Ammeter
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Posts: 46,084
Has anyone made a DC ammeter out of a Stamp? It must be fairly simple, since
you can purchase a small digital DMM with this feature for $20....I'd like
to display the reading on an LCD.
Perhaps I should be asking if anyone knows how digital DMM's accomplish
this.....
Chris
you can purchase a small digital DMM with this feature for $20....I'd like
to display the reading on an LCD.
Perhaps I should be asking if anyone knows how digital DMM's accomplish
this.....
Chris
Comments
law. By putting resistors in various types of series and parallel
combinations, different kinds of voltages and currents can be read with
accuracy.
regards,
Leroy
"Chris Loiacono (E-mail)" wrote:
>
> Has anyone made a DC ammeter out of a Stamp? It must be fairly simple, since
> you can purchase a small digital DMM with this feature for $20....I'd like
> to display the reading on an LCD.
> Perhaps I should be asking if anyone knows how digital DMM's accomplish
> this.....
>
> Chris
>
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Original Message
From: "Leroy Hall" <leroy@f...>
To: <basicstamps@yahoogroups.com>
Sent: Saturday, September 01, 2001 10:43
Subject: Re: [noparse][[/noparse]basicstamps] Ammeter
> Volt / Amp meters are made with D/A converters and applications of Ohm's
> law. By putting resistors in various types of series and parallel
> combinations, different kinds of voltages and currents can be read with
> accuracy.
>
>
> regards,
>
> Leroy
>
> "Chris Loiacono (E-mail)" wrote:
> >
> > Has anyone made a DC ammeter out of a Stamp? It must be fairly simple,
since
> > you can purchase a small digital DMM with this feature for $20....I'd
like
> > to display the reading on an LCD.
> > Perhaps I should be asking if anyone knows how digital DMM's accomplish
> > this.....
> >
> > Chris
> >
> > To UNSUBSCRIBE, just send mail to:
> > basicstamps-unsubscribe@yahoogroups.com
> > from the same email address that you subscribed. Text in the Subject
and Body of the message will be ignored.
> >
> >
> > Your use of Yahoo! Groups is subject to
http://docs.yahoo.com/info/terms/
>
>
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>
>
>
Thanks for the correction.. BTW I am getting ready to teach a 7 week
class on BASIC DC in Milford, Ohio if you would like to learn all the
details of how to make a Voltmeter. (I mean the original creator of this
post)
Leroy
"Frizz Braun Jr." wrote:
>
> You must mean A/D and NOT D/A?
>
>
Original Message
> From: "Leroy Hall" <leroy@f...>
> To: <basicstamps@yahoogroups.com>
> Sent: Saturday, September 01, 2001 10:43
> Subject: Re: [noparse][[/noparse]basicstamps] Ammeter
>
> > Volt / Amp meters are made with D/A converters and applications of Ohm's
> > law. By putting resistors in various types of series and parallel
> > combinations, different kinds of voltages and currents can be read with
> > accuracy.
> >
> >
> > regards,
> >
> > Leroy
> >
> > "Chris Loiacono (E-mail)" wrote:
> > >
> > > Has anyone made a DC ammeter out of a Stamp? It must be fairly simple,
> since
> > > you can purchase a small digital DMM with this feature for $20....I'd
> like
> > > to display the reading on an LCD.
> > > Perhaps I should be asking if anyone knows how digital DMM's accomplish
> > > this.....
> > >
> > > Chris
> > >
> > > To UNSUBSCRIBE, just send mail to:
> > > basicstamps-unsubscribe@yahoogroups.com
> > > from the same email address that you subscribed. Text in the Subject
> and Body of the message will be ignored.
> > >
> > >
> > > Your use of Yahoo! Groups is subject to
> http://docs.yahoo.com/info/terms/
> >
> >
> > To UNSUBSCRIBE, just send mail to:
> > basicstamps-unsubscribe@yahoogroups.com
> > from the same email address that you subscribed. Text in the Subject and
> Body of the message will be ignored.
> >
> >
> > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
> >
> >
> >
>
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millivolt output across its terminals which is in direct proportion to
the current passing through it. You can then take that millivolt
signal, amplify it some, and send it to an A/D converter to get a
digital reading.
Someone else here mentioned using some type of resistor network. I'm
not so sure that is what's done inside a DMM since a resistor network
would seem to me to actually take current away from the load.
An ammeter shunt is a two terminal device which is hooked in series
with the load, has negligible resistance, and produces a millivolt
output across its terminals. 100A Through the shunt may produce 100
millivolts (depending on what type of shunt it is). These are
commonly used in DC drive systems for current feedback to the
electronics which fires the SCR's. You can also use them to drive
panel meters directly. I'm not sure about part numbers or
manufacturers. I'm not even 100% sure that's how it's done inside a
DMM but I would imagine it's something similar.
--- In basicstamps@y..., "Chris Loiacono (E-mail)" <chris01@t...>
wrote:
> Has anyone made a DC ammeter out of a Stamp? It must be fairly
simple, since
> you can purchase a small digital DMM with this feature for
$20....I'd like
> to display the reading on an LCD.
> Perhaps I should be asking if anyone knows how digital DMM's
accomplish
> this.....
>
> Chris
resistance. Sometimes (like multimeters and automotive panel ammeters) they
have a built-in shunt. Others (like an instrument panel meter) use a remote
shunt.
Back in the dark ages of analog meters, you bought a meter movement of say
0-1 milivolts and used resistors to scale it accordingly for voltage. If you
wanted to measure 1 volt at full scale, you had two resistors in series with
the meter parallel to one resistor. The voltage drop across the whole thing
was 1 volt, but only 1 milivolt across the resistor the meter was tied to.
Kinda funny though, alot of DMM's no longer have a 2 amp or 10 amp current
scale -- most are 200 ma or so.
Original Message
> I believe a DMM uses what's called an ammeter shunt to produce a
> millivolt output across its terminals which is in direct proportion to
> the current passing through it. You can then take that millivolt
> signal, amplify it some, and send it to an A/D converter to get a
> digital reading.
>
> Someone else here mentioned using some type of resistor network. I'm
> not so sure that is what's done inside a DMM since a resistor network
> would seem to me to actually take current away from the load.
>
> An ammeter shunt is a two terminal device which is hooked in series
> with the load, has negligible resistance, and produces a millivolt
> output across its terminals. 100A Through the shunt may produce 100
> millivolts (depending on what type of shunt it is). These are
> commonly used in DC drive systems for current feedback to the
> electronics which fires the SCR's. You can also use them to drive
> panel meters directly. I'm not sure about part numbers or
> manufacturers. I'm not even 100% sure that's how it's done inside a
> DMM but I would imagine it's something similar.
"current sense" resistors - always in very small ohm values?
I'm still stuck on the principle that allows it to work on a wide variety of
voltages. Let's see, I would think that the same resistor would drop
different voltages in a 12 V loop than it would in a 24V loop, regardless of
the series-parallel circuit.....
> Yup. The meter measures a minute voltage drop across a *very*
> low known
> resistance. Sometimes (like multimeters and automotive panel
> ammeters) they
> have a built-in shunt. Others (like an instrument panel
> meter) use a remote
> shunt.
>
> Back in the dark ages of analog meters, you bought a meter
> movement of say
> 0-1 milivolts and used resistors to scale it accordingly for
> voltage. If you
> wanted to measure 1 volt at full scale, you had two resistors
> in series with
> the meter parallel to one resistor. The voltage drop across
> the whole thing
> was 1 volt, but only 1 milivolt across the resistor the meter
> was tied to.
>
> Kinda funny though, alot of DMM's no longer have a 2 amp or
> 10 amp current
> scale -- most are 200 ma or so.
resistor?
Leroy
GRINNING NOW
tbanez@h... wrote:
>
> I believe a DMM uses what's called an ammeter shunt to produce a
> millivolt output across its terminals which is in direct proportion to
> the current passing through it. You can then take that millivolt
> signal, amplify it some, and send it to an A/D converter to get a
> digital reading.
>
> Someone else here mentioned using some type of resistor network. I'm
> not so sure that is what's done inside a DMM since a resistor network
> would seem to me to actually take current away from the load.
>
> An ammeter shunt is a two terminal device which is hooked in series
> with the load, has negligible resistance, and produces a millivolt
> output across its terminals. 100A Through the shunt may produce 100
> millivolts (depending on what type of shunt it is). These are
> commonly used in DC drive systems for current feedback to the
> electronics which fires the SCR's. You can also use them to drive
> panel meters directly. I'm not sure about part numbers or
> manufacturers. I'm not even 100% sure that's how it's done inside a
> DMM but I would imagine it's something similar.
>
>
> --- In basicstamps@y..., "Chris Loiacono (E-mail)" <chris01@t...>
> wrote:
> > Has anyone made a DC ammeter out of a Stamp? It must be fairly
> simple, since
> > you can purchase a small digital DMM with this feature for
> $20....I'd like
> > to display the reading on an LCD.
> > Perhaps I should be asking if anyone knows how digital DMM's
> accomplish
> > this.....
> >
> > Chris
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and Body
of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
Doesn't matter series or parallel, a given current though a given
resistance produces a voltage to the equation that states Voltage equals
current times resistance (E=I*R) Therefore if a 1 amp of current is
flowing through a 1 ohm resistor I would expect to see 1 volt dropped
across that resistor. If we keep the resistance constant, we can change
one value and it will be mirrored in the other value. That is we can
read the voltage drop across a resistor and call it current. This why a
shunt works and also why it is usually a low resistance value.
Regards,
Leroy
"Chris Loiacono (E-mail)" wrote:
>
> That would make sense. Are these the resistors I see listed in catalogs as
> "current sense" resistors - always in very small ohm values?
>
> I'm still stuck on the principle that allows it to work on a wide variety of
> voltages. Let's see, I would think that the same resistor would drop
> different voltages in a 12 V loop than it would in a 24V loop, regardless of
> the series-parallel circuit.....
>
> > Yup. The meter measures a minute voltage drop across a *very*
> > low known
> > resistance. Sometimes (like multimeters and automotive panel
> > ammeters) they
> > have a built-in shunt. Others (like an instrument panel
> > meter) use a remote
> > shunt.
> >
> > Back in the dark ages of analog meters, you bought a meter
> > movement of say
> > 0-1 milivolts and used resistors to scale it accordingly for
> > voltage. If you
> > wanted to measure 1 volt at full scale, you had two resistors
> > in series with
> > the meter parallel to one resistor. The voltage drop across
> > the whole thing
> > was 1 volt, but only 1 milivolt across the resistor the meter
> > was tied to.
> >
> > Kinda funny though, alot of DMM's no longer have a 2 amp or
> > 10 amp current
> > scale -- most are 200 ma or so.
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and Body
of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
voltmeter connected across a shunt resistor.
Original Message
> That would make sense. Are these the resistors I see listed in catalogs as
> "current sense" resistors - always in very small ohm values?
>
> I'm still stuck on the principle that allows it to work on a wide variety
of
> voltages. Let's see, I would think that the same resistor would drop
> different voltages in a 12 V loop than it would in a 24V loop, regardless
of
> the series-parallel circuit.....
>
> > Yup. The meter measures a minute voltage drop across a *very*
> > low known
> > resistance. Sometimes (like multimeters and automotive panel
> > ammeters) they
> > have a built-in shunt. Others (like an instrument panel
> > meter) use a remote
> > shunt.
> >
> > Back in the dark ages of analog meters, you bought a meter
> > movement of say
> > 0-1 milivolts and used resistors to scale it accordingly for
> > voltage. If you
> > wanted to measure 1 volt at full scale, you had two resistors
> > in series with
> > the meter parallel to one resistor. The voltage drop across
> > the whole thing
> > was 1 volt, but only 1 milivolt across the resistor the meter
> > was tied to.
> >
> > Kinda funny though, alot of DMM's no longer have a 2 amp or
> > 10 amp current
> > scale -- most are 200 ma or so.
> Has anyone made a DC ammeter out of a Stamp? It must be fairly simple, since
> you can purchase a small digital DMM with this feature for $20....I'd like to
> display the reading on an LCD. Perhaps I should be asking if anyone knows how
> digital DMM's accomplish this.....
>
> Chris
>
> A comment... Dark aged meter movements consisted of a coil suspended
I could have really done without the dark aged comment but other than
that, a VERY good article Tracy !
Feeling dated, (-;
Dale Harwood [noparse][[/noparse] N4VFF ]
internet> dale@h...
ax.25> n4vff@n4vff.#cha.tn.usa.noam
#include <std_disclaimer.h>
>Back in the dark ages of analog meters, you bought a meter movement of say
>0-1 milivolts and used resistors to scale it accordingly for voltage. If you
>wanted to measure 1 volt at full scale, you had two resistors in series with
>the meter parallel to one resistor. The voltage drop across the whole thing
>was 1 volt, but only 1 milivolt across the resistor the meter was tied to.
A comment... Dark aged meter movements consisted of a coil suspended
in a magnetic field. Deflection of the pointer was proportional to
_current_ through the coil, and the full scale value might be 1
milliamp or 100 or 50 microamps. To measure voltage, you would put a
resistor in series with the coil to make it come out right. For
example, a 50 microamp meter with a resistor in series to make the
total resistance = 20kohms would deflect to full scale with one volt
across it. To make it read up to 10 volts full scale, the total
resistance for the same movement would have to be 200kohms. To turn
it into an ammeter to measure, say, 0-1 amps, it would be made put in
a series/shunt circuit:
> up to 1 amp
0.1 ohm (gives 0.1 volt with 1 amp)
----o--/\/\
o--
| |
`--(M)--/\/\-'
0-50 R+Rmeter=2000 ohms
uamps
meter movement
calibrated to read 0 to 0.1 volt or 0 to 1 amp full scale
That dark age voltmeter meter like the old Simpson in the black
bakelite case and a mirrored meter scale would be rated at "20000
ohms per volt". Nowadays, that kind of rating is no longer heard.
Ever since the vacuum tube voltmeter came along, the energy to run
the meter or display does not have to come from the signal source
itself--rather, the power comes from the battery, or whatever, that
powers the meter. The input resistance of a modern voltmeter is at
least 20 megaohms, so as not to load down the circuit being measured.
A lot of modern voltmeters are basically +/- 200 millivolts with an
input resistance of teraohms into a CMOS circuit. Voltage dividers
are used to step down higher voltages to that range of +/- 200 mV,
and shunts are used to convert current to a voltage in that range.
For example, a 0.1 ohm shunt will measure current in a 2 amp circuit,
provided that the circuit operation will not be affected by having up
to a 0.2 volt burden subtracted by the shunt. A multimeter you buy
from Radio Shack will have the appropriate shunts built in for its
various current ranges.
When used with a BASIC Stamp, the biggest question will always be
where the common for the BASIC Stamp is in relation to the common for
the circuit being measured. If the Stamp is powered by a battery and
"floats" relative to a single circuit being measured, then no
problem, it is just like a hand-held ammeter. You measure the
voltage across a shunt (and may need an amplifier if the shunt has to
be a low resistance) However, if more than one circuit is going to
be measured or the stamp is powered from the same supply as the
circuit being measured, or if there are high voltages involved, then
"it depends". The answer is not necessarily more complicated, but
more info is needed in order to answer the question. There are good
ways to let the stamp measure its own current consumption.
-- regards,
Tracy Allen
electronically monitored ecosystems
mailto:tracy@e...
http://www.emesystems.com
me is a little misleading, and could possibly be so for the person
inquring, as to how to go about constructing an ammeter. If he
doesn't know anything about circuit theory and uses resistors that are
too high of a value then he will end up limiting the current supplied
to the load and adversely affecting the circuit and ammeter. At work
we use ammeter shunts for current feedback to our GE DC-2000 drives.
I have never heard of the shunt being referred to as a "high current
resistor" even though as you mentioned, that's basically what it is.
--- In basicstamps@y..., Leroy Hall <leroy@f...> wrote:
> SO I guess you would not buy the idea that a shunt is a high current
> resistor?
>
> Leroy
> GRINNING NOW
>
> tbanez@h... wrote:
> >
> > I believe a DMM uses what's called an ammeter shunt to produce a
> > millivolt output across its terminals which is in direct
proportion to
> > the current passing through it. You can then take that millivolt
> > signal, amplify it some, and send it to an A/D converter to get a
> > digital reading.
> >
> > Someone else here mentioned using some type of resistor network.
I'm
> > not so sure that is what's done inside a DMM since a resistor
network
> > would seem to me to actually take current away from the load.
> >
> > An ammeter shunt is a two terminal device which is hooked in
series
> > with the load, has negligible resistance, and produces a millivolt
> > output across its terminals. 100A Through the shunt may produce
100
> > millivolts (depending on what type of shunt it is). These are
> > commonly used in DC drive systems for current feedback to the
> > electronics which fires the SCR's. You can also use them to drive
> > panel meters directly. I'm not sure about part numbers or
> > manufacturers. I'm not even 100% sure that's how it's done inside
a
> > DMM but I would imagine it's something similar.
> >
> >
> > --- In basicstamps@y..., "Chris Loiacono (E-mail)" <chris01@t...>
> > wrote:
> > > Has anyone made a DC ammeter out of a Stamp? It must be fairly
> > simple, since
> > > you can purchase a small digital DMM with this feature for
> > $20....I'd like
> > > to display the reading on an LCD.
> > > Perhaps I should be asking if anyone knows how digital DMM's
> > accomplish
> > > this.....
> > >
> > > Chris
> >
> > To UNSUBSCRIBE, just send mail to:
> > basicstamps-unsubscribe@y...
> > from the same email address that you subscribed. Text in the
Subject and Body of the message will be ignored.
> >
> >
> > Your use of Yahoo! Groups is subject to
http://docs.yahoo.com/info/terms/
To pose my question more directly, How can I read a constant-voltage current
output, such as that supplied by a typical process controller output, scaled
to 0-20 mA or 4-20 mA, and convert it to either a scaled voltage or 8 bit
word? You may have seen my post a few days ago where I mentioned that
different manufacturer's controllers provide the analog current output at
different fixed voltages, the two I have now are at 12 and 24V I am sure
that others provide the output at different voltages as well. I'm stuck on
trying to apply the principles in these responses to something that will
work across a variety of controllers.
Am I missing something?
Chris
>
Original Message
> From: Tracy Allen [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=bmygUx-QFoW0EGk9_6MfI-aZAgzC4gMsQC-i9mzU851PfwILRA9i7VrREgTsV9PO4YHjJk9Qgkr73iUu8mg]tracy@e...[/url
> Sent: Sunday, September 02, 2001 7:42 PM
> To: basicstamps@yahoogroups.com
> Subject: Re: [noparse][[/noparse]basicstamps] Re: Ammeter
>
>
> Rodent wrote:
> >Back in the dark ages of analog meters, you bought a meter
> movement of say
> >0-1 milivolts and used resistors to scale it accordingly for
> voltage. If you
> >wanted to measure 1 volt at full scale, you had two
> resistors in series with
> >the meter parallel to one resistor. The voltage drop across
> the whole thing
> >was 1 volt, but only 1 milivolt across the resistor the
> meter was tied to.
>
> A comment... Dark aged meter movements consisted of a coil suspended
> in a magnetic field. Deflection of the pointer was proportional to
> _current_ through the coil, and the full scale value might be 1
> milliamp or 100 or 50 microamps. To measure voltage, you would put a
> resistor in series with the coil to make it come out right. For
> example, a 50 microamp meter with a resistor in series to make the
> total resistance = 20kohms would deflect to full scale with one volt
> across it. To make it read up to 10 volts full scale, the total
> resistance for the same movement would have to be 200kohms. To turn
> it into an ammeter to measure, say, 0-1 amps, it would be made put in
> a series/shunt circuit:
>
>
> up to 1 amp
> 0.1 ohm (gives 0.1 volt with 1 amp)
> ----o--/\/\
o--
> | |
> `--(M)--/\/\-'
> 0-50 R+Rmeter=2000 ohms
> uamps
> meter movement
> calibrated to read 0 to 0.1 volt or 0 to 1 amp full scale
>
> That dark age voltmeter meter like the old Simpson in the black
> bakelite case and a mirrored meter scale would be rated at "20000
> ohms per volt". Nowadays, that kind of rating is no longer heard.
> Ever since the vacuum tube voltmeter came along, the energy to run
> the meter or display does not have to come from the signal source
> itself--rather, the power comes from the battery, or whatever, that
> powers the meter. The input resistance of a modern voltmeter is at
> least 20 megaohms, so as not to load down the circuit being measured.
>
> A lot of modern voltmeters are basically +/- 200 millivolts with an
> input resistance of teraohms into a CMOS circuit. Voltage dividers
> are used to step down higher voltages to that range of +/- 200 mV,
> and shunts are used to convert current to a voltage in that range.
> For example, a 0.1 ohm shunt will measure current in a 2 amp circuit,
> provided that the circuit operation will not be affected by having up
> to a 0.2 volt burden subtracted by the shunt. A multimeter you buy
> from Radio Shack will have the appropriate shunts built in for its
> various current ranges.
>
> When used with a BASIC Stamp, the biggest question will always be
> where the common for the BASIC Stamp is in relation to the common for
> the circuit being measured. If the Stamp is powered by a battery and
> "floats" relative to a single circuit being measured, then no
> problem, it is just like a hand-held ammeter. You measure the
> voltage across a shunt (and may need an amplifier if the shunt has to
> be a low resistance) However, if more than one circuit is going to
> be measured or the stamp is powered from the same supply as the
> circuit being measured, or if there are high voltages involved, then
> "it depends". The answer is not necessarily more complicated, but
> more info is needed in order to answer the question. There are good
> ways to let the stamp measure its own current consumption.
>
> -- regards,
> Tracy Allen
> electronically monitored ecosystems
> mailto:tracy@e...
> http://www.emesystems.com
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the
> Subject and Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to
> http://docs.yahoo.com/info/terms/
>
>
>
Original Message
From: Dale Harwood <dale@h...>
To: <basicstamps@yahoogroups.com>
Sent: September 02, 2001 9:30 AM
Subject: Re: [noparse][[/noparse]basicstamps] Re: Ammeter
| On Sun, 2 Sep 2001, Tracy Allen wrote:
|
| >
| > A comment... Dark aged meter movements consisted of a coil suspended
|
| I could have really done without the dark aged comment but other than
| that, a VERY good article Tracy !
|
| Feeling dated, (-;
|
| Dale Harwood [noparse][[/noparse] N4VFF ]
|
| internet> dale@h...
|
| ax.25> n4vff@n4vff.#cha.tn.usa.noam
|
| #include <std_disclaimer.h>
|
|
|
|
|
|
| To UNSUBSCRIBE, just send mail to:
| basicstamps-unsubscribe@yahoogroups.com
| from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
|
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|
|