11264	2015-06-30 22:45:59	ve6jf	Measuring inductance
Message	Date	From	Subject
Everyone, I am looking for something to measure L/C and one of the items I had thought about was an AADE or similar. However I have a great opportunity to acquire a GenRad unit and am reconsidering my options. One of my concerns on L measurement in particular was a note in a review by Clifton Labs on the AADE that mentions that magnetic materials have a frequency dependent permeability with type 43 being one on the highest. At 10MHz, it states a toroid (type 43) would have an inductance of about 25% of that measured at 100 KHz. Apparently permeability declines rapidly above 1MHz with 43. Type 61 is more stable WRT frequency and is less affected. I think it is a non-issue for most work but could be a consideration with some core materials. The type 61 is less affected. But I'm curious about this topic now. I'm betting that the above exception is not a great concern in most instances, but stray L & C aside, how is it possible to accurately measure L at the lower frequencies these units operate at if inductance can vary so much with frequency due to the frequency dependent permeability of some materials? Thx for any comments... Jim VE6JF
11265	2015-07-01 05:17:54	Nick Kennedy	Re: Measuring inductance
In my experience, I'm not using ferrite cores in filters or VFOs, so the exact value of inductance isn't critical and just using the 'a' value suffices. (For chokes and transformers.) For iron powder and air core inductors, those types of meters are generally right on the money, as evidenced by the circuit performing as predicted. The same goes for C. It's an interesting point alright, but I haven't found the low frequency of measurement to be a drawback in practical terms. 73- Nick, WA5BDU
11266	2015-07-01 07:17:01	Thomas S. Knutsen	Re: Measuring inductance
Hello Jim. This is one of the more interesting experiments on inductors one can do. Unfortunately its one that requires access to a Vector Network Analyzer (VNA) so you are able to get some HF information about the toroids. This is quite basic physics involved, but the experiments are less than straight forward. All toroids radiate, some just less than others, and most of them less than a air wound inductor. The amount of radiation for a ferrite transformer can be estimated by winding a transformer on it, and measuring the coupling factor (k). Given that there is no heating in the core (keep power low) then the k factor should show how much of the fields are radiated. For 43 ferrite, this should be on the order of 0.98 or 98%, leading to less than 2% of the field being radiated. The inductance will have a distribution depending on the type of ferrite. There are differences between the batches of ferrite making the whole design of inductors on ferrite a hit and miss. I did a test by winding 6 turns on a FT37-43 core and measuring the inductance over the range 100KHz to 30MHz. You can see the plot here: http://i.imgur.com/dsm6h0T.png The red trace is the inductance, smith chart is impedance as recalculated from a I\V measurement. Perhaps the more interesting part is when you add in a estimation of the Q. Notice here that I use estimation, this is one of those measurements where getting high accuracy is difficult. Solving for the Q you get the pink graph here: http://i.imgur.com/y5AlzAG.png As you can see the graph is noisy, accurate Q measurements are difficult. As you see, permeability µ of the material decreases from a couple of MHz, leading to reduced inductance. This is a fact that we can use both to make impedance transfomers with constant k factor over several octaves and to suppress EMI. Fair-Rite (those who produce Amidon cores) have quite a lot of interesting information including some formulas that explains this on their homepage. 63 materials have less permeability, and as such have less slope, leading to higher frequency usage. Its worthwhile to do some experiments to measure k factor and inductance on several types of ferrite cores with different materials, this leads to more insight into how ferrrite inductors and transformers works. Correct design of inductors and impedance transformers are quite difficult. There is a lot of lore around, and several well known designers seems to not understand the difference between ferrite and iron powder cores. This can be witnessed by those that have ferrite cores cach fire or even explode in baluns. In closing, I would like to reccomend a book: Ferromagnetic-Core Design and Application Handbook by Doug Demaw (W1FB) 73 de Thomas LA3PNA. 2015-07-01 7:45 GMT+02:00 ve6jf@yahoo.com [emrfd] <emrfd@yahoogroups.com>: Everyone, I am looking for something to measure L/C and one of the items I had thought about was an AADE or similar. However I have a great opportunity to acquire a GenRad unit and am reconsidering my options. One of my concerns on L measurement in particular was a note in a review by Clifton Labs on the AADE that mentions that magnetic materials have a frequency dependent permeability with type 43 being one on the highest. At 10MHz, it states a toroid (type 43) would have an inductance of about 25% of that measured at 100 KHz. Apparently permeability declines rapidly above 1MHz with 43. Type 61 is more stable WRT frequency and is less affected. I think it is a non-issue for most work but could be a consideration with some core materials. The type 61 is less affected. But I'm curious about this topic now. I'm betting that the above exception is not a great concern in most instances, but stray L & C aside, how is it possible to accurately measure L at the lower frequencies these units operate at if inductance can vary so much with frequency due to the frequency dependent permeability of some materials? Thx for any comments... Jim VE6JF
11267	2015-07-01 07:24:31	Ashhar Farhan	Re: Measuring inductance
A really simple way to measure inductances is to use a colpitts oscillator with known capacitances. just plug in the unknown inductor and measure the frequency. it is quite an accurate way of measuring. as accurate as your frequency meter. you can also measure up really small inductances by putting them in series with known inductances. I can measure 10nh resolution at 5 mhz with this setup. - f
11268	2015-07-01 09:56:06	ve6jf	Re: Measuring inductance
Thanks to all for the responses. > A really simple way to measure inductances is to use a colpitts oscillator with known capacitances. Great idea Ashhar & solved one of my concerns. Thomas: I have just ordered the book. For the benefit of other Canadians, it is available through Radioworld here in Canada. > snipped In closing, I would like to reccomend a book: Ferromagnetic-Core Design and Application Handbook by Doug Demaw (W1FB) 73 de Thomas LA3PNA. >
11269	2015-07-01 14:23:12	Graham / KE9H	Re: Measuring inductance
Powdered Iron materials provide a relatively stable inductance versus frequency. Examples are -2, -6, -10 materials. These can be used for tuning circuits. Ferrite materials, which include type 43 and 61, have much higher permeability, but walk around with frequency, DC current in the core, temperature. They should not be used for applications where the exact inductance is important, but are used in wide-band transformers, switching power transformers, and power chokes. --- Graham / KE9H ==
11271	2015-07-01 20:46:23	farhanbox@gmail.c...	Re: Measuring inductance
has anyone bought this http://www.smarttweezers.in/ ? ------ Original message------
11272	2015-07-02 08:30:51	mvs_sarma@ymail.c...	Re: Measuring inductance
the smart tweezers might be OK for an industry, definitely not for Hobby guys like us at few hundred $ cost. even the VK3BHR lcmeter2 using 16F628A is a great nice gift to all of us by Phil Rice, the great professor. It resolves only 10nH and not lower. I had made many of them. I really search for some one to recode it for better resolution like 1nH to cater serous RF hobby.