[Noisebridge-discuss] New Multimeter needed....

Tymm Twillman tymmothy at gmail.com
Mon Jan 24 11:22:59 PST 2011


On Jan 24, 2011, at 11:06 AM, jim wrote:

> 
> 
>    Holy Moly! Thanks for the link to the $6 MPJA meter! 
> 
>    For me, el cheapos work great, but i do power supply 
> and audio work where most of the measurements are 
> discovering catastrophic failures and continuity. 
>    I'd love to know detailed criteria for assessing a 
> multimeter. One approach might be to point to the specs 
> of a good model (fluke 17{5,7,9}, which i looked up). 
>    But it'd be really helpful to understand the why of 
> each criterion: in measuring capacitance, what are the 
> use cases and acceptable tolerances? For me, if the RC 
> figure allows, I can look to see if the "needle" moves 
> to know if it's working (can't do that with pfs, of 
> course); cap tolerances for me are +-50%, give or take.... 
>    Is there a need for a does-all meter or is it 
> acceptably useful to have a reasonably good VOA meter 
> along with separate cap and L measurement tools (maybe 
> a frequency generator and scope...)? 
> 

you know, depends.  it's nice to be able to quickly test out common ranges quickly without digging out another tool, but I find that a) a cap meter on a good multimeter is asking for someone new to hook up a charged cap & knock out the whole meter and b) most of them in multimeters are pretty limited

with caps, ESR measurements will often give a better idea of the cap's state  (which requires another special kind of meter, or a frequency generator + meter / scope + sk1llz, etc)... and for real testing, you'll want to be able to apply some real voltage.


there are a few things that set apart good general purpose meters though, like:

- high precision (how many digits)
- good accuracy (how close a reading is to the actual value of what's being measured)
- good safety & general build quality
- forgiveness (e.g. hooking up meter to voltage while it's on the continuity setting)
- low drift (cheapies can get out of spec pretty fast)
- fast readings (slow ones can be painful to watch)
- low voltages for testing continuity / resistance (less chance of damaging something, or of activating semiconductors in in-circuit tests)

eevblog had a good run of videos on DMM testing that are worth watching, btw...


(personally i'm a fan of old bench meters for this kind of stuff; the handheld units are great but they walk very easily and without much thought... with some effort / scanning on ebay, $100-$125 will buy a damn nice HP bench meter from the 90's)

>    As to "Why We Can't Have Nice Things at Noisebridge", 
> that issue makes me furious! 
>    It's horribly inconsiderate to take things away: I'm 
> guessing mainly it's a sloppy, selfish mentality to the 
> effect that "I'll just use it and bring it back after 
> I'm done", which very often fails to "I'll just use it 
> and let it sit around unused and forgotten somewhere at 
> my house forever more after I'm done." 
>    Possible approaches include 
> * We Can't Have Anything Nice at Noisebridge 
> * People can bring in their personal nice things and 
>  label them and put them in their member shelves and 
>  loan them out when/if they see fit. 
> * Have a checkout system for some things--probably a 
>  signout sheet: probably a fair number of people will 
>  sign stuff out before they take things home and leave 
>  them there, and when asked, they'll probably be able 
>  to find the things and bring them back. 
> 
> 
> 
> 
> 
> On Mon, 2011-01-24 at 09:11 -0800, Jonathan Foote wrote:
>> Hey Zach, thanks for noticing! But I'm with  Dr. J. here.
>> 
>> I wouldn't get a Fluke, it will just walk like the last one. (Another
>> demonstration of Why We Can't Have Nice Things at Noisebridge.) Sounds
>> like you could use one for yourself, though!
>> 
>> I have a spare El Cheapo I can donate. I'll bring it tonight and slap
>> some stickers on it.
>> For the price of a Fluke we can get a few of these $6 ones which will
>> work great for 99% of anything we want to do at NB.
>> (How many people not doing power engineering really need accurate
>> capacitances > 400 uF?)
>> 
>> http://www.mpja.com/Category/Test_Equipment/Digital_Multi_Meters/LARGE_CHARACTER__LCD_MULTIMETER_17191_TE.asp
>> 
>> As Dr. J mentioned we can loan ya an expensive one should you need it.
>> 
>> 
>> 
>> 
>> On Sun, Jan 23, 2011 at 10:52 PM, Dr. Jesus <j at hug.gs> wrote:
>>> 
>>> I've noticed that the people who need a trustworthy DVM just bring their own.  I have a pretty nice one you can borrow if that will help get some of the LCDs working.
>>> On Sun, Jan 23, 2011 at 10:46 PM, Zach . <organic_unity at yahoo.com> wrote:
>>>> 
>>>> Hey folks,
>>>> 
>>>>   Zach here and this is my first attempt at posting to the email list.  I'm writing this because I believe we desperately need a new multimeter to work with and am not sure how to go about the process of noisebridge getting one.  But allow me to explain first...
>>>> 
>>>> noisebridge used to have a very nice Fluke multimeter that went missing some months ago.  I have looked all over for it but it has yet to turn up.  I am in the process of repairing some LCDs for noisebridge (got one working already) and could be saved a great deal of time and effort with a better multimeter.  The best one we have now is a "Vichy" brand.  I personally find it incredibly low quality and a very large pain to use.  And its capacitance readout maxes out under 400uf...which is a joke.
>>>> 
>>>> I recommend we collect donations for this very important electrical tool for the benefit of noisebridge and everyone else at the space.  Great Fluke meters are inexpensive these days and a quick ebay search pulls up one at a good price:
>>>> 
>>>> http://cgi.ebay.com/FLUKE175-TRUE-RMS-MULTIMETER-EXC-CONDITION-CASE-/190484916097?pt=LH_DefaultDomain_0&hash=item2c59c92781
>>>> 
>>>> the Fluke 175 is a superb meter measuring capacitance to 10,000uf or TWENTY TIMES higher than our current best meter.  This will make repairs far easier.  It also has RMS frequency reading, high voltage (600v), and is far more accurate.  It also reads more than twice as fast.
>>>> 
>>>> so....what do people think?  sorry I don't know how this process is supposed to work, people just told me to post to the list so here I am...
>>>> 
>>>> best,
>>>> Zach
>>>> 
>>>> 
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>>>> 
>>> 
>>> 
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