Measuring Current

J

Jim Douglas

Guest
I currently have one nice digital VOM. So I measure voltage, then current,
back and forth having to move the cable each time, which sucks. I want a
stand-alone ammeter that I can quickly place within a circuit, I think. I
would rather not purchase another meter just to measure current and am
thinking that this might be something easy to build but didn't find alot
searching so far.

Do you guy's use a separate amp meter for this stuff? I am just a hobbyist
that likes playing around with things. One goal is to eventually build a SW
transmitter. Should I try to purchase, build? I would prefer building. I am
thinking I would like to be able to measure down to the microampere range.

Thanks for any input!

--



Jim Douglas
www.genesis-software.com
Carrollton, TX USA 75006
Latitude 32.9616
Longitude 96.8916
 
Suggest checking into the Amateur News Groups regarding additional
information regarding home brew radio transmitting and receiving equipment.
S.A. rec.radio.amateur.homebrew, etc. Most of the equipment I've worked,
repaired, etc have an actual separate ammeter (milliamp meter).
"Jim Douglas" <james.douglas@genesis-software.com> wrote in message
news:9_idnYKM8aTDZGbcRVn-sg@comcast.com...
I currently have one nice digital VOM. So I measure voltage, then current,
back and forth having to move the cable each time, which sucks. I want a
stand-alone ammeter that I can quickly place within a circuit, I think.
I
would rather not purchase another meter just to measure current and am
thinking that this might be something easy to build but didn't find alot
searching so far.

Do you guy's use a separate amp meter for this stuff? I am just a hobbyist
that likes playing around with things. One goal is to eventually build a
SW
transmitter. Should I try to purchase, build? I would prefer building. I
am
thinking I would like to be able to measure down to the microampere range.

Thanks for any input!

--



Jim Douglas
www.genesis-software.com
Carrollton, TX USA 75006
Latitude 32.9616
Longitude 96.8916
Click to expand...
 
I read in sci.electronics.design that Jim Douglas
<james.douglas@genesis-software.com> wrote (in <9_idnYKM8aTDZGbcRVn-
sg@comcast.com>) about 'Measuring Current', on Sat, 29 Jan 2005:

I want a stand-alone ammeter that I can quickly place within a circuit,
I think. I would rather not purchase another meter just to measure
current and am thinking that this might be something easy to build but
didn't find alot searching so far.
Click to expand...
An analogue ammeter with a decent milliammeter movement is costly, and
you have to hand-craft the shunts. You could buy a bare digital panel
meter module, which will make an ammeter with 200 mV drop at full scale
on all ranges. This could cost less and be easier to make.

If it were me, I'd buy another inexpensive digital multimeter.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
 
Jim Douglas wrote:
I currently have one nice digital VOM. So I measure voltage, then current,
back and forth having to move the cable each time, which sucks. I want a
stand-alone ammeter that I can quickly place within a circuit, I think. I
would rather not purchase another meter just to measure current and am
thinking that this might be something easy to build but didn't find alot
searching so far.

Do you guy's use a separate amp meter for this stuff? I am just a hobbyist
that likes playing around with things. One goal is to eventually build a SW
transmitter. Should I try to purchase, build? I would prefer building. I am
thinking I would like to be able to measure down to the microampere range.

Thanks for any input!

I agree with the other posters that it would probably be cheaper to buy
Click to expand...
another multimeter. However, I would add that your desire to measure in
the microampere range is probably wishful thinking. The equipment and
techniques involved in _accurately_ dealing in those ranges are, IMHO,
beyond what those of what you're likely to encounter in a typical
hobbyist setup.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form che...@prodigy.net.
 
Thanks for all the good input. I will be picking up another VOM for my
current measurements.

"Jim Douglas" <james.douglas@genesis-software.com> wrote in message
news:9_idnYKM8aTDZGbcRVn-sg@comcast.com...
I currently have one nice digital VOM. So I measure voltage, then current,
back and forth having to move the cable each time, which sucks. I want a
stand-alone ammeter that I can quickly place within a circuit, I think.
I
would rather not purchase another meter just to measure current and am
thinking that this might be something easy to build but didn't find alot
searching so far.

Do you guy's use a separate amp meter for this stuff? I am just a hobbyist
that likes playing around with things. One goal is to eventually build a
SW
transmitter. Should I try to purchase, build? I would prefer building. I
am
thinking I would like to be able to measure down to the microampere range.

Thanks for any input!

--



Jim Douglas
www.genesis-software.com
Carrollton, TX USA 75006
Latitude 32.9616
Longitude 96.8916
Click to expand...
 
"Jim Douglas" <james.douglas@genesis-software.com> wrote in message
news:9_idnYKM8aTDZGbcRVn-sg@comcast.com...
I currently have one nice digital VOM. So I measure voltage, then current,
back and forth having to move the cable each time, which sucks. I want a
stand-alone ammeter that I can quickly place within a circuit, I think.
I
would rather not purchase another meter just to measure current and am
thinking that this might be something easy to build but didn't find alot
searching so far.

Do you guy's use a separate amp meter for this stuff? I am just a
hobbyist
that likes playing around with things. One goal is to eventually build a
SW
transmitter. Should I try to purchase, build? I would prefer building. I
am
thinking I would like to be able to measure down to the microampere
range.

Thanks for any input!

--



Jim Douglas
www.genesis-software.com
Carrollton, TX USA 75006
Latitude 32.9616
Longitude 96.8916
Click to expand...

Hi, Jim -

For my current measurements, I bought an HP 428B (toob-type) off Ebay and
repaired it. The reason I wanted it was so I would not have to break
connections to measure current. Of course, one must have enough slack in
the wire to allow inserting the clamp-on probe.

Just an idea. Good luck.

John
(kes is not required)
 
On Tue, 1 Feb 2005 00:36:54 -0000, the renowned "Jim Douglas"
<james.douglas@genesis-software.com> wrote:

I saw some of those on Ebay today, It seems to have a scope type thing that
simply wraps around a wire??
Click to expand...
Like these ones I put up (these particular ones are sold)?

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=3870013201&ssPageName=STRK:MESO:IT
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=3867723467&ssPageName=STRK:MESO:IT

The clamp opens up and you can put it round the wire. They are *not*
for small currents-- scores of mA up to hundreds of A, depending.

If you put multiple wires through the core (like an AC line cord) they
will read about zero, unless there is a fault to ground, as they read
the difference between the two currents.

They are great for working on power stuff- you can poke around in a
panel and check motor currents etc., but for electronics you really
want some DVMs.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
 
On Sun, 30 Jan 2005 20:53:16 +0000, Ian Stirling wrote:

In sci.electronics.design CJT <abujlehc@prodigy.net> wrote:
snip
I agree with the other posters that it would probably be cheaper to buy
another multimeter. However, I would add that your desire to measure in
the microampere range is probably wishful thinking. The equipment and
techniques involved in _accurately_ dealing in those ranges are, IMHO,
beyond what those of what you're likely to encounter in a typical
hobbyist setup.

I've found common multimeters fairly accurate for measuring very small
currents.
The typical 1Mohm input resistance at 200mV full-scale drops 200nA.
(when I checked it, it seemed to be accurate).
Even my cheap $4(us) meter has a 200uA range.
Click to expand...
It's still a PITA to break the circuit to interpose the meter. If it's
something that I'll want to read the current for calibration or something,
I just put a 0R1 or 0R01 resistor in the circuit, and measure its voltage
drop.

I've also seen that technique used to increase the range of 0-1 or 1-0-1
milliammeters - a 1K resistor turns it into a 1K ohm/volt voltmeter - and
you measure the drop across the shunt. Much easier than trying to match a
shunt to a given meter's internal resistance.

Cheers!
Rich
 
Ian Stirling wrote:
In sci.electronics.design CJT <abujlehc@prodigy.net> wrote:
snip
I agree with the other posters that it would probably be cheaper to buy
another multimeter. However, I would add that your desire to measure in
the microampere range is probably wishful thinking. The equipment and
techniques involved in _accurately_ dealing in those ranges are, IMHO,
beyond what those of what you're likely to encounter in a typical
hobbyist setup.

I've found common multimeters fairly accurate for measuring very small
currents.
The typical 1Mohm input resistance at 200mV full-scale drops 200nA.
(when I checked it, it seemed to be accurate).
Even my cheap $4(us) meter has a 200uA range.
Click to expand...
Err...most DVMs have a 10Meg input resistance, not 1Meg.
However, one can use a resistive shunt (previously suggested) and
measure the voltage across it (to 200mV full scale).
 
On 31 Jan 2005 11:26:06 GMT, the renowned Ian Stirling
<root@mauve.demon.co.uk> wrote:

In sci.electronics.design Spehro Pefhany <speffSNIP@interlogdotyou.knowwhat> wrote:
On Tue, 1 Feb 2005 00:36:54 -0000, the renowned "Jim Douglas"
james.douglas@genesis-software.com> wrote:

I saw some of those on Ebay today, It seems to have a scope type thing that
simply wraps around a wire??
snip
If you put multiple wires through the core (like an AC line cord) they
will read about zero, unless there is a fault to ground, as they read
the difference between the two currents.

Though there exist probes like this that using some assumptions about the
geometry of the wire, and several sensors closely spaced arouind the
cord, can actually measure the current flowing through a balanced conductor.
Click to expand...
Is it possible to make a hand-held probe to do this?


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
 
In sci.electronics.design Spehro Pefhany <speffSNIP@interlogdotyou.knowwhat> wrote:
On 31 Jan 2005 11:26:06 GMT, the renowned Ian Stirling
root@mauve.demon.co.uk> wrote:

In sci.electronics.design Spehro Pefhany <speffSNIP@interlogdotyou.knowwhat> wrote:
On Tue, 1 Feb 2005 00:36:54 -0000, the renowned "Jim Douglas"
james.douglas@genesis-software.com> wrote:

I saw some of those on Ebay today, It seems to have a scope type thing that
simply wraps around a wire??
snip
If you put multiple wires through the core (like an AC line cord) they
will read about zero, unless there is a fault to ground, as they read
the difference between the two currents.

Though there exist probes like this that using some assumptions about the
geometry of the wire, and several sensors closely spaced arouind the
cord, can actually measure the current flowing through a balanced conductor.

Is it possible to make a hand-held probe to do this?
Click to expand...
AIUI, the probe that I referred to was 'just' another clamp-on probe,
for attachment for the meter of your choice.
Sorry, I don't recall when.
It was probably on sci.electronics, on a thread I was involved in.
"ian stirling" multiple current wire hall
may or may not turn up something on google.
 
I saw some of those on Ebay today, It seems to have a scope type thing that
simply wraps around a wire??
Are they pretty accurate, is the HP a tube based product?

"John Smith" <kd5yikes@mindspring.com> wrote in message
news:cth937024ca@enews4.newsguy.com...
"Jim Douglas" <james.douglas@genesis-software.com> wrote in message
news:9_idnYKM8aTDZGbcRVn-sg@comcast.com...
I currently have one nice digital VOM. So I measure voltage, then
current,
back and forth having to move the cable each time, which sucks. I want
a
stand-alone ammeter that I can quickly place within a circuit, I think.
I
would rather not purchase another meter just to measure current and am
thinking that this might be something easy to build but didn't find alot
searching so far.

Do you guy's use a separate amp meter for this stuff? I am just a
hobbyist
that likes playing around with things. One goal is to eventually build a
SW
transmitter. Should I try to purchase, build? I would prefer building. I
am
thinking I would like to be able to measure down to the microampere
range.

Thanks for any input!

--



Jim Douglas
www.genesis-software.com
Carrollton, TX USA 75006
Latitude 32.9616
Longitude 96.8916


Hi, Jim -

For my current measurements, I bought an HP 428B (toob-type) off Ebay and
repaired it. The reason I wanted it was so I would not have to break
connections to measure current. Of course, one must have enough slack in
the wire to allow inserting the clamp-on probe.

Just an idea. Good luck.

John
(kes is not required)
Click to expand...
 
"Spehro Pefhany" <speffSNIP@interlogDOTyou.knowwhat> wrote in message
news:7p1rv0ldima0oiov4k16gd97vbhj913gqj@4ax.com...
On Tue, 1 Feb 2005 00:36:54 -0000, the renowned "Jim Douglas"
james.douglas@genesis-software.com> wrote:

I saw some of those on Ebay today, It seems to have a scope type thing
that
simply wraps around a wire??

Like these ones I put up (these particular ones are sold)?

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=3870013201&ssPageName=STRK:MESO:IT
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=3867723467&ssPageName=STRK:MESO:IT

The clamp opens up and you can put it round the wire. They are *not*
for small currents-- scores of mA up to hundreds of A, depending.

If you put multiple wires through the core (like an AC line cord) they
will read about zero, unless there is a fault to ground, as they read
the difference between the two currents.

They are great for working on power stuff- you can poke around in a
panel and check motor currents etc., but for electronics you really
want some DVMs.


Best regards,
Spehro Pefhany
Click to expand...

No, the listings you referred to are not the HP428 DC current meters that
were mentioned previously. The HP428 meter uses a small clamp-on probe that
saves the user from having to open the circuit to measure current. The
HP428 meter has full-scale ranges from 1ma to 10A. Yes, these are vacuum
tube models, but easy to maintain and use. Well worth what you'll pay on
Ebay for these meters if you need to measure small currents without breaking
the circuit to insert a current meter.
They are not the hallmark of accuracy when compared to the digital
instruments of today's technology; +/- 3% full scale on every range, but
will absolutely get the job done.

The probes are not hall-effect sensors, but are esentially small
transformers that are excited by a 40 Khz signal. The output of the
transformer is modulated by the change in core saturation caused by the DC
current being measured. You can see great pictures of the meter and probe
at
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=25411&item=3866525538&rd=1
(for the next couple of weeks anyway).

--
Dave M
MasonDG44 at comcast dot net (Just subsitute the appropriate characters in
the address)

Never take a laxative and a sleeping pill at the same time!!
 
On Mon, 31 Jan 2005 08:17:07 -0500 Spehro Pefhany
<speffSNIP@interlogDOTyou.knowwhat> wrote:

On 31 Jan 2005 11:26:06 GMT, the renowned Ian Stirling
root@mauve.demon.co.uk> wrote:

Though there exist probes like this that using some assumptions about the
geometry of the wire, and several sensors closely spaced arouind the
cord, can actually measure the current flowing through a balanced conductor.

Is it possible to make a hand-held probe to do this?
Click to expand...
I've seen the ad, but I don't think it was particularly "hand held."
We decided that the instrument had to make certain assumptions about
the geometry of the cable you put in there. Or maybe you had to tell
it about the geometry.

In any case, I don't think they made any claims of being able to
measure balanced currents in coax.

-
-----------------------------------------------
Jim Adney jadney@vwtype3.org
Madison, WI 53711 USA
-----------------------------------------------
 
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