Magnetic Field Sensing, the common practice and available added values
Sensing a magnetic field has immensely expanded, while the demand has
been evolving the adoption of a variety of magnetic sensors, detecting presence,
strength, or direction of magnetic fields, (from the Earth as well as from
permanent magnets, fields generated from electric currents, vehicle
interferences, etc.) One of the main added values of magnetic sensors is that
the mentioned measurements can be conducted in a contactless manner.
The first documented usage of magnetic sensors dates over
2,000 years back, essentially for direction and navigation applications . Nowadays, even though
these sensors remain one of the main means of navigation, a much larger variety
of usage have evolved. A strong motivation for the growth of the knowledge and
usability of these sensors is also the need for higher sensitivity, miniature
dimensions, and the ease of compatibility with electronics.
Measuring magnetic fields is paradoxically not the main intent for using
magnetic sensors. These systems make it accessible to calibrate and analyze
physical quantities and parameters that are extracted from the changes in the
magnetic field (distance, temperature, etc.).
While the design and equipment of the measurement tools are evolving on an
almost daily basis, most methods of magnetic measurements have remained
practically unchanged .
With the vast amount of tooling available per method, lets go over the typical
magnetic sensor types:
Coiled magnetic sensors are some of the more simple,
affordable magnetic field sensing methods.
The general principle lies in their response to magnetic fields (AC/RF) that
are in the parallel axis of the coil. An analog output voltage is produced that
reflects the strength of the magnetic field. These are the simplest
commercially known sensors that can identify changes in the magnetic
flux density. The process, simply put, is as follows: the moment when a magnet
approaches the coil(s) the magnetic flux density increases in the coil (and vice
versa, when moving the magnet away from the coil).
As simple as this system is, it unfortunately is not perfect for all the
necessary applications, as the output voltage is dependent on the rate that a
magnetic flux changes: it is rather challenging, or impossible for this system
to measure a fixed magnet or one that changes the magnetic flux slowly.
Reed Switch sensors
Simply put, a reed switch is a glass capsule that has two
ferromagnetic reed blades that overlap each other at the center of the
class capsule or be off from each other at the center of the glass capsule,
these blades pass through the tube from parallel ends of the capsule.
When a magnetic field is generated in the vicinity of the reed switch sensor,
the reeds become carriers of magnetic flux (within the magnetic circuit),
essentially being charged by opposite magnetic poles, the overlapping ends in
the glass capsule attract each other. When the reed blades (reeds) are drawn to
each other the reed switch sensor actuates.
These are hermetically sealed sensors, free from condemnation risks, thus
useful in chemically aggressive, explosive environments, no electromagnetic
discharge is effective on these sensors and these can create variety of flexible
practical solutions, when accompanied with magnets and coils, however it may be
a demand of specific use cases most of the time.
Unfortunately reed switch sensors are rather delicate and prone to breakage
when in physically unstable environments, i.e. vibrating, harsh shock
environments. Over time, mechanical reed switches also tend to wear
out, which is why cell phone manufacturers had to replace these with
Hall sensors for example.
Hall Effect sensors
In the presence of a magnetic field, the current (more precisely the charges
that are carrying the current) are exposed to the Lorentz force , after which
a charge is built up on one side of the conductor and on the other side the
charge is decreased. The buildup of the charge results in Hall
Voltage (difference between the electric field and voltage potential)
that restricts the further buildup of the charge. The perpendicular components
of the magnetic field and the bias current are proportional to the Hall Voltage
(which also depends on the specific properties of the material property).
A Hall Effect Sensor is essentially a transducer, which, as
a response to a magnetic field generated by a current flow, outputs a voltage.
It is a beneficial system to monitor primary conductor current precisely, with
no effect on the circuit.
Clear advantages of Hall effect sensors are their miniature
size, which allows them to be placed in otherwise hardly accessible
locations. Sure, there is additional electronics required for the clear
detection, however a CPU can, as it is widely known, be miniaturized as well.
Distance and mechanical changes however, are an essential specified part of
these sensors, should there be a tiny misalignment when placed in the vicinity
of a metal conductor for example, the accuracy of the measurements may greatly
What holds Magnetic Sensing back and what should the future hold?
When considering forces like external magnetic fields interfering and swaying
the measurement of current flow (i.e. hall sensors), the temperature effects on
the electrical resistance, the sensitivity ranges of these sensors,
temperature/force resistance levels, the prices of i.e. MEMS
sensors, compared to the durability of magnetic sensing systems
that are commercially available nowadays – we willingly or not uncover the
Achilles' heel for magnetic sensing.
A sensing system that incorporates magnetic principles without compromising
the size, durability, cost, and overcoming the negative effects of external
magnetic/electric fields, hazardous, alkaline, extreme temperature environments,
adding to qualities like contactless, real-time measurements; the RVmagnetics MicroWire
MicroWire: Longevity, Sensitivity, Ease of implementation
The sensors: these glass-coated sensors commonly use soft
magnetic materials – meaning they are easily magnetized and demagnetized –
but also metals that exhibit magnetostriction, meaning they change their shape
when subjected to a magnetic field. The sensing can happen through the magnetic
field from inside almost any material.
The MicroWire sensor measurements have no hysteresis (unlike for example Hall
sensors), it is linear (see on the diagram) from the principle of the
Linearity is valid up to the highest value of the range. The range can be
adjusted to almost any value since the feature of MicroWire’s response (no
hysteresis/linearity) works from very low to very high fields.
The sensing: sensing is contactless. It is important to
mention that the MicroWire is a passive element with neither wiring attached to
it nor data being gathered in it. The data itself is gathered through the
sensing head and the electronics. The sensing head consists of two copper coils
(excitation coil gives out the magnetic field, sensing coil “gathers” the
MicroWires response in the local physical environment).
RVmagnetics technology employs switching between two stable magnetic states
to sense different parameters. The technical solution allows. This data is
gathered on a Central Processing Unit (CPU) which also acts as an AD
The pure added value of increased longevity, saved expenses, durability, ease
of production, etc, is of course clear to be able to choose this system over
other magnetic sensors.
However, we must recognize that this may not be true for all of the
applications, as, in the end of the day there is a wise saying “if it ain’t
broke, don’t fix it”, and if your application strives by this, than a sensor
providing a real-time data from otherwise impossibly inaccessible locations may
not add much to your operations.Nevertheless, it is clearly a system which, if
implemented in the right places, will solve issues that may bend whole
economical perspectives into a more positive route.
Take for instance the Electric
Engines – is there a sensor that may provide real-time extremely precise
data on vibrations gathered directly from the internal particles of the engine
rather than calculated based on the more external behaviour of the engine
(external and internal vibrations are not likely to be homogeneous, the same is
true for temperature).
Out of the whole idea of the future of magnetic sensors and eventually of
this example on electric motors, we can conclude that RVmagnetics enables
reaching the real data over having to conclude it.