Help with Henries - Page 1
Forum section: electronics / beginners

author: trifusion
author_rank: Contributor
timestamp: January 28, 2025, 08:39:19 pm
content: I'm working for the first time with inductors. My knowledge of them is extremely rudimentary.I was hoping to make this circuit to detect metal:So I ordered from Aliexpress some 330uh (for the circuit above) and 2.2mh (which is another option for the same circuit to double the read range by also increasing the capacitors to 4700pF) inductors from Aliexpresshttps://www.aliexpress.com/item/1005004551447275.html.The circuit I am using to base the design off is here ...https://mm.digikey.com/Volume0/opasdata/d220001/medias/docus/1171/TDA0161.pdfrefer to Table 3 for the inductor values.I just received the inductors today and when I measure them with my TC1 they measure as 370uh and 3.7mh instead of 330uh and 2.2mh.Wondering a couple of things:1. Could my TC1 be off, I can only verify that the ohm meter on the TC1 matches my ohm meter.2. Is this a normal tolerance difference?3. I can probably try and adjust my circuit values, any thoughts on what the new capacitor values would be?4. Should I ask for a refund?Thank you for any assistance.Greg

author: Terry Bites
author_rank: Super Contributor
timestamp: January 28, 2025, 09:10:19 pm
content: 1. These meters are not very relaible.2. Buy your parts from a reputable supplier.3. A TC1 is a super vague description of your kit.These horrible things appear under dozens of model numbers.

author: TimFox
author_rank: Super Contributor
timestamp: January 28, 2025, 09:31:55 pm
content: The TDA0161 circuit works with a change in the coil’s series resistance when coupled externally to the detected object. This is discussed in the data sheet.Note the the data sheet examples show a very different coil geometric configuration from your power chokes.The external field between the center core and the outer diameter edge will couple more strongly than the end of a cored solenoid.Also note that some commercial coils are magnetically shielded to minimize coupling to outside objects.

author: Benta
author_rank: Super Contributor
timestamp: January 28, 2025, 09:39:44 pm
content: Erm... the 330 uH thing is not a normal inductor bought at xxxx.It's the detector coil, and you have to wind it yourself in a shape suited for what you want to detect.

author: trifusion
author_rank: Contributor
timestamp: January 28, 2025, 09:46:36 pm
content: Quote from: Benta on January 28, 2025, 09:39:44 pmI was also basing my design off of this ...https://www.st.com/web/en/resource/technical/document/data_brief/CD00190843.pdfas shown in this videoI know nothing about inductors .. am I way off base with this part?

author: Benta
author_rank: Super Contributor
timestamp: January 28, 2025, 10:22:15 pm
content: Not necessarily if it does what you want.But it has to be an "open" inductor, meaning that the magnetic field can be disturbed from the outside.A toriodal inductor wouldn't react at all, for instance.The problem is, that it's completely unspecified from the manufacturer, unless it's designed for the task.

author: Jeff eelcr
author_rank: Frequent Contributor
timestamp: January 29, 2025, 02:23:04 am
content: Inductors reading plus or minus 20% is normal for some manufactures and this is with acurate equipment.Jeff

author: PGPG
author_rank: Frequent Contributor
timestamp: January 29, 2025, 02:49:11 pm
content: In my opinion you should not start a new thread because you have just got inductors.I have written my previous answers only looking at your schematic and not looking into TDA0161 datasheet.Now I looked into it and I have for you a few questions you should ask yourself.In datasheet I don't see exact description how L1 and C1 should be selected, but in Table 3 you can see some proportion between them:30uH ---- 120pF300uH ---- 470pF2160uH -----4700pFSo where from is at your schematic 330uH and 470 000 pF?Don't you think that using 1000 times higher capacitance than in their example is asking for the circuit to not work?The same with C2. You also used 1000 times higher capacitance than in their example. Why?From Table 2 we see that C2 should be >150/f. So it looks that it is inverse proportional to working f.But for LC circuit f = 1/(2π√(LC)) so f is inverse proportional to √C1. It suggests that even if (from any reason) you increase C1 1000 times you should increase C2 only √1000 times.In their example (Figure 3) they used C3=0, and from Table 2 it looks that C3=0 can be assumed one of typical value.You used 1nF. This suggests that you may be were following some other example and not this from datasheet.So may be also C1 and C2 values were from that other source and may be there is some explanation why they selected for C1 and C2 such surprisingly high values.May be they were selected just by experiments.When you link datasheet and than show your schematic with 1000 times higher capacitor values you should at least explain on what you based your decisions or give a link to this application you based at it.