Saturation of a Magnetic Frame

[Lakey]

Is it feasible to determine whether or not a magnetic frame is saturated by the following experiment?

Device: A small solenoid, approx 1.5inch by 2.0inch.

Method:
The solenoid is secured in a non-magnetic fixture.
The armature position is fixed half way along its stoke. [full stroke approx ¼ inch]
The armature is attached to a force gauge via a non-magnetic rod.
The coil power is increased at regular intervals whilst readings are recoded off the force gauge.

Prediction: The reading with the greatest magnitude is the point where the amp-turns are sufficient to saturate the magnetic circuit.

I appreciate that the efficiency of the magnetic circuit will be reduced by the air gap (approx 1/8 inch), but will this simple experiment provide me with sufficient information to determine if the coil frame is fully saturated? Thermal considerations negated.

I’d appreciate your comments:

Thanks & regards,

 

[MagMike]

Probably not possible.

If the amp-turns aren't sufficient to saturate the frame, then a max force reading is meaningless.

In addition, the solenoid may not have been desigend to operate near saturation. They are most efficient when operating in a region of high permeability which occurs before saturation.

 

[Lakey]

Thanks Mike.

I can confirm that I will be able to generate enough A-ts to saturate the frame. Also, to be clear, I should have mentioned that this is a DC solenoid.

I was hoping the exp will also show me how much power is required to fully saturate the frame, and to define the point on the curve where normal operation occurs. What i'm not sure about is (a) if this exp is feasible and (b) the best position for the armature e.g. fully open (max air gap), mid way, or just off its stop (min air gap).

 

[EdStainless]

Sure you can do this.
If you have enough field then I would expect to see the curve come out looking just like a magnetization curve.
As you crank the field you will continue to get increased force, but it will increase very slowly once you are into a region of lower permiability, even if you haven't reached saturation.
You can easily test at different locations, this somewhat depends on design and leakage factors, but hte highest force should be with the smallest air gap.

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[Lakey]

Thanks Ed.

That's what I was thinking.

So, for this method, I have one vote for and one vote against.

Kind regards,

 

[israelkk]

Why not just calculate the magnetic circuit and see if it is saturated or, even better see at each distance how many amper turns needed to saturate the electromagnet. Who told you that the frame will be the saturated part? It may be the plunger. Thats depend on the design of the electromagnet. Only calculations will tell you which part will saturate first and where.

 

[dgallup]

Saturation is a gradual effect with most magnetic materials. You will not see a peak or even a sharp knee in your force vs amp-turns curve, just a change in slope. Plot the first derivative to find saturation.

Be sure to measure actual current and not supply voltage because the resistance of your winding will go up as you increase power to the solenoid.