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From: Tim on 4 May 2010 18:20
Does anyone have any experience with one of these?

I have been trying to get a simple ac waveform to measure correctly on
this and it just won't display it properly.

Basically if I attach the 10:1 probe to an AC transformer with say 6 VAC
output, the displays says it is 7.3 VAC, but the waveform will occupy 4
divisions on the scale at 5V setting, indicating over 20 volts.

Have I missed something here?

Normally, on my old CRT scope, you just pick the volt per division and
the the waveform sits nicely within them, and will be sized accordingly.

Also it seems that device automatically adjusts the scale so the
waveform fits within a few divisions.

A have the unit to manual config.

I have borrowed this unit to measure the transients in a project I am
working on. The pdf manual I got from Fluke doesn't go into the voltage
settings, except to basically raise or lower them.

I have reset the device, and calibrated the probes.

Any help would be appreciated.

Thanks,

- Tim -
From: Joel Koltner on 4 May 2010 18:30
"Tim" <tim(a)tim.tim> wrote in message
news:MPG.264a75e4d2dc173b98974d(a)news.aliant.net...
> I have been trying to get a simple ac waveform to measure correctly on
> this and it just won't display it properly.
>
> Basically if I attach the 10:1 probe to an AC transformer with say 6 VAC
> output, the displays says it is 7.3 VAC, but the waveform will occupy 4
> divisions on the scale at 5V setting, indicating over 20 volts.
>
> Have I missed something here?

Probably. A "6VAC" transformer is spec'd as putting out ~6V RMS at its rated
load, typically, and under *no* load will put out rather more... such as 7.3V
RMS.

A 7.3V RMS sine wave have a peak-peak amplitude of 2*sqrt(2)*7.3=20.6V, which
if what you're getting by counting divisions, right?

This gets even more fun when you go from dBm to volts or divisions...

From: Peter Bennett on 4 May 2010 18:59
On Tue, 4 May 2010 19:20:58 -0300, Tim <tim(a)tim.tim> wrote:

>Does anyone have any experience with one of these?
>
>I have been trying to get a simple ac waveform to measure correctly on
>this and it just won't display it properly.
>
>Basically if I attach the 10:1 probe to an AC transformer with say 6 VAC
>output, the displays says it is 7.3 VAC, but the waveform will occupy 4
>divisions on the scale at 5V setting, indicating over 20 volts.
>
>Have I missed something here?

Yes - 7.3 VAC RMS (what the meter shows) is 20.4 volts peak-peak (what
the scope shows).

It is likely that the transformer will output somewhat more than its
labelled voltage when lightly loaded, or with high line voltage.
Measure the transformer with a "normal" meter to confirm (or
otherwise) the 7.3 VAC reading.


>
>Normally, on my old CRT scope, you just pick the volt per division and
>the the waveform sits nicely within them, and will be sized accordingly.
>
>Also it seems that device automatically adjusts the scale so the
>waveform fits within a few divisions.
>
>A have the unit to manual config.
>
>I have borrowed this unit to measure the transients in a project I am
>working on. The pdf manual I got from Fluke doesn't go into the voltage
>settings, except to basically raise or lower them.
>
>I have reset the device, and calibrated the probes.
>
>Any help would be appreciated.
>
>Thanks,
>
>- Tim -

--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca
From: Tim on 4 May 2010 19:02
In article <Le1En.91519$3k7.8275(a)en-nntp-13.dc1.easynews.com>,
zapwireDASHgroups(a)yahoo.com says...
> "Tim" <tim(a)tim.tim> wrote in message
> news:MPG.264a75e4d2dc173b98974d(a)news.aliant.net...
> > I have been trying to get a simple ac waveform to measure correctly on
> > this and it just won't display it properly.
> >
> > Basically if I attach the 10:1 probe to an AC transformer with say 6 VAC
> > output, the displays says it is 7.3 VAC, but the waveform will occupy 4
> > divisions on the scale at 5V setting, indicating over 20 volts.
> >
> > Have I missed something here?
>
> Probably. A "6VAC" transformer is spec'd as putting out ~6V RMS at its rated
> load, typically, and under *no* load will put out rather more... such as 7.3V
> RMS.
>
> A 7.3V RMS sine wave have a peak-peak amplitude of 2*sqrt(2)*7.3=20.6V, which
> if what you're getting by counting divisions, right?
>
> This gets even more fun when you go from dBm to volts or divisions...
>
>

OK, so if I work the waveform equation backwards, I can work out the
voltage of the transient strikes that are killing the circuitry on the
other side.

I take it the scope is reading the peak and the meter side is is reading
RMS values.

I must have known this stuff at some point in my life....

Thanks for the info.

- Tim -
From: Joerg on 4 May 2010 19:15
Tim wrote:
> In article <Le1En.91519$3k7.8275(a)en-nntp-13.dc1.easynews.com>,
> zapwireDASHgroups(a)yahoo.com says...
>> "Tim" <tim(a)tim.tim> wrote in message
>> news:MPG.264a75e4d2dc173b98974d(a)news.aliant.net...
>>> I have been trying to get a simple ac waveform to measure correctly on
>>> this and it just won't display it properly.
>>>
>>> Basically if I attach the 10:1 probe to an AC transformer with say 6 VAC
>>> output, the displays says it is 7.3 VAC, but the waveform will occupy 4
>>> divisions on the scale at 5V setting, indicating over 20 volts.
>>>
>>> Have I missed something here?
>> Probably. A "6VAC" transformer is spec'd as putting out ~6V RMS at its rated
>> load, typically, and under *no* load will put out rather more... such as 7.3V
>> RMS.
>>
>> A 7.3V RMS sine wave have a peak-peak amplitude of 2*sqrt(2)*7.3=20.6V, which
>> if what you're getting by counting divisions, right?
>>
>> This gets even more fun when you go from dBm to volts or divisions...
>>
>>
>
> OK, so if I work the waveform equation backwards, I can work out the
> voltage of the transient strikes that are killing the circuitry on the
> other side.
>

If it's really transients, chances are that a scopemeter is too slow for
that, not enough bandwidth. Depends on what sorts of spikes you suspect.
You might need some TVS there.


> I take it the scope is reading the peak and the meter side is is reading
> RMS values.
>

That's the customary way. Meters read RMS and scopes show the waveform,
they cannot "show" RMS because they display the whole sinewave. What
some scopes can do is calculate the RMS and display it in a corner
somewhere as a numerical value.

[...]

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
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