How do you Measure the Strength of a Magnet?

Since a magnet's strength is only partially determined by its cubic size, its weight, or its face area, some other standard is needed to measure its ability to perform a work function. One way to approach this problem is to measure the force it takes to pull a piece of iron or steel away from the magnet. Pull testers are available in kit form for smaller permanent magnets. For research work, one pull tester uses hydraulic power to separate the magnet being tested from a steel plate. This instrument can measure forces up to 40,000 pounds, and can be used to determine two very useful magnetic strength measurements: "Pulling Power" and "Holding Power". Pulling Power is a measure of the strength of a magnet's attraction or pull exerted on a magnetic object at some distance from the magnet. Holding Power is simply a measurement of the force required to pull the steel away from a position on the face of the magnet.

A magnetic field can be calculated in terms of flux density and gauss by some fairly complicated math. Fortunately, it is not necessary to go through such an exercise to determine gauss. All you need is a gauss meter. This instrument gives you gauss readings and those readings are then used in the other two important mathematical measurements of industrial magnets, the "Gauss Gradient" and the "Force Density." Gauss Gradient is important because it is a measurement of the rate of change in gauss as a magnetic object gets nearer to the surface of the magnet. It is this change in magnetic strength that pulls the object to the magnet's face. Force Density takes the gauss measurements and gauss gradients of a magnetic circuit one step further. Force Density is the force per unit volume exerted on a ferrous object at any given distance from the face of a magnet. Force Density is expressed in Dynes per CM³ in the metric system. This measurement is especially important in selecting the proper magnet for magnetic separation. It has been proven that a magnet with a flux density of only 400 gauss at a specific distance can actually have a greater attractive force than on with a flux density of 500 gauss at the same distance. This is an example of why a number of different measurements of magnetic strength are necessary. It is also an example of why it is important to have experts in magnet design and applications assist you in selecting the magnet that best fits your particular needs.