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Killed my meter (again)

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Adam Munich

Wed Feb 02 2011, 04:34AM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

Ugh, so I'm not going to buy any more expensive multimeters. I'll stick with the $3 cheap ones, and i f I need a true RMS reading I'll just use my scope. I do need a method of testing capacitance though, so I found this on egay.

It's an LC meter, supposedly capable of the following,

Measurement accuracy:1%
Capacitance measuring range: 0.01 pF - 10uF minimum resolution 0.01 pF
Big Capacitance measuring range 1uF-100mF minimum resolution:0.01UF
Inductance measuring range: 0.001 uH - 100mH minimum resolution 0.001uH
Big inductance measuring range: 0.001 mH - 100H minimum resolution 0.001mH
Test frequency range: L/C about 500KHZ/Big inductance 500HZ
Effective display digits: 4 digits

So... does anyone know if this this thing legit? I've never had an L meter and it would be very useful if I start doing radio circuits.

Patrick

Wed Feb 02 2011, 05:22AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

I had a BK Precision 875B ($299 years ago), LCR would measure down to 0.001ohms, 200pf and 2uH, it was great very useful saves me from guessing and calculating, I mean youd pick it up and poof theres your answer. But there sensitive, Id look at BK and fluke and others. Spec them out for function versus cost, 0.01pf sounds suspicous both my old BK and new no-name have trouble with 0.0 up to 3.0 pF not being steady and flickering alot, so that 0.01pF sounds like crap.

get one it will save you trouble and pain later. cant speek to the one which you site though.

Adam Munich

Wed Feb 02 2011, 05:28AM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

Yeah I figured that sounded fishy, but 5pf resolution is good enough for radio stuff. I'll look around, but $50 is kind of my maximum budget.

Patrick

Wed Feb 02 2011, 05:42AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

yeah well I got a no-name china one for 69$ only does C though, as I blew out my BK when I measured a electrolytic cap that was totally discharged, then I removed the resistor, waited a minute to do some set up... then measured it and SNAP!!! a spark (it self recovered a slight bit) and the meter never worked on any range ever again not r -c or l. Bricked the dam thing.

Conundrum

Wed Feb 02 2011, 06:05AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

hah, i fried a meter once like that.
Figured that the energy stored in a bottle capacitor once shorted was nil, so was safe to measure a few seconds later. BAD move.
Strangely enough the frequency range still worked...

Then there was the meter a friend toasted the resistance range on by trying to measure the impedance on a CB but not realising you were supposed to have it unpowered.

-A

Matt Edwards

Wed Feb 02 2011, 06:12AM

Registered Member #2838 Joined: Fri Apr 30 2010, 07:55PM
Location: tehachapi, CA
Posts: 333

That sucks dude! I always check with my $3 meter first when I am unsure. I killed two good meters before I started doing that... Now it is a must!

Adam Munich

Wed Feb 02 2011, 06:22AM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

Hmm, same item only a couple bux cheaper. This listing also gives some realistic accuracy values and some pictures.

Nicko

Wed Feb 02 2011, 07:02AM

Registered Member #1334 Joined: Tue Feb 19 2008, 04:37PM
Location: Nr. London, UK
Posts: 615

Grenadier wrote ...

Ugh, so I'm not going to buy any more expensive multimeters. I'll stick with the $3 cheap ones, and i f I need a true RMS reading I'll just use my scope. I do need a method of testing capacitance though, so I found this on egay.

We've been looking at this very item on one of the UK audio forums - one of the guys got one and compared it against his Fluke - it came out pretty well (within a few %). There are a couple of versions available, including an "enhanced range" one...

klugesmith

Wed Feb 02 2011, 09:00AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Grenadier wrote ...
So... does anyone know if this this thing legit? I've never had an L meter and it would be very useful if I start doing radio circuits.

I think it's a knock-off or derivative of this product, which was a project published in a EE magazine almost 20 years ago.

They all use a microcontroller to measure the frequency of an internal LC oscillator before and after adding the unknown L or C. Here's another knock-off showing the schematic:

You can get the same accuracy more cheaply, if not more conveniently, by building just the oscillator with LM311, reference L and C, and a few resistors. Measure the frequency with DVM or other instrument of your choice, before & after switching in the unknown. Do the calculation on your computer.

Real inductors, esp. with ferrous cores, and to a lesser extent capacitors have significantly non-ideal behavior. The "correct" L value depends on frequency and amplitude, neither of which is fixed in these cheapie "meters".
These are not in the same class as "real" LCR meters, which have a defined sinusoidal stimulus frequency and amplitude, measure the response amplitude and phase, and report L+R or C+R or vector impedance at the given excitation condition.

But the guy I take to be the "inventor" reports excellent accuracy in measuring high quality standard inductors & capacitors, as summarized at the bottom of

Nicko

Wed Feb 02 2011, 10:02AM

Registered Member #1334 Joined: Tue Feb 19 2008, 04:37PM
Location: Nr. London, UK
Posts: 615

Klugesmith wrote ...

Grenadier wrote ...
So... does anyone know if this this thing legit? I've never had an L meter and it would be very useful if I start doing radio circuits.

I think it's a knock-off or derivative of this product, ...

The basic principle has been around forever - applying a uP to it and a budget price is what's different.

Main issue is that the OP mentions radio circuits - there is no "Q" measurement from these cheapo devices, and measurement is (typically) at a fixed, fairly low, frequency. You also have potential issues in zeroing and measurement of small (if doing RF) inductors & caps. They can also be confused by some boundary conditions and easily damaged if you forget to discharge caps before testing.

For general workshop day-to-day stuff, I use a Peak Electronics Atlas LCR (available in the USA too)

- this is a great device and the company provide excellent after-sales service (re-cal etc.). Nice people. I have their DCA (component analyzer) too - life saver when dealing with odd SMDs

Cheers

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