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Electronics => Beginners => Topic started by: Matthematik on November 21, 2016, 03:21:53 pm

Title: Can someone help me understand handheld LCR meter accuracy ratings?
Post by: Matthematik on November 21, 2016, 03:21:53 pm
It says in the keysight U1731C/U1732C/U1733C manual that accuracy is given as ±(% of reading + counts of least significant digit. I don't know what to make of the 'counts of least significant digit'. I get that the least significant digit would be the rightmost, but what exactly is the count of that digit? Is higher count better?
Title: Re: Can someone help me understand handheld LCR meter accuracy ratings?
Post by: TheAmmoniacal on November 21, 2016, 03:32:50 pm
The U1733C is a 20 000 count LCR meter, with a resistance measurement accuracy on the 2 Ohm range of 0.7% + 50

That means +- (0.7% + 0.005), i.e. a "count" is just a number (counting). A lower count is better.


If you're measuring 1.9 ohm exactly, your meter is guaranteed to display a value between 1.9183 and 1.8817 ohm.

 1.9 +- (0.7% of 1.9 + 0.005) = 1.9 +- 0.0183

Title: Re: Can someone help me understand handheld LCR meter accuracy ratings?
Post by: Cerebus on November 22, 2016, 01:59:14 am
If you prefer, you can think of 'counts' as percentage of range. So for the above example, the range is 2.0000 ohms (i.e. 20,000 counts), the 50 counts as a percentage of range is 50/20000 * 100 % => 0.25%. So the full specification would be "+/- (0.7% of reading plus 0.25% of range)".
Title: Re: Can someone help me understand handheld LCR meter accuracy ratings?
Post by: Brumby on November 22, 2016, 07:06:27 am
Quote from: Matthematik on November 21, 2016, 03:21:53 pm
It says in the keysight U1731C/U1732C/U1733C manual that accuracy is given as ±(% of reading + counts of least significant digit. I don't know what to make of the 'counts of least significant digit'.
Quote
I get that the least significant digit would be the rightmost,
Exactly right.

Quote
but what exactly is the count of that digit?
1 - more specifically, any change in that value by 1.

Quote
Is higher count better?
Absolutely not.  It is a measure of error.  You want this value to be as low as possible.
Title: Re: Can someone help me understand handheld LCR meter accuracy ratings?
Post by: Matthematik on November 22, 2016, 01:22:26 pm
Thanks everyone.
Title: Re: Can someone help me understand handheld LCR meter accuracy ratings?
Post by: Brumby on November 22, 2016, 11:35:37 pm
Quote from: Brumby on November 22, 2016, 07:06:27 am
Quote
Is higher count better?
Absolutely not.  It is a measure of error.  You want this value to be as low as possible.

Just a clarification....

When talking about 'count' in the context of accuracy - the above applies.

However, when talking about the general capabilities of a digital meter, 'count' is also used to describe the resolution of that meter.  For example, the EEVblog BM235 is described as a '6,000 count' meter - because it can display numbers from 0000 to 6000 (you ignore decimal points in this assessment).  Just think of the display as being that of a decimal counter and you can see where the term comes from.  (This is actually closer to the truth than you might think - because of the basic operation an ADC.)

Obviously, a meter with 60,000 count has better resolution than one with 6,000 - so, in this assessment, the higher the count, the better the resolution.  Be aware, though, that - although it is usual - higher resolution does not necessarily translate into higher accuracy.
Title: Re: Can someone help me understand handheld LCR meter accuracy ratings?
Post by: Matthematik on November 23, 2016, 04:12:43 am
Quote from: TheAmmoniacal on November 21, 2016, 03:32:50 pm
The U1733C is a 20 000 count LCR meter, with a resistance measurement accuracy on the 2 Ohm range of 0.7% + 50

That means +- (0.7% + 0.005), i.e. a "count" is just a number (counting). A lower count is better.


If you're measuring 1.9 ohm exactly, your meter is guaranteed to display a value between 1.9183 and 1.8817 ohm.

 1.9 +- (0.7% of 1.9 + 0.005) = 1.9 +- 0.0183

How did you go from 50 to .005?
Title: Re: Can someone help me understand handheld LCR meter accuracy ratings?
Post by: Brumby on November 23, 2016, 06:18:22 am
Count of meter20000
Error on count00050
Measurement range = 2 ohm
Measurement maximum1.9999
Error on Measurement0.0050

The difference is just a decimal point.