APPLICATION STORY
 


        

          



Automotive Sensor Technology.

          
Penny + Giles
          provides an insight into the sensor technologies

          used in the motorsport and heavy-duty automotive applications

          - including potentiometer, inductive and Hall Effect.

          

          Displacement sensors are used throughout the automotive industry
          to

          monitor the position of moving parts on a vehicle, providing
          continual

          feedback on the operating conditions. As a result, they allow
          designers

          and engineers to maximise the operation of the vehicle and improve

          operator safety.



          Automotive applications are typically hostile environments and
          sensors

          have to endure extreme shock, vibration and high temperatures.
          With

          current demands in the motorsport market requiring ultimate reliability

          to achieve peak performance, and demands in the heavy duty, off-road

          vehicle market for more reliable and long-lasting sensors, it
          is clear to

          see why non-contacting technologies are fast becoming the preferred

          choice amongst vehicle designers and OEMS.



          Sensor technologies are chosen to provide optimum performance
          and

          reliability in specific applications.



          Potentiometer

          Potentiometer technology is well established and has provided
          reliable

          position measurement in a wide variety of applications for over
          40 years.

          Two of the key advantages of this technology are its linear output
          and the

          versatility it derives from its simplicity. It consists of a
          printed carbon-based

          track (or 'hybrid' conductive plastic-on-wire track) with no
          complex circuitry

          or electronics. As such it is not susceptible to electromagnetic
          interference

          or magnetic fields. As a contacting device, it can be susceptible
          to the

          effects of shock and dither vibration and is not always the most
          appropriate

          choice for high intensity use applications, or high dither or
          vibration induced

          operation.



          The majority of suspension position monitoring on saloon cars,
          single seat

          race cars and motorbikes use hybrid linear potentiometers. They
          are simple

          voltage dividers and don't need any special conditioning electronics
          - they

          simply work off a dc supply and supply a dc signal. In addition,
          they monitor

          in real-time, without any signal lag from electronics, to give
          an accurate

          representation of what the suspension is doing.

          





          In heavy duty applications, linear sensors such as Penny + Giles'
          SLS320

          are used on refuse trucks for sensing the position of the hydraulic
          rams

          that move the lifting arms on front loader and side loader vehicles.
          Again,

          potentiometer technology is used because it is a simple solution
          without

          the need for complex electronics. Rotary sensors are used to
          monitor the

          movement of vehicle pivot points.

          
Inductive

          Inductive sensors used in the automotive industry are constructed
          from

          one primary and two secondary coils forming a transformer. These
          work

          on the principle of mutual inductance, producing an electrical
          signal

          proportional to a separate moving core. Also known as linear
          or rotary

          variable differential transformers (LVDTs or RVDTs), they are
          non-contacting

          and provide a long operational life which is not affected by
          vibration.



          Inductive sensors, however, require sophisticated signal conditioning
          electronics

          to condition and linearise the coil signal. This complexity is
          the main reason

          why they have been superseded with other non-contact sensors
          such as those

          based on the Hall Effect which generally cost less and are simpler
          to use.



          In the motorsport market they can be used to provide measurement
          and feedback

          for brake pad wear or steering angle. These applications are
          not critical to the

          control of the vehicle, but give data to assist engineers in
          performance improvements. Developments in GT and Fl brake caliper
          designs have given the option of monitoring

          the wear of the brake pads and discs during a race - the movement
          of the calliper

          position is sensed by a very small LVDT embedded in the caliper
          body. The sensors must withstand extremely high temperatures
          of up to 2000G. Two LVDTs are fitted

          to each caliper and the signals are fed to the car's data acquisition
          system and

          alert engineers to the condition of the brake pad and disc wear.



          The sensors are also used in control functions such as throttle
          pedal position

          and clutch actuator position, which are fundamental to the operation
          of the car.

          Failure of displacement sensors in these applications would have
          an immediate

          effect on the car. Engine throttle uses a closed loop electro-hydraulic
          system

          that requires a displacement sensor on the driver's foot pedal
          and another on

          the actuating mechanism mounted on the engine. An on-board computer
          monitors

          the demand from the throttle pedal and the feedback signal from
          the engine-mounted sensor and the closed loop system works to
          match the signals. This arrangement

          allows faster acceleration and can preserve engine life by restricting
          the driver from

          going beyond the maximum safe rev limit for the engine.

          





          In heavy-duty, off-road vehicles, single coil inductive linear
          sensors are fitted inside

          the hydraulic actuators to monitor and operate the lifting mechanisms
          of buckets. Traditionally this movement is measured using linear,
          contacting potentiometers

          to give the operator feedback about the position of the arm.
          However, the conditions inside the hydraulic actuators are harsh
          and problems can often occur because

          of a lack of, or uncontrolled, maintenance. The hydraulics systems
          can become contaminated and this can affect the contacts on potentiometer
          sensors. Designers looking for increased reliability are turning
          towards inductive sensors because

          they are non-contacting and are unaffected by the condition of
          the hydraulic fluid.

          
Hall Effect

          Hall Effect sensors are based on the small electrical potential
          created when a

          stationary magnetic field is placed perpendicular to a current-carrying
          conductor.

          They produce a digital or analogue output proportional to the
          magnetic field

          strength which is amplified to enable different voltage outputs.
          Hall Effect

          sensors are fast becoming an attractive alternative to inductive
          sensors,

          offering the same reliable, virtually unlimited life as a non-contacting
          technology,

          but at lower cost as they do not require sophisticated electronics.
          The main

          disadvantage is that they are sensitive to electromagnetic interference
          but

          this can be overcome with the use of appropriate shielding and
          good internal

          circuit design for all but the most demanding environments.



          These are particularly suitable for designers in motorsport and
          heavy-duty

          applications who are looking for the long-life of a non-contacting
          sensor, but

          without the complex signalling that inductive sensors require.
          In most cases,

          wherever a rotary potentiometer is being used, it could (in theory)
          be replaced

          by a Hall Effect device depending on the surrounding environment.



          For example, Penny + Giles engineers are designing a rotary Hall
          Effect

          sensor, SRH2BO, which could be suitable for existing potentiometer
          applications

          such as those used in sequential gearbox indicators. These indicators
          combine

          a set of electronics and a highly accurate rotary sensor fitted
          to the selector

          barrel. The action of the gearstick rotates this barrel to set
          a position

          corresponding to the selected gear and the rotary Hall Effect
          sensor measures

          this position precisely and allows the electronic control unit
          to calculate and

          display which gear is selected. This method of sensing the selected
          gear

          offers highly reliable and repeatable results, compared to microswitches
          that

          count the number of times the gearstick has been knocked forwards
          or backwards

          by the driver.

          
Automotive
          demands

          Traditionally, designers in motorsport and heavy-duty applications
          favoured the

          use of simple potentiometers for position monitoring. This is
          because they can

          be connected directly to the data acquisition system without
          the need for the

          complex signal conditioning. Demands within the automotive industry
          for ultimate reliability, however, mean designers are switching
          to inductive displacement

          sensors.



          Rotary and linear position sensors are used extensively throughout
          the automotive industry, especially in motorsport cars and off-highway
          vehicles. Developments

          in sensor technology from potentiometer to Hall effect technology
          provide designers

          with a range of long-life sensing elements which provide a highly
          reliable solution

          for all position sensing problems.

          ________________________________________________

          
For more information
          contact:-

          
Penny &
          Giles Controls Ltd.

          Tel:
          +44(0) 1202 409409

          E-mail: mike.iles@pennyandgiles.com

          Website: www.pennyandgiles.com

          
October 2005

          



                
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