Accuracy !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! - Page 1
Forum section: electronics / beginners

author: Unknown
author_rank: Unknown
timestamp: July 21, 2013, 10:37:41 am
content: I have noticed on some other channels accuracy of voltages measurements on even 60000 count meters, seem to stir interest,maybe unhealthy interest,& i wonder WHY,surely in hobbyist electronics it doesn't have to be that accurate does it, take a 5 volt measurement 5.000007, surely the .0000007 , what does it matter, are some getting paranoid about this, doesn't near enough count anymore, personally I'm not bothered , as long as it's near enough and works, take a resistor I was looking for a 100 ohm in my box I found one 97.5 ohm, good enough, the circuit works, are there people out there that will only put in a 99/100 ohm resistor in, after all it's a hobby isn't it.

author: Rerouter
author_rank: Super Contributor
timestamp: July 21, 2013, 10:49:30 am
content: it depends on what your doing, if you know your meter is accurate to those counts (remembering counts reference precision not accuracy) and for instance your confirming or calibrating some other bit of equipment those few counts may be important, for instance a frequency standard of 10.000000Mhz as opposed to 10.000070Mhz is critical to very high bandwidth applications, otherwise you have frame alignment issues,same for resistance, perhaps your making a mega-ohm bridge to measure even higher resistances, those few ohms difference can really countplease recall most of us applying out skills in some way at our respective jobs and we are not all kiddies playing around with an arduino dev board and a linear power supply, some people actually need high accuracy measurements,

author: Psi
author_rank: Super Contributor
timestamp: July 21, 2013, 10:56:10 am
content: yep, most of the time it really doesn't matter.However there are exceptions, even for a hobbyist.Suppose they were trying to measure a 0-20V signal using a 5v MCU adc, something thats pretty common. They might use a 4x voltage divider so 20V = 5V.If they used 5% resistors, say 2k and 6kthen the worst cases are2100R 5700R = 3,7x 10V input becomes 10.8V1900R 6300R = 4.35x 10V input becomes 9.2VWhich is pretty damn terrible.

author: amyk
author_rank: Super Contributor
timestamp: July 21, 2013, 10:58:17 am
content: Quote from: Telequipment on July 21, 2013, 10:37:41 amIf it was a 100R 5% it's perfectly within tolerance, on the other hand that would be defective for a 2% or less. It definitely depends on the application.

author: AndyC_772
author_rank: Super Contributor
timestamp: July 21, 2013, 11:05:31 am
content: I have a 6.5 digit meter, and yes, most of the time it's overkill for many purposes.The extra resolution over and above a hand held meter is sometimes useful, though. For example, a while ago I had a job which involved measuring the resistance of power cables, and so the ability to accurately measure very small resistances was essential. I could even see how the resistance changes with temperature as the cable warmed up.It's that resolution that's most useful for me, rather than the absolute accuracy.

author: Unknown
author_rank: Unknown
timestamp: July 21, 2013, 11:41:29 am
content: Oh I see, well I'll just keep playing with my toy circuits and having fun

author: SeanB
author_rank: Super Contributor
timestamp: July 21, 2013, 11:53:53 am
content: In many cases 3 digits are fine, some 4 digits are fine but you always want to check with something that has more digits than your device. Then you can be sure that the error is in the device under test, not part of the uncertainty of the source. If you try to check a meter with 2 decimal point of reading, and the source has an error that is 5 least significant digits at the 2 decimal setting then either the meter being checked is inaccurate or the source is, but you cannot tell which. If the source is accurate to 3 digits then you can tell that the meter being checked is accurate.Then again most people are happy to 1 decimal or even to no decimal point. It depends, you would not like to pay for food where they say 10kG with an accuracy of 1 kg, either you get 9kg or 11 kg, and as the manufacturer will not like to lose all will be 9kg.

author: Unknown
author_rank: Unknown
timestamp: July 21, 2013, 12:02:52 pm
content: Quote from: SeanB on July 21, 2013, 11:53:53 amHi Sean mine is a 22000 count, which doesn't mean anything to me that's what i bought, it works ok.

author: Bloch
author_rank: Unknown
timestamp: July 21, 2013, 12:57:08 pm
content: Quote from: Telequipment on July 21, 2013, 10:37:41 amOr even work.And I do blame Dave for itNo more serious there are a some ... that do not know then or that details that are important.If there are someone to blame is maybe the "maker movement" vs instead of skilled / schooled.

author: c4757p
author_rank: Super Contributor
timestamp: July 21, 2013, 01:01:01 pm
content: Sometimes itisyour interest. My favorite hobby area is measurement. I don't just buy accurate and precise equipment, I actually like to design and build it. In that case, I don't have them because I naively think I need them to make Blinkenlights, I have them because I just like them.

author: KJDS
author_rank: Super Contributor
timestamp: July 21, 2013, 01:11:29 pm
content: It's been very rare in 25 years of professional RF design that I've needed better then 0.1% accuracy.

author: AlfBaz
author_rank: Super Contributor
timestamp: July 21, 2013, 02:23:40 pm
content: To some of us, be it a hobby or work, we have a keen interest in the very wide field of electronics and having sensitive high precision gear lets us see things you normally can't. Clearly its not needed for day to day measurements but its nice to have it when you need it.Here's a poor example but it's recent so...I had my laptop sitting on top of a 6.5 digit meter doing a trend plot of a resistance. at first glance the plot looked very erratic, jumping up and down all over the place. I turned the laptop off and surprise, surprise it calmed down substantially. Nominal resistance of 17.980k, the part that looked erratic was jumping a mere 0.3 of an ohm. Would never have seen that with lower precision

author: Bloch
author_rank: Unknown
timestamp: July 21, 2013, 02:47:59 pm
content: Quote from: AlfBaz on July 21, 2013, 02:23:40 pmSo that was the lesson learn ?The higher Accuracy the more difficult it will be to measure the right value. So how often do 99.9999987654321% need to know that that a 17980 ohm is jumping peak +-0,15 ohm ?

author: Amarbir[Lynx-India]
author_rank: Frequent Contributor
timestamp: July 21, 2013, 02:51:51 pm
content: Quote from: AlfBaz on July 21, 2013, 02:23:40 pmDamn ,Laptop Noise Trickling To The Precision 6.5 Circuit

author: c4757p
author_rank: Super Contributor
timestamp: July 21, 2013, 02:52:53 pm
content: Not everything is about what youneed. Sometimes it's fun to learn about how things work. I love seeing how little things like that affect measurements. Hobby electronics especially isn't just about getting something done by a deadline.

author: Rufus
author_rank: Super Contributor
timestamp: July 21, 2013, 03:32:33 pm
content: Quote from: Telequipment on July 21, 2013, 10:37:41 amFor a proportion of people here it isn't just a hobby. Don't know what that proportion is, might be an interesting topic for a poll.

author: AlfBaz
author_rank: Super Contributor
timestamp: July 21, 2013, 04:02:35 pm
content: Quote from: Bloch on July 21, 2013, 02:47:59 pmIt amazes me that engineering ever got beyond using a rock as a hammer.The religious fervour with which some people approach certain subjects is beyond me. I provided precious little in my post with regards to why I was doing such measurements, so for you to go off on some half cocked tangent without having any data to back your misguided assertions, leads me to believe that you are a person with little to no regard to free and open discussion about technical matters. If that is the case then how about abstaining from threads that whish to explore matters that you disagree with.To me this thread is about exploring situations that require precision measurements and I attempted to participate citing the caveatQuote

author: c4757p
author_rank: Super Contributor
timestamp: July 21, 2013, 04:06:26 pm
content: We've got two extremes here who always chime in. There's the "you can't do anything without two 8.5 digit multimeters and a four-channel 1 GHz oscilloscope made in the last two months" brigade, and the "you're wasting your money if you buy more than a beer, a hammer, a 9V battery and a length of nichrome to make resistors" brigade. Anyone who advocates moderation invites one or both.

author: AlfBaz
author_rank: Super Contributor
timestamp: July 21, 2013, 04:13:03 pm
content: Quote from: c4757p on July 21, 2013, 04:06:26 pmSometimes I think I would be of saner mind if I converted my lab into a home brew setup

author: ejeffrey
author_rank: Super Contributor
timestamp: July 21, 2013, 04:40:06 pm
content: Quote from: KJDS on July 21, 2013, 01:11:29 pmI'm working on a system right now that needs better than 0.01% amplitude accuracy microwave pulses (.001% would be better, but is really hard), _but_ we calibrate them in-situ. Even if we had an instrument that could measure to that accuracy, we would never be able to get it correct at the DUT due to connector and cable losses. So we use a high resolution DAC and mixer, and find a way to measure when the amplitude is correct. We do care about stability, and we do have to recalibrate every day to get to that level, but it works.The point is, sometimes accuracy matters, but sometimes you can find a better way to measure it than brute force. When possible that is almost always preferable. The only real exception is frequency. Frequency is so easy and cheap to make accurate that if you care about it you might as well always start with 9 digit accuracy.To be sure, there are some applications where you really need an instrument that can measure 6.5 digits. In real engineering the trick is always to figure out what you actually need, and what you can get away with.

author: Unknown
author_rank: Unknown
timestamp: July 21, 2013, 05:07:44 pm
content: See here we go again, All you pro's out there missing the point, glad your not doctors, you'd scare me to death, my point IS, for a hobbyist like me,who enjoys the hobby making things that works is the fun, I at my level just cannot see the point of measuring down to 6,7,8,9,10,11,digits or what ever else. AND as note a" HOBBYIST" making all these measurements down to .000001 or whatever is just every so slightly Anal. That's all, reel your necks back in and calm down a bit, so some of you are pro's that's fine. I'm not, I think by some of the replies ,some of you should take a step back and take a good look at yourselves. for some of us it's a hobby isn't it.

author: G7PSK
author_rank: Super Contributor
timestamp: July 21, 2013, 05:10:42 pm
content: It seems to me that there are some in the world who worry about the number of digits on the meter and not the accuracy. A case of never mind the accuracy as long as its got more digits than an Arab states gas meter,just watch the numbers go around is the name of the game. 99% of what I do can be achieved with an analogue meter quite satisfactorily, and most probably applies to many out there as well, but we are now in the digital world and the more digits there are the better it sells, I expect that a three and half digit Fluke is more accurate than many of the six or more digit cheapo Chinese meters. Most accuracy at the end of the day will depend on the user any way.

author: Unknown
author_rank: Unknown
timestamp: July 21, 2013, 05:18:24 pm
content: Quote from: G7PSK on July 21, 2013, 05:10:42 pmI quite agree, yes I have a fancy meter bought for me , by a sister in law who has far to much money,but she's my sister in law and is lovely so a welcomed gift, the meters I use for everything are analogue A Farnell, and a AVO

author: Dave
author_rank: Super Contributor
timestamp: July 21, 2013, 05:29:36 pm
content: There is one thing you aren't taking into account: the challenge. I (and probably many other forum members) like pushing the boundaries of what's possible. If you want to create precision circuitry, you need the right tools for the job. This is where 6.5 digit multimeters and rubidium frequency standards come into play.

author: c4757p
author_rank: Super Contributor
timestamp: July 21, 2013, 05:37:46 pm
content: Quote from: Telequipment on July 21, 2013, 05:07:44 pmDid you miss the part where we said sometimes measurementisthe hobby? Obviously you don't need that sort of thing if that's not what you're interested in, but don't try to say precision is useless because hobby.

author: Unknown
author_rank: Unknown
timestamp: July 21, 2013, 05:43:11 pm
content: Quote from: c4757p on July 21, 2013, 05:37:46 pmOh I just give up

author: AlfBaz
author_rank: Super Contributor
timestamp: July 21, 2013, 06:09:49 pm
content: Quote from: Telequipment on July 21, 2013, 05:43:11 pmSounds like you gave up a long time agoDou you want to know if there is reason for precision and accuracy or do you just want to be argumentative?You must understand that interest in electronics spans a massive field and if the part of ityouare interested in does not involve this sort of thing it doesn't mean there is no need for it.If you are blinking leds or wiring up 2 way light switches then great, a set of test lamps will suffice but if you have an interest in analogue electronics and use opamps other than 741's then you would be wasting the advancement in readily available analogue IC's if you don't delve down into parasitics. That's one of the beauties of high precision measuring gear like multimeters. You can use them to measure extremely small signals or differences in them prior to designing a circuit to measure and utilise them. If you don't have the precision to characterise these signals then the output of circuit you design will most likely be giving you nothing but amplified matter that you don't know (or seem to care) exists.Whilst accuracy also has its place, especially for those who are interested in metrology, precision and repeatability is where its at with these meters. It opens up a vast array of ideas and possibilities which you will inevitably be blind to with lesser equipment.Here's something interesting, in my small lab measuring a thermistor designed for temperature, feeding the data into the pc it can measure a difference in temperature between me, my wife and our pet dog entering the room. Granted, utterly useless at this point in time but this may become useful in some other application further down the line.

author: AlfBaz
author_rank: Super Contributor
timestamp: July 21, 2013, 06:16:16 pm
content: Quote from: AlfBaz on July 21, 2013, 06:09:49 pm...and another one, again with the thermistor and trend plot, as I near my finger towards it the temperature starts rising when it gets within 10mm. On the trend plot the jump looks huge but its only minute changes in resistance, again undetectable without high precision measurement

author: Unknown
author_rank: Unknown
timestamp: July 21, 2013, 06:19:27 pm
content: Quote from: AlfBaz on July 21, 2013, 06:09:49 pm

author: Unknown
author_rank: Unknown
timestamp: July 21, 2013, 06:24:35 pm
content: Quote from: Telequipment on July 21, 2013, 06:19:27 pm

author: Unknown
author_rank: Unknown
timestamp: July 21, 2013, 06:25:11 pm
content: Thanks for the insult I appreciate it

author: AlfBaz
author_rank: Super Contributor
timestamp: July 21, 2013, 06:26:59 pm
content: Quote from: Telequipment on July 21, 2013, 06:19:27 pm

author: Lightages
author_rank: Unknown
timestamp: July 21, 2013, 06:56:59 pm
content: Yes there are sometimes reasons to worry about more than 0.1% accuracy. And there are many other situations where 1% is good enough. So?

author: Anson
author_rank: Regular Contributor
timestamp: July 21, 2013, 07:03:23 pm
content: Part of my hobby is buying and restoring older equipment. And every once in a while I doneedthe extra resolution and accuracy.

author: robrenz
author_rank: Super Contributor
timestamp: July 22, 2013, 01:22:13 am
content: Just because I enjoy it. just because I can, just because it can be very educational, Just because it allows me to calibrate other equipment. Just because its fun, just because I don't have to have a rational explanation.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: July 22, 2013, 02:41:03 am
content: Quote from: Lightages on July 21, 2013, 06:56:59 pmYeah, but that's like three digits.I've tried to live by the idea that if I'm using more than 4 digits of precision (in anything) then I'm doing something wrong.

author: vk6zgo
author_rank: Super Contributor
timestamp: July 22, 2013, 03:23:19 am
content: Quote from: AlfBaz on July 21, 2013, 06:16:16 pmNo,that's sensitivity!

author: Rick Law
author_rank: Super Contributor
timestamp: July 22, 2013, 04:43:32 am
content: I am not a professional EE guy. My projects are just for fun, for learning, and to keep my mind active. I don't need to do any of them, consequently any equipment I use for them are not need based.So, I don't really need more accuracy, but at times, I sure can use more accuracy.For example, I was going to validate something I know is true, but I want to experiment and see for myself: such as resistors increase in resistance as it get hotter. I like to do a plot. I like to compare carbon film against metal film resistors. I like to compare if the drop between 20C to 10C is the same as 30 to 20C... I don't need it, but I sure like a more accurate temperature-probe. Until I get a good temperature probe, I can get to square-one with this project.Right now, I am (re)doing an Arduino voltmeter (converting a one time volt logger to something I can use again). I can buy a DT830B for less than I spend on the project so far, and it would be more accurate, more flexible, and better protected than a a wire into the bare Arduino ADC. But just clicking BUY on ebay is not nearly as educational nor is it as much fun.I don't really need a Porsche 911 Turbo, but I sure like to have one... I take that over even a Ferrari. I don't really need it... No one really need that much car. A Fiat or a KIA will get you from point A to point B just the same...

author: AlfBaz
author_rank: Super Contributor
timestamp: July 22, 2013, 06:37:01 am
content: Quote from: vk6zgo on July 22, 2013, 03:23:19 amSensitivity which will be undetectable without the extra digits. At this time my measurement techniques are pedestrian, to say the least, it's the trend of these insignificant digits that reveals repeatable results, without which I would have no change at all