Specifications

Comparison of voltage output from industrial motor VFD without and with
Low Pass Filter functionality.
Sometimes, a maintenance check on the
motor and VFD reveals that the actual
output voltage and frequency from the
VFD differs from the readings on the VFD
display. This shows that the VFD might be
faulty and may therefore need replace-
ment or repair. The difference in voltage
readings could also be contributed by
harmonics produced by the output of the
VFD. This problem must be addressed
quickly because if this situation prolongs,
the motor may overheat and eventually
fail, causing downtime.
It is diffi cult to identify the root cause of
this error using a typical wide bandwidth
handheld digital multimeter (DMM).
A handheld multimeter with a built-in
low pass fi lter would help technicians
to quickly determine if the problem is
contributed by unwanted high frequency
Low impedance mode (Z
LOW
)
Electrical conduit is commonly found in
buildings, from manufacturing plants to
residential homes. It provides enclosed
conductors protection from moisture,
chemical vapors and impact. The use
of electrical conduit simplifi es wiring
changes as existing conductors can be
withdrawn and new conductors installed
with little disruption along the path of the
conduit.
Although convenient and safe, unused
wires can sometimes run parallel with
energized wiring. This may induce
capacitive coupling between these wires,
causing an undesirable transfer of energy
from the energized wiring to the unused
wiring. This complicates installation or
maintenance of electrical wiring as volt-
age may be detected on the unused wir-
ing. This is known as ‘stray voltage’. This
causes complications for technicians, who
would have to spend time troubleshooting
or isolating wires in order to determine
the source of the voltage.
Smart Ω
In integrated circuit (IC) manufacturing
plants, ground continuity measurements
on workstations are important to ensure
that electrostatic discharge (ESD) is mini-
mized. As electronic components become
further miniaturized, these components
are more sensitive to ESD. In order to
maintain a workstation, the common
ground point for continuity to earth or
electrical ground should be checked
periodically.
During this continuity check, leakage
current may be found fl owing through
the common ground conductor to earth
ground. This leakage current causes
inaccurate ground continuity measurement.
The Agilent U1272A/U1273A handheld
digital multimeters (DMM) allow you to
read the leakage current with its Smart
Ω function. With the U1272A/U1273A's
dual display and 30 Ohms range, you can
obtain accurate resistance measurement
and read leakage current simultaneously.
Multimeters with a low impedance mode
are able to identify the presence of stray
voltages in non-energized wiring. The
low impedance mode eliminates false
readings by providing a load to the circuit
during voltage testing.
The Agilent U1272A/U1273A are dual
impedance digital multimeters, offering
both high and low impedance modes. The
DMM’s high impedance function can be
used in most electrical measurements in
the industrial environment because it will
not load the circuit under test. Switching
to the low impedance mode allows the
U1272A/U1273A to perform accurate
measurements on circuits that may con-
tain stray voltages. This eliminates the
need of an additional low impedance
multimeter, such as a solenoid tester. If
this mode is used when real voltage is
present, the Agilent U1272A/U1273A has
a built-in positive temperature coeffi cient
(PTC) thermistor as an overcurrent protec-
tion element.
components generated by the VFD. The
Agilent U1270 Series handheld DMMs
offer a 1 kHz low pass fi lter to provide
accurate VFD output measurement.
This function eliminates unwanted high
frequency noise signals and components
generated by the VFD. Therefore, a
technician would be able to reduce
troubleshooting time and ultimately
reduce system downtime.
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