Review: High-precision L/C Inductance Capacitance meter (35-50 USD)

[vizer]

Has anyone tried out this eBay USB L/C meter?   The listing looks like this:  
Update High-precision L/C Inductance Capacitance meter,
one url is:
http://cgi.ebay.com/Update-High-precision-L-C-Inductance-Capacitance-meter-/190472431824?pt=LH_DefaultDomain_0&hash=item2c590aa8d0

(Note: Another model without range of Big capacitance costs less by 10-15 USD. )

Description (as claimed ):  
Measurement Accuracy: 1% (except for portions of ranges where it is up to 5% or more! )
Capacitance measuring range: 0.01pF-10uF
Minimum resolution: 0.01pF
Inductance Range: 0.001uH-100mH
Minimum resolution: 0.001uH
Large inductance measurement range: 0.001mH-100H
Minimum resolution: 0.001mH
Large capacitance measuring range: 1uF-100mF
Minimum resolution: 0.01uF
Test Frequency: capacitors, inductors file of about 500kHz, a large inductance of about 500Hz,
          Can display the current value of the test frequency
Effective display digits: 4
Display: 1602 LCD
Power supply:Mini USB interface to take power
What's include?
       Update High-precision L/C Inductance Capacitance meter
       Short USB cable (some sellers may not include cable)

[Mechatrommer]

i've been very bad at analog design. i saw something like this open schematiced online, but no open source code and no buy option. this is what i'm looking for, just buy ready made stuff, should i go along?
and let say if i manage to change/hack the mcu... is there any possiblity modding this analog circuit to esr as well? need an expert insight on this.

[vizer]

Further capabilities for handling esr, usb communications, etc., are definitely desired and more than welcome. Qualified designers are definitely encouraged to look into such chores.

Until such further features appear, however, the existing capabilities allow some handy measurements that I haven't before had at so low cost. For example, hanging the unit off a usb port of my netbook displaying some coil equations and calculators, together with some wire and a small caliper, I've been easily exercizing the 4-5 inductance readings/sec. to become better acquainted with the inductance of many configurations of air-core coils. Adding various cores will surely contribute their own complications to explore. 

[Bored@Work]

i've been very bad at analog design. i saw something like this open schematiced online, but no open source code and no buy option. this is what i'm looking for, just buy ready made stuff, should i go along?
and let say if i manage to change/hack the mcu... is there any possiblity modding this analog circuit to esr as well? need an expert insight on this.

These meters are easy to DIY. Here is one, including source code http://cappels.org/dproj/EvenBetterLCMeter/Even_Better_LC_Meter.html

Scroll down to the end to see with what construction technique the author got away (classic breadbording style).

[vizer]

Very interesting reading. I would also like to find more detail on the accuracy and other limitations when such meters are in use as working  instruments.

[saturation]

You can make your own even simpler since the relationship in high pass filters are:

http://www.play-hookey.com/ac_theory/hi_pass_filters.html


So you can build this very quickly and measure either capacitance or inductance; getting a meter really matters if you don't have the time to calculate it as listed here:

https://www.eevblog.com/forum/index.php?topic=533.msg7756#msg7756

[Mechatrommer]

and here is the diy link i was talking about http://electronics-diy.com/lc_meter.php

[vizer]

That looks much like the version without the range of Big capacitance values.

[Mechatrommer]

one of my concern is how to get all those parts bought in one piece of package. buying from many separate sellers (probably in bulk for cheaper parts) might ends me at the same price (or more) as the already made one. not to mention the time needed for coding, assembling, blowing, disasembling, blowing, coding etc etc. actually just found out the site selling it at $60, with nice casing though. the ebay link in OP uses arm as its processor, not pic.

[vizer]

All that is very much to the point for me at this time. A good case would be really nice. Could you provide a URL?

[Balaur]

I've built this version myself:
http://sites.google.com/site/vk3bhr/home/index2-html

I like it, very useful for all these inductors I have around.

Seems quite precise for small value caps too.
For tens ~ hundreds of nanofarads, it compares very favorable to an Agilent bench multimeter.

[Mechatrommer]

All that is very much to the point for me at this time. A good case would be really nice. Could you provide a URL?

do you mean this? http://electronics-diy.com/store.php?sel=kits

[vizer]

Yes, shafri, that's a nice case. Will have to check on some of these fine options!
Lots of great help  (and without making a lot of how far behind the curve I am on this topic  ). Thanks all around! 

[saturation]

That's good math work, safri, but the equation to use is different and far simpler.

Notice how all LCR meters use a specific freuquency for a range of C or L, that's roughly how this works.









Resistor here is a constant, use any thin film or carbon composite.  Don't use wirewound as its a inductor too.

Now, put your unknown capacitor or inductor in the circuit above, as necessary.

Get a function or audio generator generator as Vin, and measure its output Voltage with a scope for say 500kHz or 500 Hz, just to copy the frequencies the device in the original post used.  Say adjust it for 1 Vp-p  so its easy to read.

If your cap is as big as your pinky or your inductor is fairly large, use the 500 Hz.

Now connect the generator to Vin and the scope to Vout.  Adjust the output frequency precisely until the output voltage is 0.707Vp-p.  That's the fc.

Now that you have fc, substitute it algebraically into the equation and that's your L or C.

Units:

fc= Hz
R = ohms
C = farads
L = henry

For example, you have an unknown small inductor.
 
Use the inductor high pass circuit above.  You have some resistor lying around that is 500,000 ohms.

You pass 500kHz into it and it comes out 1V p-p.  Adjusting frequency down [ since its a high pass filter its already passing everything ABOVE the cutoff] , at 300kHz the Vout is 0.707 p-p.

Solving:

L = R / 2 x pi x fc

L = 500,000 / 2 x pi x 300,000 Hz

L = 0.265 H or 265 mH.



As alm and I suggested in a old post, most hobbyist only need a good scope, like the Rigol 1052E, a function generator, a good DMM and PSU.  An LCR meter is nice to have, but if you don't measure C or L often, and a good DMM comes with C meter already too, you can rig one up fairly quickly and get very accurate results with it.

Some modifications of the same rig can calculate ESR, DF, and Q too.  But they can be more tedious to do on-the-fly, so it would be worth it to buy or build an ESR meter than a LCR meter without ESR built in.

http://octopus.freeyellow.com/esr.html









 

[vizer]

Having this thread mostly for review of the device first identified, moving some/most of this analysis and design over to the section for technical discussion, along with cross references between both threads seems a good idea. I also think you advanced members could best advise on this move. How about it?

[Mechatrommer]

the analysis is moved to https://www.eevblog.com/forum/index.php?topic=1869.msg25864#msg25864

[alm]

Now connect the generator to Vin and the scope to Vout.  Adjust the output frequency precisely until the output voltage is 0.707Vp-p.  That's the fc.

I would probably measure both Vin and Vout with two scope channels (or DMM's if they're accurate at that frequency), to account for your circuit loading the generator's output circuit. Making sure the impedance is significantly larger than the output impedance of your generator (probably either 50ohm or 600ohm) is another solution.

[vizer]

The move of some analysis and design (and maybe more to move, too) is surely appropriate, even if I am happy as punch to have had such fine material show up in a thread I started!

[saturation]

Yes, these are very good ideas; if you have a Rigol 1052E you can put one channel each as Vin and Vout.

To minimize loading, its a good idea to use high resistance, 100x the expected generator and scope impedance, say 5000 ohm and up.

That said, there was enough curiosity in this that I tried measuring a few caps with the Rigol, as I used to do this with my old analog Trio scope.

I've posted my experiences on the 'design' thread.

Thanks a bunch alm for pointing out those reminders.

Now connect the generator to Vin and the scope to Vout.  Adjust the output frequency precisely until the output voltage is 0.707Vp-p.  That's the fc.

I would probably measure both Vin and Vout with two scope channels (or DMM's if they're accurate at that frequency), to account for your circuit loading the generator's output circuit. Making sure the impedance is significantly larger than the output impedance of your generator (probably either 50ohm or 600ohm) is another solution.

[saturation]

You're very welcome, some analog approaches are far simpler than the digital and require just the very basics tools in a lab and a calculator.  But, a digital meter is something that makes life easier in the long run; if you had to measure caps all day, the method I show will eventually lead to user measurement error from repetitive measurement fatigue.

The move of some analysis and design (and maybe more to move, too) is surely appropriate, even if I am happy as punch to have had such fine material show up in a thread I started!

[Mechatrommer]

You're very welcome, some analog approaches are far simpler than the digital...

The move of some analysis and design (and maybe more to move, too) is surely appropriate...

i think he meant... "move the hell of your all very nice analysis out of here! this thread is meant to review the cheapy LCR meter only!"... well... with some exageration

[vizer]

I'm sure you "didn't mean that in a bad way," shafri. Also, while I've not seen my mother wear combat boots, and not heard her friends mention such proclivities on her part, you may not find that at all conclusive. I admit to being not so swift, having first taken the five star shapes next to your Hero-Member designation to represent gold stars for laudable contribution, though I now more clearly see they represent shurikens. ... well... with some exaggeration.

[Bored@Work]

Having this thread mostly for review of the device first identified, moving some/most of this analysis and design over to the section for technical discussion, along with cross references between both threads seems a good idea.

I was about to offer an opinion on that  high-precision L/C inductance capacitance meter. But then I saw your "get of my lawnthread" request and couldn't be bothered.