Gauss meters, also called Tesla meters, are used to measure electromagnetic fields (EMF) from wiring or power lines, magnetic fields around critical equipment, or measure magnetic shielding performance. When selecting a Gauss meter, consider the range, resolution, axis, accuracy, and outputs.
| gauss | |
|---|---|
| Unit system | Gaussian and emu-cgs |
| Unit of | magnetic flux density (also known as magnetic induction, or the B-field, or magnetic field) |
| Symbol | G or Gs |
| Named after | Carl Friedrich Gauss |
| Conversions | |
| 1 G or Gs in ... | ... is equal to ... |
| SI derived units | 10−4 tesla |
| esu-cgs | 1/ccgs esu[Note 1] |
Features: - High sensitivity 3 mV/G. Digital display voltmeter. North- South Pole. Designs and manufactures gaussmeters, air ion counters, electrostatic voltmeters and other instruments for scientific and industrial applications.
The gauss, symbol G (sometimes Gs), is a unit of measurement of magnetic induction, also known as magnetic flux density. The unit is part of the Gaussian system of units, which inherited it from the older CGS-EMU system. It was named after the German mathematician and physicist Carl Friedrich Gauss in 1936. One gauss is defined as one maxwell per square centimetre.
As the cgs system has been superseded by the International System of Units (SI), the use of the gauss has been deprecated by the standards bodies, but is still regularly used in various subfields of science. The SI unit for magnetic flux density is the tesla (symbol T),[1] which corresponds to 10,000gauss.
Name, symbol, and metric prefixes[edit]
Albeit not a component of the International System of Units, the usage of the gauss generally follows the rules for SI units. Since the name is derived from a person's name, its symbol is the uppercase letter G. When the unit is spelled out, it is written in lowercase ('gauss'), unless it begins a sentence.[2]:147–148 The gauss may be combined with metric prefixes,[3]:128 such as in milligauss, mG (or mGs).
Unit conversions[edit]
The gauss is the unit of magnetic flux density B in the system of Gaussian units and is equal to Mx/cm2 or g/Bi/s2, while the oersted is the unit of H-field. One tesla (T) corresponds to 104 gauss, and one ampere (A) per metre corresponds to 4π × 10−3 oersted.
The units for magnetic flux Φ, which is the integral of magnetic B-field over an area, are the weber (Wb) in the SI and the maxwell (Mx) in the CGS-Gaussian system. The conversion factor is 108, since flux is the integral of field over an area, area having the units of the square of distance, thus 104 (magnetic field conversion factor) times the square of 102 (linear distance conversion factor, i.e., centimetres per metre). 108 = 104 × (102)2.
Typical values[edit]
- 10−9–10−8 G – the magnetic field of the human brain
- 10−6–10−3 G – the magnetic field of Galactic molecular clouds. Typical magnetic field strengths within the interstellar medium of the Milky Way are ∼5 μGs.
- 0.25–0.60 G – the Earth's magnetic field at its surface
- 25 G – the Earth's magnetic field in its core[4]
- 50 G – a typical refrigerator magnet
- 100 G – an ironmagnet
- 1500 G – within a sun spot[5]
- 10000 to 13000 G – remanence of a neodymium-iron-boron (NIB) magnet[6]
- 16000 to 22000 G – saturation of high permeability iron alloys used in transformers[7]
- 3000–70000 G – a medical magnetic resonance imaging machine
- 1012–1013 G – the surface of a neutron star[8]
- 4 × 1013 G – the quantum electrodynamic threshold
- 1014 G – the magnetic field of SGR J1745-2900, orbiting the supermassive black hole Sgr A* in the center of the Milky Way.
- 1015 G – the magnetic field of some newly created magnetars[9]
- 1017 G – the upper limit to neutron star magnetism[9]
See also[edit]
Notes[edit]
- ^ccgs = 2.99792458×1010 is the dimensionless magnitude of the speed of light when expressed in cgs units.
References[edit]
- ^NIST Special Publication 1038, Section 4.3.1
- ^International Bureau of Weights and Measures (2019-05-20), SI Brochure: The International System of Units (SI)(PDF) (9th ed.), ISBN978-92-822-2272-0
- ^International Bureau of Weights and Measures (2006), The International System of Units (SI)(PDF) (8th ed.), ISBN92-822-2213-6, archived(PDF) from the original on 2017-08-14
- ^Buffett, Bruce A. (2010), 'Tidal dissipation and the strength of the Earth’s internal magnetic field', Nature, volume 468, pages 952–954, doi:10.1038/nature09643
- ^Hoadley, Rick. 'How strong are magnets?'. www.coolmagnetman.com. Retrieved 2017-01-26.
- ^Pyrhönen, Juha; Jokinen, Tapani; Hrabovcová, Valéria (2009). Design of Rotating Electrical Machines. John Wiley and Sons. p. 232. ISBN0-470-69516-1.
- ^Laughton, Michael A.; Warne, Douglas F., eds. (2003). '8'. Electrical Engineer's Reference Book (Sixteenth ed.). Newnes. ISBN0-7506-4637-3.
- ^'How strong are magnets?'. Experiments with magnets and our surroundings. Magcraft. Retrieved 2007-12-14.
- ^ abDuncan, Robert C. (March 2003). 'Magnetars, Soft Gamma Repeaters and Very Strong Magnetic Fields'. University of Texas at Austin. Archived from the original on 2007-06-11. Retrieved 2007-05-23.
Make a Magnetometer
Make a magnetometer for under $10!
We describe one way to make a simple tool that can measure the strength and direction of a strong magnetic field near neodymium magnets, using off-the-shelf components and items you might already have.
Built around an off-the-shelf, inexpensive sensor
There are a number of off-the-shelf electronic components that measure the strength of a magnetic field. They’re used in all sorts of devices, so the cost is very reasonable. We chose an Allegro A1302, a “Ratiometric Linear Hall Effect Sensor IC.” It’s commonly available for under $2.
This part is available from many online electronics parts vendors, such as Jameco, Mouser, Digikey or Newark.
The Hall Effect sensors we discussed in a previous article were simple on-off switches. When they “see” a magnetic field that’s strong enough, they switch on. Remove the magnetic field, and it switches back off.
The A1302 sensor operates differently; it is not an on/off switch. You supply it with power at 5 Volts, and it gives an output voltage that’s related to the magnetic field it sees. That's what 'ratiometric' means: the voltage coming out of the sensor is directly proportional to the magnetic field it reads.
Materials needed:
- Allegro A1302 Ratiometric Linear Hall Effect Sensor IC
- USB cable: steal one from an old device, as long as it has the plug that goes into your PC’s USB port.
- Resistors: a few values.
- Multi-meter: Use a multi-meter you might already own, which measures voltage.
That’s it! That's all that's needed. We also used a soldering iron to solder wires together.
The next few sections describe how we wired this sensor to our multi-meter. If circuit design doesn't interest you, scroll past to where we show what the finished sensor can do.
Circuit Design 1A
To power the sensor, we need a steady 5 Volt supply. For something inexpensive, we used the end of an old USB cable. By plugging it into the front of a PC, we get a great 5 Volt supply.
A USB cable has 4 wires inside. Two of them are 5V and Ground, and the other 2 are for data (which we won’t use).
We soldered wires to the ends of the 3 pins on the sensor. Wire the ground pin to the ground wire of the USB cable (usually black), and Vcc to the 5V line (usually red).
By placing the two probes of a multimeter on points A and B of that circuit diagram, we can measure the raw voltage output of the sensor.
The output varies from 0 to 5 Volts, where the no-magnetic-field point is in the middle at 2.5 Volts. With no magnets nearby, you should see 2.5V.
When exposed to a magnetic field normal to (into) the flat face of the sensor, the voltage will vary away from that 2.5V midpoint. A conversion table to convert this voltage to a field strength expressed in Gauss looks like this:
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Circuit Design 1B – Make the zero field strength read zero on the meter!
While that setup does work, the output is somewhat less than intuitive. One has to do a lot of math in their head to convert the number on the meter to a field strength. It would be better if we could make the voltmeter read zero when there is no magnetic field, and give positive or negative values depending on the direction of the magnetic field.
We do this by adding a few resistors, as shown in Circuit 1B. By using 2 identical resistors, we can expect the voltage at a point between them (point C) to be 2.5V above ground. We chose resistors large enough to keep the current flow fairly low – the USB port on a PC can only supply so much power. We used two 330 Ohm resistors, for a current of about 7.5mA (only about 0.04 Watts).
Now, by placing the voltmeter on points C and B, we can see readings that are zero when there is no field. The meter is comparing the output voltage to 2.5V, instead of comparing the output voltage to ground. You still need a table to compare the numbers on the meter to actual field strength expressed in gauss, but at least zero equals zero.
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Use the table, or divide the number on the meter by 0.0013 (Volts per Gauss). So, if you see 1 Volt, that’s 1 Volt / 0.0013 V/G = 769 Gauss.
Circuit Design 1C – Make 1,000 Gauss Appear as 1V on the Meter
As long as we’re fiddling with resistors, we might take this one step further. Some judicious use of a few more resistors can scale the number the meter shows, so that 1V = 1,000 Gauss. This we can read without having to do any math!
Gauss Meter Kit
We used much larger resistor values in this leg, to minimize affecting what we’re measuring. We used 47,000 Ohm resistor for R3, and 11,000 (A 10k and a 1k) Ohm value for R4. You could use other values, but this ratio is what we needed to make 1 Volt on the meter correspont to 1,000 Gauss.
(How did we choose those values? Because in the '1B' circuit, 1.3V corresponded to a field strength of 1,000 Gauss. To make it work out, we wanted to measure about 1/1.3 or 77% of the voltage across that leg. Since 47 kOhms is about 80% of 47+11 kOhms, it works out.)
By placing the leads from our multi-meter on points C and D now, we get a number that relates to the field strength and is easily read. Now 1V equals 1,000 Gauss, 1.5V equals 1,500 Gauss, 2V equals 2,000 Gauss, etc.
What is this makeshift magnetometer capable of?
This sensor can read field strengths up to about 1,750 - 2,000 gauss. If exposed to stronger magnetic fields, the sensor wouldn’t be damaged but the output is limited to or “pegged” at this number.
Below about 10 gauss you won’t get any reading at all. Consider the accuracy as decent but rough numbers. We wouldn’t use this as a calibrated setup to test magnet strength, but it’s a great way to study and compare the relative strength of magnetic fields.
What is it good for?
A magnetometer is a great way to help see what a magnetic field is at a point. It's a good way to put some numbers to something that is otherwise invisible. There are a number of ways this might be used by hobbyists, magnetic enthusiasts, and engineers. Anytime you want to know the field strength at a point, it’s a great tool. Uses might include:
- Measuring the strength of a magnet by measuring the magnetic field strength at a fixed distance from the surface
- Evaluate the effectiveness of shielding by measuring field strength before and after adding shielding to an assembly.
- Help visualize the strength and direction of a magnetic field.
Cautions and common questions:
Don’t treat the readings as perfect numbers. The sensor only operates in a narrow range. You can find stronger field strengths near neodymium magnets. It also has a pretty rough tolerance. Note: the resistors we added to adjust the readings all have 5% tolerances. Expect your results to be in the right ballpark, but not calibrated or exact.
In fact, we used a variable resistor and tweaked that R4 value to get our device closer to reality.
You won’t see listed Surface Field numbers when pressing this sensor directly on the surface of a disc magnet. Why not? The actual sensing portion of the sensor is located about 0.5mm behind the face of it. When pressed against the magnet’s surface, the sensor actually measures the field strength at this 0.5mm distance, not at the surface. This can make a big difference in the values you see, especially with small magnets.
The sensor only senses the magnitude (strength) of the magnetic field along one axis. It senses magnetic field strength in the direction that’s into the flat surface of the sensor. Twisting it will change the direction you’re measuring.
Need a more capable instrument? Consider these instruments: Here’s links to Trifield, Lakeshore and Magnet-Physics.
50 0 50 Gauss Meter