Low-ohm meter, or what? - diyAudio
Go Back   Home > Forums > Design & Build > Equipment & Tools

Equipment & Tools From test equipment to hand tools

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 18th April 2011, 09:33 AM   #1
diyAudio Member
 
Join Date: Sep 2005
Default Low-ohm meter, or what?

I know nothing about electronics, and in another forum:
Driver TS crosscheck.

there was suggested to use a low-ohm meter to measure speaker driver Re as you would then get more reliable results.

There was one suggested (Low Ohm Meter - Measures 0.001 up to 1.999 Ohm), but its range is only 0.001 - 1.999 ohms, is that range common for low-ohm meters? I guess drivers have higher ohm values as well? You would also need a reliable ammeter to calibrate the device. There was also some issues for causion (on a native forum) about thermal effects, etc.

There was also suggested these parts:
Kjell & Company - Nordens bredaste sortiment av tillbehr fr hemelektronik
Kjell & Company - Nordens bredaste sortiment av tillbehr fr hemelektronik
(in swedish, but I guess you will know what it is anyway)

which I don't really understand what you could do with for my inteded purpose.

The good thing about the low-ohm meter is its four point measuring for example. A bench multi meter has also been suggested, but then I guess that prices really go up for reliable ones?

It got much more complicated than I first expected. I intend further on start building power amp. kits, but would I be better served just go measuring Re with a DMM?

Last edited by buggsson; 18th April 2011 at 09:46 AM.
  Reply With Quote
Old 18th April 2011, 10:56 AM   #2
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
Yes that is a normal range for low-ohm meters. They are not appropriate for measuring speakers, they are intended for things like measuring resistance of earth cabling etc.

All you need to do with your meter is short the probes to obtain the lead resistance then subtract this from your reading.

Note that in the thread you linked to, Ron suggested BUILDING a low-ohm measuring device using a current source, not an actual low-ohm meter.
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more.

Last edited by richie00boy; 18th April 2011 at 10:58 AM.
  Reply With Quote
Old 18th April 2011, 11:26 AM   #3
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Using a current source and calibrating your DMM & source with a high accuracy resistor, gives very good amateur results at very low cost.
A "normal DMM set to lowest resistance measures 199.9ohm at full scale.
The resolution of this scale is 0r1. Not nearly good enough for low ohm measurements.

With a range of 10mA and 100mA and 1A CCSs, you can use your 199.9mVdc scale to measure to milli-ohms (0r00x) accurately.
__________________
regards Andrew T.

Last edited by AndrewT; 18th April 2011 at 11:29 AM.
  Reply With Quote
Old 18th April 2011, 04:01 PM   #4
diyAudio Member
 
Join Date: Jul 2010
Heres my PRACTICAL METHOD 1. you need to get a constant current diode, ccd 2. let say you get a nominal 1.8ma ccd 3. connect it up to a 9v supply and measure the current flow, say its 1767uA 4. now connect in series with ccd, your driver and measure the voltage across it 5. Re=Vdriver/1767uA (check the accuracy of your results by measuring a 10R 0.1% resistor)

Last edited by Henry8; 18th April 2011 at 04:04 PM.
  Reply With Quote
Old 18th April 2011, 05:47 PM   #5
diyAudio Member
 
Join Date: Nov 2005
I'm not sure I understand the reasoning behind the high tech resistance measurements.

On a 5 ohm copper coil at 20C, you get 5.4 ohms at 40C. If you can resolve to .1 ohm with your measurement you're doing pretty good.

Getting the accuracy from a regular DMM on the lowest range will probably require that you zero the leads before you measure.

.1 Ohm will not significantly affect the response of an 8 ohm nominal speaker unless it's in a bandpass box or something, and even then, it's going to go out of tune by more than that if you run it to max power.
  Reply With Quote
Old 19th April 2011, 03:53 AM   #6
diyAudio Member
 
Join Date: Jan 2011
Default A Idea

Just buy a fluke lol
  Reply With Quote
Old 19th April 2011, 10:44 PM   #7
diyAudio Member
 
Bksabath's Avatar
 
Join Date: Dec 2007
Constant current methode works a treat

LM317 and one resistor to set the constant current
Drawing in the LM317 spec sheet
with 100 mA I have measured a batch of MPC74 0.22 homs and go the meter reading volt across them in milli volts.

There is here a tread about a LCR meter designed for speakers that may be worth looking at
An awesome ZLCR meter


How do you post links to treads is what get me cornered
so if you could help me on how to do this I will find it for you
  Reply With Quote
Old 19th April 2011, 11:02 PM   #8
AJT is offline AJT  Philippines
diyAudio Moderator
 
AJT's Avatar
 
Join Date: May 2003
Location: Palatiw, Pasig City
easy way is just copy the url address on your browser pane and paste it on your posts...
  Reply With Quote
Old 19th April 2011, 11:25 PM   #9
Ron E is offline Ron E  United States
diyAudio Member
 
Ron E's Avatar
 
Join Date: Jun 2002
Location: USA, MN
Quote:
Originally Posted by Andrew Eckhardt View Post
I'm not sure I understand the reasoning behind the high tech resistance measurements.
This thread came from a discussion about crosschecking T/S measurements. I suggested a (low tech) way to build an add-on to get more precision in DCR measurements (helps with inductors too ) Some of my inexpensive meters bounce ~+/- 0.2 ohms or so with the leads shorted, so what should I subtract?

I wouldn't suggest buying a milliohmmeter unless you have another use for it.
__________________
Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. --Carl Sagan
Armaments, universal debt, and planned obsolescence--those are the three pillars of Western prosperity. Aldous Huxley
  Reply With Quote
Old 20th April 2011, 09:25 AM   #10
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Quote:
Originally Posted by Ron E View Post
Some of my inexpensive meters bounce ~+/- 0.2 ohms or so with the leads shorted,
Don't use the ohm-meter function unless there is absolutely no other way to get your measurement. It's really a very last resort.

Use the voltmeter function. One of the scales of the voltmeter will be the most accurate of all the functions with the DMM. It might be 1.999Vdc or just possibly 199.9mVdc, check the specification.

Use a current and voltage to measure resistances accurately.
__________________
regards Andrew T.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
A LED meter, Volt meter, power meter or light indicator... a nice gadget destroyer X Solid State 5 25th February 2011 06:30 PM
2 ohm stable low power amp oublie Class D 18 17th December 2009 01:20 PM
PPI 2050AM low ohm led flashes on and off Rigs64 Car Audio 8 28th September 2006 09:55 PM
Fs Measurement - Baffle, low ohm amp? kimbo Multi-Way 27 30th January 2005 03:01 AM
Plate amps- high vs low ohm connections? amt Solid State 1 30th January 2004 10:24 PM


New To Site? Need Help?

All times are GMT. The time now is 04:30 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2