Lewis Hartswick wrote:

Josepi wrote:

The guys used to laugh when I would get out the old AVO analogue needle
meter, with the mirrored scale, from time to time but the digital ones
(with all their so-called accuracy) would get confused in certain
applications.

Anyone who ever had to tune a circuit for a peak or a null
should be on the analog meter side of that discussion.
Those GD blinking digits, you cant tell if the reading
is going up or down.


I've never seen a 4 1/2 digit analog equivalent, or an analog meter
that displays a .01 dB signal change.


--
You can't fix stupid. You can't even put a Band-Aid™ on it, because it's
Teflon coated.

John wrote:

Jim Wilkins wrote:
On Mar 17, 1:25 am, Lewis wrote:
Josepi wrote:

The guys used to laugh when I would get out the old AVO analogue needle
meter, with the mirrored scale, from time to time but the digital ones
(with all their so-called accuracy) would get confused in certain
applications.

Anyone who ever had to tune a circuit for a peak or a null
should be on the analog meter side of that discussion.
Those GD blinking digits, you cant tell if the reading
is going up or down.
...lew...

I know, the analog meter feels easier, but you can read it to perhaps
1 part in 100 while the digital ones resolve 1 part in 1999, the
better ones 1 in 19,999, and if they let you play around inside the
+/- indicator can be zeroed to half a count or less.

jsw

If you are tuning to a peak or null an analog meter is the easiest to
use. If you are tuning to a set value the digital meter works best.
Some digitals have the bar under the digits which makes it somewhat
similar to the analog meter.


Not always true.


--
You can't fix stupid. You can't even put a Band-Aid™ on it, because it's
Teflon coated.

"DoN. Nichols" wrote:

On 2011-03-17, Lewis Hartswick wrote:
Josepi wrote:

The guys used to laugh when I would get out the old AVO analogue needle
meter, with the mirrored scale, from time to time but the digital ones
(with all their so-called accuracy) would get confused in certain
applications.

Anyone who ever had to tune a circuit for a peak or a null
should be on the analog meter side of that discussion.
Those GD blinking digits, you cant tell if the reading
is going up or down.

Yes. Some of the digital multimeter, e.g. the Fluke ones which
I have, have a bargraph approximation of a needle. Not as much
resolution, but a fairly good guide until you get near the very fine
detail part of the job.

If you want to really be driven nuts by a digital, look at the
really old NLS (Non Linear Systems) DVMs. (From the late 1950s.) A
Kelvin-Varley divider, switched by a collection of (four) stepper
switches. One bank of each stepper illuminates a single lamp (of the
327 style) which illuminates the edge of a sheet of Lucite with a digit
engraved in it. This results in a single digit visible with a bunch of
invisible ones which are not illuminated. The stack of sheets is thick
enough so the different digits have a very visible depth offset.

When The voltage being measured is creeping up, there will be a
tick ... tick ... tick as it tracks. However, when the voltage is
creeping *down*, since the steppers can only move in one direction,
there is a brapp brapp brapp brapp as all four steppers reset to zero
position and then step up -- at about twenty steps per second, so there
is a several second delay before the divider again matches the input
voltage -- until it creeps down yet another step leading to another
series of brapps.

For tuning for a peak or a null, it is a nightmare. The case of
the thing is loaded with sound deadening foam rubber -- but when you
have one opened up to work on it, it is *very* noisy. :-)


HP made a DVM plugin for their 5245L counter that used 'end view'
Nixie tubes.

--
You can't fix stupid. You can't even put a Band-Aid™ on it, because it's
Teflon coated.

Josepi wrote:

Digital meters are not good for indicating fast changing signals.

They can be 50% out at times.


What kind of crap do you use?


--
You can't fix stupid. You can't even put a Band-Aid™ on it, because it's
Teflon coated.

On Mar 17, 2:48*pm, "Michael A. Terrell"
wrote:
Josepi wrote:

Digital meters are not good for indicating fast changing signals.

They can be 50% out at times.

* *What kind of crap do you use?

I have before me an audio oscillator tagged "Do Not Remove From Area
51" and an analog multimeter set on 15VAC. Down to 20Hz the needle is
stable at 10VAC. At 10Hz it wobbles about a volt, ~2V at 5Hz, and
below 3Hz it goes crazy, swinging nearly full scale. Below 1.5Hz it
makes a noise when the needle bangs into the stop.

On DC, swinging from 0 to 4V at 0.1Hz, the response falls off fast
above 1Hz and 10Hz looks like 2VDC with a slight wiggle.

It's so old it uses 709 op amps, and it doesn't have a front panel DC
offset control, just a small trim in back.

jsw

Jim Wilkins wrote:
On Mar 17, 12:08 am, wrote:
The point was in certain applications the digital meter can have all the
digits you want but when they are out by 20 or 50% of the reading sometimes
the analogue meters did a better job.

This is usually a problem with digital updates not syncronizing or actually
in synch with a bouncing signal. The averaging is missing on the digital
instrument. Use a strobe on a rotating part and when it is in synch the mark
on the engine is always at the top. In reality it is turning and all the way
around but the sampling give a false impression that the mark is always at
the top. This is analogous to some of the simpler errors on a digital meter.

"Know your instruments"

Analog meter movements have inertia and mechanical resonance issues
too. Neither type is reliably accurate for rapidly varying signals,
they just fail differently. The right method is to capture the signal
on a digital storage scope and read the signal level at the point you
want with the cursor, or calculate RMS or whatever with the math
functions.

I've got a nice 1 Gig HP, but a PC sound card can be hacked into an
audio frequency digital storage scope if you need one and have more
time than money:
http://www.zeitnitz.de/Christian/scope_en

If you add a level shifter you can inject the signal after the input
blocking cap and make it read down to DC.

jsw



I once worked with an analog meter with mirror scale that was huge. I
don't remember exactly how large it was but it sure was easy to read.
It had to be at least 10 inches across the scale face.

John

On 2011-03-17, Josepi J.R.M wrote:
"DoN. Nichols" wrote in message
...

Build in a shunt to give 50 mV (common shut output voltage to
meter movements), amplify that with one op-amp to get enough voltage to
make the amplified rectifier work with minimal distortion.

I don't think you understand. The diodes are inside the meters under
calibration and are injected with up to a 200 ampere current. 40 diode
junction drops distorts the crap out of the current (I) waveform. You would
need a precision rectifier circuit with a 200 ampere output and it usually
consumes about 3 kVA...LOL

I was thinking in terms of a shunt in *place* of the meter --
200 A and 50 mV equals 250 mOhms -- and a maximum dissipation of 10 kVA.
Make the shunt a permanent part of the circuit.

Take the signal from that shunt, amplify it with one op-amp, and
then use a precision rectifier circuit to convert that to a DC drive for
whatever kind of meter you want -- analog or digital.

Your 40 diode drops suggests that you are measuring the voltage,
not the current -- or you are measuring both in a wattmeter. If that is
the case, a few more op amps -- to scale the voltage and to multiply the
processed voltage reading by the processed current reading. Or -- if
you are after instantaneous power, don't convert to DC at all -- but
your analog meters aren't going to give you that either.

If you aren't familiar with the precision rectifier circuit(s),
here is a nice discussion of them:

http://sound.westhost.com/appnotes/an001.htm

Granted, it's (the web site's) focus is audio applications, but
that should not matter here. Anything good enough for audio bandwidths
is more than sufficient for whatever distortion is likely in power
applications (unless you are running wired wireless on top of the power
line. :-)

Enjoy,
DoN.

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On 2011-03-17, Michael A. Terrell wrote:

Josepi wrote:

Digital meters are not good for indicating fast changing signals.

They can be 50% out at times.


What kind of crap do you use?

Note that he said "fast changing".

It is more a question of how fast is the signal changing.
Remember that most digital meters measure AC by sampling at a specific
point in time (often timed to match the power line frequency), or by
integrating over a full cycle to get an approximation of RMS. If the
signal is changing more rapidly than that (including significant
distortion levels), your readings can be quite far out. Digital is not
a magic cure-all. It gives more resolution more quickly than analog
meters -- or things like the really old Fluke differential voltmeters,
where you dial in decade voltage steps to balance out the signal under
test (for DC signals only -- lots of precision, but *very* slow.) And
actually -- early digital voltmeters (e.g. the NLS brand ones which I
described in another post in this thread) were an attempt to automate
this nulling process.

Enjoy,
DoN.

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In article ,
John wrote:

I once worked with an analog meter with mirror scale that was huge. I
don't remember exactly how large it was but it sure was easy to read.
It had to be at least 10 inches across the scale face.

John

I used to have a lovely ammeter with a low-mass needle - there was a
mirror on the sensing coil, and a light beam was projected onto it and
reflected to be the "needle". The scale was a good 8 inches across. By
the time I was using it it was a historical oddity, but I suspect it was
a very significant purchase when it was new.

--
Cats, coffee, chocolate...vices to live by

Michael A. Terrell wrote:
Lewis Hartswick wrote:
Josepi wrote:
The guys used to laugh when I would get out the old AVO analogue needle
meter, with the mirrored scale, from time to time but the digital ones
(with all their so-called accuracy) would get confused in certain
applications.

Anyone who ever had to tune a circuit for a peak or a null
should be on the analog meter side of that discussion.
Those GD blinking digits, you cant tell if the reading
is going up or down.


I've never seen a 4 1/2 digit analog equivalent, or an analog meter
that displays a .01 dB signal change.


And I've never had to "tune" a cicuit to anywhere near 0.1 percent
of max. So that argument is pure bull$hit.
...lew...

"DoN. Nichols" wrote:

On 2011-03-17, Michael A. Terrell wrote:

Josepi wrote:

Digital meters are not good for indicating fast changing signals.

They can be 50% out at times.


What kind of crap do you use?

Note that he said "fast changing".


Then he needs a true RMS voltmeter that integrates the input before
reading the level. Something like the Fluke 8920A or a Boonton 9200
digital RF milivoltmeter, instead of a $4 meter from Harbor Freight.

The Fluke is good to 20 MHz and the boonton is good from 10 MHz into
the GHz range.


It is more a question of how fast is the signal changing.
Remember that most digital meters measure AC by sampling at a specific
point in time (often timed to match the power line frequency), or by
integrating over a full cycle to get an approximation of RMS. If the
signal is changing more rapidly than that (including significant
distortion levels), your readings can be quite far out. Digital is not
a magic cure-all. It gives more resolution more quickly than analog
meters -- or things like the really old Fluke differential voltmeters,
where you dial in decade voltage steps to balance out the signal under
test (for DC signals only -- lots of precision, but *very* slow.) And
actually -- early digital voltmeters (e.g. the NLS brand ones which I
described in another post in this thread) were an attempt to automate
this nulling process.


I have a rack mount Fluke differential meter I picked up for parts.
Days that it is useful on a production bench are long past.


--
You can't fix stupid. You can't even put a Band-Aid™ on it, because it's
Teflon coated.

Lewis Hartswick wrote:

Michael A. Terrell wrote:
Lewis Hartswick wrote:
Josepi wrote:
The guys used to laugh when I would get out the old AVO analogue needle
meter, with the mirrored scale, from time to time but the digital ones
(with all their so-called accuracy) would get confused in certain
applications.

Anyone who ever had to tune a circuit for a peak or a null
should be on the analog meter side of that discussion.
Those GD blinking digits, you cant tell if the reading
is going up or down.


I've never seen a 4 1/2 digit analog equivalent, or an analog meter
that displays a .01 dB signal change.


And I've never had to "tune" a cicuit to anywhere near 0.1 percent
of max. So that argument is pure bull$hit.


To you. I did it daily for over four years. I worked on telemetry
receivers that sold for $20,000 to $80,000. I've seen specs that tight
on a lot of broadcast TV gear as well. If you've never worked on gear
with those specs, then your opinion is pure bull****.

--
You can't fix stupid. You can't even put a Band-Aid™ on it, because it's
Teflon coated.

On 2011-03-18, John wrote:

[ ... ]

I once worked with an analog meter with mirror scale that was huge. I
don't remember exactly how large it was but it sure was easy to read.
It had to be at least 10 inches across the scale face.

I've got an interesting one which is a 360 degree scale with
mirror. It measures phase angle in line power voltage vs current. Came
from a hamfest last summer. Nice if you are trying to tune a rotary
converter for minimum current drain -- and checking the difference
between the converter loaded and unloaded.

Not much use for most people, but for hobby metalworkers
generating three phase from single phase -- a nice instrument.

Probably about 11" diameter for the mirrored part (without going
downstairs to measure it. :-)

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--- Black Holes are where God is dividing by zero ---

Michael A. Terrell wrote:
Lewis Hartswick wrote:
Michael A. Terrell wrote:
Lewis Hartswick wrote:
Josepi wrote:
The guys used to laugh when I would get out the old AVO analogue
needle meter, with the mirrored scale, from time to time but the
digital ones (with all their so-called accuracy) would get confused
in certain applications.

Anyone who ever had to tune a circuit for a peak or a null
should be on the analog meter side of that discussion.
Those GD blinking digits, you cant tell if the reading
is going up or down.

I've never seen a 4 1/2 digit analog equivalent, or an analog meter
that displays a .01 dB signal change.

And I've never had to "tune" a cicuit to anywhere near 0.1 percent
of max. So that argument is pure bull$hit.

To you. I did it daily for over four years. I worked on telemetry
receivers that sold for $20,000 to $80,000. I've seen specs that tight
on a lot of broadcast TV gear as well. If you've never worked on gear
with those specs, then your opinion is pure bull****.

I once had a temp job as an "assembler" (at assembler pay), and they
found out that I'm really a techie, so they had me calibrating their
instruments (called a "Stimulus Unit") to within a microvolt. When I
fired up a new unit, I had time go go out for a smoke while I waited
for it to warm up and stabilize. This was only volts out of a 24-bit
DAC, but I'd think that the same principles apply.

Cheers!
Rich

Jim Wilkins wrote:

On Mar 14, 4:46*pm, Winston wrote:
...
Did you mean 'thermally capacitive' in that the resistance
change of the filament lags the voltage change across it?

--Winston-

No, I meant it in the way that black is white, war is peace and I love
Big Brother.

jsw

Impersonating Jim is doubleplusungood.

Wes
--
"Additionally as a security officer, I carry a gun to protect
government officials but my life isn't worth protecting at home
in their eyes." Dick Anthony Heller

Wes wrote:
Jim wrote:

On Mar 14, 4:46 pm, wrote:
...
Did you mean 'thermally capacitive' in that the resistance
change of the filament lags the voltage change across it?

--Winston-

No, I meant it in the way that black is white, war is peace and I love
Big Brother.

jsw

Impersonating Jim is doubleplusungood.

Careful Wes,

Impersonator minitrue?

--Winston

"Rich Grise" wrote in message
...

Josepi wrote:

The point was in certain applications the digital meter can have all the
digits you want but when they are out by 20 or 50% of the reading
sometimes the analogue meters did a better job.

This is usually a problem with digital updates not syncronizing or
actually in synch with a bouncing signal. The averaging is missing on the
digital instrument. Use a strobe on a rotating part and when it is in
synch the mark on the engine is always at the top. In reality it is
turning and all the way around but the sampling give a false impression
that the mark is always at the top. This is analogous to some of the
simpler errors on a digital meter.

Or the wagon wheels turning backwards in the old westerns. ;-)

Cheers!
Rich


Reply:

Known as Aliasing. I used to do Digital Signal Processing, and one of the
things you had to be aware of.