Magnetics Business & Technology - Summer 2011 - (Page 10)

FEATURE ARTICLE By JoHn BeigeL • Meder eLeCtroniC, inC. Growth in the Sensor Market Led by Magnetically Actuated Reed and Hall Sensors With the advent of new and improved technologies, sensors are The ‘No Touch’ Sensing Approach (Reed and Hall) expanding dramatically and are finding new requirements across There are many applications in which sensors cannot come many market segments including telecom, instrumentation, secu- in contact with the moving member that needs to be sensed. rity, medical, automotive, home apHere are some examples: pliance, marine, consumer products 1. An assortment of under the hood and general purpose. Each of these automotive sensors, one of which market segments has unique qualities measures the brake level fluid. Brake and requirements, which has further fluid is very corrosive and most matefueled the rapid growth of sensors. rials are destroyed by this fluid when Magnetically actuated sensor rein contact for long periods of time. quirements are especially in demand With this in mind, the sensor is exbecause more and more applications ternal to the brake fluid reservoir and are calling for the ‘no touching’ assenses the movement and position pect of these sensors. Also, the ‘see of a plastic float riding on the fluid. through’ effect of magnetic fields A magnet is imbedded in the plastic through all non-ferromagnetic metals Figure 1. A physical portrayal of an EM sensor float establishing the communication. and plastics is clearly needed and on 2. Rotational monitoring applicathe rise, as this allows switching to tions: as gas, water and/or electricity take place where the magnetic source are used in the home, a disk located does not ever come in contact with inside their individual meters rotates the sensor. This attribute is a key with increasing speed depending design-in requirement for many new upon the usage. Touching the disk sensing applications. in any way would disrupt its rotaElectromechanical (EM) sensors tion, negating its accuracy. A sensor also offer unique sensing attributes. is used to count the disk revolutions, Specifically, they can switch directly which is then electronically conand under relatively heavy power verted to the volume of gas, water or loads. They require a direct connecelectricity used. tion to their spring loaded lever con3. Telephone off-hook sensing, tact (see Figure 1). The EM sensor along with flip phone sensing: offused to be a very cost effective op- Figure 2. A schematic diagram of the wiring hookup of a hook sensing used a direct mechanition, but that is no longer the case Hall sensor cal connection. In this case, allowas Hall and Reed sensors have exances had to be made with a lever panded and have become very competitive. Also, with more and opening in the body of the phone. This opening allowed for spillmore sensors needing the ‘no touch’ requirement, this has directly age to occur that would seep into the sensitive electronic circuits, limited some of the EM sensor growth. either corrosively opening or shorting out the voice signals. GoInductive sensors are another technology that uses the ‘no ing to a no touch sensor, the problem was solved. Here a magnet touch’ approach. They use the principle of changing inductance built into the phone handle and then placed in the holder would by inserting a metal probe into a coil form. The applications activate a reed sensor. This in turn, would give the indication that require strict control and cannot be widely used. They are also the phone had been hung up. very expensive. 4. Commercial coffee makers must keep track of their fluid While there are many sensor technologies available, the most levels, some of which are under pressure and are super heated commonly used are the Reed and Hall sensors. This is due to the above 100°C. The sensors need to carefully monitor the posifact that these technologies are able to fulfill the parameters and tion of the fluid and communicate this directly to power loads requirements of a large number of applications. Below, we will or the electronics. discuss each technology and provide a comparison of them (as 5. Many medical applications require no touch sensing, such well as comparison to EM) in order to guide decisions regarding as pacemakers, implantable defibrillators, video camera pills, which type of technology to design in to a new application. muscle stimulation, animal tracking, drug dispensing and hearing We will also explain how certain applications have been made aids. Many of these applications require the sensor to be enclosed possible only through these new technologies and their new add- in the body with the electronics. Activating the sensor is done ed features. These features affect size, packaging, added built-in with an external magnet. This allows for transfer of information features, improved cost and improved electrical specifications. and/or mode or parameter adjustment. 10 Magnetics Business & Technology • Summer 2011

Table of Contents for the Digital Edition of Magnetics Business & Technology - Summer 2011

Magnetics Business & Technology - Summer 2011
Editor’s Choice
Designing Permanent Magnet Systems for Critical Applications
Growth in the Sensor Market Led by Magnetically Actuated Reed and Hall Sensors
Extending the Possibilities of Iron
Research & Development
Magnets • Materials • Measurement
Application • Component Developments
Guest Column: Cue-less About Q of an Inductor?
Industry News
Calendar of Events
Advertising Index
Spontaneous Thoughts: Sputnik Moments

Magnetics Business & Technology - Summer 2011