suggestions for multimeter????

Discussion in 'General Electronics Chat' started by cvedrick, Sep 3, 2013.

  1. cvedrick

    Thread Starter New Member

    Sep 3, 2013
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    I have a need, but am not sure what to do to fill it.

    I am looking for a multimeter that will read resistance fairly accurate between 0.5Ω and 3Ω. by fairly accurate I mean ±0.1Ω at the worst.

    I am building resistant heating coils for use with personal vaporizers (electronic cigarettes)

    I know I can use the manufacturers specifications on the resistant wire and calculate the theoretical resistance based on length, but I like to double check.

    There is a gadget that will do this for me, and it costs around 20 to 30 dollars, IF you can find one or even the kit, but again it only does one thing.... And seems to be forever out of stock....

    This is a safety issue for me, high output batteries, low resistance coils, sticking the thing in my face.......

    Anyhow anyone out there know of a cost effective multimeter that is accurate at low Ω?

    Pretty sure Fluke and maybe Omega have one, but out of my budget until I get an inheritance or discover the IRS screwed up in my favor for the past 30 years.....
     
  2. #12

    Expert

    Nov 30, 2010
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  3. PackratKing

    Well-Known Member

    Jul 13, 2008
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    Chantix works !!! :D
     
  4. cvedrick

    Thread Starter New Member

    Sep 3, 2013
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    For about 1% of the people who try it and manage to quit with it, it does not last forever, re-lapses of the 1% are about 95%

    NOT being snotty, I take it you are tongue in cheek so....

    over 30 years I have tried:

    gum
    patches
    cold turkey
    tapering off
    chantix
    hypnotism
    boot camp
    etc.

    This works for me!!!!!

    Wrong forum for a big discussion on this, and what I am using is considerably more advanced than those toys yo get at the gas station or they give out free.... If you are interested, a minimum google search of "personal vaporizer" should get you to the correct forum.
     
    Last edited: Sep 3, 2013
  5. cvedrick

    Thread Starter New Member

    Sep 3, 2013
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    Much as I appreciate this, I am looking to purchase a muti-meter, I may someday decide to source all the parts and built your meter, but for my purposes something that can be used for more than 1 application is ideal.
     
  6. strantor

    AAC Fanatic!

    Oct 3, 2010
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    cheap & accurate (+reliable) usually mix like oil & water. Check out the listings on ebay. The first result, shipping from Hong Kong, claims accuracy to 0.1 ohm. Do you trust it? I don't. I trust Fluke. I'll spare you the lecture and just simply state that you get what you pay for.

    There is another meter in the results, a Vichy VC97, for $28. It claims accuracy of .8%; at 3 ohms, that's 24milliohms. Do you trust this fluke wannabe? I don't.
     
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  7. #12

    Expert

    Nov 30, 2010
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    I have a really good Fluke meter, but it only goes down to .1 ohm. If you can't see the next digit, there is always a concern that it isn't a "0". If you want to trust your meter to tell you about numbers in the .1 ohm range, it has to show to .01 ohms, and those are hard to find in the retail category. If you do find one, please report back here. We are always watching and learning.
     
  8. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    HP makes some meters with low range Ohm accuracy but they cost several grand. You must have "four wire" capability to measure tenths of an Ohm.
     
  9. cvedrick

    Thread Starter New Member

    Sep 3, 2013
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    might be looking for too much, how about ±0.1Ω ?
     
  10. strantor

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    :confused: that's what you originally requested, and that's what I linked to.
     
  11. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    I know five people who quit smoking by reading a book.

    Look up "alan carr". He wrote a book titled "the easy way to quit smoking."

    My wife is one of the five and she tried hypnosis, patches, everything but those electronic cigarettes. Of the few people I know who use the electronic cigarettes, over half have went back to the real deal. I know the sample of people is small, but that is what I see.

    On the topic of the book, Alan Carr does not recommend you quitting while reading the book. Everyone I know who read the book, has well over 1 year of smoke free, even though two of them, frequent bars (playing pool) that still allow smoking.

    I quit because the nurses stopped me from smoking when I was in the ICU, just before my quad bypass. Imagine that, they won't allow smoking in the ICU.
     
  12. cvedrick

    Thread Starter New Member

    Sep 3, 2013
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    Sorry Stranthor, the multimeter is a good suggestion, but its lowest range is 400 and that works out to ±3.2Ω

    Not sure about the capacitance meter, I am too ignernt to know if it will work or not..

    Guess I am going to have to pop for the fluke or build my own...

    #12..... I did look at your posting, it was for the source, not the meter.


    Seems I am not the first, this guy is looking for the same thing more or less. but limits himself to the Ω only for checking resistance heating coils.

    http://forum.allaboutcircuits.com/showthread.php?t=73372
     
  13. cvedrick

    Thread Starter New Member

    Sep 3, 2013
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    Understand there is a difference between gas station e-cigarettes and personal vaporizers.

    Kind of like a walmart continuity tester and a $500+ fluke multimeter.

    And yes I agree with you the itty bitty cigarette look alikes with teensy batteries, underpowered heating coils, tiny liquid tanks and usually nasty tasting chinese nicotene liquids are about the least satisfying things out there.

    As far as it goes, I had to actually see one to realize what one was.

    Been tobacco free since May 10th and am so glad I am.

    NOTE not nicotine free, just dont use tobacco, no fits, no aggressive behavior, no depression.
     
  14. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    Why not build a constant current device and use a series resistor?

    When your 1.2 ohm resistance is placed in series, the constant current through your "device under test" and the series known tolerance resistor, can be calculated. Below is an example, except the actual Constant Current Source circuit is not illustrated.

    BTW, those who I know who use the "e-cigarettes", they talk about spending a lot of money on them, and walmart or gas stations were never mentioned as their "source". Most were "rechargeable" and yes, they could replenish their nicotine habit with various strengths and flavors. So I guess my choice of words, "e-cigarette" is not entirely correct.
     
    Last edited: Sep 4, 2013
  15. #12

    Expert

    Nov 30, 2010
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    That is a good idea. The constant current source would not have to be a precise amount, it only has to be stable. The resistor only has to be a known value. It doesn't have to be a 1% resistor as long as you can measure it within 1%, and most modern digital meters can do that. So, if you measure the larger resistance, measure the voltage across that resistance, and measure the voltage across the DUT (device under test), Ohm's Law will tell you the answer.

    I have a $4 meter than can resolve voltage to .0001 volts. 10 ma through .01 ohm will show up as .0001 volts, therefore you can read as low as a tenth of an ohm.

    This circuit is not exactly a constant current source, it is an almost "constant voltage across a constant resistance" source. If the DUT is less than 6.8 ohms, the current will still be within 1% of the current through a 0.00 ohm short.
     
    Last edited: Sep 4, 2013
  16. JoeJester

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    I did simulate a test set with an defective DUT indicator.

    It can energize an LED whenever a 1.2 ohm device is greater than .1 ohm from the desired.

    Attached is a block diagram of what to consider and the graph of the LED current. I used a LM317 as the Constant Current Source and 4AA batteries to provide 6V. The test current was approximately 100 mA. You could add one green LED and limiting resistor to indicate a "good" device under test.
     
    Last edited: Sep 4, 2013
  17. strantor

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    The spec that is provided is +/- .8%. It doesn't actually say this, but a spec like that is usually given to mean of measured. So yes, if you were measuring something that was 400 ohms, thé spec is +/- 3.2 ohms. But if you're measuring something that's 3 ohms, the spec is +/-24 milliohms, like I already said.

    ..aaaaand my first link to the one out of Hong Kong is spec'd for .1 ohms too. So what's wrong with that one?
     
  18. JoeJester

    AAC Fanatic!

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    Spend your money on a good DMM. For a simple tester, use two resistors (E96 or E192 series), one to set the current to 100 mA and one resistor to use as a standard.

    Attached is a LM317 based Constant Current source.

    Calculations can be done in your head.

    On edit ... added a scale to demonstrate the limitations. Keep your resistors on the linear portion of the chart.
     
    Last edited: Sep 4, 2013
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  19. cvedrick

    Thread Starter New Member

    Sep 3, 2013
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    For the stranthor, maybe I am reading this wrong....

    Resistance

    400Ω/4kΩ/40kΩ/400kΩ/4MΩ/40MΩ ±(0.8%+1)

    The lowest resistance scale is 400Ω if the tolerances are full scale, the deviation can easily be 3.2 +1 If indicated value, then 1.5Ω could well be off 1.012Ω
     
  20. strantor

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    good point. I didn't notice the +1. I must admit, I'm not sure what that means. This Vichy is a shameless copy of the Fluke 170, which has a similar spec:
    Like I said, I don't know, but I suspect that the +1 may be taking into consideration meter lead resistance. I know that if I put my Fluke into ohms mode and touch the two probes together, I will read 1.XXΩ. This isn't a fault, it is the resistance of my leads. On my Fluke 189 I can touch my leads together, hit REL (relative measurement) and it will zero the display so that my future measurements do not include the meter lead resistance. The Fluke 189 manual seems to jive with my +1 theory (note 3, pg 7-8). The Vichy VC97 does not have this feature, nor does the Fluke 170. But with either meter, you could simply touch your leads together and record the resistance, then subtract this from your readings.

    This is all discussion for the sake of discussion; the optimal solution has already been presented a few posts up, with the constant current source, measuring millivolts across the load. (but you still need a decent meter to measure the millivolts)


    EDIT: actually, it looks like the Vichy meter DOES have a "REL" function.
     
    Last edited: Sep 4, 2013
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