Looking For Help with a Fluke 196 Scopemeter

[Tim]

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 -

 

[Tim]

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 -

 

[Joerg]

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.

[...]

 

[Tim]

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.

[...]

I believe that is what this one has been doing, and I was too dumb to
see it.

I check the machine, and it was peaking at around 142 VAC, with a 50VAC
mechanical meter counting the pulses. Now I know the values to put in to
stop the problem. The voltage was exceeded by about 50% of the max for
the components. No question as to why they failed.

Thanks to all for your concise replies.

- Tim -

 

[Jamie]

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?

Lets see here at 6 V RMS
6*1.414=8.484*2=16.968 P-P
Now at 7.3 RMS
7.2*1.414=10.3222*2=20.64444

Rup.
Looks like I know Kentucky math!

it appears that your scope is working fine because what you're seeing
is a Peak To Peak reading when accounting for those 4 divisions vertically.
20VPP is what you're seeing..

But your scope is giving you the base line to RMS reading from what I
can tell. Which is most likely what you're after.

Here, this may help you!