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Error of % + digits?...

C

Commander Kinsey

Guest
I just bought an amp clamp meter, and it states the error is \"+/- 1.9% + 3 digits\". What does the \"3 digits\" part mean?
 
C

Commander Kinsey

Guest
On Thu, 18 Jun 2020 14:03:42 +0100, Commander Kinsey <CFKinsey@military.org.jp> wrote:

> I just bought an amp clamp meter, and it states the error is \"+/- 1.9% + 3 digits\". What does the \"3 digits\" part mean?

Answering my own question, I found this page, it means aswell as the percentage error, the last digit (eg the 2 in 147.2V) can vary by 3.:

https://www.baylor.edu/content/services/document.php/49697.pdf
 
P

Pimpom

Guest
On 6/18/2020 6:33 PM, Commander Kinsey wrote:
I just bought an amp clamp meter, and it states the error is \"+/- 1.9% + 3 digits\". What does the \"3 digits\" part mean?
If your meter should read, say 1.875 A, the correct reading could
be anywhere from 1.872 to 1.878. This is a possible error in the
display presented to you in the analog-digital display conversion
process. The +/-1.9% possible error is about the measurement
taken including - but not only - any error made by the sensor.

To put it another way: If the actual current is 1.875 A,
inaccuracies in the sensor and associated circuits may process it
as somewhere between 1.875 A +/-1.9%. The analog-digital process
may introduce a further error of +/- 3 counts in the least
significant display digit. Therefore a current of 1.875 A may be
displayed as anywhere from 1.836 to 1.913 A.
 
C

Commander Kinsey

Guest
On Thu, 18 Jun 2020 15:38:46 +0100, Pimpom <nobody@nowhere.com> wrote:

On 6/18/2020 6:33 PM, Commander Kinsey wrote:
I just bought an amp clamp meter, and it states the error is \"+/- 1.9% + 3 digits\". What does the \"3 digits\" part mean?


If your meter should read, say 1.875 A, the correct reading could
be anywhere from 1.872 to 1.878. This is a possible error in the
display presented to you in the analog-digital display conversion
process. The +/-1.9% possible error is about the measurement
taken including - but not only - any error made by the sensor.

To put it another way: If the actual current is 1.875 A,
inaccuracies in the sensor and associated circuits may process it
as somewhere between 1.875 A +/-1.9%. The analog-digital process
may introduce a further error of +/- 3 counts in the least
significant display digit. Therefore a current of 1.875 A may be
displayed as anywhere from 1.836 to 1.913 A.
Thanks, I wonder why all my other meters only list a % error. Is it included within it somehow, or are they just lying, or do some meters not have this error?
 
R

Ralph Mowery

Guest
In article <op.0meweog5wdg98l@glass>, CFKinsey@military.org.jp says...
If your meter should read, say 1.875 A, the correct reading could
be anywhere from 1.872 to 1.878. This is a possible error in the
display presented to you in the analog-digital display conversion
process. The +/-1.9% possible error is about the measurement
taken including - but not only - any error made by the sensor.

To put it another way: If the actual current is 1.875 A,
inaccuracies in the sensor and associated circuits may process it
as somewhere between 1.875 A +/-1.9%. The analog-digital process
may introduce a further error of +/- 3 counts in the least
significant display digit. Therefore a current of 1.875 A may be
displayed as anywhere from 1.836 to 1.913 A.

Thanks, I wonder why all my other meters only list a % error. Is it included within it somehow, or are they just lying, or do some meters not have this error?
Most that use a digital meter should know the last digit is not accurate
because of a rounding error. Say it shows 1.5 volts. It could be 1.45
to 1.55 or so and still show 1.5. Some meters such as the one under
discussion is less accurate and can be 3 numbers high or low on the last
digit. That is why on digital meters you should try to use a range that
shows as many digits as you can.

-My several hundred dollar Fluke meter shows DC volts to be .05 % +- 1
digit.
 
C

Commander Kinsey

Guest
On Thu, 18 Jun 2020 15:38:46 +0100, Pimpom <nobody@nowhere.com> wrote:

On 6/18/2020 6:33 PM, Commander Kinsey wrote:
I just bought an amp clamp meter, and it states the error is \"+/- 1.9% + 3 digits\". What does the \"3 digits\" part mean?


If your meter should read, say 1.875 A, the correct reading could
be anywhere from 1.872 to 1.878. This is a possible error in the
display presented to you in the analog-digital display conversion
process. The +/-1.9% possible error is about the measurement
taken including - but not only - any error made by the sensor.

To put it another way: If the actual current is 1.875 A,
inaccuracies in the sensor and associated circuits may process it
as somewhere between 1.875 A +/-1.9%. The analog-digital process
may introduce a further error of +/- 3 counts in the least
significant display digit. Therefore a current of 1.875 A may be
displayed as anywhere from 1.836 to 1.913 A.
Thanks, I wonder why all my other meters only list a % error. Is it included within it somehow, or are they just lying, or do some meters not have this error?
 
C

Commander Kinsey

Guest
On Thu, 18 Jun 2020 23:16:50 +0100, Ralph Mowery <rmowery28146@earthlink.net> wrote:

In article <op.0meweog5wdg98l@glass>, CFKinsey@military.org.jp says...

If your meter should read, say 1.875 A, the correct reading could
be anywhere from 1.872 to 1.878. This is a possible error in the
display presented to you in the analog-digital display conversion
process. The +/-1.9% possible error is about the measurement
taken including - but not only - any error made by the sensor.

To put it another way: If the actual current is 1.875 A,
inaccuracies in the sensor and associated circuits may process it
as somewhere between 1.875 A +/-1.9%. The analog-digital process
may introduce a further error of +/- 3 counts in the least
significant display digit. Therefore a current of 1.875 A may be
displayed as anywhere from 1.836 to 1.913 A.

Thanks, I wonder why all my other meters only list a % error. Is it included within it somehow, or are they just lying, or do some meters not have this error?

Most that use a digital meter should know the last digit is not accurate
because of a rounding error. Say it shows 1.5 volts. It could be 1.45
to 1.55 or so and still show 1.5. Some meters such as the one under
discussion is less accurate and can be 3 numbers high or low on the last
digit. That is why on digital meters you should try to use a range that
shows as many digits as you can.
Yes, but I was surprised to see up to 7 digits out on this one, depending on the range. I think DC amps is 3 or 5 dependant on range, and AC amps is 5 or 7.

-My several hundred dollar Fluke meter shows DC volts to be .05 % +- 1
digit.
The meters I have are not several hundred dollars, so are you saying they\'re only +/- 1 digit? Is the error much higher on the one under discussion because it\'s a clamp meter?
 
C

Commander Kinsey

Guest
On Thu, 18 Jun 2020 23:16:50 +0100, Ralph Mowery <rmowery28146@earthlink.net> wrote:

In article <op.0meweog5wdg98l@glass>, CFKinsey@military.org.jp says...

If your meter should read, say 1.875 A, the correct reading could
be anywhere from 1.872 to 1.878. This is a possible error in the
display presented to you in the analog-digital display conversion
process. The +/-1.9% possible error is about the measurement
taken including - but not only - any error made by the sensor.

To put it another way: If the actual current is 1.875 A,
inaccuracies in the sensor and associated circuits may process it
as somewhere between 1.875 A +/-1.9%. The analog-digital process
may introduce a further error of +/- 3 counts in the least
significant display digit. Therefore a current of 1.875 A may be
displayed as anywhere from 1.836 to 1.913 A.

Thanks, I wonder why all my other meters only list a % error. Is it included within it somehow, or are they just lying, or do some meters not have this error?

Most that use a digital meter should know the last digit is not accurate
because of a rounding error. Say it shows 1.5 volts. It could be 1.45
to 1.55 or so and still show 1.5. Some meters such as the one under
discussion is less accurate and can be 3 numbers high or low on the last
digit. That is why on digital meters you should try to use a range that
shows as many digits as you can.
Yes, but I was surprised to see up to 7 digits out on this one, depending on the range. I think DC amps is 3 or 5 dependant on range, and AC amps is 5 or 7.

-My several hundred dollar Fluke meter shows DC volts to be .05 % +- 1
digit.
The meters I have are not several hundred dollars, so are you saying they\'re only +/- 1 digit? Is the error much higher on the one under discussion because it\'s a clamp meter?
 
R

Ralph Mowery

Guest
In article <op.0mfizcwhwdg98l@glass>, CFKinsey@military.org.jp says...
-My several hundred dollar Fluke meter shows DC volts to be .05 % +- 1
digit.

The meters I have are not several hundred dollars, so are you saying they\'re only +/- 1 digit? Is the error much higher on the one under discussion because it\'s a clamp meter?
The larger error is because of the price difference. It costs more to
make a part that is .01 % than it does to make one that is 2 %. The
..01% parts may just be the 2 % ones that are hand sorted to .01%.

I am sure that the clamp part does play some part in how accurate the
meter is.
 
R

Ralph Mowery

Guest
In article <op.0mfizcwhwdg98l@glass>, CFKinsey@military.org.jp says...
-My several hundred dollar Fluke meter shows DC volts to be .05 % +- 1
digit.

The meters I have are not several hundred dollars, so are you saying they\'re only +/- 1 digit? Is the error much higher on the one under discussion because it\'s a clamp meter?
The larger error is because of the price difference. It costs more to
make a part that is .01 % than it does to make one that is 2 %. The
..01% parts may just be the 2 % ones that are hand sorted to .01%.

I am sure that the clamp part does play some part in how accurate the
meter is.
 
C

Commander Kinsey

Guest
On Fri, 19 Jun 2020 00:38:29 +0100, Ralph Mowery <rmowery28146@earthlink..net> wrote:

In article <op.0mfizcwhwdg98l@glass>, CFKinsey@military.org.jp says...
-My several hundred dollar Fluke meter shows DC volts to be .05 % +- 1
digit.

The meters I have are not several hundred dollars, so are you saying they\'re only +/- 1 digit? Is the error much higher on the one under discussion because it\'s a clamp meter?



The larger error is because of the price difference. It costs more to
make a part that is .01 % than it does to make one that is 2 %. The
.01% parts may just be the 2 % ones that are hand sorted to .01%.

I am sure that the clamp part does play some part in how accurate the
meter is.
But what I\'m surprised at is a £5 multimeter (not clamp) not giving a digits error. Maybe precision on a simple voltmeter is cheap as chips nowadays?
 
C

Commander Kinsey

Guest
On Fri, 19 Jun 2020 00:38:29 +0100, Ralph Mowery <rmowery28146@earthlink..net> wrote:

In article <op.0mfizcwhwdg98l@glass>, CFKinsey@military.org.jp says...
-My several hundred dollar Fluke meter shows DC volts to be .05 % +- 1
digit.

The meters I have are not several hundred dollars, so are you saying they\'re only +/- 1 digit? Is the error much higher on the one under discussion because it\'s a clamp meter?



The larger error is because of the price difference. It costs more to
make a part that is .01 % than it does to make one that is 2 %. The
.01% parts may just be the 2 % ones that are hand sorted to .01%.

I am sure that the clamp part does play some part in how accurate the
meter is.
But what I\'m surprised at is a £5 multimeter (not clamp) not giving a digits error. Maybe precision on a simple voltmeter is cheap as chips nowadays?
 
R

Ralph Mowery

Guest
In article <op.0mg7zmz6wdg98l@glass>, CFKinsey@military.org.jp says...
But what I\'m surprised at is a £5 multimeter (not clamp) not giving a digits error. Maybe precision on a simple voltmeter is cheap as chips nowadays?
You have to be careful how you throw precision and accurecy around.

A meter that shows 4 digits is more precice than one that shows only 3
digits, however the 4 digit one may only be 1% accurate and the 3 digit
one may be .5% accurate.

It is easy to get precision, but difficule to be accurate. Think of it
as shooting a gun. Precision may be how close the bullets land to each
other where ever they land on the target, but to be accurate the bullets
have to land on the center of the target. Such as all the bullets could
land very close to each other, but not even hit the target.

As I mentioned, a good meter will not have a digits error outside the +-
one digit due to rounding.
 
R

Ralph Mowery

Guest
In article <op.0mg7zmz6wdg98l@glass>, CFKinsey@military.org.jp says...
But what I\'m surprised at is a £5 multimeter (not clamp) not giving a digits error. Maybe precision on a simple voltmeter is cheap as chips nowadays?
You have to be careful how you throw precision and accurecy around.

A meter that shows 4 digits is more precice than one that shows only 3
digits, however the 4 digit one may only be 1% accurate and the 3 digit
one may be .5% accurate.

It is easy to get precision, but difficule to be accurate. Think of it
as shooting a gun. Precision may be how close the bullets land to each
other where ever they land on the target, but to be accurate the bullets
have to land on the center of the target. Such as all the bullets could
land very close to each other, but not even hit the target.

As I mentioned, a good meter will not have a digits error outside the +-
one digit due to rounding.
 
C

Commander Kinsey

Guest
On Fri, 19 Jun 2020 23:55:42 +0100, Ralph Mowery <rmowery28146@earthlink..net> wrote:

In article <op.0mg7zmz6wdg98l@glass>, CFKinsey@military.org.jp says...

But what I\'m surprised at is a £5 multimeter (not clamp) not giving a digits error. Maybe precision on a simple voltmeter is cheap as chips nowadays?



You have to be careful how you throw precision and accurecy around.

A meter that shows 4 digits is more precice than one that shows only 3
digits, however the 4 digit one may only be 1% accurate and the 3 digit
one may be .5% accurate.

It is easy to get precision, but difficule to be accurate. Think of it
as shooting a gun. Precision may be how close the bullets land to each
other where ever they land on the target, but to be accurate the bullets
have to land on the center of the target. Such as all the bullets could
land very close to each other, but not even hit the target.

As I mentioned, a good meter will not have a digits error outside the +-
one digit due to rounding.
That didn\'t help. I interchange the two. I just want to know how close to the correct reading the readout is. Adding another digit doesn\'t improve anything if it\'s incorrect. And shooting all the bullets in one place doesn\'t help if they all miss.
 
P

Pimpom

Guest
On 6/20/2020 4:29 AM, Commander Kinsey wrote:
On Fri, 19 Jun 2020 23:55:42 +0100, Ralph Mowery <rmowery28146@earthlink.net> wrote:

In article <op.0mg7zmz6wdg98l@glass>, CFKinsey@military.org.jp says...

But what I\'m surprised at is a £5 multimeter (not clamp) not giving a digits error. Maybe precision on a simple voltmeter is cheap as chips nowadays?



You have to be careful how you throw precision and accurecy around.

A meter that shows 4 digits is more precice than one that shows only 3
digits, however the 4 digit one may only be 1% accurate and the 3 digit
one may be .5% accurate.

It is easy to get precision, but difficule to be accurate. Think of it
as shooting a gun. Precision may be how close the bullets land to each
other where ever they land on the target, but to be accurate the bullets
have to land on the center of the target. Such as all the bullets could
land very close to each other, but not even hit the target.

As I mentioned, a good meter will not have a digits error outside the +-
one digit due to rounding.

That didn\'t help. I interchange the two. I just want to know how close to the correct reading the readout is. Adding another digit doesn\'t improve anything if it\'s incorrect. And shooting all the bullets in one place doesn\'t help if they all miss.
Take pi as an example. It can be said that 3.14 is accurate as a
three-digit value, but 3.1416 is more precise because it has a
higher resolution.

OTOH, deriving it from 22/7 or 3.1429 has the same 5-digit
resolution and is just as precise as far as the number it
represents is concerned but is less accurate.

In this particular case, 3.1416 is both more precise and more
accurate than 3.14 but that\'s not always the case with measurements.

My mechanical slide caliper has a resolution of 0.001 inch. This
means that it can display measurements with a precision of 1 mil,
but that doesn\'t guarantee that a measurement taken with it will
be accurate to 1 mil. I may not always press the jaws snugly
enough and the scale may not be perfectly accurate.
 
C

Commander Kinsey

Guest
On Sat, 20 Jun 2020 07:39:37 +0100, Pimpom <nobody@nowhere.com> wrote:

On 6/20/2020 4:29 AM, Commander Kinsey wrote:
On Fri, 19 Jun 2020 23:55:42 +0100, Ralph Mowery <rmowery28146@earthlink.net> wrote:

In article <op.0mg7zmz6wdg98l@glass>, CFKinsey@military.org.jp says....

But what I\'m surprised at is a £5 multimeter (not clamp) not giving a digits error. Maybe precision on a simple voltmeter is cheap as chips nowadays?



You have to be careful how you throw precision and accurecy around.

A meter that shows 4 digits is more precice than one that shows only 3
digits, however the 4 digit one may only be 1% accurate and the 3 digit
one may be .5% accurate.

It is easy to get precision, but difficule to be accurate. Think of it
as shooting a gun. Precision may be how close the bullets land to each
other where ever they land on the target, but to be accurate the bullets
have to land on the center of the target. Such as all the bullets could
land very close to each other, but not even hit the target.

As I mentioned, a good meter will not have a digits error outside the +-
one digit due to rounding.

That didn\'t help. I interchange the two. I just want to know how close to the correct reading the readout is. Adding another digit doesn\'t improve anything if it\'s incorrect. And shooting all the bullets in one place doesn\'t help if they all miss.


Take pi as an example. It can be said that 3.14 is accurate as a
three-digit value, but 3.1416 is more precise because it has a
higher resolution.

OTOH, deriving it from 22/7 or 3.1429 has the same 5-digit
resolution and is just as precise as far as the number it
represents is concerned but is less accurate.

In this particular case, 3.1416 is both more precise and more
accurate than 3.14 but that\'s not always the case with measurements.

My mechanical slide caliper has a resolution of 0.001 inch. This
means that it can display measurements with a precision of 1 mil,
but that doesn\'t guarantee that a measurement taken with it will
be accurate to 1 mil. I may not always press the jaws snugly
enough and the scale may not be perfectly accurate.
I\'d need to contract OCD to understand that. There\'s only one thing in question here, how close is the reading to the correct value. You can\'t split that into two. 3.1416 is better than 3.14, and that\'s it. All you can state with a reading is it\'s correct to within a certain percentage.
 
R

Ralph Mowery

Guest
In article <op.0miefkhkwdg98l@glass>, CFKinsey@military.org.jp says...
I\'d need to contract OCD to understand that. There\'s only one thing in question here, how close is the reading to the correct value. You can\'t split that into two. 3.1416 is better than 3.14, and that\'s it. All you can state with a reading is it\'s correct to within a certain percentage.
Try this.

A doctor does a very complicated operation on your left arm like a joint
replacement. It all goes very well. Very precise.

However he should have done the operation on the right arm that was
causing trouble. Not accurate.


That is why a voltmeter can show 3 digits and be accurate to only the
last digit being in question by one number either way, but a 5 digit
volt meter can show many numbers, but if it is not calibrated corrctly
the 2nd digit to the 5 th digit could be way off and the meter not
accurate at all.
 
C

Commander Kinsey

Guest
On Sat, 20 Jun 2020 16:24:41 +0100, Ralph Mowery <rmowery28146@earthlink.net> wrote:

In article <op.0miefkhkwdg98l@glass>, CFKinsey@military.org.jp says...

I\'d need to contract OCD to understand that. There\'s only one thing in question here, how close is the reading to the correct value. You can\'t split that into two. 3.1416 is better than 3.14, and that\'s it. All you can state with a reading is it\'s correct to within a certain percentage.

Try this.

A doctor does a very complicated operation on your left arm like a joint
replacement. It all goes very well. Very precise.

However he should have done the operation on the right arm that was
causing trouble. Not accurate.
Nope, because the first one is 100% useless. I wouldn\'t call that precise at all, as he was out by half a metre.

That is why a voltmeter can show 3 digits and be accurate to only the
last digit being in question by one number either way, but a 5 digit
volt meter can show many numbers, but if it is not calibrated corrctly
the 2nd digit to the 5 th digit could be way off and the meter not
accurate at all.
Showing those extra two numbers is pointless if they\'re wrong. All that matters is how many volts difference between the actual voltage and what is shown.
 
C

Commander Kinsey

Guest
On Fri, 19 Jun 2020 23:55:42 +0100, Ralph Mowery <rmowery28146@earthlink..net> wrote:

In article <op.0mg7zmz6wdg98l@glass>, CFKinsey@military.org.jp says...

But what I\'m surprised at is a £5 multimeter (not clamp) not giving a digits error. Maybe precision on a simple voltmeter is cheap as chips nowadays?



You have to be careful how you throw precision and accurecy around.

A meter that shows 4 digits is more precice than one that shows only 3
digits, however the 4 digit one may only be 1% accurate and the 3 digit
one may be .5% accurate.

It is easy to get precision, but difficule to be accurate. Think of it
as shooting a gun. Precision may be how close the bullets land to each
other where ever they land on the target, but to be accurate the bullets
have to land on the center of the target. Such as all the bullets could
land very close to each other, but not even hit the target.

As I mentioned, a good meter will not have a digits error outside the +-
one digit due to rounding.
That didn\'t help. I interchange the two. I just want to know how close to the correct reading the readout is. Adding another digit doesn\'t improve anything if it\'s incorrect. And shooting all the bullets in one place doesn\'t help if they all miss.
 
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