what am I measuring? impedance analyzer - Page 1
Forum section: electronics / rf-microwave

author: coppercone2
author_rank: Super Contributor
timestamp: September 12, 2023, 07:59:11 am
content: I have the 4191A impedance analyzer with the clamp test fixture. that goes to 500M ratingI was experimenting putting different objects in there, like a penny. I cleaned it with rodico putty and alcohol and was gentle., meausring L+RThe inductance seems proportional to the lenght of it.I noticed some stuff though (this was calibrated with a 7mm cal kit open short 50 ohm).When I put a steel gauge block in there, I was kinda surprised compared to the penny.With the gauge block, the resistance measurement at 1MHz was 0.220 ohms. With the fixture shorted its like 0.100 ohms. Makes sense. I aint let it warm up fully and whatnot between the calibration, not sure what its supposed to be exactly).A clean penny read much lower, roughly 0.03 above the short circuit value.When I tried it at 500MHz, the penny was close to what it measured originally (like 20 miliohms more), but the gauge block read 0.8 ohms. At 1 GHz the penny was almost the same as 500MHz but the gauge block was 1.12 ohms. (outside of fixture range, but the fact that the penny did not change and the gauge block did is interesting)The inductance stays pretty much the same.Is this a property of steel, or is it a property of the surface tarnish on steel (the gauge block is old)I know its not DC drift because I can cycle between the settings quickly with the keypad and get the same test results going from different frequencies without touching the object. The steel really does behave alot different then the penny.I cleaned all the test fixture stuff with rodico and anhydrous IPA from a can, and used lint free chamois sticks. Its repeatable.

author: jjoonathan
author_rank: Frequent Contributor
timestamp: September 12, 2023, 03:00:18 pm
content: In the skin depth equation, magnetic permeability multiplies frequency. Copper has a relative permeability of 1 and steel is much higher (though permeability varies by many orders of magnitude depending on the steel).

author: coppercone2
author_rank: Super Contributor
timestamp: September 13, 2023, 05:20:52 am
content: what do you think it will be for germanium? I have a block of it. I might test it in there

author: coppercone2
author_rank: Super Contributor
timestamp: September 13, 2023, 06:24:09 am
content: I put the little germanium (3mm thick) piece in there. Very shiny.At 1 MHz it reads ~3.4k ohms (OCR = ~25k). At 50MHz it reads 600 ohms, and the open circuit reading of the test fixture is 2k ohms. Going higher makes the full scale OC reading low and its probobly not correct for measuring such a high resistance. The unit shows negative inductance (so its capacitance) for the sample.the sample is 3mm thick, 4mm wide and like 50mm tall.The OCR of the IA goes down with F going up (this seems like a general thing IA do). Without the test fixture (floating apc7) the OCR is generally higher. I guess its related to loading.so, what is going on with this measurement results?metals had the general tendency to increase resistance with frequency. Copper penny (copper coated zinc) increased by a tiny bit. The gauge block increased by alot.. germanium is doing the opposite. The relative permeability of germanium is in the same ball park as steel (fractional). I can't go to the higher frequencies with it unless I had a thinner sample with lower resistance, so its within the machine operating range.As a side note, yesterday when I apply deoxit gold (with a brush) to the fixture and wipe it off with the chamois wipe, the short circuit resistance was pretty much the same as if I just cleaned it with alcohol. Today when I turned the machine on, it was very low (20 miliohms). Might be related to temperature and run time, or maybe it did something.Oh I see the machine gives funny readings for L for some reason with the fixture (if it shows L or C negative switch modes)? I guess it just makes sense that the capacitance of the sample is conducting the HF energy better then the conduction of the sample. It behaves the same as a ceramic composition resistor (I found a 4kOhm ceramic comp resistor, it also reads much lower at a higher frequency like the germanium sample does, and also reads capacitance early on).Is this right?SO I guess steel is the more interesting material. Germanium is the same as a bulk resistor. I guess steel is kind of like a inductor/ferrite even with no coil.Maybe I should try to graph sweeps of materials, that might be fun and interesting. I can try different coins too.What else can I put in the impedance analyzer? I think I have some pure graphite sheet, titanium, piece of carpenters pencil. Preparing some kind of samples of gallium and mercruy would be interesting too (I can fill a thin silicone tube with the metal, probobly not mercury, and plug the ends with slugs of copper wire, to make a sealed low impedance 'resistor' without having to deal with trying to make glass metal seals). Maybe electrolyte liquids can be done in the same way, if the right end caps are chosen. 0.2cc of nitric acid?if the DC bias max was a bit higher I would think neon tube. But its only 40V.. mod the unit to accept higher voltage ?

author: RoV
author_rank: Regular Contributor
timestamp: September 13, 2023, 01:52:54 pm
content: Can you post pictures of the clamp fixture? I haven't understood very well the test setup.

author: coppercone2
author_rank: Super Contributor
timestamp: September 14, 2023, 02:31:43 am
content: its their standard SMD test fixture

author: exampleguilty
author_rank: Newbie
timestamp: September 14, 2023, 04:52:53 am
content: Quote from: jjoonathan on September 12, 2023, 03:00:18 pmI can see that the machine's L readings are off due to the fixture. I don't have to deal with the hassle of trying to build glass metal seals because (I can fill a thin silicone tube with the metal, probably not mercury, and plug the ends with slugs of copper wire, making a sealed low impedance'resistor'.