Results of measurement using a magnetic sensor

[ChrisCOD]

TL;DR Summary

Results of measurement using a magnetic sensor

Hello. I am seeking some advice or information regarding a measurement I made using a magnetic sensor. Essentially, to summarize, I measured the socket for a ceiling light using a magnetic sensor, taking the necessary safety precautions. In so doing, in the immediate proximity of the socket, I measured up to 190 microteslas. It is important to note that the measurement was taken with the lightbulb screwed in, but the light bulb was then unscrewed and the lightbulb was measured independently and was found to give a measurement of roughly 60 microteslas so no higher than the background magnetic field strength.

Therefore the measurement of 190 microteslas came from the socket. I have attached a picture to show the measurement and a picture to show the socket, and the pictures also give an indication of how close the magnetic sensor was to the socket (it was right beside it/tight to it) and of course they also give a view of the socket itself . Additionally, the magnetic field strength in the general area of the socket but not right beside it was roughly 60 microteslas, thus the background magnetic field strength was roughly 60 microteslas. Is this result normal, what explains this result, and can you provide any further information in general regarding this result?

 

[berkeman]

I have to ask some obvious questions (unfortunately, since you didn't mention some stuff...). Are these measurements DC or AC? If DC, you know that the Earth's magnetic field is in the ballpark of $60\mu T$, right? If AC, what bandwidth does your probe support, and what frequency was this AC measurement centered on?

Can you link to the datasheet for your magnetic field sensor? Thanks.

 

[marcusl]

You are probably measuring the field from the steel lamp assembly which either is weakly magnetized, is concentrating the earth’s field, or both.

 

[ChrisCOD]

You are probably measuring the field from the steel lamp assembly which either is weakly magnetized, is concentrating the earth’s field, or both.

The lamp is not steel. It is made of plastic. Considering this, what would your response be?

 

[ChrisCOD]

I have to ask some obvious questions (unfortunately, since you didn't mention some stuff...). Are these measurements DC or AC? If DC, you know that the Earth's magnetic field is in the ballpark of $60\mu T$, right? If AC, what bandwidth does your probe support, and what frequency was this AC measurement centered on?

Can you link to the datasheet for your magnetic field sensor? Thanks.

The measurement are in DC I believe.

 

[marcusl]

Aren’t there screws or other hardware?

 

[ChrisCOD]

Aren’t there screws or other hardware?

There could in theory be screws and other hardware although you have not mentioned the nature of such hardware, but would screws or this other proposed hardware you speak of manifest such a results in your expert opinion?

 

[berkeman]

The measurement are in DC I believe.

If they are DC, then you are most likely measuring Earth's magnetic field and residual magnetization of other nearby ferromagnetic materials, as mentioned by @marcusl

With such magnetic fields, you should be able to null them out to zero based on the orientation of the probe. What does the pickup probe itself look like? Are you able to turn the probe slowly in orientation in 3-D to minimize/zero the measured field? Also, is that your cellphone that you are using for the display in the picture in your Post #1?

EDIT/ADD -- Are you familiar with what the Earth's magnetic field looks like in your area of the world? It is a magnetic vector field that has inclination, declination and intensity. If you are making these kinds of measurements for whatever reason, it would be good if you understood what the background B-Field from the Earth looks like:

https://en.wikipedia.org/wiki/Earth's_magnetic_field

Definition of terms: https://unacademy.com/content/neet-...agnetic-declination-and-inclination-of-earth/

 

[ChrisCOD]

If they are DC, then you are most likely measuring Earth's magnetic field and residual magnetization of other nearby ferromagnetic materials, as mentioned by @marcusl

With such magnetic fields, you should be able to null them out to zero based on the orientation of the probe. What does the pickup probe itself look like? Are you able to turn the probe slowly in orientation in 3-D to minimize/zero the measured field? Also, is that your cellphone that you are using for the display in the picture in your Post #1?

EDIT/ADD -- Are you familiar with what the Earth's magnetic field looks like in your area of the world? It is a magnetic vector field that has inclination, declination and intensity. If you are making these kinds of measurements for whatever reason, it would be good if you understood what the background B-Field from the Earth looks like:

View attachment 334233
https://en.wikipedia.org/wiki/Earth's_magnetic_field

Definition of terms: https://unacademy.com/content/neet-...agnetic-declination-and-inclination-of-earth/

I can confirm that I am using a smartphone the a magnetic sensor to perform the measurement. I did some quick research and it seemed as though smartphone magnetic sensors typically measure in DC and so I reasonably assumed this to be the case with my smartphone.

I would just like to clarify something. First, are you aware of whether or not it is normal for a socket like this to give a measurement like this? Second, in terms of what you said about me most likely measuring the earth's magnetic field and residual magnetization, are you saying that if, as I have indicated, the earth's magnetic field was 60 microteslas near the socket such that if the socket was not there and the measurement was performed in the precise spatial location of where the socket was then I would get a measurement of 60 microteslas, then these proposed ferromagnetic materials contribute additional magnetic field strength to the location of the measurement such that, as indicated, these ferromagnetic materials are contributing 130 additional microteslas (190-60), then you are implying that the there is a ferromagnetic material measuring 130 microteslas.

What could these proposed ferromagnetic materials be and are they typically found in sockets? I also note as per my reply to @marcus that the lamp or the thing you see with no light bulb is not made of steel, it is made of plastic.

 

[berkeman]

I would just like to clarify something. First, are you aware of whether or not it is normal for a socket like this to give a measurement like this? Second, in terms of what you said about me most likely measuring the earth's magnetic field and residual magnetization, are you saying that if, as I have indicated, the earth's magnetic field was 60 microteslas near the socket such that if the socket was not there and the measurement was performed in the precise spatial location of where the socket was then I would get a measurement of 60 microteslas, then these proposed ferromagnetic materials contribute additional magnetic field strength to the location of the measurement such that, as indicated, these ferromagnetic materials are contributing 130 additional microteslas (190-60), then you are implying that the there is a ferromagnetic material measuring 130 microteslas.

Please take care to use good sentence structure, punctuation, etc. I've edited the rest of your post to add paragraph structure and whitespace, but this run-on sentence is hopeless. Just sayin'...

 

[berkeman]

A smartphone is an imprecise sensor for this type of measurement. Why are you making these measurements? What is your goal? If you want to make precise measurements, you will need to invest in at least a moderate quality B-field meter and learn more about the Earth's magnetic field and ferromagnetic materials, IMO.

 

[ChrisCOD]

A smartphone is an imprecise sensor for this type of measurement. Why are you making these measurements? What is your goal? If you want to make precise measurements, you will need to invest in at least a moderate quality B-field meter and learn more about the Earth's magnetic field and ferromagnetic materials, IMO.

What is your evidence to support a smartphone as having an imprecise sensor for measuring magnetic field strength?

 

[berkeman]

Whelp, I've used a number of magnetic sensors over the years, and the most useful were ones that had obvious sensor geometries. That means that I could see the physical extent of the sensor, what its principle axis was, and could control its orientation in 3-space without bumping into other stuff in the test setup.

That would typically mean that the sensor was about a cubic cm in size, and had a well-defined sensing axis. A smartphone offers none of that, is way too big, and contains magnetic materials that interact with the measurement (look up PMICs and what-all is associated with them).

You did not answer my question -- what is your reason for doing this, and what are you hoping to find?

 

[ChrisCOD]

Whelp, I've used a number of magnetic sensors over the years, and the most useful were ones that had obvious sensor geometries. That means that I could see the physical extent of the sensor, what its principle axis was, and could control its orientation in 3-space without bumping into other stuff in the test setup.

That would typically mean that the sensor was about a cubic cm in size, and had a well-defined sensing axis. A smartphone offers none of that, is way too big, and contains magnetic materials that interact with the measurement (look up PMICs and what-all is associated with them).

You did not answer my question -- what is your reason for doing this, and what are you hoping to find?

First, I know where the magnetic sensor is in the smartphone, and so I hold the phone taking that into consideration when trying to measure an object. Thirdly, if it contained magnetic materials that interacted with the measurement then would you expect large increases in measurement to be something that could occur? What I mean by this is that, removed from other objects, there was a measurement of 60 microteslas, which according to your description would include the magnetic materials in the smartphone. Therefore, these magnetic materials implicitly contribute to the measurement automatically. A substantial increase implies a stronger magnetic field due to some other object in the vicinity of that measurement, does it not? Additionally, can you clarify your point about ferromagnetic materials in relation to your previous answer? And once again, are you aware of whether or not it is normal for a socket like this to give a measurement like this considering the initial point I have made in this reply? I also note that although you can get more accurate sensors, smartphones will give a possible range of inaccuracy of 3-5 microteslas.

 

[berkeman]

First, I know where the magnetic sensor is in the smartphone, and so I hold the phone taking that into consideration when trying to measure an object. Thirdly,

Stop that!

Additionally, can you clarify your point about ferromagnetic materials in relation to your previous answer? And once again, are you aware of whether or not it is normal for a socket like this to give a measurement like this considering the initial point I have made in this reply? I also note that although you can get more accurate sensors, smartphones will give a possible range of inaccuracy of 3-5 microteslas.

Not until you go first and answer my question:

You did not answer my question -- what is your reason for doing this, and what are you hoping to find?

 

[Vanadium 50]

Seventhly, the field you are measuring is tiny. Perhaps 3x that of the earth.

Fifthly, smartphones have loudspeakers and loudspeakers need magnets - magnets much more powerful than the earth's field (even a refrigerator magnet is hundreds of times stronger than the earth's field) and these magnets are right up against the sensor.

Sure, the manufacturer of the phone will try and compensate for this, but they are not building a precision device. They are building a device that can tell whether you are facing north or south. If you need a trustworthy measurement, use a meter designed for the purpose. You can get a crappy one for $50.

Eleventhly, various bits of steel, e.g. screws, will distort the ambient magnetic field, so it will not just be the geomagnetic field. What you are measuring may or may not having anything to do with what you think the cause is.

 

[ChrisCOD]

Stop that! Not until you go first and answer my question:

I was curious and performed the measurement and now I am seeking advice on the result.

 

[ChrisCOD]

Seventhly, the field you are measuring is tiny. Perhaps 3x that of the earth.

Fifthly, smartphones have loudspeakers and loudspeakers need magnets - magnets much more powerful than the earth's field (even a refrigerator magnet is hundreds of times stronger than the earth's field) and these magnets are right up against the sensor.

Sure, the manufacturer of the phone will try and compensate for this, but they are not building a precision device. They are building a device that can tell whether you are facing north or south. If you need a trustworthy measurement, use a meter designed for the purpose. You can get a crappy one for $50.

Eleventhly, various bits of steel, e.g. screws, will distort the ambient magnetic field, so it will not just be the geomagnetic field. What you are measuring may or may not having anything to do with what you think the cause is.

Are you trolling?

 

[ChrisCOD]

Are you trolling?

The question fundamentally is what in a pure physics sense causes the quantity of measurement. Can we describe it as a function of specific components that are well defined and with reasonable description. Therefore, I am not concerned with your notion of it being a tiny magnetic field, nor do you seem to understand the point made before which is that the internal components of the device will implicitly contribute to the measurement continuously, such that increases in measurement are a function of external objects.

 

[ChrisCOD]

Are you trolling?

Furthermore, are you proposing that screws will contribute 130 units of magnetic field strength?

 

[berkeman]

Are you trolling?

Nope. Thread us closed temporarily for Moderation...

 

[berkeman]

Pending some answers in my PM conversation with the OP, this thread will remain closed.