# Measuring Peak Current with a Fluke 87 III

Discussion in 'Electronic Basics' started by FunFred, Jan 29, 2009.

1. ### FunFredGuest

Just recently I was using a Fluke 87 III to measure the peak current
in an AC circuit.

It was pointed out that I should be using the 1ms sampling range with
the Min/Max mode to catch it (it was on the default 100ms sampling).
OK, I didn't know it was available but you learn...

What confused me a little is that when you step through the readings
(max, min average) in 100ms mode I got a good 12A etc reading for max,
and a small negative value. I just ignored it as an irelivent

Once the 1ms mode is used I now seem to have a valid Max(positive)

I have looked in the manuls and googled etc, I'm still can not find a
statement as to what it means. Is it the Min reading in fact the max
negative current?

It would make sense to me.. it's just when you blow a fuse some times
the Min value is larger than the Max value (ignoring the sign).

So the question is, do I look at both the max and Min values, which
ever is largest it the real maximum current?

FunFred, Jan 29, 2009

2. ### ShaunGuest

Hello Alan,

Here is a link to an article from fluke, see below.

If you google "measure inrush current", you'll get lots of other results
too.

I hope this Helps,

Shaun

"FunFred" <> wrote in message
news:...
> Just recently I was using a Fluke 87 III to measure the peak current
> in an AC circuit.
>
> It was pointed out that I should be using the 1ms sampling range with
> the Min/Max mode to catch it (it was on the default 100ms sampling).
> OK, I didn't know it was available but you learn...
>
> What confused me a little is that when you step through the readings
> (max, min average) in 100ms mode I got a good 12A etc reading for max,
> and a small negative value. I just ignored it as an irelivent
>
> Once the 1ms mode is used I now seem to have a valid Max(positive)
>
> I have looked in the manuls and googled etc, I'm still can not find a
> statement as to what it means. Is it the Min reading in fact the max
> negative current?
>
> It would make sense to me.. it's just when you blow a fuse some times
> the Min value is larger than the Max value (ignoring the sign).
>
> So the question is, do I look at both the max and Min values, which
> ever is largest it the real maximum current?
>
>

Shaun, Jan 31, 2009

3. ### ShaunGuest

It me again,

Here is another inrush current article from fluke, see link below:

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

Shaun

"FunFred" <> wrote in message
news:...
> Just recently I was using a Fluke 87 III to measure the peak current
> in an AC circuit.
>
> It was pointed out that I should be using the 1ms sampling range with
> the Min/Max mode to catch it (it was on the default 100ms sampling).
> OK, I didn't know it was available but you learn...
>
> What confused me a little is that when you step through the readings
> (max, min average) in 100ms mode I got a good 12A etc reading for max,
> and a small negative value. I just ignored it as an irelivent
>
> Once the 1ms mode is used I now seem to have a valid Max(positive)
>
> I have looked in the manuls and googled etc, I'm still can not find a
> statement as to what it means. Is it the Min reading in fact the max
> negative current?
>
> It would make sense to me.. it's just when you blow a fuse some times
> the Min value is larger than the Max value (ignoring the sign).
>
> So the question is, do I look at both the max and Min values, which
> ever is largest it the real maximum current?
>
>

Shaun, Jan 31, 2009
4. ### FunFredGuest

Thanks Shaun.

Whilst the notes explain similar information to what's in the manual
with some history, it still does not say which is the highest reading

for example

meter is monitoring some AC current... an event occurs and the meter
has recorded the following

Max 2.86 Amps
Min -3.08 Amps

so in AC can you have -3.08 amps? (now i'm confused.)

I'm sort of assuming that these are the outputs from two a/d stages.
one for each polarity... every one says use the biggest but the manual
does not say anything.

I'm just concerned with the assumptions being made.

regards

Fred

FunFred, Jan 31, 2009
5. ### ShaunGuest

Well your right, it is kinda strange that the meter gives a negative number
on AC range for MIN in MIN / MAX mode. I have the exact same model of meter
you have but I haven't really played with that function.

I'd suggest you ask your question on the Fluke Community Forum, here is the

http://www.flukecommunity.com/forums/index.php

At the top of the page is "register" - go to that first so that you can post
a question.

Shaun

"FunFred" <> wrote in message
news:...
> Thanks Shaun.
>
> Whilst the notes explain similar information to what's in the manual
> with some history, it still does not say which is the highest reading
>
> for example
>
> meter is monitoring some AC current... an event occurs and the meter
> has recorded the following
>
> Max 2.86 Amps
> Min -3.08 Amps
>
> so in AC can you have -3.08 amps? (now i'm confused.)
>
> I'm sort of assuming that these are the outputs from two a/d stages.
> one for each polarity... every one says use the biggest but the manual
> does not say anything.
>
> I'm just concerned with the assumptions being made.
>
> regards
>
> Fred

Shaun, Jan 31, 2009
6. ### FunFredGuest

Hi Shaun et all

I've got on to the forums, looked through them and searched etc...
found some messages about min/max on resisitance and comparisons of
various meters etc..

I have asked for permission to post, but I'm still waiting..

I wish I had the time to do a comparison...

regards

Alan

FunFred, Feb 6, 2009