Prev: Design Electronic Vehicle Anti-theft Gadget
Next: What's on your test bench?
From: notme on 11 Nov 2009 14:34
> 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

From: Phil Allison on 12 Nov 2009 02:15

"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


From: notme on 12 Nov 2009 02:55
> 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

From: Phil Allison on 12 Nov 2009 03:09

"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


From: Andy on 12 Nov 2009 10:10
On Nov 12, 1:09 am, "Phil Allison" <phi...(a)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%.
First  |  Prev  |  Next  |  Last
Pages: 1 2 3 4 5
Prev: Design Electronic Vehicle Anti-theft Gadget
Next: What's on your test bench?