Re: Re: Power Supply & Gecko's (test results)

Hi Pete,

Nice job on the test results!

I was wondering by chance if you could run a test on a Fluke 77
(or other non rms Fluke meter) and see what results you get.

I love my Fluke 77, and would love to see how it stands up to the rest.

Jim...

> Date: Sat, 13 Aug 2005 15:52:07 -0400
> From: "Peter Reilley" <micrio@...>
> Subject: Re: Re: Power Supply & Gecko's (test results)
>
>
> ----- Original Message -----
> From: "Roy J. Tellason" <rtellason@...>
> To: <CAD_CAM_EDM_DRO@yahoogroups.com>
> Sent: Saturday, August 13, 2005 1:26 PM
> Subject: Re: [CAD_CAM_EDM_DRO] Re: Power Supply & Gecko's
>
>
> > On Saturday 13 August 2005 12:48 pm, turbulatordude wrote:
> >> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Roy J. Tellason"
> >> <rtellason@b...> wrote:
> >> > On Saturday 13 August 2005 11:42 am, Peter Reilley wrote:
> >> > > I believe that you cannot measure AC ripple with an AC meter where
> >> > > there is a DC component. The meter does not filter out the DC.
> >> > > Thus, it get confused. You really need a scope to measure AC
> >> > > ripple.
> >> >
> >> > I think this depends on the meter...
> >>
> >> Not sure if this is 100% correct,
> >> from Newport's website
> >> http://www.newportus.com/manuals/ACGUIDE.htm
> >>
> >> True-RMS voltmeters use an integrated circuit which computes the true
> >> root-mean-square value of complex signals. AC coupling allows the
> >> measurement of the AC component (or ripple) from a signal with both AC
> >> and DC components. DC coupling allows the measurement of total RMS, or
> >> "heating value", including DC and AC components to over 30 kHz.
> >> (Maximum crest factor (Vp/Vrms) is 3:1). Screw terminals allow the
> >> selection of AC or DC coupling. True-RMS meters are especially useful
> >> in monitoring voltage and current supplied to motors or heaters
> >> controlled by an SCR or triac circuit.
> >
> > Yep, and "true RMS" meters are few and far between, and much more
> > expensive
> > than most of what we're likely to be using...
> >
> > It depends on the meter... :-)
> >
>
>
> This piqued my interest. I have the equipment to do the actual testing.
> I tested;
>
> meter 1) Fluke 87 true RMS meter about 8 years old, bought new.
> meter 2) Simpson 269, the best movement meter that you could buy 30
> years
> ago. Bought at a flea market.
> meter 3) Ramsey KD-508, a cheap Radio Shack digital meter about 10 years
>
> old, bought new.
>
> None of there meters have been calibrated since I have owned them.
> I used a Racal-Dana signal generator that can add a DC offset to it's
> output
> signal.
> I used a scope to watch the signal to make sure that I was getting what I
> expected.
> All tests were done at 60 Hz.
>
> Three test signals were measured by all meters;
> Signal 1) 3 VAC with 0 VDC
> Signal 2) 3 VAC with 3 VDC
> Signal 3) 0 VAC with 3 VDC
>
> Each meter read the signal at with it's AC setting and then it's DC
> setting.
> Here are the results.
>
> Fluke AC Fluke DC Simpson AC Simpson DC Ramsey AC
> Ramsey DC
>
> Signal 1) 3 0 3.1 0
> 2.7 0
> Signal 2) 3 3 3.95 3.1
> 6.1 3
> Signal 3) 0 3 3.5 3.1
> 5.1 3.1
>
> I hope this chart comes out OK.
>
> It is clear that the Fluke will read only the AC component when the setting
>
> is AC and the
> signal has both an AC and a DC component. In the DC setting the AC is
> ignored as
> expected.
>
> The Simpson does the right thing on the DC setting when measuring a
> combined
> AC/DC signal.
> On the AC setting it is wrong. Movement meters like the Simpson are
> average reading but RMS
> calibrated. This works OK for pure sinusoidal AC but gives weird
> readings
> for anything else.
>
> The Ramsey does the right thing for DC but the AC reading is wrong. Cheap
>
> digital
> meters are peak reading but RMS calibrated. Thus the reading is wrong for
>
> complex signals and
> the error is different than for movement meters like the Simpson.
>
> The moral of the story is that the Fluke is correct. You get what you pay
>
> for.
>
> Pete.

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