Application Note

2 Fluke Corporation The power of a waveform: Expanded troubleshooting options with the Fluke 345 Power Quality Clamp Meter
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The ability to monitor both ac and dc loads.
When it comes to long-term data logging, users
of earlier meters said they needed to monitor
single-phase ac and dc loads. Healy notes that
most loggers only read ac. Some are dc-only
loggers. By contrast, the Fluke 345 offers ac
current monitoring up to 1400 A and dc up to
2,000 A.
The dual-current capability could only be
engineered into a clamp meter. Healy explains:
“There is no technology available for measuring
dc current using a flexible probe. So, the clamp
itself is a Hall-effect sensor, and it can measure
ac and dc current simultaneously. By contrast, a
Rogowski-type device can only measure ac. We
wanted one self-contained tool that didn’t need
extra leads to measure current.”
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A large, flexible memory configuration. The
Fluke 345 has three distinct memory locations,
where three separate logs can be stored at the
same time. Using this feature, an electrician can
go into the field and make a log of, say, twenty
minutes and then hour-long logs in two other
places, all without returning to the office to
download data.
Alternatively, if the electrician needs to sam
-
ple data for a longer period, the logger can be
left at a single location for an extended period of
time. There, it can store data in all three memory
areas during the sampling period. According to
Healy, an electrician could record for hundreds
of days, depending upon the averaging period
(sample frequency). The data is stored in mem
-
ory, and, following downloading to a PC via USB,
can be analyzed using the Power Log software
shipped with the instrument.
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The ability to easily measure inrush. When
a motor starts, some electrical systems may
experience a surge in load demand called
inrush. It can be enough to trip breakers, dim
the lights, and cause other anomalies. To log
inrush data on the Fluke 345, says Healy, “just
set the trigger level for current and put the
instrument in pulse. Then, when the meter sees
a high level of current, it finds it and captures
its characteristics.”
Swanson ties the easy monitoring of power-
switching events—the rapid adding or
removing of loads from a system—to the Fluke
345’s versatile data storage capabilities. “I was
happy to discover that regardless of the sample
frequency, the instrument records peak, low,
and average readings—all three. If I take the
time to do the math, I can even figure out the
duration of an event.”
Who’s the Fluke 345 designed for?
While the Fluke 345 Power Quality Clamp Meter
was designed with many users in mind, Frank
Healy says utility trouble-shooters and field install/
service techs will find it especially useful.
Utility personnel can use the Fluke 345 to
measure high current on large cables, thanks to
the oversized jaws and current rating to 2,000 A
dc. Most clamp meters are limited to 1,000 A.
Electrical maintenance personnel can use the
Fluke 345 as a predictive maintenance tool. “With
this meter,” says Paul Swanson, “we could regu
-
larly measure the secondary on our VFDs, establish
operational bench marks, and watch for condi
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tioning issues and other potential problems. We’d
establish the nominal operating parameters for
each drive’s output, like taking snapshots and stor
-
ing them. Then, we’d go back every six months or
every year to see if there had been any noticeable
deterioration on the drive output waveform.”
Installers and maintainers of UPSs, VFDs,
and other switching loads will appreciate the
meter’s ability to measure both ac and dc, as well
as its low-pass filter. With a 345, an electrical
technician could go through a UPS checking the
input currents and inrush and look for harmonics.
Inside the UPS, the tech could check the dc link
and see the dc current prior to conversion into ac
on the opposite side.
Swanson explains that instead of one large,
centralized UPS, the King County Justice Center has
38 UPS units throughout the facility. They supply
backup power to the computerized security and
alarm systems and to various computer networks.
“We’ve spread out the UPSs,” Swanson explains.
“We have more points of potential failure, but
when one does fail it takes less out of our system.”
In monitoring a UPS, Swanson asks questions
that the Fluke 345 waveform display can answer:
What do my input and output look like? Do I have
harmonics? Is the UPS deteriorating in any way?
“Both on the input and the output, I can see if
anything’s being
pushed out onto
the lines,” Swan
-
son says, “and
I can determine
whether the UPS
is actually doing
its job. I might be
able to do some of
that with a DMM,
but the findings
would be much
less clear.”