The Hall Effect: Noise and its Effects
When designing a high quality Hall Effect transducer, or sensor, there are many things which a designer needs to take into account. Along with sensitivity, linearity, and input and output resistance, another particular area is vital – noise.
You might think that noise shouldn’t come into measuring magnetic fields, and it’s easy to see why you would think that. Despite that common thought however, electricity produces noise regardless, whether it is audible to the human ear or not. This can of course be measured by electric measurement devices, such as a Hall Effect transducer, and it can interfere with the measurements it is meant to be taking!
There are two types of noise which can affect the measurements a sensor takes – Johnson noise and flicker noise. The first one is totally unavoidable and doesn’t really cause too much of an issue. On the other hand, the second one, flicker noise, can be a troublesome, but can also be reduced.
It’s first important to understand how something as simple as noise can interfere with magnetic field measurements when using a Hall Effect transducer. This is because whenever a signal of voltage is produced, electrical noise is also produced, unavoidably. This is from the actual electronics itself, and has nothing to do with noise which comes from the environment around the equipment. This noise isn’t audible to humans, but can be measured by high sensitivity equipment. The more noise, the more interference, the more likely there is going to be an inaccurate result.
For this reason, you need to cut out the noise as much as possible.
We mentioned that there are two types of noise – Johnson noise, and flicker noise.
Johnson noise cannot be avoided, but it doesn’t cause too much of a problem. This is caused by the movement of electrons in a material that is conductive, and it is all down to temperature. You can reduce this amount of noise by reducing the temperature. Obviously however, this really depends on the material itself. On top of this, the bandwidth which the signal is taken from is also important in terms of how much noise is going to be created – the wider in terms of the frequency range, the more noise.
On the other hand, flicker noise is more of a problem.
Flicker noise is generated due to a number of issues, and interferes more with readings than Johnson noise. The good news is that you can take steps to reduce it somewhat.
The amount of flicker noise seen is completely proportional to the frequency of the bandwidth, and it can be created by many different issues. The noise is however also created because of the materials which the sensor is built from, so creating a sensor, or transducer from a different material, can cut down on the amount of flicker noise created.
Noise is one particular area which affects the accuracy of a Hall Effect transducer/sensor, but it’s important to realise that this is just part of the deal. There are many other characteristics that need to be taken into account when designing and using a sensor of this type. This particular piece of equipment is highly sensitive to any type of electrical current, but there are varying degrees of sensitivity. There are also varying degrees of noise created by them, and if you can cut down on the amount of flicker noise, you’re onto a better bet. Johnson noise is unavoidable, but the good news is that it is very minimal, and is unlikely to cause any major difference in your final readings.