Forums

Error of % + digits?

Started by Commander Kinsey June 18, 2020
I just bought an amp clamp meter, and it states the error is "+/- 1.9% + 3 digits".  What does the "3 digits" part mean?
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
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.
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?
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.
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?
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.
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 dis= cussion 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 =A35 multimeter (not clamp) not giving a = digits error. Maybe precision on a simple voltmeter is cheap as chips n= owadays?
In article <op.0mg7zmz6wdg98l@glass>, CFKinsey@military.org.jp says...
> > But what I'm surprised at is a &#2013266083;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.
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 &#2013266083;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.