I bought this bargain basement clamp-on
current probe on eBay. It doesn't even
seem to have a manufacturer (shamed out of existence?), but the model number is
CP06. It's $70 shipped, and is probably
worth it, especially if you plan to measure DC and 50/60Hz AC waveforms. It will not do high-frequency measurements. The DC accuracy seems good enough for many
different applications where cutting into the test wire is not preferable.
Note:
Hold down the "zero" button for a couple seconds, then
release.
I recently bought
this low-cost clamp on
current meter from ebay this was about
70 dollars shipped and it doesn't even
really have a brand on it the model
number is CP 0-6
and if you've shopped for one of these
clamp on current probes before you've
probably noticed that they're the good
ones are extremely expensive some are
like over $1,000 a tech clamp on current
probe that's capable with high-frequency
measurement so in this video I'm just
going to try to do some basic tests on
this just to characterize it and see if
it's if it's even worth the 70 dollars
it came with this sort of a cable with a
BNC on one end and the other end had
banana plugs that go into the current
probes sockets there unfortunately this
was totally broken it was actually open
from the pin and the BNC connector to
the to the panic of connector so I cut
that up and just made a a makeshift one
myself and I currently have the probe
connected to the tech scope here which
is just making a voltage measurement
I've been kind of stalling on buying a
second multimeter there's too many
choices so I haven't picked one yet so I
just have this one multimeter and I'm
going to use this scope today to do the
a voltage measurement the probe also
came with this cheesy case and it also
came with banana two banana plug so that
you can connect the probe to a
multimeter that actually works pretty
well these aren't terrible so these
probes are often rated either AC or DC
and some are built differently the AC
probes
sometimes use a transformer here to
couple the current flowing through the
the sensing hole into the circuitry and
the DC probes often use a Hall effect
sensor so the problem with the Hall
effect sensors is that they're sensitive
to you know outside magnetic field even
the Earth's magnetic field if you're
measuring small currents so the DC
probes all have a zeroing button or a
zeroing dial so that you can make sure
to get a zero reading before actually
measure
the current that you want to measure so
let's try it I'm going to hook this over
this wire here and then disconnect the
circuit so we know that no current is
flowing I'm going to press the zero
button and we've got a measurement of
like negative 2 millivolts which is well
within the oscilloscopes noise range
there and I'll connect this back up and
on my power supply I'm just going to
pick some arbitrary value so the meter
shows we've got 39 milliamps and lo and
behold 30 point zero three eight 38 36
millivolts on the scope which indicates
a good agreement between the the probe
and the meter here so on its lowest
scale 400 milliamps scale it's 1
millivolt per milliamp so let's crank
the power up a little bit now we've got
96 milliamps flowing and perfect
agreement there 96 millivolts
keep going actually haven't done this
test by the way so you're seeing the
results the first time that I am 218
over here 224 there 377 this one's
starting to come up a little bit now
it's reading 390 over here so it's a
little high just switch into a higher
range on the multimeter pretty soon but
so we've got 377 and 390 so it's reading
just a touch high let's let me switch
this into the higher range and I will
also switch the probe here and I'll
reserve it out too just to be fair on it
zero in the new range
and crank it up a little bit okay so we
got point five two amps here got point
five or four nine they're good
okay about two amps here yeah point two
of a volt there looks good I'm actually
not using a load resistor I mean
basically the load resistor is the meter
itself and the the power supply is only
putting out half a volt I mean it's
there's very little power dissipation so
let's see we got here three point four
six so we've got 0.34 four so still
pretty close just round out this range
here three point nine nine and point
three nine eight
so DC accuracy is looking good let's try
the next scale up it has three ranges
400 milliamps four amps and 40 amps and
the sensitivity is 1 millivolt per
milliamp in the highest sensitivity
range 100 millivolts per amp in the
medium range and 10 millivolts per amp
in the highest range which is where we
are now but that's pretty good I mean I
think that's that's actually reasonable
accuracy so let's move up to a measuring
AC okay here's my setup for measuring an
AC current I'm going to use the kilowatt
meter to measure AC voltage coming in
through the wine and the meter is set up
to measure a voltage AC voltage coming
out of the probe so I'll press the zero
button hold it down for a while and let
it back up and this is a 40 watt plain
old incandescent bulb and we've got 0.3
amps on the kilowatt meter and 0.027
this is on the 4 amp range so that's
pretty good that's been try a bigger
bulb this is a 75 watt bulb
Oh point six four in the kilowatt and
point six on the probe they're pretty
good you know not bad just for laughs
let's put in a compact fluorescent so
this those incandescent bulbs are just
purely resistive loads but this compact
fluorescent is not so let's see what
happens with that yeah so now we've got
interesting stuff going on the kilowatt
meter shows 0.25 but we're only getting
point o 1/3 on the the I mean it's
multiplied by 10 to get amps because
it's in the scale there so 0.2 4 verses
point 1 3 because the waveform the
current waveform of this cfl light is
not sinusoidal it's it's wacky so let's
hook the probe up to the scope which is
really what this thing is useful for I
mean if you just wanted to know what the
value was you could use one of those
eggs tech clamp-on meters that just has
a readout right on the meter the whole
point of getting a current probe is to
actually analyze the current waveform on
an oscilloscope so let's hook it up okay
so let's take a look at the waveform
that's coming out of this current probe
in this setup I've got my isolation
transformer back here I've got a 15 ohm
resistor in the circuit and I'm
measuring the voltage across that 15 ohm
resistor to get the actual current
measurement what we're going to use as a
reference and then the current probe is
clamped on to want the other side of the
line there so let's take a look at the
scope and I'm not really too concerned
about exact values here are mostly
interested in the in the shape of the
waveform for this test so as you can see
very similar I don't see any differences
in the shape of the waveform there so I
wanted I don't even know I think this
one's a little bit noisier than this
trace so this this is the the current
probe okay let me switch to the compact
fluorescent light
okay so now we're looking at that
compact fluorescent bulb and looks like
a very nice matchup of the waveform
again yeah so as you can see the the
current probe has an interesting sort of
pattern to it it's not noise it's
actually interference it looks like
there's maybe a power supply it uses a
switching power supply that has a bit of
ripple to it so there's fuzz in the
output okay for this setup I'm using
this capacitive discharge system that I
built and I've got my one milli ohm
shunt here measured on channel 1 on the
scope and I've also got the current
probe set to it's 40 amp range clamped
on to the same shunt where the current
is going through so if we take a look at
the scope channel one is the actual
current the shunt and it's 200
millivolts per division which translates
to 200 amps per division and the
horizontal scale is was it 0.1
millisecond per division now the bottom
trace channel 2 is what's coming out of
the current probe and as you can see
there's not much there the scale is 2
volts per division and the probe is set
on its highest scale which means you get
10 millivolts per amp so it should be
comparable scales here it should be 200
amps per division for each trace and as
you can see it is really nothing going
on if it completely missed the waveform
so that the frequency response of this
current probe is not high enough to
detect a hundred microseconds which is
not surprising I mean it's it's really
not meant for that I think they even
SPECT the frequency response it's
something like 2 kilohertz or 5
kilohertz or something in that range but
I was kind of curious to see what it
would pick up if anything the answer is
not much so overall I you know I suppose
it's worth $70 it's good at measuring DC
and low frequency AC and it's good
enough to see the waveform for 60 Hertz
stuff which is
probably one of the major uses for this
if you're curious how nonlinear your
your device is or if you're building a
power supply and you want to know what
the current waveform looks like this is
this is pretty good for that and the
scales all seem to work
overall the construction is pretty
cheesy you know it's not absolutely
terrible but it's definitely cheesy but
then again this is $70 and the I don't
know what the next comparable probe
would cost but as you scan eBay I mean
they're well into the hundreds of
dollars and some are over a thousand so
if budgets an issue this looks like the
way to go okay I hope that was helpful
see you next time bye
s
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