How to Measure Magnetic Sweeper Pickup Power
To understand pickup power to compare magnets you need to know how we measure pickup power and performance.
Pickup power is a very difficult thing to explain or for a potential buyer to ask about and still have it mean anything. This is why Bluestreak measures pickup power in terms of the “maximum lifting height using a two and a half inch nail”. Everyone knows what a two and a half inch nail looks like. This measure indicates the maximum height that the sweeper can pick up a two and half inch nail from in a bench test.
We provide maximum lifting height comparisons for all of our magnetic sweepers. An example of one of these graphics is below.
Comparison of maximum lifting height of a selection of Push Magnet Models
Holding Force of a Magnet
We do not measure the “holding force” in terms of the pounds of steel that a magnet can hold onto because we believe it is a flawed measurement for several reasons;
- The form that the pounds of steel is in highly matters. For example, 50 pounds of nails is much harder to “hold” onto than a 50 pound steel bar. The steel bar is flat and dense and can get very close to the magnet where the magnet’s gauss strength is highest thereby enabling the magnet to “hold” onto much more weight in the form of a steel bar than it could in terms of nails. 50 pounds of nails by comparison is a mess of intertwined nails with a lot of air gaps and space between them that prohibit more of the nails from getting extremely close to the magnet where the magnet gauss strength is highest. So when a manufacturer reports the “holding force” of a magnet in terms of pounds of steel, the question is which form is the steel in?
- Holding onto something is completely different than picking it up in the first place and the real objective of a magnetic sweeper is to pick up debris first, then hold onto it. Therefore, measuring how a magnet holds onto ferrous debris, whether it’s a steel bar or nails isn’t really measuring how it will perform in picking up debris. Because if you can’t pick it up, nothing else matters.
Gauss, symbol G (sometimes Gs), is a unit of measurement of magnetic induction, also known as magnetic flux density. The Gauss measurement is also often used to indicate the strength of a magnetic sweeper or the magnets inside the magnetic sweeper. In the past Bluestreak has been reluctant to report these measurements because of how they can be misused or misconstrued. For example, the earth’s magnetic field is 0.5 Gauss and a refrigerator magnet is 10 Gauss, therefore considering only this without further understanding one would think that the refrigerator magnet is more powerful than the earth. However, the earth due to its immense size is much more powerful. To understand this more, Gauss measurements are usually provided without indicating what distance the measurement was taken from but it’s usually understood that the gauss measurement is obtained from the surface of the object if a distance isn’t specified. So in the example provided the measurement of 10 Gauss was obtained from the surface of the refrigerator magnet. As you increase the distance from the surface of the refrigerator magnet the gauss measurement, or strength of the magnetic field decreases. Everyone knows and understands this. At a very small distance from the refrigerator magnet the strength of the magnetic field drops to almost zero, whereas the earth’s magnetic field of 0.5 Gauss still exists at great distances. So size does matter and a measurement of gauss from the surface of a magnet is not the best indication of which magnet will perform best in picking up metal debris. Why? Because a magnet is almost always picking up debris from a distance or height above the ground. What really matters is what the gauss reading is at the distance above the ground the magnet will be picking up the debris from. Yet gauss readings are rarely provided for magnets are various distances from their surfaces, and even when a surface gauss reading is provided its unclear if it’s a measurement taken from the actual surface of the magnet so that the gauss field strength looks larger, or from the surface of the magnetic sweeper housing which contains the magnet where the gauss reading would be lower.
Given all this potential confusion we have been reluctant to provide any Gauss measurements in the past. However, because what really matters is what the gauss reading is at the distance above the ground the magnet will be picking up the debris from we are now also providing Gauss strength measurements at various distances from the bottom surface of our magnetic sweepers so that you can compare them to our other magnetic sweepers. One factor to consider in picking a magnetic sweeper is which one has the highest gauss reading at the most likely sweeping height you will be using.
If you’re looking for another general measurement to compare sweeper to sweeper the “Maximum lifting height” measurement is still a pretty good one to look at because of its simplicity and understandability.
Not everyone selects the most powerful magnet however, and there can be some good reasons for doing so. If you’re a mobile contractor type like a roofer, many roofers want something light that they can put behind the seat of their pickup truck because they don’t have to clean a very large job site normally and if they have to pass over an area several times with a smaller magnet that’s acceptable to them.
Therefore take a close look at all the features, some magnets have very easy auto debris release levers to make clean off easy, others have lots of wheel hole settings to make fine tuning easy for your normal application.
To the extent we can reasonably do so, you can count on one thing, we make all of these sweepers to last.