Author Topic: Bench LCR Options?  (Read 18482 times)

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Offline PA4TIM

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Re: Bench LCR Options?
« Reply #25 on: June 24, 2013, 04:36:05 pm »
Negative resistance can be caused by open/short calibration with longer wires or an other fixture or the use of something like a relative or zero function. Mayby some former owner has changes standard start up setting so it keeps relative on ( i do not know the meter so it is just a suggestion)
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Offline branadic

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Re: Bench LCR Options?
« Reply #26 on: June 24, 2013, 07:46:24 pm »
What about buying a vector network analyzer? It includes LCR meter as well and comes with a few other measurement possibilities. I recommend the VNWA by DG8SAQ:

http://www.sdr-kits.net/Webshop/index.php?cPath=5&osCsid=bbpke74flue2i4ush8gotsv0a4

I have the VNWA2.6 and developed a 36MHz tcxo upgrade so it's also possible to measure crystals and crystal filters. With such a device you are able to evaluate the equivalent circuit parameters for nearly every device, active or passive.
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Offline PA4TIM

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Re: Bench LCR Options?
« Reply #27 on: June 24, 2013, 08:11:25 pm »
I agree, i have build one ( a 2.6 with one of the first with a USB options and builded a testset)  and I have a full features 3 version with RF-IV head that I have builded to in an RF tight enclusure with its own powersupply.  ( and an ancient  HP VNA from 1968) beside that I have a whole bunch of GR bridges, some ESR meters and LCR meters. I can measure capacitance with aF resolution , selfinductance with 200 pH resolution en Resistance from < 1 mOhm upto 10E15 Ohm ( that is peta Ohm if I have it right ?)

For those interested in VNAs: I have written a serie turorials about using a vna. They are on my website.
( also a page about using capacitance bridged and a page with explnations about LCR meters.
www.pa4tim.nl my collection measurement gear and experiments Also lots of info about network analyse
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alm

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Re: Bench LCR Options?
« Reply #28 on: June 24, 2013, 09:28:00 pm »
Is it really practical to use a VNA as a glorified LCR meter? I know you can measure L/C/R, including frequency dependency and other fancy stuff, but how long would it take to say measure C and D for a cap, something that would take a few seconds on your average LCR meter?
 

Offline dr.diesel

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Re: Bench LCR Options?
« Reply #29 on: June 24, 2013, 09:30:12 pm »
VNA does add a few nice features, but then also requires a computer to operate.  I much prefer a dedicated instrument.  But thanks for the suggestion!

Offline PA4TIM

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Re: Bench LCR Options?
« Reply #30 on: June 24, 2013, 10:13:53 pm »
No, a VNA is not a replacement for a good LCR meter. It can not measusre a broad range without the right technics and fixtures. It need to be calibrated and it takes time. Result is as good as your calibration and calibration it self is close to voodo  ;)

But it is a good addition. When you want to know the selfinductance or capacitance vs frequency and paracitic parameters. I measured things like fF and very low  ESR values but that are not standard measurement. I use special made fixtures, and use things like de-embedding and customtraces. Using a vna realy the right way will cost you a few years and a lot of a study. And you need good fixtures, perfect cables, calibration kits etc. But they are great.

This is a capacitor over a 100 MHz sweep using an old HP vna. You see it does not stay a capacitor


I use it for instance as LCR meter when I make RF filters. I calculate values, build a dummy filterbox like the final filter and then measure and tune the parts at the working frequency on the right location. i then build the filter and 9 out of 10 times it is perfect and build without adjustable parts.
www.pa4tim.nl my collection measurement gear and experiments Also lots of info about network analyse
www.schneiderelectronicsrepair.nl  repair of test and calibration equipment
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Offline Conrad Hoffman

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Re: Bench LCR Options?
« Reply #31 on: June 25, 2013, 08:05:33 pm »
I love all my old GR equipment but there's a huge hole in the frequency range that starts at 10 kHz for most bridges. If I could have only one bridge it would be the 1608, but it's best at 1kHz. A used better model of the Digibridge will do various frequencies. Another idea is to use something like the free Visual Analyser- http://www.sillanumsoft.org/

It has an LCR meter built in and some sound cards will go 100 kHz and higher.
 

Offline branadic

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Re: Bench LCR Options?
« Reply #32 on: June 25, 2013, 08:40:50 pm »
Quote
No, a VNA is not a replacement for a good LCR meter. It can not measusre a broad range without the right technics and fixtures.

Can't agree tha. It's the same with dedicated LCR meters too, as long as you are not able to understand what you want to measure and as long as you don't have the right cables/fixtures you measure everthing but not the dut, but stray capacitance and stray inductance off your cable.
The advantage of a vna is that you can see the behavior over frequency and in most cases this is the important thing as you want a cap to act as a cap in your application and an inductor as an inductor. LCR meters often measure only at a single frequency, for example at 1kHz, 100kHz or 1MHz. Some more expensive meters allow to vary the measurement frequency. But my guess is an Agilent 4284A Precision LCR Meter (measures also Re & Im or |Z| & phase angle form 75kHz up to 30MHz) is not within the budget.

Calibrating a vna is no voodoo, 'cause in most cases you don't want to measure the hole frequency range up to a few GHz, 1kHz up to 100MHz is more than enough in normal cases. And you can save cal data for several test fixture setups and frequency ranges. Using a vna is not that difficult and you don't need special background, as long as you don't want to develope your own complex equivalent circuits by measuring the S-parameters.

On the other hand an impedance analyzer (have the good old HP 9194A at work, 100Hz up to a few MHz) is also good choise. Gives you nearly the same results like the vna does (|Z| and phase angle), but the working principle is different, which explains the frequency range.

There is this USB device called miniVNA, it's much easier to calibrate but not off the same reolution and accuracy in frequency and magnitude, but it's a good point to start from and can be used as a simple LCR meter with a free excel tool too, as far as I know.
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Offline PA4TIM

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Re: Bench LCR Options?
« Reply #33 on: June 25, 2013, 10:03:33 pm »
Brainadict, just picture, you are repairing a TV or audio amp and want to know the capacitance and D or ESR of the 10.000 uF electrolitic filter cap at 100 Hz. Do you think a VNA will be helpfull ? Or a 1000 uF with a ESR of 0.05 Ohm in a switcher at 15 kHz, that is Z=(0.05-j0,0106) Not the area a vna is very good. It gives impressive values with lots of digits but the accuracy in that area is very bad unless you use special measure techniques. Probably you will manage to measure this with a vna, and I can do to, but people who need advise about a LCR meter will not become happy with a VNA. And one mistake with a bit of charge and you kill your vna.
Besides that,  I do not see my self power up the laptop, vna, calibrate it, solder a cap to the fixture and make a sweep. If you have it always powered on, why not, but it is like dragging a caravan behind a ferrari, or drivinf a defender over a circuit....  In that time I have measured 10 caps with my GR1608 and then I'm sure the value is correct. Even my 1620 is quicker, but like Conrad, I love my bridges but for quick results during building or repairing I use a IET DE-5000. For radiowork, filters, component research I use the vna.

(@conrad,  the GR-1608 is also one of my favorites in use (but the 1620 is my pride), but a beautifull GR-1603A and an original manual  is now on it journey to Holland)

For me and a lot of experienced users calibration is no voodoo, but for many users it is. And your results will be as good as the calibration.

You developed the Xtal option so you can measure Xtals ? I do not have that option, not in my 2.6 and my 3 is production number 1, Toms proto, as far as I remember it has a tcxo or something like that, not the normal Xtal but I never really looked )  both are able to measure Xtals with the Xtal tool in Toms software. If you install the Xtal, do you need extra software ? But my 2.6 performs slighty better as my 3. My 3 will not go over 1300, the 2.6 I have used it over 1500 but that was more indication then measurement)
www.pa4tim.nl my collection measurement gear and experiments Also lots of info about network analyse
www.schneiderelectronicsrepair.nl  repair of test and calibration equipment
https://www.youtube.com/user/pa4tim my youtube channel
 

Offline dr.diesel

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Re: Bench LCR Options?
« Reply #34 on: July 20, 2013, 06:11:25 pm »
Took it long enough to get here!

Offline The Electrician

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Re: Bench LCR Options?
« Reply #35 on: July 21, 2013, 03:32:09 am »
What accessories did you get with it?  I see cables; are those cables from Hameg, perhaps the HZ33 or HZ34?  Did you get a test fixture, such as the HZ181?

Now that you have a meter with the standard 4 BNC interface you can use one of the standard fixtures, such as this:

http://www.ebay.com/itm/Agilent-HP-16047A-Test-Fixture-Axial-and-Radial-Warranty-/230851509277?pt=LH_DefaultDomain_0&hash=item35bfd27c1d

It's a little pricey, however.  There is a fairly good one available from China:

http://www.ebay.com/itm/TH26001A-4-terminal-test-fixture-for-LCR-meter-TH2811D-/130715715329?pt=LH_DefaultDomain_0&hash=item1e6f438701

I bought one of them, and it works fine up to 200 kHz.

Do the cables you show on the instrument terminate in Kelvin clips?  There are inexpensive Kelvin clips available on eBay for this interface.

Edit:  I think I see the answer to my question about accessories you got with it.  The data sheet says you get the HZ184 with Kelvin test cable and the HZ188 SMD test fixture.  Is that what you got?
« Last Edit: July 21, 2013, 03:38:59 am by The Electrician »
 

Offline Vgkid

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Re: Bench LCR Options?
« Reply #36 on: July 21, 2013, 05:25:52 am »
Is there a standard spacing for the bnc adapters?
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Offline The Electrician

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Re: Bench LCR Options?
« Reply #37 on: July 21, 2013, 07:52:57 am »
For modern instruments, yes, although I've seen a couple of much older units with oddball spacing.
 

Offline dr.diesel

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Re: Bench LCR Options?
« Reply #38 on: July 21, 2013, 01:43:07 pm »
Edit:  I think I see the answer to my question about accessories you got with it.  The data sheet says you get the HZ184 with Kelvin test cable and the HZ188 SMD test fixture.  Is that what you got?

Yup.  I might at some point spring for a through hole stab in fixture, but the probes are nice.

I'm quite surprised how much the value changes depending on how I clip the kelvin probes on small toroids.  I'll have to figure out what foot to stand on to get it right!


Offline The Electrician

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Re: Bench LCR Options?
« Reply #39 on: July 21, 2013, 03:56:25 pm »
I'm quite surprised how much the value changes depending on how I clip the kelvin probes on small toroids.  I'll have to figure out what foot to stand on to get it right!

I'm surprised by that.  Please tell us more, with details; perhaps in a new thread.
 

Offline dr.diesel

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Re: Bench LCR Options?
« Reply #40 on: July 21, 2013, 04:02:52 pm »
I'm surprised by that.  Please tell us more, with details; perhaps in a new thread.

I think I might, currently rearranging my lab, then I'll get back to it!

Offline KJDS

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Re: Bench LCR Options?
« Reply #41 on: July 22, 2013, 11:16:09 am »
Whilst VNAs are wonderful pieces of equipment, and I do love my HP8753C, they are not very accurate at measuring impedances that are a long way from 50 ohms.

If you want to measure LCR, then an LCR meter is far more useful.

Offline dr.diesel

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Re: Bench LCR Options?
« Reply #42 on: July 22, 2013, 11:22:16 am »
If you want to measure LCR, then an LCR meter is far more useful.

I am really happy with it, pissed off that I waited as long as I did to order one.

This has me really pondering about my next purchase.  I had planned to by one of the new MSO4000s from Rigol, but their support guys have been irritating me.  I'm going to give Hameg a more serious look before I go any further.


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