- #1
Interpreting the BH curve obtained experimentally
- Thread starter Prerana
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Discussion Overview
The discussion revolves around the experimental tracing of the B-H curve of soft magnetic materials, specifically focusing on the observed phenomena of loops at the end of the curve. Participants explore the setup, methodology, and potential reasons for the results obtained.
Discussion Character
- Exploratory
- Technical explanation
- Debate/contested
Main Points Raised
- One participant expresses confusion about the presence of two loops at the end of the B-H curve and seeks assistance.
- Another participant requests clarification on the test setup and the axes used in the oscilloscope plot.
- A third participant speculates that the core may be saturating but acknowledges a lack of information about the core material and setup.
- Details about the experimental setup are provided, including the use of Mu metal, a primary and secondary coil, and the frequency of the input current set at 50 Hz.
- Questions are raised about the effect of frequency on hysteresis parameters and how to determine if the material has reached saturation.
- One participant suggests that the trace may not actually show loops and prompts the original poster to verify the conditions under which the data was collected.
- Another participant discusses the implications of eddy currents and phase shifts in the observed results, suggesting that these could contribute to the small loop seen in the oscilloscope trace.
- There are suggestions to use different waveforms for testing, such as a triangle wave, to observe the effects of magnetic retardation and frequency on the induced voltage.
Areas of Agreement / Disagreement
Participants do not reach a consensus on the cause of the observed loops in the B-H curve, and multiple competing views regarding the experimental setup and interpretation of results remain present.
Contextual Notes
Participants note limitations in the information provided, such as the nature of the core material and the specifics of the experimental setup, which may affect the interpretation of the results.
- #2
berkeman
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Prerana said:
Welcome to the PF.
Can you post a diagram of your test setup? What exactly are you plotting on the x-y axes of that oscilloscope?
- #3
jim hardy
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Indeed Berkman's questions are immediate response to your question.
My first guess was you're saturating the core
but that's premature. I don't even know if you're using a toroid core or an old iron bolt.
What is nature of your soft iron core,
What is frequency,
Is excitation current a sinewave,
Can we assume you use some sort of integrator to calculate flux?
very interesting experiment, fellows . Don't quit now !
My first guess was you're saturating the core
but that's premature. I don't even know if you're using a toroid core or an old iron bolt.
What is nature of your soft iron core,
What is frequency,
Is excitation current a sinewave,
Can we assume you use some sort of integrator to calculate flux?
very interesting experiment, fellows . Don't quit now !
- #4
Prerana
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Hi Jim and Berkeman
We are using the principle of Electromagnetic induction to trace the bh curve of the soft magnetic material ( Mu metal) . The test setup consists of a primary and secondary coil..The primary coil is wound on a aluminium rod of square cross section. The input current is controlled through a resistor in series with the primary coil and the frequency of input current is 50 Hz. The hysteresis material on which the secondary coil is wound is placed in the solenoid. The hysteresis material is in the form of rod having circular cross section of length of 1.1mm x 80 mm. The emf induced in the secondary coil is given to the power amplifier and then to the integrator. The integrator output is plotted on the Y axis and the input current given to the primary coil is plotted on the X axis of the CRO.
@ Jim and Berkeman:
Does the frequency of the input current affect my hysteresis parameters?
How do I conclude that my material has reached saturation?
Thank you for the quick response!
We are using the principle of Electromagnetic induction to trace the bh curve of the soft magnetic material ( Mu metal) . The test setup consists of a primary and secondary coil..The primary coil is wound on a aluminium rod of square cross section. The input current is controlled through a resistor in series with the primary coil and the frequency of input current is 50 Hz. The hysteresis material on which the secondary coil is wound is placed in the solenoid. The hysteresis material is in the form of rod having circular cross section of length of 1.1mm x 80 mm. The emf induced in the secondary coil is given to the power amplifier and then to the integrator. The integrator output is plotted on the Y axis and the input current given to the primary coil is plotted on the X axis of the CRO.
@ Jim and Berkeman:
Does the frequency of the input current affect my hysteresis parameters?
How do I conclude that my material has reached saturation?
Thank you for the quick response!
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- #5
jim hardy
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Well what an interesting setup you have there !
That trace attached to your new post has no loops on end - what is it? Your setup with core not inserted perhaps? Or did you solve the mystery already?
(I assume your amplifier has high input impedance so there's not much current in sense coil compared to excitation coil.)
Since your excitation is sinewave, set your 'scope for ordinary time display and observe current & induced voltage as you slide the core into the solenoid.
Then take a look at input and output of "power amplifier" .
As core is inserted the induced signal gets much larger and we should look to see if we are overdriving that amplifier... if output sinewave peaks flatten out you are saturating the amplifier. You shouldn't be able to saturate an iron rod since so much of the magnetic path is through air.
NEXT -------------------------------
Think about what's going on inside that iron...
With an ideal inductor current and flux would be in phase and your test would show a straight line on your oscilloscope. That's what you'll get with air core and that's almost what the more recent trace looks like...
With real inductor you have hysteresis so expect a B-H loop.
Inside real iron you also have eddy currents which retard the flux because of Lenz's law.
Recall Gauss' h(dot)dl = ienclosed counts ALL the current, not just what current you applied. If you use a voltage sensing coil to measure flux, even the current flowing in it counts.
Your 'scope trace on second post shows a small loop - if it's not your successful B-H loop, then perhaps it's just a little phase shift from eddy currents in your aluminum coil form or imperfect integration, or perhaps even an iron leg brace on bottom of work table underneath your solenoid. So take a look at table's underside..
Also note the aluminum coil form constitutes one shorted turn, if that turns out problematic maybe you can find some square plastic or use balsawood??
use 'scope to observe current and induced voltage vs time as you increase current . As you approach saturation, voltage will depart from a sine shape and i think get "spikey".
If you have a function generator and power amplifier that could drive current, , try this:
I've done it myself and it is a real eye-opener.
drive your setup with a triangle wave current instead of a sinewave and look at induced voltage.
A triangle wave current should give a square wave voltage and you'll see effect of "magnetic retardation" by eddy currents as rounded shoulders on your square wave.
You will see effect of frequency as dramatic rounding of the square wave's edges as frequency increases.
If i can find my old 'scope photos i'll photocopy and attempt to post them.
That trace attached to your new post has no loops on end - what is it? Your setup with core not inserted perhaps? Or did you solve the mystery already?
(I assume your amplifier has high input impedance so there's not much current in sense coil compared to excitation coil.)
Since your excitation is sinewave, set your 'scope for ordinary time display and observe current & induced voltage as you slide the core into the solenoid.
Then take a look at input and output of "power amplifier" .
As core is inserted the induced signal gets much larger and we should look to see if we are overdriving that amplifier... if output sinewave peaks flatten out you are saturating the amplifier. You shouldn't be able to saturate an iron rod since so much of the magnetic path is through air.
NEXT -------------------------------
Think about what's going on inside that iron...
With an ideal inductor current and flux would be in phase and your test would show a straight line on your oscilloscope. That's what you'll get with air core and that's almost what the more recent trace looks like...
With real inductor you have hysteresis so expect a B-H loop.
Inside real iron you also have eddy currents which retard the flux because of Lenz's law.
Recall Gauss' h(dot)dl = ienclosed counts ALL the current, not just what current you applied. If you use a voltage sensing coil to measure flux, even the current flowing in it counts.
Your 'scope trace on second post shows a small loop - if it's not your successful B-H loop, then perhaps it's just a little phase shift from eddy currents in your aluminum coil form or imperfect integration, or perhaps even an iron leg brace on bottom of work table underneath your solenoid. So take a look at table's underside..
Also note the aluminum coil form constitutes one shorted turn, if that turns out problematic maybe you can find some square plastic or use balsawood??
i doubt you could saturate it but-
use 'scope to observe current and induced voltage vs time as you increase current . As you approach saturation, voltage will depart from a sine shape and i think get "spikey".
If you have a function generator and power amplifier that could drive current, , try this:
I've done it myself and it is a real eye-opener.
drive your setup with a triangle wave current instead of a sinewave and look at induced voltage.
A triangle wave current should give a square wave voltage and you'll see effect of "magnetic retardation" by eddy currents as rounded shoulders on your square wave.
You will see effect of frequency as dramatic rounding of the square wave's edges as frequency increases.
If i can find my old 'scope photos i'll photocopy and attempt to post them.
Last edited:
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