Re: Panel Meter Question

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Yurtle Turtle <yurtle_t@xxxxxxxxx>

Thanks. That's kinda what I expected. I mapped out the
input voltage directly to the meter without resistors,
to read 100, 110, 120, etc. up to 300. I measured the
resistance of the meter, then used an Excel
spreadsheet to calculate a resistance to get the right
voltage split. Unfortunately, that didn't quite work
out either. Apparently the meter has enough inductance
to throw it off from my calcs. I'll probably just
throw my 25k pot in line and dial it until the high
end is close, then replace it with some resistors.
Hey, here's a thought. I believe the blown resistor
was a wire wound one, and the one I tried was a carbon
one. Is it possible the manufacturer picked a sligtly
inductive resistor? I'm having trouble wrapping my
head around this, but since the meter is (I assume) a
coil and a magnet, will its impedance change,
depending on the coils  position, relative to the
magnet?

Adam

--- Tesla list <tesla@xxxxxxxxxx> wrote:

> Original poster: "S&JY" <youngsters@xxxxxxxxxxxxxxx>
>
> Adam,
>
> Welcome to the real world of imperfect analog
> meters.  There are three
> approaches you can take:  1) Pick a resistor value
> that give you the most
> accuracy in the middle of your range of interest
> (i.e. the range of voltages
> will you be measuring most of the time),  2) take
> off the meter face, turn
> it around, and make a new meter scale on the back,
> using your Fluke DMM to
> mark the intervals (e.g. every 10 volts), or 3) Do
> number 1, and print out a
> little conversion table so you can read your meter,
> look at the table & see
> the corrected value.
>
> You might consider getting one of the el-cheapo DMMs
> from Harbor Freight
> (about $3 on sale) and just use it instead.  It may
> be off a few percent,
> but at least the percent error is likely to be
> linear across the meter
> range.
>
> --Steve Y.
> ----- Original Message -----
> From: "Tesla list" <tesla@xxxxxxxxxx>
> To: <tesla@xxxxxxxxxx>
> Sent: Saturday, October 01, 2005 10:30 PM
> Subject: Panel Meter Question
>
>
>  > Original poster: Yurtle Turtle
> <yurtle_t@xxxxxxxxx>
>  >
>  > I have a Weston 7544 panel meter that I bought
> used.
>  > It that reads from 0 to 300 VAC. It came with two
> 22k
>  > resistors in series with one of the leads,
> located in
>  > a small compartment. One of them is blown. The
> other
>  > reads 22.36k on my Fluke DMM. I went to my
> resistor
>  > drawer and found one that also reads 22.36k. When
> I
>  > place it in series with the good resistor, the
> meter
>  > reads too low across the scale. At 100VAC, it
> reads
>  > 90, and at 279 it reads 273. So I hooked it
> straight
>  > up to a variac without any resistors, and
> measured the
>  > input voltage and meter readings from 100 to 300.
> I
>  > figured I could simply find the ratio and
> calculate a
>  > better fit for a resistor. The problem is that
> it's
>  > not linear. It ranges from 21.86 volts input to
> read
>  > 100 volts, up to 59.1 volts to read 300 volts. I
>  > created a spreadsheet and played around a bit. If
> I
>  > pick a resistor value to make 300 volts correct,
> I'm
>  > 10 volts too low at 100. If I correct at 100, I'm
> 35
>  > volts too high at 300. Is there a better way to
> do
>  > this, or should I pick an average value, and call
> it
>  > close enough?
>  >
>  > thanks
>  > Adam
>  >
>  >
>  >
>  >
>  >
>
>
>



		
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