Response time of an electromagnet

[amgo100]

Hi!

I'm designing an electromagnet used to guide electrons through a device. The electrons come in bunches at 1kHz. The electromagnet must be able to change field intensity between two consecutive bunches. I'm concerned about its response time. Does anyone know where I can find how to estimate it?

Adam

 

[MagnetDave]

Treat your electromagnet as an inductor. The inductance of your circuit should dominate your calculations.

 

[electricpete]

I agree - current can lag voltage and L/R time constant can govern the dynamics.

But I'm not clear what is meant by: "The electrons come in bunches at 1kHz. The electromagnet must be able to change field intensity between two consecutive bunches."

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(2B)+(2B)' ?

 

[IRstuff]

Is this for school?

TTFN

FAQ731-376

 

[Warpspeed]

Actually it is not so much L/R as the voltage applied to the electromagnet.
The higher the applied voltage the faster the current will ramp either up or down for any given inductance.

 

[electricpete]

One could certainly argue from linear systems theory that the response of the system to an impulse (in voltage) is characterized by the L/R time constant (along with a magnitude) and so determines the dynamic response of the system.

I also agree with your characterization, at least if we are talking about a dc or low frequency voltage applied to an inductor such that a current ramp occurs.

It's not clear to me what the scenario of interest really is and which aspects of the circuit will be relevant. Original poster has not bothered to log back in to clarify.

=====================================
(2B)+(2B)' ?

 

[Warpspeed]

And that ramping current will ramp much steeper with a higher applied voltage.

 

[electricpete]

Yes, the response of a linear system is proportional to the input. No argument from me.

=====================================
(2B)+(2B)' ?

 

[electricpete]

to be more precise I should have said the response of a linear system scales proportionately to the input. But again no argument.

=====================================
(2B)+(2B)' ?

 

[sreid]

Take a look at LA400 Linear Power Amplifiers from Varedan Technologies.

http://www.varedan.com

A voltage command sets the current level. The current loop can be set to match the inductive load and a small signal 10 kHz current loop bandwidth can be easily achieved. The ultimate limit to how fast current can be changed is deternined by the supply voltage. It can be up to +/- 150 VDC across the coil.

Not intuitively obvious is that the higher the coil resistance, the smaller the L/R time constant is. But for power loss in the coil, one wants the resistance to be as low as possible. Near the limit, there may be a power loss vs. speed trade-off.

A side note: these amplifiers are almost un-killable.