Anthony Fremont wrote:
ehsjr wrote:

Anthony Fremont wrote:

ehsjr wrote:


But I'm curious as to what home circuits need meters
that can read voltage accurately to 3 decimal places?
2 decimal places? The question for current measurement:
in what home brew circuit design/troubleshooting do you
need accuracy below the tens of mA digit ? *Need*, not


You surely didn't mean tens of _mA_, did you?

I surely meant tens of mA.

I build stuff with PICs as

you know, and some of it is designed to run on batteries and needs
to go for long periods of time unattended. The current draw for a
12F683 running at 31kHz is 11uA, sleep current is 50nA. If I could
only measure current to "tens of mA", I'd never know if the PIC was
setup right for low current draw and I certainly couldn't have any
idea of expected battery life. I wouldn't even know if it was
sleeping until it ate thru some batteries in a few days instead of
six or eight months. I think I have a need to measure fractions of
a uA.

You may, but not accuracy below the tens of _mA_ digit.
When you need accuracy below tens of mA, you measure
voltage across a resistance. It doesn't make a lot of


Isn't that exactly how my DMM does it?

I don't know what your meter does. I assume it's
like any other. If so, it uses a shunt and develops
a voltage across the shunt so it is the same principle
as what I'm taking about, but not the same values.
AFAIK, they don't use a megohm neighborhood shunt
for low current - but then, I don't have any
meters with an nA scale.



sense to look for your meter to be accurate to 8 decimal
places for your .00000005 amp reading.


Now come on, the 8 decimal places is only assuming that the scale is in an
Amps range. The meter would be in the 500uA full scale range where 50nA is
only 2 decimal places.


Perhaps I did not make the point clearly.
When you are using your DMM and measuring something in
the neighborhood of 8 decimal places, like tens of nA,
your meter, regardless of scale, will be less accurate
than when it is measuring something in the 2 decimal
place neighborhood. The meter itself is more susceptable
to uncertainty the lower you go. AFAIK, the current
shunt even for low current scales has a much lower
resistance than the 2meg or 100 k I mentioned. That
means that the meter has to work with a lower level
than the 110 mv those resistors produce.

Regarding scaling - DMM's have tens of mV in 2 decimal
places. Most DMM's do not have tens of nA in 2 decimal
places. To get an 8th decimal point current reading into
the 2 decimal point range, convert it to mV with a resistor.

To put it in another perspective, consider a Fluke 187.
It will give .01 uA resolution (2 digits after the decimal)
on the 500 ua scale at a claimed accuracy of +/- .25%.
We'll ignore the further 20 count uncertaincy. That's
a +/- 1.25 uA error. That measurement is useless for the
55 nA current measurement you need. The meter could show
500.00 or 500.05 or 501.25 or whatever and you would not
know whether you had 55 nA or not. On that scale, the
meeter cannot be accurate to 2 decimal places. And you
cannot throw away the third digit after the decimal - it
doesn't exist on the meter, the resolution is too poor.

The same meter, on the 3 volt (3000mV) scale is accurate
to within +/- .025% which is +/- 75 uV - again, ignoring
the further 5 count uncertainty. On the 3 volt scale
with the technique I mentioned where you throw away the
third digit after the decimal, the error is meaningless.
That digit happens to be accurate on this meter and scale,
so the error is meaningless, even if you keep it.




Here's how you do it with accuracy at the tens of _mV_ digit:

For 11 uA, put a 10K .01% resistor in series with
the supply and measure .11 volts across it. The voltage
would range from 0.109989 to 0.110011. Keep only
2 decimal places. Your computed current, worst case,
would be off by 1 uA


For 50 nA, use a 2 meg 1% resistor and measure .10
volts across it. The voltage would range from .099
to .101 taking the 1% into account. Throw out the
last digit. Your current computation would be off
worst case, by 5 nA.


Those are fine ways to measuring static current levels, but they will not
work for me. Until the PIC goes to sleep, the current draw is much higher.
So much so that it would never power up thru a 2M resistor.

So I guess you're stuck with a need that the fancy Fluke
mentioned above cannot meet. How _do_ you measure the
55 nA?

What I would do is bypass the resistor with a switch so
the PIC can power up and run, and monitor it while it
is active by whatever technique you choose, so that you
know it is active. When it goes inactive, open the switch
to measure the voltage across the resistor.



With a voltmeter accurate to 2 decimal places.
I don't know why you would


If your volt meter has a 1V maximum at full scale and one can live with 10%
error, then I agree. If it has a 100V range, then you need .01% accuracy on
your equipment to make your measurements, right?



Anyone who is not smart enough to turn his meter
range down from the 100V scale to measure mV
is not smart enough to need nA measurements.

Measuring mV with the range set to 100 is stupid.
And 10% error for a DMM is stupid. I know you are
*not* stupid. So what is your point?

Ed

ehsjr wrote:
Anthony Fremont wrote:
ehsjr wrote:

sense to look for your meter to be accurate to 8 decimal
places for your .00000005 amp reading.


Now come on, the 8 decimal places is only assuming that the scale is
in an Amps range. The meter would be in the 500uA full scale range
where 50nA is only 2 decimal places.


Perhaps I did not make the point clearly.
When you are using your DMM and measuring something in
the neighborhood of 8 decimal places, like tens of nA,

The meter doesn't change accuracy based upon the scale it's using, it only
changes resolution. It remains .03% accurate. Whether reading Amps,
milliamps, or microamps.

your meter, regardless of scale, will be less accurate
than when it is measuring something in the 2 decimal
place neighborhood. The meter itself is more susceptable

I guess I wasn't clear or we're not understanding each other. The meter
will be in a ranger where 500uA is the full scale reading. 10's of nA is
two decimal places.

to uncertainty the lower you go. AFAIK, the current
shunt even for low current scales has a much lower
resistance than the 2meg or 100 k I mentioned. That
means that the meter has to work with a lower level
than the 110 mv those resistors produce.

Regarding scaling - DMM's have tens of mV in 2 decimal
places. Most DMM's do not have tens of nA in 2 decimal
places. To get an 8th decimal point current reading into
the 2 decimal point range, convert it to mV with a resistor.

To put it in another perspective, consider a Fluke 187.
It will give .01 uA resolution (2 digits after the decimal)
on the 500 ua scale at a claimed accuracy of +/- .25%.
We'll ignore the further 20 count uncertaincy. That's
a +/- 1.25 uA error. That measurement is useless for the
55 nA current measurement you need. The meter could show
500.00 or 500.05 or 501.25 or whatever and you would not
know whether you had 55 nA or not. On that scale, the

Your error calculation is assuming a full scale reading. The error
(neglecting the count uncertainty) at 50nA is only .125nA, it wouldn't even
show on the display.

But at 50nA it would read .03 to .07uA on my meter including the 2d
uncertainty, plenty good enough for me.

meeter cannot be accurate to 2 decimal places. And you
cannot throw away the third digit after the decimal - it
doesn't exist on the meter, the resolution is too poor.

The same meter, on the 3 volt (3000mV) scale is accurate
to within +/- .025% which is +/- 75 uV - again, ignoring
the further 5 count uncertainty. On the 3 volt scale
with the technique I mentioned where you throw away the
third digit after the decimal, the error is meaningless.
That digit happens to be accurate on this meter and scale,
so the error is meaningless, even if you keep it.

Try looking at the Extech I just ordered. .1%+2d 50000 count.


Here's how you do it with accuracy at the tens of _mV_ digit:

For 11 uA, put a 10K .01% resistor in series with
the supply and measure .11 volts across it. The voltage
would range from 0.109989 to 0.110011. Keep only
2 decimal places. Your computed current, worst case,
would be off by 1 uA


For 50 nA, use a 2 meg 1% resistor and measure .10
volts across it. The voltage would range from .099
to .101 taking the 1% into account. Throw out the
last digit. Your current computation would be off
worst case, by 5 nA.


Those are fine ways to measuring static current levels, but they
will not work for me. Until the PIC goes to sleep, the current draw
is much higher. So much so that it would never power up thru a 2M
resistor.

So I guess you're stuck with a need that the fancy Fluke
mentioned above cannot meet. How _do_ you measure the
55 nA?

That's why I didn't buy the Fluke. The meter I bought will give me 10nA
resolution. I know it won't be dead on when reading 50nA, but it will be
close enough that I know that I didn't leave some pull-ups turned on or some
other peripheral pidling away the juice. In current mode the Extech will be
good enough for me to be sure of what's happening. Any worse accuracy, and
I couldn't be sure.

What I would do is bypass the resistor with a switch so
the PIC can power up and run, and monitor it while it
is active by whatever technique you choose, so that you
know it is active. When it goes inactive, open the switch
to measure the voltage across the resistor.

Yes, I have done time-wasting methods like this before, that's why I want a
new meter, DSO and a logic analyzer.
:-)



With a voltmeter accurate to 2 decimal places.
I don't know why you would


If your volt meter has a 1V maximum at full scale and one can live
with 10% error, then I agree. If it has a 100V range, then you need
.01% accuracy on your equipment to make your measurements, right?



Anyone who is not smart enough to turn his meter
range down from the 100V scale to measure mV
is not smart enough to need nA measurements.

Measuring mV with the range set to 100 is stupid.
And 10% error for a DMM is stupid. I know you are
*not* stupid. So what is your point?

The 10% error is due to your technique not the DMM, you said so yourself,
and I quote:

" For 11 uA, put a 10K .01% resistor in series with
the supply and measure .11 volts across it. The voltage
would range from 0.109989 to 0.110011. Keep only
2 decimal places. Your computed current, worst case,
would be off by 1 uA

For 50 nA, use a 2 meg 1% resistor and measure .10
volts across it. The voltage would range from .099
to .101 taking the 1% into account. Throw out the
last digit. Your current computation would be off
worst case, by 5 nA."

By my calculations, a 5nA error on a 50nA reading is a 10% error or did I
miss something?

I agree that these techniques are valid and worthwhile at times, but I will
stick with the convenience and accuracy of a $200 meter instead of buying $5
resistors. :-) I've got a tracking number and it should be here tomorrow,
I can't wait. I reall can't wait til my scope gets here. :-)))))))

Anthony Fremont wrote:
ehsjr wrote:

Anthony Fremont wrote:

ehsjr wrote:


sense to look for your meter to be accurate to 8 decimal
places for your .00000005 amp reading.


Now come on, the 8 decimal places is only assuming that the scale is
in an Amps range. The meter would be in the 500uA full scale range
where 50nA is only 2 decimal places.


Perhaps I did not make the point clearly.
When you are using your DMM and measuring something in
the neighborhood of 8 decimal places, like tens of nA,


The meter doesn't change accuracy based upon the scale it's using, it only
changes resolution. It remains .03% accurate. Whether reading Amps,
milliamps, or microamps.


Take a look at the specs. They most certainly
do change, depending on the scale you are using.
Read the Fluke app note Understanding DMM Specifications.
Noise becomes a significant factor at the low end of a
range within the meter, and in general when measuring very
small voltage or current. And the specs, regardless of
noise, vary from range to range.

http://assets.fluke.com/datasheets/2153ExtSpecs.pdf

http://us.fluke.com/usen/support/app...lukeProducts)#




your meter, regardless of scale, will be less accurate
than when it is measuring something in the 2 decimal
place neighborhood. The meter itself is more susceptable


I guess I wasn't clear or we're not understanding each other. The meter
will be in a ranger where 500uA is the full scale reading. 10's of nA is
two decimal places.

Ok, I see what you are saying. To get accuracy on
that scale, you would need at least 6 digits displayed,
and that's before you consider any error in the
circuitry. But I now undertsnd what you have in
mind based on what you said at the bottom of your
note, where a reading of anything from .03 ua
to .07 ua will meet your needs for your .05 ua
current. That's not the accuracy I thought you
were talking about. A +/- 20 nA variation on a
50 nA measurement is an error of 40 percent - which
I call innacurate.

But now that I understand what you have in mind,
I see your point. The way I was thinking about
it was too stringent for the example you posted,
so your example does prove the case of a kind
of measurement that fits into the under tens of
mA that I was talking about. Now that I understand
what you are saying, I think the confusion was at my end.




to uncertainty the lower you go. AFAIK, the current
shunt even for low current scales has a much lower
resistance than the 2meg or 100 k I mentioned. That
means that the meter has to work with a lower level
than the 110 mv those resistors produce.

Regarding scaling - DMM's have tens of mV in 2 decimal
places. Most DMM's do not have tens of nA in 2 decimal
places. To get an 8th decimal point current reading into
the 2 decimal point range, convert it to mV with a resistor.

To put it in another perspective, consider a Fluke 187.
It will give .01 uA resolution (2 digits after the decimal)
on the 500 ua scale at a claimed accuracy of +/- .25%.
We'll ignore the further 20 count uncertaincy. That's
a +/- 1.25 uA error. That measurement is useless for the
55 nA current measurement you need. The meter could show
500.00 or 500.05 or 501.25 or whatever and you would not
know whether you had 55 nA or not. On that scale, the


Your error calculation is assuming a full scale reading. The error
(neglecting the count uncertainty) at 50nA is only .125nA, it wouldn't even
show on the display.

But at 50nA it would read .03 to .07uA on my meter including the 2d
uncertainty, plenty good enough for me.

That statement clears it up for me, as I mentioned above.
To me it's a 40% error, but for what you are doing it
is accurate.



meeter cannot be accurate to 2 decimal places. And you
cannot throw away the third digit after the decimal - it
doesn't exist on the meter, the resolution is too poor.

The same meter, on the 3 volt (3000mV) scale is accurate
to within +/- .025% which is +/- 75 uV - again, ignoring
the further 5 count uncertainty. On the 3 volt scale
with the technique I mentioned where you throw away the
third digit after the decimal, the error is meaningless.
That digit happens to be accurate on this meter and scale,
so the error is meaningless, even if you keep it.


Try looking at the Extech I just ordered. .1%+2d 50000 count.

I'd like to - if you have a handy url, please post it.
If not handy, don't go digging for it. All ths talk
has piqued my interest in buying yet another DMM
(that I don't need - too many DMM's not enough time)
or at least drooling over the specs.

Is there an antidote for "test equipment lust"?




Here's how you do it with accuracy at the tens of _mV_ digit:

For 11 uA, put a 10K .01% resistor in series with
the supply and measure .11 volts across it. The voltage
would range from 0.109989 to 0.110011. Keep only
2 decimal places. Your computed current, worst case,
would be off by 1 uA


For 50 nA, use a 2 meg 1% resistor and measure .10
volts across it. The voltage would range from .099
to .101 taking the 1% into account. Throw out the
last digit. Your current computation would be off
worst case, by 5 nA.


Those are fine ways to measuring static current levels, but they
will not work for me. Until the PIC goes to sleep, the current draw
is much higher. So much so that it would never power up thru a 2M
resistor.

So I guess you're stuck with a need that the fancy Fluke
mentioned above cannot meet. How _do_ you measure the
55 nA?


That's why I didn't buy the Fluke. The meter I bought will give me 10nA
resolution. I know it won't be dead on when reading 50nA, but it will be
close enough that I know that I didn't leave some pull-ups turned on or some
other peripheral pidling away the juice. In current mode the Extech will be
good enough for me to be sure of what's happening. Any worse accuracy, and
I couldn't be sure.


What I would do is bypass the resistor with a switch so
the PIC can power up and run, and monitor it while it
is active by whatever technique you choose, so that you
know it is active. When it goes inactive, open the switch
to measure the voltage across the resistor.


Yes, I have done time-wasting methods like this before, that's why I want a
new meter, DSO and a logic analyzer.
:-)



With a voltmeter accurate to 2 decimal places.
I don't know why you would


If your volt meter has a 1V maximum at full scale and one can live
with 10% error, then I agree. If it has a 100V range, then you need
.01% accuracy on your equipment to make your measurements, right?



Anyone who is not smart enough to turn his meter
range down from the 100V scale to measure mV
is not smart enough to need nA measurements.

Measuring mV with the range set to 100 is stupid.
And 10% error for a DMM is stupid. I know you are
*not* stupid. So what is your point?


The 10% error is due to your technique not the DMM, you said so yourself,
and I quote:

" For 11 uA, put a 10K .01% resistor in series with

the supply and measure .11 volts across it. The voltage
would range from 0.109989 to 0.110011. Keep only
2 decimal places. Your computed current, worst case,
would be off by 1 uA


For 50 nA, use a 2 meg 1% resistor and measure .10
volts across it. The voltage would range from .099
to .101 taking the 1% into account. Throw out the
last digit. Your current computation would be off
worst case, by 5 nA."


By my calculations, a 5nA error on a 50nA reading is a 10% error or did I
miss something?

No, I did. I thought you were talking about meter accuracy
when you said 10% - you were talking about measurement
error.

I agree that these techniques are valid and worthwhile at times, but I will
stick with the convenience and accuracy of a $200 meter instead of buying $5
resistors. :-) I've got a tracking number and it should be here tomorrow,
I can't wait. I reall can't wait til my scope gets here. :-)))))))



Go ahead - make me drool! Enjoy the meter. :-)
And the scope. :-)

Ed

ehsjr wrote:
Anthony Fremont wrote:
ehsjr wrote:

Anthony Fremont wrote:

ehsjr wrote:


sense to look for your meter to be accurate to 8 decimal
places for your .00000005 amp reading.


Now come on, the 8 decimal places is only assuming that the scale
is in an Amps range. The meter would be in the 500uA full scale
range where 50nA is only 2 decimal places.


Perhaps I did not make the point clearly.
When you are using your DMM and measuring something in
the neighborhood of 8 decimal places, like tens of nA,


The meter doesn't change accuracy based upon the scale it's using,
it only changes resolution. It remains .03% accurate. Whether
reading Amps, milliamps, or microamps.


Take a look at the specs. They most certainly
do change, depending on the scale you are using.
Read the Fluke app note Understanding DMM Specifications.
Noise becomes a significant factor at the low end of a
range within the meter, and in general when measuring very
small voltage or current. And the specs, regardless of
noise, vary from range to range.

http://assets.fluke.com/datasheets/2153ExtSpecs.pdf

http://us.fluke.com/usen/support/app...lukeProducts)#

According to the specs, the accuracy is a percentage of the reading that is
being observed. I take that to mean that at small readings, you have an
equivalently small error since it's a percentage (well...+ uncertainty
digits which never changes and is certainly a large part of the reading when
trying to measure 50nA). Hence the 30-70nA expected reading. Now that I've
read the manual, I see that their marketing material was a little optimistic
on the number of digits in current mode. Turns out to be 20 and not 2 like
the marketing slick says, hmmm..... is there no truth in advertising
anymore? At least there is a delta button to erase away the noise reading
of about 10nA after it settles down.

I would hope that the days of needing to keep things in the upper third of
the scale went out with the analog meters. But aparently they haven't. I
was looking at the manual and they mention that true RMS readings are
specified over 5% - 100% range. Tell me what this means: "Maximum Crest
Factor 5:1 at full scale, 10:1 at half scale" and then they add some extra
that makes it sound like they are only referring to AC signals that are
non-sinusoidal with that.




your meter, regardless of scale, will be less accurate
than when it is measuring something in the 2 decimal
place neighborhood. The meter itself is more susceptable


I guess I wasn't clear or we're not understanding each other. The
meter will be in a ranger where 500uA is the full scale reading. 10's of
nA is two decimal places.

Ok, I see what you are saying. To get accuracy on
that scale, you would need at least 6 digits displayed,
and that's before you consider any error in the
circuitry. But I now undertsnd what you have in
mind based on what you said at the bottom of your
note, where a reading of anything from .03 ua
to .07 ua will meet your needs for your .05 ua
current. That's not the accuracy I thought you
were talking about. A +/- 20 nA variation on a
50 nA measurement is an error of 40 percent - which
I call innacurate.

And you're right, it is inaccurate when you look at it like that.
Fortunately by using the delta button or just a little quick math to
subtract the idle reading, I can obtain what I need. Sort of.... ;-)

But now that I understand what you have in mind,
I see your point. The way I was thinking about
it was too stringent for the example you posted,
so your example does prove the case of a kind
of measurement that fits into the under tens of
mA that I was talking about. Now that I understand
what you are saying, I think the confusion was at my end.




to uncertainty the lower you go. AFAIK, the current
shunt even for low current scales has a much lower
resistance than the 2meg or 100 k I mentioned. That
means that the meter has to work with a lower level
than the 110 mv those resistors produce.

Regarding scaling - DMM's have tens of mV in 2 decimal
places. Most DMM's do not have tens of nA in 2 decimal
places. To get an 8th decimal point current reading into
the 2 decimal point range, convert it to mV with a resistor.

To put it in another perspective, consider a Fluke 187.
It will give .01 uA resolution (2 digits after the decimal)
on the 500 ua scale at a claimed accuracy of +/- .25%.
We'll ignore the further 20 count uncertaincy. That's
a +/- 1.25 uA error. That measurement is useless for the
55 nA current measurement you need. The meter could show
500.00 or 500.05 or 501.25 or whatever and you would not
know whether you had 55 nA or not. On that scale, the


Your error calculation is assuming a full scale reading. The error
(neglecting the count uncertainty) at 50nA is only .125nA, it
wouldn't even show on the display.

But at 50nA it would read .03 to .07uA on my meter including the 2d
uncertainty, plenty good enough for me.

That statement clears it up for me, as I mentioned above.
To me it's a 40% error, but for what you are doing it
is accurate.



meeter cannot be accurate to 2 decimal places. And you
cannot throw away the third digit after the decimal - it
doesn't exist on the meter, the resolution is too poor.

The same meter, on the 3 volt (3000mV) scale is accurate
to within +/- .025% which is +/- 75 uV - again, ignoring
the further 5 count uncertainty. On the 3 volt scale
with the technique I mentioned where you throw away the
third digit after the decimal, the error is meaningless.
That digit happens to be accurate on this meter and scale,
so the error is meaningless, even if you keep it.


Try looking at the Extech I just ordered. .1%+2d 50000 count.

I'd like to - if you have a handy url, please post it.
If not handy, don't go digging for it. All ths talk
has piqued my interest in buying yet another DMM
(that I don't need - too many DMM's not enough time)
or at least drooling over the specs.

Sorry about that, here you go:
http://www.extech.com/instrument/pro...MM560_570.html


Is there an antidote for "test equipment lust"?

Not that I can see.




Here's how you do it with accuracy at the tens of _mV_ digit:

For 11 uA, put a 10K .01% resistor in series with
the supply and measure .11 volts across it. The voltage
would range from 0.109989 to 0.110011. Keep only
2 decimal places. Your computed current, worst case,
would be off by 1 uA


For 50 nA, use a 2 meg 1% resistor and measure .10
volts across it. The voltage would range from .099
to .101 taking the 1% into account. Throw out the
last digit. Your current computation would be off
worst case, by 5 nA.


Those are fine ways to measuring static current levels, but they
will not work for me. Until the PIC goes to sleep, the current
draw is much higher. So much so that it would never power up thru
a 2M resistor.

So I guess you're stuck with a need that the fancy Fluke
mentioned above cannot meet. How _do_ you measure the
55 nA?


That's why I didn't buy the Fluke. The meter I bought will give me
10nA resolution. I know it won't be dead on when reading 50nA, but
it will be close enough that I know that I didn't leave some
pull-ups turned on or some other peripheral pidling away the juice. In
current mode the Extech will be good enough for me to be sure of
what's happening. Any worse accuracy, and I couldn't be sure.


What I would do is bypass the resistor with a switch so
the PIC can power up and run, and monitor it while it
is active by whatever technique you choose, so that you
know it is active. When it goes inactive, open the switch
to measure the voltage across the resistor.


Yes, I have done time-wasting methods like this before, that's why I
want a new meter, DSO and a logic analyzer.
:-)



With a voltmeter accurate to 2 decimal places.
I don't know why you would


If your volt meter has a 1V maximum at full scale and one can live
with 10% error, then I agree. If it has a 100V range, then you
need .01% accuracy on your equipment to make your measurements,
right?

Anyone who is not smart enough to turn his meter
range down from the 100V scale to measure mV
is not smart enough to need nA measurements.

Measuring mV with the range set to 100 is stupid.
And 10% error for a DMM is stupid. I know you are
*not* stupid. So what is your point?


The 10% error is due to your technique not the DMM, you said so
yourself, and I quote:

" For 11 uA, put a 10K .01% resistor in series with

the supply and measure .11 volts across it. The voltage
would range from 0.109989 to 0.110011. Keep only
2 decimal places. Your computed current, worst case,
would be off by 1 uA


For 50 nA, use a 2 meg 1% resistor and measure .10
volts across it. The voltage would range from .099
to .101 taking the 1% into account. Throw out the
last digit. Your current computation would be off
worst case, by 5 nA."


By my calculations, a 5nA error on a 50nA reading is a 10% error or
did I miss something?

No, I did. I thought you were talking about meter accuracy
when you said 10% - you were talking about measurement
error.

I agree that these techniques are valid and worthwhile at times, but
I will stick with the convenience and accuracy of a $200 meter
instead of buying $5 resistors. :-) I've got a tracking number and
it should be here tomorrow, I can't wait. I reall can't wait til my
scope gets here. :-)))))))

Go ahead - make me drool! Enjoy the meter. :-)
And the scope. :-)

Got it today, I like it so far. :-) See the new thread on the Extech vs.
Micronta shootout.

On Tue, 06 Mar 2007 20:34:32 GMT, ehsjr Gave
us:

Take a look at the specs. They most certainly
do change, depending on the scale you are using.
Read the Fluke app note Understanding DMM Specifications.
Noise becomes a significant factor at the low end of a
range within the meter, and in general when measuring very
small voltage or current. And the specs, regardless of
noise, vary from range to range.


This is why when I use a meter to measure current, I use very short,
huge gauge 14Ga SPC leads. When I measure low voltages, I twist the
meter leads together to cancel any local "injection" sources.

Trust me, both methods have a positive effect. Typical meter leads
are very small ga, and are a poor choice for current measure as there
is an error introduced by the lead resistances. Twisted meter leads
most certainly do cancel out local disturbances that could render your
readings in error. Both practices work well.

On Mon, 05 Mar 2007 20:27:02 GMT, ehsjr Gave
us:

I don't know what your meter does. I assume it's
like any other. If so, it uses a shunt and develops
a voltage across the shunt so it is the same principle
as what I'm taking about, but not the same values.
AFAIK, they don't use a megohm neighborhood shunt
for low current - but then, I don't have any
meters with an nA scale.


They don't. It is a precision, low value shunt resistor, and they
read voltage across it to determine the current through it.

MassiveProng wrote:
On Mon, 05 Mar 2007 20:27:02 GMT, ehsjr Gave
us:


I don't know what your meter does. I assume it's
like any other. If so, it uses a shunt and develops
a voltage across the shunt so it is the same principle
as what I'm taking about, but not the same values.
AFAIK, they don't use a megohm neighborhood shunt
for low current - but then, I don't have any
meters with an nA scale.



They don't. It is a precision, low value shunt resistor, and they
read voltage across it to determine the current through it.
And that is *exactly* what i proposed with the "trick"; place the DVM
on the 200mVFS scale, add a shunt 1.11Meg resistor (that means in
parallel; use the dictionary) across the meter and the sensitivity of
this network is 200nAFS.
Simple ohms law...

On Tue, 06 Mar 2007 19:06:50 +0000, Robert Baer wrote:
MassiveProng wrote:
On Mon, 05 Mar 2007 20:27:02 GMT, ehsjr Gave

I don't know what your meter does. I assume it's like any other. If so,
it uses a shunt and develops a voltage across the shunt so it is the
same principle as what I'm taking about, but not the same values. AFAIK,
they don't use a megohm neighborhood shunt for low current - but then, I
don't have any meters with an nA scale.

They don't. It is a precision, low value shunt resistor, and they
read voltage across it to determine the current through it.
And that is *exactly* what i proposed with the "trick"; place the DVM
on the 200mVFS scale, add a shunt 1.11Meg resistor (that means in
parallel; use the dictionary) across the meter and the sensitivity of this
network is 200nAFS.
Simple ohms law...

And cover everything in the lab with aluminum foil, so your body
capacitance doesn't zap your meter first time out. ;-)

Cheers!
Rich

Rich Grise wrote:
On Tue, 06 Mar 2007 19:06:50 +0000, Robert Baer wrote:

MassiveProng wrote:

On Mon, 05 Mar 2007 20:27:02 GMT, ehsjr Gave


I don't know what your meter does. I assume it's like any other. If so,
it uses a shunt and develops a voltage across the shunt so it is the
same principle as what I'm taking about, but not the same values. AFAIK,
they don't use a megohm neighborhood shunt for low current - but then, I
don't have any meters with an nA scale.

They don't. It is a precision, low value shunt resistor, and they
read voltage across it to determine the current through it.

And that is *exactly* what i proposed with the "trick"; place the DVM
on the 200mVFS scale, add a shunt 1.11Meg resistor (that means in
parallel; use the dictionary) across the meter and the sensitivity of this
network is 200nAFS.
Simple ohms law...


And cover everything in the lab with aluminum foil, so your body
capacitance doesn't zap your meter first time out. ;-)

Cheers!
Rich

Why?
I made that shunt box and use it on occasions where i need to measure
low currents, and have seen no problems whether i use it with my 3.5
digit DMM or my 4.5 digit DMM.

On Tue, 06 Mar 2007 21:08:44 GMT, Rich Grise Gave
us:

On Tue, 06 Mar 2007 19:06:50 +0000, Robert Baer wrote:
MassiveProng wrote:
On Mon, 05 Mar 2007 20:27:02 GMT, ehsjr Gave

I don't know what your meter does. I assume it's like any other. If so,
it uses a shunt and develops a voltage across the shunt so it is the
same principle as what I'm taking about, but not the same values. AFAIK,
they don't use a megohm neighborhood shunt for low current - but then, I
don't have any meters with an nA scale.

They don't. It is a precision, low value shunt resistor, and they
read voltage across it to determine the current through it.
And that is *exactly* what i proposed with the "trick"; place the DVM
on the 200mVFS scale, add a shunt 1.11Meg resistor (that means in
parallel; use the dictionary) across the meter and the sensitivity of this
network is 200nAFS.
Simple ohms law...

And cover everything in the lab with aluminum foil, so your body
capacitance doesn't zap your meter first time out. ;-)

You're an idiot, and this is not a useful, relevant, or practical
post.

Robert Baer wrote in
hlink.net:

MassiveProng wrote:
On Mon, 05 Mar 2007 20:27:02 GMT, ehsjr Gave
us:


I don't know what your meter does. I assume it's
like any other. If so, it uses a shunt and develops
a voltage across the shunt so it is the same principle
as what I'm taking about, but not the same values.
AFAIK, they don't use a megohm neighborhood shunt
for low current - but then, I don't have any
meters with an nA scale.



They don't. It is a precision, low value shunt resistor, and they
read voltage across it to determine the current through it.
And that is *exactly* what i proposed with the "trick"; place the DVM
on the 200mVFS scale, add a shunt 1.11Meg resistor (that means in
parallel; use the dictionary) across the meter and the sensitivity of
this network is 200nAFS.
Simple ohms law...


After reading all this,I checked the $3 DMM I bought at a Harbor Freight
sidewalk sale,and it turns out the *input Z is only ONE megohm*. YUK!

I only bought it as a 2nd DMM,for monitoring PS outputs and the like.
The manual did not list that particular spec,either....

--
Jim Yanik
jyanik
at
kua.net

Jim Yanik wrote:

Robert Baer wrote in
hlink.net:


MassiveProng wrote:

On Mon, 05 Mar 2007 20:27:02 GMT, ehsjr Gave
us:



I don't know what your meter does. I assume it's
like any other. If so, it uses a shunt and develops
a voltage across the shunt so it is the same principle
as what I'm taking about, but not the same values.
AFAIK, they don't use a megohm neighborhood shunt
for low current - but then, I don't have any
meters with an nA scale.



They don't. It is a precision, low value shunt resistor, and they
read voltage across it to determine the current through it.

And that is *exactly* what i proposed with the "trick"; place the DVM
on the 200mVFS scale, add a shunt 1.11Meg resistor (that means in
parallel; use the dictionary) across the meter and the sensitivity of
this network is 200nAFS.
Simple ohms law...



After reading all this,I checked the $3 DMM I bought at a Harbor Freight
sidewalk sale,and it turns out the *input Z is only ONE megohm*. YUK!

I only bought it as a 2nd DMM,for monitoring PS outputs and the like.
The manual did not list that particular spec,either....

I bet it also does not state the input Z onthe current scales, or the
current(s) to be expected on the resistance scales.
OTH, most meter manuals leave out most of those (significant, at
times) details.

On Tue, 06 Mar 2007 22:45:47 GMT, Robert Baer
Gave us:

I bet it also does not state the input Z onthe current scales

You are truly clueless.

Typically two groups of scaling, and two shunt resistors, one for
each group.

BOTH VERY LOW resistance.

Jim Yanik wrote:
Robert Baer wrote in
hlink.net:


MassiveProng wrote:

On Mon, 05 Mar 2007 20:27:02 GMT, ehsjr Gave
us:



I don't know what your meter does. I assume it's
like any other. If so, it uses a shunt and develops
a voltage across the shunt so it is the same principle
as what I'm taking about, but not the same values.
AFAIK, they don't use a megohm neighborhood shunt
for low current - but then, I don't have any
meters with an nA scale.



They don't. It is a precision, low value shunt resistor, and they
read voltage across it to determine the current through it.

And that is *exactly* what i proposed with the "trick"; place the DVM
on the 200mVFS scale, add a shunt 1.11Meg resistor (that means in
parallel; use the dictionary) across the meter and the sensitivity of
this network is 200nAFS.
Simple ohms law...



After reading all this,I checked the $3 DMM I bought at a Harbor Freight
sidewalk sale,and it turns out the *input Z is only ONE megohm*. YUK!

I only bought it as a 2nd DMM,for monitoring PS outputs and the like.
The manual did not list that particular spec,either....

That is 333 kohms per dollar. That is a lot cheaper than the 10 kohms
per dollar my hp34401s cost. I have a bunch of these for 30th -40th
meters. (You cannot be serious about second meter). It is necessary
to have a meter within arm's reach anywhere you are in the house. Also
a digital caliper. We used to have three optical monochromators on the
end table in the living room. They were handy when you wanted to check
the spectrum of a new fluorescent bulb.

The cheap meters are accurate encough for a lot of work and you do not
care if they get broken. It is always a shock to my system to see how
cheaply things can be sold.

Jim Yanik wrote:



After reading all this,I checked the $3 DMM I bought at a Harbor Freight
sidewalk sale,and it turns out the *input Z is only ONE megohm*. YUK!

But that's the greatest "extra" meter since sliced bread.
Seriously. It costs next to nothing, so you are not afraid
of abusing it, which means you can toss it in your tool box
or your glove box or the trunk. If you fry it, drop it, the
dog eats it, aliens from the UFO beam it up and disect it,
whatever, it is essentially no loss. You treat (or should
treat) your "real" meter far more kindly, and use it when
you need more confidence in your measurements. That Harbor
Freight meter is surprizingly accurate, in the sense that
you expect that a $3.00 meter just _has_ to be way out of
whack. It's not. If you absolutely have to know the exact
number, you wouldn't use it - you'd measure with your "real"
meter. But for most of the measurements people make with a
DMM, the $3.00 meter is fine. And that $3.00 includes the
9v battery!


I only bought it as a 2nd DMM,for monitoring PS outputs and the like.
The manual did not list that particular spec,either....


Perfect use for that meter. :-)

Ed

Jim Yanik wrote:
After reading all this,I checked the $3 DMM I bought at a Harbor Freight
sidewalk sale,and it turns out the *input Z is only ONE megohm*. YUK!

My first meter cost five times that, was analog, and only had 20K ohms
per volt.

For those young folk who aren't familiar with that, yes, the meter input
impedance changed depending on the range you set the meter to.

--
Martians drive SUVs! http://oregonmag.com/MarsWarm307.html

clifto wrote:
Jim Yanik wrote:
After reading all this,I checked the $3 DMM I bought at a Harbor
Freight sidewalk sale,and it turns out the *input Z is only ONE
megohm*. YUK!

My first meter cost five times that, was analog, and only had 20K ohms
per volt.

For those young folk who aren't familiar with that, yes, the meter
input impedance changed depending on the range you set the meter to.

My first meter (a cheapie my dad's friend gave me when I was about 10) was
in that range (could it have been 10k?). The better meters I had in my
younger days were a whopping 50k ohms/volt.

Anthony Fremont wrote:

clifto wrote:

Jim Yanik wrote:

After reading all this,I checked the $3 DMM I bought at a Harbor
Freight sidewalk sale,and it turns out the *input Z is only ONE
megohm*. YUK!

My first meter cost five times that, was analog, and only had 20K ohms
per volt.

For those young folk who aren't familiar with that, yes, the meter
input impedance changed depending on the range you set the meter to.


My first meter (a cheapie my dad's friend gave me when I was about 10) was
in that range (could it have been 10k?). The better meters I had in my
younger days were a whopping 50k ohms/volt.


I do remember seeing one of those 50K/V meters whan i was young; what
the heck has happened to them?

clifto wrote:
Jim Yanik wrote:

After reading all this,I checked the $3 DMM I bought at a Harbor Freight
sidewalk sale,and it turns out the *input Z is only ONE megohm*. YUK!


My first meter cost five times that, was analog, and only had 20K ohms
per volt.

For those young folk who aren't familiar with that, yes, the meter input
impedance changed depending on the range you set the meter to.

Check; the neatthing is that on higher voltage scales, the input
resistance exceeds that of a DMM.
Which is why i built a voltmeter/currentmeter around a 5 microamp
movement giving 200K per volt sensitivity.

Robert Baer wrote in
news
clifto wrote:
Jim Yanik wrote:

After reading all this,I checked the $3 DMM I bought at a Harbor
Freight sidewalk sale,and it turns out the *input Z is only ONE
megohm*. YUK!


My first meter cost five times that, was analog, and only had 20K
ohms per volt.

For those young folk who aren't familiar with that, yes, the meter
input impedance changed depending on the range you set the meter to.

Check; the neatthing is that on higher voltage scales, the input
resistance exceeds that of a DMM.
Which is why i built a voltmeter/currentmeter around a 5 microamp
movement giving 200K per volt sensitivity.


Then there's the Fluke differential voltmeters,that have nearly infinite
impedance at null. ISTR a HP diff VM that had a 100Meg Z on it's off-null
mode.Then there are Keithley hi-Z meters,with gigohm input Zs.

--
Jim Yanik
jyanik
at
kua.net

"clifto" wrote in message
...

My first meter cost five times that, was analog, and only had 20K ohms
per volt.

Mine was 2K IIRC. I still have it.

On Thu, 08 Mar 2007 13:34:45 -0600, clifto Gave us:

My first meter cost five times that, was analog, and only had 20K ohms
per volt.

For those young folk who aren't familiar with that, yes, the meter input
impedance changed depending on the range you set the meter to.


Lemmie guess... An RCA Master Volt Ohmist?

I still have one of those as well.

Have a couple Heathkit MMs around too.

On Tue, 06 Mar 2007 19:06:50 GMT, Robert Baer
Gave us:

MassiveProng wrote:
On Mon, 05 Mar 2007 20:27:02 GMT, ehsjr Gave
us:


I don't know what your meter does. I assume it's
like any other. If so, it uses a shunt and develops
a voltage across the shunt so it is the same principle
as what I'm taking about, but not the same values.
AFAIK, they don't use a megohm neighborhood shunt
for low current - but then, I don't have any
meters with an nA scale.



They don't. It is a precision, low value shunt resistor, and they
read voltage across it to determine the current through it.
And that is *exactly* what i proposed with the "trick"; place the DVM
on the 200mVFS scale, add a shunt 1.11Meg resistor (that means in
parallel; use the dictionary) across the meter and the sensitivity of
this network is 200nAFS.
Simple ohms law...


Simple Ohms's law also states that when you series that mess with
your circuit under test, all the voltage will drop on your precious
resistor/meter set-up , and there won't be any in the circuit you wish
to examine.

In other words, dumbass, the reason that shunts are of low ohmic
value is so they do not modify the circuit you are attempting to
examine.

Your stupid **** certainly would do just that. Your lack of
understanding that a current meter needs to be of low resistance is
quite a tell as well. You must be a digital guy, and seemingly not a
very good one to miss this basic.

MassiveProng wrote:
On Tue, 06 Mar 2007 19:06:50 GMT, Robert Baer

And that is *exactly* what i proposed with the "trick"; place the
DVM on the 200mVFS scale, add a shunt 1.11Meg resistor (that means in
parallel; use the dictionary) across the meter and the sensitivity of
this network is 200nAFS.
Simple ohms law...


Simple Ohms's law also states that when you series that mess with
your circuit under test, all the voltage will drop on your precious
resistor/meter set-up , and there won't be any in the circuit you wish
to examine.

Really now. And I thought that Ohm's Law stated that the voltage would be
split up in a predictable way.

In other words, dumbass, the reason that shunts are of low ohmic
value is so they do not modify the circuit you are attempting to
examine.

Stupid me, I thought they were for fire prevention.

Your stupid **** certainly would do just that. Your lack of
understanding that a current meter needs to be of low resistance is
quite a tell as well. You must be a digital guy, and seemingly not a
very good one to miss this basic.

You really aren't getting it are you? This is about measuring very small
currents, the large resistance doesn't have to drop any significant voltage.
I can't believe you have such an inept understanding of Ohm's law that you
keep harping about. The world is not all about 200A and 15kV there are
people getting things done with nanowatts of power. Just think about it,
how much voltage drop do you get with 50nA thru a .01Ohm resistor? How
would you measure 500 femtovolts? You have no concept of scale.

On Tue, 6 Mar 2007 20:18:10 -0600, "Anthony Fremont"
Gave us:

Really now. And I thought that Ohm's Law stated that the voltage would be
split up in a predictable way.


It will, dumbass. Most of it will be on his 1 M Ohm SERIES "shunt"
(Bwuahahahahah). That means there wont be much left for the circuit.
Can you really be that ****ing stupid?

If you are at 5Volts and passing 2 amps in a circuit, and add a 1M
resistor in series with it, what do YOU think happens to the voltage
presented to that ten ohm loading?

Oh and it wouldn't just drop voltage. The current that the circuit
WAS used to seeing will be a lot less as well.

Ohm's law INDEED!

MassiveProng wrote:
On Tue, 6 Mar 2007 20:18:10 -0600, "Anthony Fremont"
Gave us:

Really now. And I thought that Ohm's Law stated that the voltage
would be split up in a predictable way.


It will, dumbass. Most of it will be on his 1 M Ohm SERIES "shunt"
(Bwuahahahahah). That means there wont be much left for the circuit.
Can you really be that ****ing stupid?

Can you???? You just can't accept the facts of this can you?

If you are at 5Volts and passing 2 amps in a circuit, and add a 1M
resistor in series with it, what do YOU think happens to the voltage
presented to that ten ohm loading?

Do you know how to calculate it? WE ARE TALKING ABOUT 50nA YOU MORON. Now
get with the program or just STFU.

Oh and it wouldn't just drop voltage. The current that the circuit
WAS used to seeing will be a lot less as well.

Ohm's law INDEED!

50nA you idiot. DO THE MATH!

On Tue, 6 Mar 2007 20:18:10 -0600, "Anthony Fremont"
Gave us:

In other words, dumbass, the reason that shunts are of low ohmic
value is so they do not modify the circuit you are attempting to
examine.

Stupid me, I thought they were for fire prevention.

Stupid you indeed. That's not what the INLINE fuse is for, dip****.
It is in the meter, but is there to limit the voltage presented to the
meter mechanism or when current is being shunted through the resistor.

The shunt has nothing to do with fire prevention. They are a
precision shunt meant to provide a precision voltage to a high
impedance volt meter such that it can provide the user with a reading
of the current in the circuit that it was placed into WITHOUT
modifying the operation of the circuit.

Your 1 M setup would NOT qualify for a device that does NOT modify
the circuity to a great degree. It would qualify as a device that so
badly modifies the circuit being tested that it no longer represents
the circuit that was originally given.

Anthony Fremont wrote:
MassiveProng wrote:

On Tue, 06 Mar 2007 19:06:50 GMT, Robert Baer


And that is *exactly* what i proposed with the "trick"; place the
DVM on the 200mVFS scale, add a shunt 1.11Meg resistor (that means in
parallel; use the dictionary) across the meter and the sensitivity of
this network is 200nAFS.
Simple ohms law...


Simple Ohms's law also states that when you series that mess with
your circuit under test, all the voltage will drop on your precious
resistor/meter set-up , and there won't be any in the circuit you wish
to examine.


Really now. And I thought that Ohm's Law stated that the voltage would be
split up in a predictable way.


In other words, dumbass, the reason that shunts are of low ohmic
value is so they do not modify the circuit you are attempting to
examine.


Stupid me, I thought they were for fire prevention.


Your stupid **** certainly would do just that. Your lack of
understanding that a current meter needs to be of low resistance is
quite a tell as well. You must be a digital guy, and seemingly not a
very good one to miss this basic.


You really aren't getting it are you? This is about measuring very small
currents, the large resistance doesn't have to drop any significant voltage.
I can't believe you have such an inept understanding of Ohm's law that you
keep harping about. The world is not all about 200A and 15kV there are
people getting things done with nanowatts of power. Just think about it,
how much voltage drop do you get with 50nA thru a .01Ohm resistor? How
would you measure 500 femtovolts? You have no concept of scale.



I gave p ersponding to him a while back as being a useless waste of time.

On Wed, 07 Mar 2007 06:25:09 GMT, Robert Baer
Gave us:


I gave p ersponding to him a while back as being a useless waste of time.


Learn about reading current in a circuit.

Your little suggestion that I read the definition of the word shunt
backfired too.

Run home and cry now, little baer... errr... boy.

Anthony Fremont wrote:
MassiveProng wrote:

On Tue, 06 Mar 2007 19:06:50 GMT, Robert Baer


And that is *exactly* what i proposed with the "trick"; place the
DVM on the 200mVFS scale, add a shunt 1.11Meg resistor (that means in
parallel; use the dictionary) across the meter and the sensitivity of
this network is 200nAFS.
Simple ohms law...


Simple Ohms's law also states that when you series that mess with
your circuit under test, all the voltage will drop on your precious
resistor/meter set-up , and there won't be any in the circuit you wish
to examine.


Really now. And I thought that Ohm's Law stated that the voltage would be
split up in a predictable way.


In other words, dumbass, the reason that shunts are of low ohmic
value is so they do not modify the circuit you are attempting to
examine.


Stupid me, I thought they were for fire prevention.


Your stupid **** certainly would do just that. Your lack of
understanding that a current meter needs to be of low resistance is
quite a tell as well. You must be a digital guy, and seemingly not a
very good one to miss this basic.


You really aren't getting it are you? This is about measuring very small
currents, the large resistance doesn't have to drop any significant voltage.
I can't believe you have such an inept understanding of Ohm's law that you
keep harping about. The world is not all about 200A and 15kV there are
people getting things done with nanowatts of power. Just think about it,
how much voltage drop do you get with 50nA thru a .01Ohm resistor? How
would you measure 500 femtovolts? You have no concept of scale.



I gave up responding to him a while back as being a useless waste of
time.

On Wed, 07 Mar 2007 06:25:48 GMT, Robert Baer
Gave us:


I gave up responding to him a while back as being a useless waste of
time.

Ahh... so you're a double posting dope too!

This dope is still running windows 98!