Author Topic: There is any Standard Frequency For Measurng Inductors With LCR Meter?  (Read 1251 times)

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Offline 2XTopic starter

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Hello,
 I would like to ask if there is any standard frequency for measurng inductors with LCR meter (I have the LCR meter "U1733C"). For example I measured an unknown (black axial package) inductor value (I desoldered it from a working circuit just for making a test - my LCR is officially calibrated) and the LCR gave me the below values at a certain frequencies. I know that the inductance etc. changes with the frequency but what value in what frequency I have to select in order to buy a new one inductor?


P.S. From the reading of the manual (pages 49-50) it says how to measure resistor in "R" mode, but I beleive when you have connect an inductor in "R" mode it measures the XL Inductive Reactance of the inductor because there is the selection of changing frequencies (if this mode will be only for measuring resistors I beleive it will measuring with DC voltage).

 

Offline CaptDon

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It would largely depend on the core material of the inductor. Iron, probably 100Hz, Ferrite core 10KHz to 100KHz, and an open air inductor or inductor wound over a resistor perhaps 100KHz.
Collector and repairer of vintage and not so vintage electronic gadgets and test equipment. What's the difference between a pizza and a musician? A pizza can feed a family of four!! Classically trained guitarist. Sound engineer.
 
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Offline 2XTopic starter

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This is the inductor that I made the tests... don't have any marking at all.
 

Online Sensorcat

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There is no single standard frequency, it depends on the inductor. For instance, many components used in linear power supplies are tested at 100Hz and/or 120Hz, because this is the operating frequency they have. It is the line frequency doubled, the frequency you have after a bridge rectifier.

Using 100 or 120Hz makes not much sense for components used at much higher frequencies. Hence your U1733C supports higher values, which are often found as test frequencies in datasheets.

If you need to replace a component, looking at the data sheet is the key: The data sheet of the original component will tell at which frequency to test, and this is the best choice when testing such a component. If you cannot identify the component, try to find something that has a similar value and a similar 'role' in a similar circuit. Or try to identify the operating frequency in your target circuit.

Looking at your table, the differences are not that much. Keep in mind that many inductive components come with a tolerance of 10% or 20%.
 
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Online Benta

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This is the inductor that I made the tests... don't have any marking at all.

Inductor? Looks more like a ferrite bead. I think you've been measuring the inductance of your test leads.
 
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Offline TimFox

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Many inductor data sheets use one of a discrete set of frequencies used in old-school “Q meters”.
Each half-decade frequency range (for HP 4342A) has one frequency where the DUT inductance can be read easily from the capacitance dial.
25, 80, 250, 800 kHz; 2.5, 8, 25 MHz approximate frequencies.
 
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Offline radiolistener

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The standard frequency for such kind of measurement is a frequency which will be used in circuit where you're planning to use this inductor or capacitor. If you're using professional LCR meter, you can setup frequency for measurement
 
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Online T3sl4co1l

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I wonder if that's a special ferrite bead... usually, R should be going up pretty well with X.  Perhaps the frequency is still on the low side, and you're close to the Q peak frequency (at the top end of that range, that is).

If it's a normal ferrite bead, the region of interest is above 1MHz, and typically by 10MHz or so, until several 100 MHz or a GHz, the impedance rises slowly, peaks, then falls off; over the same range, R ~ X, thus a fair amount of loss is introduced to the circuit.

The impedance also depends on signal level or bias current, though it should be pretty easy to stay in the linear range; a bead-on-lead typically handles a couple 100 mA DC before impedance declines much.

Tim
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Offline Wallace Gasiewicz

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It does look like a ferrite bead. As I recall,  I measured some of these at about ONE micro Henry vs a wire of the same length at about 30 nano Henries. I Measured at One MHz.The really low resistance value also goes along with a ferrite bead. Essentially a wire.

My old HP 4332 tests at One KHz for high values and 100 KHz for lower values. for resistance only uses One KHzI think this was quite typical.
The old digital LCR HP 4271 measures at One MHz and can go much lower than the 4332.Your fancy LCR meter measures Ohms at different frequencies that you specify.

Edit: There is also a DC R setting. on some of the Agilent LCRs, I dont think yours has one.

The newer LCRs have more freq options, Yours is pretty fancy compared to mine. The little cheapo LCR/Component testers use some sort of pulse, I Think.
« Last Edit: May 26, 2024, 11:55:30 pm by Wallace Gasiewicz »
 
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Offline mawyatt

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Most quality LCR Meters have a table which illustrates the frequency range for DUT measurements for Inductors and Capacitors, best consult the manual for details.

If one studies these quality LCR meters, they operate by measuring the complex (Magnitude and Phase) voltage across the DUT and the complex current thru the DUT, and it's best to keep these within the "sweet spot" of the measurement frequency range for best results. Note the LCR Meter does not directly measure L, C or R, it computes these based upon the complex DUT voltage and current measurements.

Measuring a small value inductor at low frequency produces a large DUT current but low DUT voltage which limits the measurement accuracy, so increasing the measurement frequency is advised for higher DUT voltage. For small capacitance DUT the current is low and thus better to increase the measurement frequency for higher DUT current. For larger value Inductors or Capacitors the opposite is true, lowering the frequency produces better results.

Things get more complicated when one considers parasitic effects of ESR, ESL and resonance effects, as the simple L, C and R become more complex. Again, best to consult the manual for details and how these effects influence LCR measurements.

One quickly finds, LCR measurements aren't quite as simple as DMM R measurements!!

Best,
Curiosity killed the cat, also depleted my wallet!
~Wyatt Labs by Mike~
 
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Offline Doctorandus_P

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Common measurement frequencies are 1kHz, 10kHz and 100kHz, but there are no real standards. There are also other ways of measuring inductance such as dI/dt. Yet other RLC meters make the DUT a part of an oscillator, and thus the measurement frequency can vary between a few Hz and several hundred KHz.

I never really understood the use of high accuracy RLC measurement equipment, as most inductors are not very stable parts. Their inductance varies both with frequency and current, but also with other things such as temperature.

The shown picture looks indeed like a ferrite bead, and those usually do not do much below around 10MHz, and at 1MHz is mostly just a piece of wire.
 
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Offline mawyatt

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100 and 120Hz should be also included as well as 1MHz for "Standard Frequencies". First two are used for high value electrolytic type capacitors as they generally work at 2 times mains frequency (full wave rectification), 1MHz is more common for small values of capacitance and inductance, and even higher frequencies for very small values. We have a DE-5000 (100KHz), Tonghui TH2830 (100KHz), Hioki IM3536 (8MHz) and Siglent (3.2GHz) VNA to cover the ranges for our evaluations.

It's best to use the same frequency (and same LCR meter) to verify components against the DUT OEM.

WRT measurement technique, the older lower cost types tended to use the "Oscillator" approach, and more modern but inexpensive meters utilize the pulse technique, whereas the higher quality LCR meters utilize a DUT Volt/Current method. All don't directly "measure" L, C or R but compute such based upon DUT measurement parameters.

The low cost "Pulse Type" LCR Meters produce surprisingly good results for most components, and an entire thread is dedicated to those types for improving performance/features, if one likes to "tinker" this is the ultimate  :-+

https://www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/

However, for more accurate results modern LCR Meters based upon the Volt/Current method are preferred. The handheld DE-5000 is an example of this type that utilize a special Chip Set to perform most of the measurement work and results in an affordable meter with excellent performance, why we have one ;)

The more expensive types have a variable frequency range that covers a wide span, and some have DC bias capability with nice visual graphing displays!

Here's some links for using a DSO with Bode capability to measure/plot capacitors and inductors, nowhere near a proper LCR Meter, but still maybe useful.

https://www.eevblog.com/forum/testgear/capacitive-impedance-plots-with-sds2104x-plus-bode-function/msg4342009/#msg4342009

https://www.eevblog.com/forum/testgear/admittance-measurements-with-dso-awg-with-bode-function/msg4491952/#msg4491952

Best,   
Curiosity killed the cat, also depleted my wallet!
~Wyatt Labs by Mike~
 
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Offline 2XTopic starter

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When I measure R in different frequencies at an inductor with my LCR is essentially the reactive inductance XL? 
 

Offline coromonadalix

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This is the inductor that I made the tests... don't have any marking at all.

this is not an inductor    its a short wire with a ferrite bead, supposed to be some noise supressor,    does the ferrite turn around the wire ?
« Last Edit: May 27, 2024, 03:49:46 pm by coromonadalix »
 
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Offline TimFox

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When I measure R in different frequencies at an inductor with my LCR is essentially the reactive inductance XL?

In a proper LCR meter, the fundamental measurement is of the two complex components  R (real part of impedance, called "resistance") and jX (imaginary part of impedance, called "reactance").
The complex impedance is Z = R + jX.
In general, both components are functions of frequency, and the resistance R at f > 0 differs from the DC value (f = 0).
 
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Offline Wallace Gasiewicz

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I do not have your meter.
If you have a DCR test signal level  (DC Resistance)  It will measure the same as a normal resistance meter, like a multimeter.  Try this with your new meter and a normal multimeter.

If the part which we think is a ferrite bead, actually is a ferrite bead,  the  DCR should be a few milliohms.  DC Ohms should be the same as a short piece of wire , you can try this also.AC (RF) resistance goes up with freq and this is because of "skin effect"

If it is a ferrite bead, It will have an inductance.     This kinda goes along with your measurements in the original post.   
The inductance is determined by material used.
Unfortunately the inductance or capacitance of real components is not the same at different frequencies, it is only the same for "IDEAL" components and unfortunately I have been unsuccessful at finding these.   
As has been pointed out, at MHZ freq  ferrite beads behave more like resistors. Your LCR Meter does not measure at MHZ Freq.


Remember that Impedance  = 2 pi * freq * inductance + Resistance    (with Inductors)     
You may want to giggle ferrite beads and read something about them.
 
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Offline 2XTopic starter

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I measured the unknown inductor with two multimeters and they didn’t measure the same resistance,

0,21ohm (Fluke 28II)
0,065ohm (U1272A)

also, I design a schematic from a part of his PCB (image below). On the PCB silkscreen this component is marked as L1.


I have two queries:

1st: The “R” from the impedance’s equation isn’t the ohmic Resistance where should be independent from the frequency changing? For instance, a 10ohm resistor is 10ohm in all frequencies (in real even the resistors in high frequencies have a tiny inductance and capacitance as I know). I confused because the U1733C has a DRC (Direct Current Resistance) mode where it measures the resistance with 1Vdc (page 55 of the manual), so what is the reason (if I am right and the “R” isn’t change with frequency) to have a separate DRC measurement mode and in “R” mode to have the selection of the frequency(100Hz, 120Hz, 1KHz, 10KHz, 100KHz)?

2nd: My LCR in “Z” scale measures the Complex Impedance where is the sum of the Resistance “R” and the Reactive Component “jX”.
Z-R+jX, where:
X=Xc+XL
Xc=1/2*pi*f*C (Capacitive Component)
XL=2*pi*f*L (Inductive Reactance)
Just from curiosity, if I measure with my LCR meter the “Z”, “R”, ” L”, “C” e.g. at 1KHz, then can I calculate the Xc and XL values separate? Most expensive LCRs measures Xc & XL seperatly?


P.S. Thanks all of you for your replies and I apologize for my many queries.
« Last Edit: May 29, 2024, 09:40:25 pm by 2X »
 

Offline TimFox

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In general, the real part R of the impedance of a component is a function of frequency.
The DC resistance is measured either at DC (f = 0), or at a very low frequency (close to 0).

The difference between your two DC resistance measurements is almost certainly due to the test leads and probes of the two meters.  To get an accurate measurement of resistance around 0.1 ohms requires a four-wire measurement (aka Kelvin probe).
 
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Offline Wallace Gasiewicz

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Tim is correct.   

But you will not likely see any real measurable difference in resistance of a wire until you get to MHz frequencies. You did see some increase in R at 100 KHz as you stated in your OP.
There are other effects that you may wish to read about.  If you can get through the Wikipedia article on skin effect  you will know more than most.....certainly more than I.
 
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Offline TimFox

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Another important case is the real part of the impedance for “resistors” (two-terminal devices labeled as such).
Due to their construction (e.g, helixes or carbon composition), the internal capacitances “short out” some of the physical resistance at high frequencies, changing the effective resistance measured at the terminals.
 
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Online pdenisowski

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The standard frequency for such kind of measurement is a frequency which will be used in circuit where you're planning to use this inductor or capacitor. If you're using professional LCR meter, you can setup frequency for measurement

Exactly this.  Always test at the intended frequency (range) of use. 

Note that older LCR meters (and all handheld LCR meters I've ever used) can only test at a set of discrete frequencies - usually about a dozen on handhelds and up to several dozen on benchtop meters.  Newer benchtop LCR meters (should) allow you to enter a specific frequency.

I mention both of these in my video on LCR meters:

Test and Measurement Fundamentals video series on the Rohde & Schwarz YouTube channel:  https://www.youtube.com/playlist?list=PLKxVoO5jUTlvsVtDcqrVn0ybqBVlLj2z8
 
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