit.
Such devices include most small appliances, test equipment, and other devices that plug into a branch outlet or socket.
The instrument may be used to make measurements with the HI and LO inputs connected to AC mains power in such
devices, or to the branch outlet itself (up to 300 VAC). However, the instrument may not be used with its HI and LO
inputs connected to AC mains power 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 instrument’s protection capabilities.
Voltages above 300 VAC may be measured only in circuits that are isolated from AC mains power.
However, transient overvoltages are also present on circuits that are isolated from ACmains power. The
instrument is designed to safely withstand occasional transient overvoltages up to 1500 Vpk when
measuring voltages greater than 300 VAC. Do not use this equipment to measure circuits where transient
overvoltages could exceed this level.
8 Agilent Truevolt Series DMM Operating and Service Guide
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