Can someone help me understand handheld LCR meter accuracy ratings?  - Page 1
Forum section: electronics / beginners

author: Matthematik
author_rank: Contributor
timestamp: November 21, 2016, 03:21:53 pm
content: 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?

author: TheAmmoniacal
author_rank: Unknown
timestamp: November 21, 2016, 03:32:50 pm
content: The U1733C is a 20 000 count LCR meter, with a resistance measurement accuracy on the 2 Ohm range of 0.7% + 50That 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

author: Cerebus
author_rank: Super Contributor
timestamp: November 22, 2016, 01:59:14 am
content: 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)".

author: Brumby
author_rank: Unknown
timestamp: November 22, 2016, 07:06:27 am
content: Quote from: Matthematik on November 21, 2016, 03:21:53 pmQuoteExactly right.Quote1 - more specifically, any change in that value by 1.QuoteAbsolutely not. It is a measure of error. You want this value to be as low as possible.

author: Matthematik
author_rank: Contributor
timestamp: November 22, 2016, 01:22:26 pm
content: Thanks everyone.

author: Brumby
author_rank: Unknown
timestamp: November 22, 2016, 11:35:37 pm
content: Quote from: Brumby on November 22, 2016, 07:06:27 amJust 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 - higherresolutiondoes notnecessarilytranslate into higheraccuracy.

author: Matthematik
author_rank: Contributor
timestamp: November 23, 2016, 04:12:43 am
content: Quote from: TheAmmoniacal on November 21, 2016, 03:32:50 pmHow did you go from 50 to .005?

author: Brumby
author_rank: Unknown
timestamp: November 23, 2016, 06:18:22 am
content: Count of meter20000Error on count00050Measurement range = 2 ohmMeasurement maximum1.9999Error on Measurement0.0050The difference is just a decimal point.