DC Magnetometer
Manufactured in the USA by AlphaLab, Inc.
A digital gaussmeter designed to measure field and approximate pull force of magnets, and other strong sources of magnetic field. Click for other types of gaussmeters.
The DC Magnetometer (gaussmeter) comes with a universal (axial/transverse) magnetic sensor and NIST - traceable certificate. Price is $380 (USD), which includes shipping in the US. For shipping to Canada by Express Post add $20 (USD). Outside the US and Canada add $40. BUY IT NOW. Another model of digital gaussmeter, without NIST cert, is only $260 including US shipping. Click here for a description.
This magnetometer measures in three ranges, and indicates the sign (north or south). An offset control on the gaussmeter lets you adjust the "zero" field level by ± 10 gauss. The gaussmeter's output is monotonic to the last digit (± 0.005%), linear to ± 1 % at 19,999 gauss. Accuracy is +/- 1% of the reading at room temperature, or +/-2% of reading in the full temperature range of 30° F – 110° F (-1° C to 43° C). The meter comes with a NIST- traceable calibration certificate.
The strongest rare-earth magnets have a field strength (flux density) of up to about 14,000 gauss in a gap configuration. With a range of 19,999 gauss, this gaussmeter can easily measure the strength of any type of magnet in any configuration. With a large 4 ½ digit display, the meter has a resolution 10 times better than 3 ½ digit meters; you can measure a change of one gauss in the 19,999 gauss range. This allows you to measure very small fractional changes in a magnet’s field. These changes may result from slight damage to the magnet or even from small temperature changes in the magnetic material. Turn-on is immediate, and the display updates three times a second. There is normally no need to rezero, unless you manually want to add or subtract up to +/- 10 gauss to the reading, using the “OFFSET” knob.
The universal Hall sensor shown is at the end of a 1-meter (40”) very flexible cable and it does not need recalibration for at least 10 years to remain within specified accuracy. This standard sensor tip can be kept straight or bent at right angles repeatedly (it is shown bent in the picture). By bending, it can measure magnetic field either parallel (axial) or perpendicular (transverse) to the cable direction. This sensor tip is only .044” (1.1 mm) thick and .170" (4.3 mm) wide. It can be placed precisely on any region of a magnet or inside a gap. The sensitive area is 1.5 mm back from the end of the sensor tip and the measurement direction is parallel to the .044” (1.1 mm) thickness of the tip. The actual sensor area is a square only 1/5mm on a side. (This is a 1-axis meter; that is, the gaussmeter reads a single component of the field, which is itself a vector. If the tip is placed with the flat surface against the south pole of a magnet, for example, the meter will display a negative number [negative = south] equal to the field strength in gauss of the vector component of the field perpendicular to the face of the magnet there. If the tip then reoriented so it is not flat against the face, the meter will display a smaller number than the actual field strength because the field at a pole face of a magnet is generally perpendicular to that face.) The display updates three times per second; however, on the 199.99 (most sensitive) range, a 1-second time constant filter slows the response, because of a noise level of a few hundredths of a gauss.
When measuring the surface of magnets, magnetic gaps, or the field inside solenoids, a small external probe on a flexible cable is essential so that you can place the tip exactly where you want to. Although absolute error at room temperature is as much as +/-1% of the reading, this gaussmeter can detect fractional changes in the field of a magnetic that are much smaller than 1%. As long as you place the tip at the same spot on the magnet every time you measure a magnet, you can detect very small deviations in a given magnet from month to month if you suspect the magnet has been weakened (due to overheating, mechanical stress, or demagnetization in an electric motor or an external field).
A typical use for the meter is measurement of permanent magnets, such as in DC motors. These can be partially demagnetized if driven beyond their amperage rating, even if for a brief time. Other uses include electromagnets, speaker gaps, and measurement of high current. With this meter, you can also compare magnets to see if they are magnetized properly and you can map the magnetic field on magnetized structures. When doing measurements with a gaussmeter, please note that the actual field at the surface of a magnet is at most one half of the rated residual magnetism for that magnetic material. If a rare-earth magnet is rated at 14,000 gauss for example, a bar magnet made from that material will have an actual field of at most 7000 gauss at the north pole and -7000 gauss at the south pole. The readings may be even less than 7000 gauss. If the bar magnet is thin (that is, its diameter is less than 1/10 times its length) then the field will be close to 7000 gauss. If the bar magnet’s diameter is more than 1/10 its length, the field at either pole will be weaker. For example, if a magnet is in the shape of a cube, and it has a residual magnetization of 14,000 gauss, then the surface field will be only about 4500 gauss. The full 14,000 gauss field can only be created if two long bar magnets are in a gap configuration. This means that the magnets must be held close together so that one south pole of one magnet is held very close to one north pole of the other. The distance between the magnets (the gap width) must be small compared to the magnet diameters, and each magnet’s length must be at least 10 x its diameter. Then the field in the gap will be approximately the full value of the magnetic material’s residual magnetism, which is 14,000 gauss in this example. Because of this geometric effect, magnets that are flat (like a pancake) have a very low surface field.
Magnetic pull force between equal magnets or between a magnet and a steel or iron block can be calculated from field strength. This force is approximately [Force in grams] = 0.00016 x [Field on the magnet face in gauss]2 x [Magnet face area in square cm]. Note in the formula that the number of gauss must be squared. Also, this reading should be taken at the magnet face, while the magnet is away from other magnets or magnetic metal. Use the maximum gauss reading on that face. If the formula is used for pull force to steel or iron, the thickness of the block or sheet should be at least half of the magnet diameter; otherwise the force is somewhat less.
The DC Magnetometer has a minimum resolution of 0.01 gauss on the minimum range of 200 gauss (however, the effective stability is +/- 0.06 gauss; see Available Options below for a meter that is stable down to 0.01 gauss).
Available Options
Higher sensitivity: The High-Stability version of the DC Magnetometer is preferred for measuring residual magnetism in steel parts and for magnetic field mapping around large magnets. It is also $380 but has only one measurement range of .01 - 200 gauss. This version is more stable and has a faster update speed (in this low-field range) than does the standard DC Magnetometer. (Generally, the maximum residual magnetism that steel parts can retain is about 50 gauss.) A much higher sensitivity DC Milligauss Meter (0.00001 - 2 gauss) is also available.
Output jack: DC - 2 KHz. Add $8.
DC/AC Measurement Switch: AC is pseudo - RMS +/-3% 45 Hz - 2000 Hz. Measures 0.1 - 10,000 gauss AC. Add $40.
Peak Hold: Displays the highest (positive) field reading since the "reset" button was last pressed. Add $80.
External power plug-in: Bypasses internal battery. Add $30.
Dedicated axial probe: Size of a pen; 6.7 mm diameter: No extra charge. Just specify this type probe when ordering.
Extra probes, axial or universal: Add $80 each. (One probe is included with each meter.)
Special size or shape probes: Inquire.
Audio alarm or magnet strength pass/fail test: Inquire.
2 - or 3 - axis meters: Inquire.
For more information about magnetic fields
DC Magnetometer (gaussmeter)
Minimum resolution is 0.01 gauss. Standard version has effective stability of +/- 0.06 gauss and Maximum range 19,999 gauss.
High-Stability version has effective stability of +/- 0.01 gauss and Maximum range 199.99 gauss.
Includes a control box with battery and sensor on a one-meter-long cable. This magnetometer also comes with a calibration certificate. DC Magnetometer (gaussmeter): Price $380 (USD). BUY IT NOW. Price includes shipping in the US. For shipping to Canada by Express Post add $20 (USD). Outside the US and Canada add $40. Warranty for this meter is one year. Made by AlphaLab, Inc, Salt Lake City (USA).
For information or to place
an order:
Telephone +1-801-487-9492
Fax +1-801-487-3877
Toll free (USA and Canada) 1-800-658-7030
E-mail mail@trifield.com
To place an online secure order, go to DetectorTechnologies.com
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AlphaLab, Inc. / 3005 South 300
West / Salt Lake City UT 84115 USA
Home Page: TriField.com (Includes other meter categories, such as electric fields, conductivity, etc.)