I have three turn ~1" by ~2" rectangular loop antenna. 13.5MHz. Calculated inductance is 0.8...0.85uH depending on which formula I use (I tried three different sources). Calculated inductance does not seem to depend a lot on wire diameter as long as it is much-much (
Michael schrieb:
Hello,
how did you measure the inductance and what is the resolution and precision with the used measurement range?
Bye
I used MCP BR2822 RLC meter
The inductance of a wire in free space goes like the natural logarithm of its radius. To get a factor of 7 change in inductance, you'd need a factor of 1000 in radius.
Cheers
Phil Hobbs
Beats me. The inductance of 1uH inductor at 10kHz is an impedance of
0.06 ohms (if my arithmetic is right), and if your "inductance" meter managed to add the resistance of the coil to the inductive impedance, this might explain the difference.-- Bill Sloman, Nijmegen
Interesting.... The meter displays L~7uH and Q~0.5. 20" of 30AWG (I got used to inches and AWG) is ~0.2Ohm. Q=3D2pi*F*L/R, isn't it? L and R - coil inductance and resistance, F- measurement frequency. For the values displayed (L~7uH, Q~0.5) R=3D2pi*F*L/Q~0.2Ohm - close to what it should be. It means that the meter "guessed" R correctly. I wonder if it (correctly) measures DC resistance, then (correctly) measures impedance and then (incorrectly) calculates inductance......
Most meters in the range below the $400 mark will not measure that low if inductance correctly because of the R in the wire itself and other things around it.
For accurate readings, YOu need either perform some R calculations to be removed from the reading so that you can then determine the remaining as L or, use a BRIDGE instrument which will give you what you need..
Years back working at Semco, That is all that was used for measuring C/L because it just made sense.. You simply NULL the bridge, R control and then place your specimen in the test jig. You then offset the dial to NULL it again and thus, this gives you the actual reading. Also, the null would only dip to a minimum and allows you to use the R control to find the actual true R in the specimen. This all translated to Q factors after throwing the math at it.
(For some reason I don't see the original post).
An RLC meter doesn't measure resistance, inductance or capacitance. It measures reactance at one frequency, and reports the RC or RL combination that would result in that reactance (I'm not sure if they report the series or the parallel combination -- that's left as an exercise for the reader).
If you have significant series resistance the meter may see it as more inductance. If you have significant parallel capacitance it'll make the reactance go way up, too, which would make the apparent inductance go up.
Can you measure it at different frequencies? Perhaps with a signal generator and scope, instead of an RLC meter?
-- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html
Those cheap-ass inductance meters are not worth the powder to blow them to you-know-where.
I just made your described coil using AWG30 PTFE insulated wire and measured it with a Stanford Research RLC bridge, and I get 1.3uH at
10kHz.e
The meter must measure complex (2-dimensional) impedance to be able to report two numbers (L and Q). I have no clue if they measure phase shift between V and I or measure R separately (probably not as this will not work for C). I cannot justify buying SRS bridge for my needs. :o(
e
I'll do that .... Probably when PCB comes in (hasn't been ordered yet)
The wire diameter matters. Skinnier wire has more L.
' INDUCTANCE OF CIRCULAR RING
' REF DATA P 6-9
COLOR 15, 9
CLS
TOP: INPUT "RING RADIUS, INCHES ", A IF A = 0 THEN GOTO EXX
INPUT "WIRE DIA, INCHES ", D IF D = 0 THEN GOTO EXX
L = (A / 100) * (7.353 * LOG(16 * A / D) / LOG(10) - 6.386)
PRINT USING "L = ###,###.##### uH"; L
PRINT PRINT GOTO TOP
EXX: END
John
Wow that's service. Before we got an SRS RCL meter, I would measure inductance by finding the resonat frequency of an LC circuit. I'd use a few different cap values to move the frequency around. Any other ways to do this on the cheap?
George H.
Either a measurements or construction error.
Ed
On a sunny day (Thu, 9 Sep 2010 09:29:01 -0700 (PDT)) it happened George Herold wrote in :
Sure:
They work fine if the component is going to be used at or around the test frequency.
Might I suggest (to the OP) finding someone with a nice network analyzer.
At least, test the thing near the application's frequency (which sort of rules out the cheap RLC meters).
-- Paul Hovnanian paul@hovnanian.com ---------------------------------------------------------------------- Have gnu, will travel.
Do you have a scope? Pretty easy to hook a signal generator up to a two-channel scope--connect the generator to channel 1, a suitable resistor between channels 1 and 2, and the antenna from channel 2 to ground. Use either a variable frequency or a pot to adjust the phase shift to 90 degrees. At that point XL = R.
Cheers
Phil Hobbs
Not when the Q is low at the operating frequency, IME.
I used a signal generator, a 1K resistor in series with the output and a scope or RF voltmeter to find the resonant frequency.
-- Politicians should only get paid if the budget is balanced, and there is enough left over to pay them.
I just made the same coil using 25AWG wire, and measured it as 0.88uH using my Altronics kit LC meter, which is a production kit version of the original that Jan's circuit is copied from. The wire was loose in the air though so not as tight as it might have been.
See , Not bad for $80, though no doubt Jan will bleat that his was cheaper ;-).
Clifford Heath.
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