Coils and magnetic fields

AFAICS, that's for steady "DC" magnetic fields, not high frequency fields.

It's possible that Jim Thompson, of this parish, had something to do with its design.

Your best course is to use a small single turn coil. You could make it on PCB. Its dimensions need to be accurately known. Its voltage versus flux characteristics can be calculated from its dimensions. See any electromagnetics textbook.

I had nothing to do with the sensor design. But I did design the analog portions of the chip that drives such a sensor....

The measurement cycle time is 18ms, and measures only "DC" fields, such as for use in compasses, etc.

...Jim Thompson

Jessica Shaw wrote in news:ee81954d-1653-4a67-862f- snipped-for-privacy@do4g2000vbb.googlegroups.com:

The bandwidth is 5Mhz.

Jessica Shaw schrieb:

Hello,

the name is Gauß, Carl Friedrich Gauß, but in english you may write also Gauss.

Bye

The coil output will be proportional to its area. You won't need a fancy calculator to figure that out unless you are trying to get some very high accuracy. If so, you'll need to model the physical layout of the windings (PC board flat vs wound).

The selection of sensor type depends on what sort of data you need to collect about the field in question. If you are taking single strength measurements at some fixed point, the coil will do just fine. A three axis sensor would be better if you need to characterize the field's strength and direction at multiple points.

Also, I wonder about the parallel capacitor's effect on your measurements. If the field frequency is fixed, then perhaps tuning the cap (or just calibrating the LC output at that frequency) will suffice. But if the field frequency changes with respect to your LC resonant frequency, you'll have to account for that effect on the magnitude measurement.

I talked to honey well support today. They are saying that this sensor HMC1043 can measure alternating magnetic fields upto 5MHz. I am little confused. jess

Wasn't it Strauss? Oh wait, no, that was Franz-Josef :-)

Why confused? That's most likely the bandwidth where the measured signal has fallen off by 3dB versus DC. Since you wrote that you don't need more than 100kHz that's plenty of bandwidth. That Honeywell sensor is quite pricey though.

That's the sensor's own response time to a magnetic field change. To actually get data you have to push it into alternating saturation, so the limit is your instrumentation capability.

Read the data sheet.

I think many others have suggested that you use a coil. That's your best bet. ...Jim Thompson

Huh? AFAIK you always get data out. There's offset and reset straps for incident field cancellation but why do you have to push into saturation?

Jessica wrote that the 6 grams of weight for her coil is too much, wants the same number of turns for some reason, and is already at 36AWG wire. That pushes into skin effect turf. I think the hair off of our Labradors is thicker than that.

Hi,

The developement kit for this sensor uses LMV324 op amps ( Band width = 1MHz) , seems like the intsrumentation can handle it. I agree with the loop measurement method. But I want to see why this magnetic sensor will not work.

What is alternating saturation? How will it effect the sensor reading?

jess

The P-P signal amplitude of the second harmonic of the driving frequency is proportional to field.

Did a similar gadget in NY last summer, except that was for a truck clutch ;-) ...Jim Thompson

Reading what she said, it's 18 turns of 24x36AWG litz.

Described Helmholz arrangement is resonant, hence sinusoidal field. I guess you were assuming square or pulsed excitation.

EMF in a coil is N.d(phi)/dt = N.A.dB/dt

For sinusoidally varying field, B = B (peak) sin(omega.t), that becomes:

E = N.A.omega.B(peak).cos(omega,t), where A is the loop cross sectional area.

Or E(peak)=omega.N.A.B(peak)

For a single loop, N=1, hence:

E(peak) = omega.A.B(peak)

E.&O.E.

Yes. And a core that saturates (or at least changes with current).

...Jim Thompson

I guessed so. The discussion, (that's been going round in circles since last October, IIRC) has been about air cored Helmholz coil fields.

The ARL document that Jessica turned up on the subject makes quite interesting reading. Using a 3577A network analyzer to measure the field is quite neat, though they don't say what the amplifier used to drive the Helmholz was. It says "audio amplifier", but the plotted results go to

Hi,

I think that I figured out why the HC1043 magnetic sensor will not work.

I followed the ARL document and managed to make a 1" diameter loop ( One turn) . I am sending it to a company for calibration. They will put the coil in the uniform magnetic field and let me know the ouptut voltage. I will use the info. to calculate magnetic field generated by my HHCoils. I do not have a network analyzer.

jess

Ok, I understood that as 36AWG consisting of 24 strands. But if not then there'd be room for improvement. I just don't know why it absolutely has to remain at 18 turns or same inductance.

If you want to perform a basic magnetic calibration test..

This is magnetic flux measurements other wise know as a single Weber "WB"

Now I suppose you could apply a DC current to your coils that would be equal to that of what you're doing with the arrangement you have now, just for testing purposes?

Jamie