Clamp meters: Peak vs. In-rush?

Fluke clamp current meters have 2 features that seem similar: peak and
in-rush. The older models have Max (some: Peak). The recent advent in Fluke
clamps is "In-rush".

How do these differ? Isn't in-rush current the short, max current at
motor-turn on? Shouldn't meters with a Max feature capture this accurately?

Compare, for example, my old Fluke 36 (Max):

<http://assets.fluke.com/manuals/36______iseng0000.pdf>

and the 334 (In-Rush):

<http://us.fluke.com/VirtualDemos/330shock.asp>

(click "Explore" then "Selection Guide").

How do Max & In-rush differ? Only in the marketing department?
Or is there a real-world difference?

Thanks,
Dave

I found this description on the Fluke 33x virtual demo page:

"Note: In-rush current measurements done with a 330 Series Clamp Meter will
differ from Min/MAX, Peak, or Peak-Hold measurements which are not triggered
events."

Sounds like other than auto-triggering, the results are the same.

Dave

On Wed, 11 Nov 2009 00:18:20 -0800, notme <(E-Mail Removed)> wrote:

>I found this description on the Fluke 33x virtual demo page:
>
>"Note: In-rush current measurements done with a 330 Series Clamp Meter will
>differ from Min/MAX, Peak, or Peak-Hold measurements which are not triggered
>events."
>
>Sounds like other than auto-triggering, the results are the same.
>
>Dave


Like this?

Apply power, inrush current is 10A for .2 seconds.
Current drops to 1.2A for 2 seconds.
Current rises to 12.5A for 1 second.
Current drops to 1.2A until termination.

So the Inrush reading would be 10A, and the Max reading would be
12.5A. I can see some usefulness for this, since a max only meter
would falsly read 12.5A which the user might attribute to the inrush
current, instead of the event at 2 seconds.

"notme" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Fluke clamp current meters have 2 features that seem similar: peak and
> in-rush. The older models have Max (some: Peak). The recent advent in
> Fluke
> clamps is "In-rush".
>
> How do these differ? Isn't in-rush current the short, max current at
> motor-turn on? Shouldn't meters with a Max feature capture this
> accurately?
>
> Compare, for example, my old Fluke 36 (Max):
>
> <http://assets.fluke.com/manuals/36______iseng0000.pdf>
>
> and the 334 (In-Rush):
>
> <http://us.fluke.com/VirtualDemos/330shock.asp>
>
> (click "Explore" then "Selection Guide").
>
> How do Max & In-rush differ? Only in the marketing department?
> Or is there a real-world difference?
>
> Thanks,
> Dave
>

In the usual Max measurement, the input (current) is sampled and the maximum
sample is displayed, but the true maximum could have occurred between the
samples and in that case you miss the true maximum or inrush current that
your looking for. In inrush current measurements first off it's a triggered
measurement and measures for a very short period of time and it doesn't
depend on samples, I think it's an analog approach.

Shaun

> In the usual Max measurement, the input (current) is sampled and the maximum
> sample is displayed, but the true maximum could have occurred between the
> samples and in that case you miss the true maximum or inrush current that
> your looking for. In inrush current measurements first off it's a triggered
> measurement and measures for a very short period of time and it doesn't
> depend on samples, I think it's an analog approach.
>
> Shaun

After a short phone conversation with a tech support person at Fluke, I think
I understand the difference: it's the acquisition speed. (The new clamps also
have triggered event feature, but that's icing on the cake.)

In the clamp meters in Fluke's present product lineup that have the "In-rush"
feature, the acquisition speed is listed as 100 mS. In the older clamp meters
(eg. my model 36) that have the "Max" feature, the acquisition speed is
listed as 250 mS.

In other words, old (model 36) meters sample 4 times a second. New (model
33x) meters sample 10 times a second (overhead aside).

Help me understand the implications of the faster acq. speed. Obviously for a
quick event to be measured, the speed needs to be quick or the event will
pass unnoticed. Having said that, as long as the event overlaps *any* period
of time with the acquisition window, the peak value will be measured. Yes?
It's kind of a random chance of getting the acquisition (for events <
acquisition speed) isn't it? But not impossible.

Thanks,
Dave

alt.engineering.electrical Access Test - Please Ignore

"notme"

> After a short phone conversation with a tech support person at Fluke, I
> think
> I understand the difference: it's the acquisition speed. (The new clamps
> also
> have triggered event feature, but that's icing on the cake.)
>
> In the clamp meters in Fluke's present product lineup that have the
> "In-rush"
> feature, the acquisition speed is listed as 100 mS.

** The term actually used is "integration time " - very important .

> In other words, old (model 36) meters sample 4 times a second. New (model
> 33x) meters sample 10 times a second (overhead aside).

** Not at all what Fluke claim.

See page 2 of this pdf.

http://assets.fluke.com/appnotes/1629920_.pdf

The 33x meters are actually sampling the current surge wave a " large number
" of times in the crucial first few cycles of applied AC power, so that the
peak value can be found.

This is quite unlike your typical DMM that *ANALOGUE * samples a DC input
voltage a few times a second - with these, an AC to DC converter ( true rms
or average rectified value ) is needed to measure any AC wave.



.... Phil

> http://assets.fluke.com/appnotes/1629920_.pdf

Very good description of the In-rush feature. I wish the guy at Fluke would
have recommended it.

Thanks for your observations, Phil. You've been very helpful.

Dave

"notme"
>
>> http://assets.fluke.com/appnotes/1629920_.pdf
>
> Very good description of the In-rush feature. I wish the guy at Fluke
> would
> have recommended it.

** The link was very hard to find, Fluke's site alluded to its existence but
was not clear on where it was.

Google helped out ....


> Thanks for your observations, Phil. You've been very helpful.


** DMMs baffle the masses, it seems.

Mainly cos the name is so misleading.



..... Phil

Andy wrote:
> On Nov 12, 1:09 am, "Phil Allison" <phi...@tpg.com.au> wrote:
>> "notme"
>>
>>
>>
>>>> http://assets.fluke.com/appnotes/1629920_.pdf
>>> Very good description of the In-rush feature. I wish the guy at Fluke
>>> would
>>> have recommended it.
>> ** The link was very hard to find, Fluke's site alluded to its existence but
>> was not clear on where it was.
>>
>> Google helped out ....
>>
>>> Thanks for your observations, Phil. You've been very helpful.
>> ** DMMs baffle the masses, it seems.
>>
>> Mainly cos the name is so misleading.
>>
>> .... Phil
>
> I recently did some tests on the inrush current on a wound rotor
> motor. I used two fluke meters, both with inrush capacity. And I
> also built my own circuit using CT, a few resistors, a couple op amps,
> and a data acquisition card. The data acquisition card was set to
> sample at 1000Hz. I ran the tests by starting the data acquisition,
> and then starting the motor. The samples were taken for 1 second.
> With the data card I was able to get very good graphs of the
> asymmetric starting current. However, the max amplitude of the
> starting current measured by the data acquisition card was remarkably
> different from that measured by the Fluke. The fluke does not
> necessarily see the max waveform. The fluke takes a bunch of samples
> in the first few cycles, and then spits out the max of what it
> measured. I think the flukes are fine, but it should be noted that
> they can be off by quite a bit. In my tests, the difference between
> the fluke and the data circuit ranged from a few percent to almost
> 100%.

Now you've introduced another nuance to the discussion.

Reading the app note it seems that Fluke designed there 33 meters to
read the symetrical currents for motor starting.

But as you mentioned, large inductive loads often have a DC offset
component to their starting current. This comes as an artifact of
closing the starter when the sine wave is not at zero-crossing
(inevitable in a three-phase motor).

You can see this in oscillograph traces, or hi frequency samping such as
your set up. But it's hard to get repeatability unless you have a
zero-crossing motor starter. Each time the motor/transformer is
energized, it's likely to be at a different point on the sine wave.

(some large motor/transformer protection schemes avoid false-tripping on
this in-rush by using various techniques such has harmonic-restraint, or
simple time delays)

I wonder if Fluke deliberately filter out the DC offset just so they
don't have to explain why the reading changes each time you start the
motor :-)

daestrom