Maker Pro
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100ua panel meters

A

amdx

Jan 1, 1970
0
I'm looking for two 100 ua meters (50 au is ok). I'd like the size to be no
larger than 2 1/4", smaller is better, round, square, or rectangle I don't
care.
I want to pay less than $12.00 ea. Surplus is good. I slogged through 60
google hits without success.
Any thoughts?
Mike
 
A

Al

Jan 1, 1970
0
I'm looking for two 100 ua meters (50 au is ok). I'd like the size to be
no larger than 2 1/4", smaller is better, round, square, or rectangle I
don't care.
I want to pay less than $12.00 ea. Surplus is good. I slogged through 60
google hits without success.
Any thoughts?
Mike

If you're in the Boston area, go to the MIT Flea Market which is held on
the third Sunday of each month. There is a guy there who has zillions of
meters for sale. I bought one a while back and it was good.

Al
 
A

amdx

Jan 1, 1970
0
Robert Baer said:
The problem is that there are almost no meters available at that price.
Relax the specs to any surplus meter in that price *range* .OR. similar
in a surplus POJ that you can dismantle.
Thenput an opamp around it for the desired sensitivity(ies).

Thanks Robert, but actually there are a lot of meters available under
$12.00.
I'm just haveing trouble finding a meter smaller than 2-1/4"
When I get the meters I want, I'll add resistors to make one a 60 volt FS
meter
and the other a 200 amp FS meter.
I'm also looking into these digital meters to see if I can modify the
current shunt
so it will measure higher current.
http://www.astroflight.com/index.php?main_page=index&cPath=2
Mike
 
A

amdx

Jan 1, 1970
0
DaveM said:
I sent an email to BGMicro and ask about the internal resistance of this
50ua meter.

http://www.bgmicro.com/index.asp?PageAction=VIEWPROD&ProdID=10969

I got a response that it is 1.95K ohms. That would mean (1,950 x .0005= .975
volts).
So, the meter is 1 volt FS. Does 1,950 ohms seem right? If I tried to use
that as a 200 amp meter, I would need a .005 ohm 200 watt resistor.
I guess I need a 50mv or 100mv meter.
Mike
 
A

amdx

Jan 1, 1970
0
DaveM said:
Nope.. you missed the decimal point placement in your math. 50 uA is
0.00005 A.
The meter would drop 0.0975V, making the 20A shunt 0.0005 ohms @ approx
50W
--

Thanks Dave, That makes a whole lot more sense. I need to look back
I think I did that same mistake on some other calculations.
And then also note; it's a 200 amp meter, so .0975V / 200A=.0005 ohms.
Then .975V x 200A= 20Watts. A 20 watt shunt will work.
Thanks again, Mike
Hope I'm right this time :)
 
R

Rich Grise

Jan 1, 1970
0
I sent an email to BGMicro and ask about the internal resistance of this
50ua meter.

http://www.bgmicro.com/index.asp?PageAction=VIEWPROD&ProdID=10969

I got a response that it is 1.95K ohms. That would mean (1,950 x .0005= .975
volts).
So, the meter is 1 volt FS. Does 1,950 ohms seem right? If I tried to use
that as a 200 amp meter, I would need a .005 ohm 200 watt resistor.
I guess I need a 50mv or 100mv meter.

(Just noticed you screwed up your arithmetic -= 50 uA is .00005 ;-)

You can determine the internal resistance by experiment. Since it's a 50
uA meter, put a resistor in series that with your power supply provides
50 uA (20K/1V,100K/5v, etc), and adjust it for full-scale. Then, put
another pot (maybe 10K) in parallel with the meter, and adjust it until
the meter shows exactly half-scale. Dismantle your setup, and measure
the resistance of the pot. That will be equal to the meter's internal
resistance (they're in parallel, so half the current each, right?) :)

As I mentioned, you can make a voltmeter out of an ammeter, but it makes
more sense to just get a current shunt; yes, they make .005 ohm 200 watt
"resistors" - they're a calibrated brass bar between two brass terminals
mounted on some nonconductive plate, with separate connections for volts
and amps:
http://www.deltecco.com/catalog.html#Shunts

It says 50 mV - Hmm - when I check your math, I get 97.5 mV - you'd have
to get a 100 mV shunt, or put two in series (at probably $20 a pop!), then
add a little series resistance to bring up your meter to 100 mV FS.

Have Fun!
Rich
 

neon

Oct 21, 2006
1,325
Joined
Oct 21, 2006
Messages
1,325
harbor frreeight has meters on sale digital for $2.99 4 digit the display is less in size that you require.
 
A

amdx

Jan 1, 1970
0
Rich Grise said:
(Just noticed you screwed up your arithmetic -= 50 uA is .00005 ;-)

You can determine the internal resistance by experiment.

Yea, thanks Rich.
I can do all that but I don't have the meters and I'm trying to purchase
the one I can make work with my first purchase.
As I mentioned, you can make a voltmeter out of an ammeter, but it makes
more sense to just get a current shunt; yes, they make .005 ohm 200 watt
"resistors" - they're a calibrated brass bar between two brass terminals
mounted on some nonconductive plate, with separate connections for volts
and amps:
http://www.deltecco.com/catalog.html#Shunts
It seems I only need a 20 Watt shunt if I use a 100 mv meter.
It says 50 mV - Hmm - when I check your math, I get 97.5 mV - you'd have
to get a 100 mV shunt, or put two in series (at probably $20 a pop!), then
add a little series resistance to bring up your meter to 100 mV FS.
I'm not sure what it is you're saying is 50mv, if it's the meter
referenced then it is 50ua.
BGMicro has some shunts for $7.95.

Thanks, Mike
 
R

Rich Grise

Jan 1, 1970
0
Yea, thanks Rich.
I can do all that but I don't have the meters and I'm trying to purchase
the one I can make work with my first purchase.
It seems I only need a 20 Watt shunt if I use a 100 mv meter.

I'm not sure what it is you're saying is 50mv, if it's the meter
referenced then it is 50ua.
BGMicro has some shunts for $7.95.
When I said, "It says 50 mV", I was referring to the web page of that
shunt - I'm usre they come in different values (i,e, you could get
one that's 100mV/200A), And to turn a 50uA meter into a 0-100 mV meter,
you'd need a total series resistance of 2K, which if your meter is really
1,950 ohms, then you'd need 50 ohms in series with it. You can get
49.9 ohm precision resistors at any distributor - heh - just looked up
precision resistors - 2X 100K in parallel should be dandy. :)

Cheers!
Rich
 
A

amdx

Jan 1, 1970
0
Rich Grise said:
When I said, "It says 50 mV", I was referring to the web page of that
shunt - I'm usre they come in different values (i,e, you could get
one that's 100mV/200A), And to turn a 50uA meter into a 0-100 mV meter,
you'd need a total series resistance of 2K, which if your meter is really
1,950 ohms, then you'd need 50 ohms in series with it. You can get
49.9 ohm precision resistors at any distributor - heh - just looked up
precision resistors - 2X 100K in parallel should be dandy. :)

Cheers!
Rich
So Rich, heard any good jokes, I've always enjoyed your humor.
You haven't been here as much lately, are you busy earning capital
to pay your share of the bailout.
Mike
 
R

Richard The Dreaded Libertarian

Jan 1, 1970
0
So Rich, heard any good jokes, I've always enjoyed your humor.
You haven't been here as much lately, are you busy earning capital
to pay your share of the bailout.
I've been gettting tired of the political crap - there's the leftist
socialists (communists) and the "right"-ist socialists, aka fascists.

The people's socialists want to take your money to pay the bills of
the lazy and negligent poor people, and the national socialists want
to take your money to pay the bills of the lazy and negligent rich
people.

Either way, the country's going down the toilet - I'm just going to
hang on to my jewels, and hope to enjoy the ride as I watch the card
house come collapsing down around me. ;-)

Cheers!
Rich
 

neon

Oct 21, 2006
1,325
Joined
Oct 21, 2006
Messages
1,325
All analog meters are current reading devices usualy 50ua but with the proper outside influence they can be made to read volts ,ohms, beta, I forward, current and/or ac/dc. AND MORE
 
J

JosephKK

Jan 1, 1970
0
I'm looking for two 100 ua meters (50 au is ok). I'd like the size to be no
larger than 2 1/4", smaller is better, round, square, or rectangle I don't
care.
I want to pay less than $12.00 ea. Surplus is good. I slogged through 60
google hits without success.
Any thoughts?
Mike

Hmmm. That is 10 K per volt. Perhaps you could live with either 100
k per volt (10uA) or 1 k per volt (1 mA) full scale movements. A
small circuit change could accommodate either.
 
J

JosephKK

Jan 1, 1970
0
I sent an email to BGMicro and ask about the internal resistance of this
50ua meter.

http://www.bgmicro.com/index.asp?PageAction=VIEWPROD&ProdID=10969

I got a response that it is 1.95K ohms. That would mean (1,950 x .0005= .975
volts).
So, the meter is 1 volt FS. Does 1,950 ohms seem right? If I tried to use
that as a 200 amp meter, I would need a .005 ohm 200 watt resistor.
I guess I need a 50mv or 100mv meter.
Mike

What actually determines deflection (in d'Arsonval and taut band
movements) is current, it is a physics thing. Is the current you are
trying to measure AC or DC, it makes some differences.
 
J

JosephKK

Jan 1, 1970
0
Thanks Robert, but actually there are a lot of meters available under
$12.00.
I'm just haveing trouble finding a meter smaller than 2-1/4"
When I get the meters I want, I'll add resistors to make one a 60 volt FS
meter
and the other a 200 amp FS meter.
I'm also looking into these digital meters to see if I can modify the
current shunt
so it will measure higher current.
http://www.astroflight.com/index.php?main_page=index&cPath=2
Mike

If you had said so in the first place you would have gotten much
better results.
 
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