Sensor Business Digest
SENSOR INDUSTRY DEVELOPMENTS AND TRENDS
August 1999

Capteur finds roust business opportunities
BD underscores that young sensor companies--which offer enhanced, customer-focused sensor products targeted at growth applications that are truly enabled by advances in sensor technology--can find dynamic opportunities in the marketplace.

Capteur Sensors and Analysers Ltd. (Didcot, Oxfordshire, England, ++44-1235-750300)--a provider of enhanced semiconductor gas sensors aimed at burgeoning applications that benefit from improved air quality monitoring/control--illustrates how a young sensor company can find robust business opportunities by developing products that customers need, working closely with customers to ensure that their sensors enhance the customer's application, and focusing on key markets/applications which increasingly require cost-effective gas sensing devices that offer performance benefits.

Dr. Graham Hine, CEO, explained that Capteur, which was founded in 1992, focuses on working with the customer to ensure that their designed-in sensors provide value-added performance for the customer's application. Capteur has segmented the market for their mixed-metal oxide gas sensors into key areas (e.g., residential and commercial buildings, automotive, aerospace, industrial, and agriculture), and key individuals at Capteur are devoted to serving customers in each application area. Over the past three years, Capteur's sensor sales have increased ten-fold, and the company currently produces nearly one million sensors annually.

Hine notes that, while gas sensor manufacturers have, historically, primarily used tin oxide semiconductor technology in their solid-state gas sensors, over the past 10 years more advanced mixed-metal oxide semiconductor technology has been introduced, which provides enhanced performance and sensor stability. Unlike tin oxide gas sensors, mixed-metal oxide sensors do not require catalysts or reagents to increase their sensitivity. Mixed-metal oxide sensors do not suffer from aging, which is typically associated with such reagents and catalysts, and these devices are less susceptible to interference from relative humidity.

Solid-state gas sensors employing semiconducting oxides typically operate at temperatures above ambient temperature. The electrical resistance of the sensor material depends on the temperature and on the chemical composition of the surrounding atmosphere. When heated, most oxides undergo a resistance change, as the oxygen concentration in the atmosphere changes.

The resistance of most of the semiconducting materials used in solid-state gas sensors depends on the concentration of the target in the surrounding atmosphere. For most gases, except oxygen, the change in resistance per unit change in gas concentration is greatest at lower concentrations of the target gas; and it decreases as the concentration of the target gas increases. Such behavior can generally be fitted either to a logarithmic curve, or to one which varies in accord with the square root of the concentration of the target gas.

Mixed-metal oxide semiconductor sensors are compact, light-weight, and offer long operational life without the need for routine replacement. While lifetimes are application-dependent, such newer, advanced technology sensors typically last more than five years, which, Hine notes, exceeds the longevity of other gas sensing technologies, such as electrochemical.

Hine notes that, traditionally, gas sensors have been primarily used to monitor hazardous gases in industrial applications. However, the increasing concern for air quality has expanded the applications for gas sensors in such areas as automotive, HVAC, environmental monitoring, medical, industrial, aerospace, residential, commercial, agricultural, and toxic gases. Key gases that need to be monitored include carbon monoxide (CO), oxides of nitrogen (NOx), ozone, LPG (liquefied petroleum gas), propane, butane, methane, hydrogen sulfide, VOCs (volatile organic compounds), chlorine, ammonia, and other constituents impacting air quality (such as those comprising household odors, or cigarette smoke).

Increasing emissions of noxious pollutants is generating an escalating concern for consumer comfort and safety. This pressing issue, coupled with more stringent pollution controls, is driving an increasing demand for gas sensing devices.

Capteur is the major, global provider of advanced technology mixed-metal oxide semiconductor gas sensors. The company employs state-of-the-art ceramic fabrication processes, which allow for the sensor's micro structure to be precisely controlled, advanced thick-film processing, and a unique heater driver (which is incorporated in the sensor and provides complete temperature compensation).

Capteur's thick-film MMOS gas sensor is comprised of a small ceramic strip, with a integral platinum heater printed on one side, and the sensing element on the other side. Utilizing innovative materials, such as chromium titanium oxide, the sensor undergoes an increase in resistance in the presence of the target gas. Since the sensor displays an increase in resistance when exposed to the gas to be measured, it does not any catalysts to enhance its response, resulting in superior poison resistance. Such gas sensors provide high stability and reliability, and have a typical lifetime of well beyond five years. Capteur's CO sensor, which has very low cross contamination, has an expected life of over 10 years.

Capteur provides sensors that address a wide range of applications, such as air purification, HVAC controls, automobile cabin air quality, aerospace climate control and ozone monitoring, toxic gas detection, environmental, medical, cooking, industrial, consumer safety (e.g., CO detectors), and agriculture (e.g., detecting ammonia and hydrogen sulfide in poultry houses and animal farms).

The company offers a comprehensive range of sensors, including those for ammonia, butane, carbon monoxide, chlorine, ethanol, ethylene, heptane, hydrogen, hydrogen sulfide, iso propyl alcohol, LPG, methane, methanol, nitrogen dioxide, ozone, propane, sulfur dioxide, toluene, general IAQ (indoor air quality), and VOCs. Capteur provides solutions and services to help its customers effectively integrate the gas sensors into a diverse range of finished products. The company also offers off-the-shelf interface electronics; and, through their customer service center, they provide bespoke design, consultancy, and support services.

A major market for Capteur's sensors consists of residential equipment (e.g., extract fans, air conditioning systems, CO detectors, and furnaces). The extract fans and air conditioners utilize CO and VOC sensors to help enhance air quality, while CO sensors are used to measure carbon monoxide leakage in furnaces/boilers.

Additional key markets for Capteur include monitoring indoor air quality in commercial buildings, automotive electronic climate control systems, aircraft (for cabin air quality and ozone measurement), agriculture, air purifiers, and ozone generator control.

In IAQ applications, the measurement of VOCs, as well as carbon dioxide (which has, historically, served as a surrogate indicator of the accumulation of bioeffluents and of inadequate ventilation) allows for optimized ventilation (based on occupancy) and efficient heating of the building.

Capteur is finding expanding opportunities for monitoring CO, hydrocarbons, and NOx in the intake air to control the air quality within the vehicle's passenger compartment. When the sensors detect a decrease in the quality of air entering the passenger compartment, a signal is sent to the electronic climate control system, enabling the system to recirculate the air or direct the air through an odor filter.

Capteur has launched a dual sensor, which detects CO, hydrocarbons, and NOx emitted from engine exhaust. Moreover, their "G" sensors (which measure CO and hydrocarbons) and "LG" sensors (which measure NOx) allow for detecting the difference between gasoline and diesel fumes. The sensors can be used with an odor removal filter and will provide a warning when the filter is faulty or nearing the end of its life. Capteur's air quality sensors are presently used in vehicles in the field; and Capteur plans to sell about five million air quality sensors to the automotive market over the next two to three years.

Capteur is working with aircraft manufacturers and air carriers to design-in their sensors for measuring cabin air quality, and for measuring ozone entering the aircraft.

In the U.S., Capteur is finding key opportunities for incorporating their VOC air quality sensors (designed to detect household odors, including cigarette smoke) in air purifiers for domestic and commercial environments. Such air quality sensors allow for automatically switching the air cleaner on or off as required, resulting in improved fuel consumption and enhanced control of household pollutants, compared to manual air cleaning systems. The sensors also serve to verify the efficiency of the carbon filter and to indicate filter lifetime.

Another key application in the U.S. for Capteur entails the control of ozone generators (which are incorporated in air purifiers that are used in residential and commercial environments (e.g., hotels, hospitals, offices, homes) to remove stale odors). Capteur's "LG" ozone sensors allow the ozone generator to maintain a level of ozone that is sufficiently high to ensure clean air, while not exceeding safe levels.

Additional applications for the company's ozone sensors include atmospheric ozone detection, roadside environmental monitoring, and performance monitoring of catalytic ozone destruction. Moreover, Capteur is finding opportunities for measuring background ozone concentrations generated by office equipment (e.g., photocopiers and laser printers).

As part of their growth strategy, Capteur is developing new products and an expanded sensor product portfolio. Moreover, the company is finding opportunities for providing systems for monitoring environmental pollutants. A key promising application for Capteur's air quality instruments involves monitoring the evolution of ozone in cities due to traffic congestion. Capteur's ozone measuring instruments, linked to a city's traffic ocntrol system, allow for optimized control of traffic patterns in order to reduce pollution.

Optek Acquired By DKM

On June 21, 1999, The Dyson-Kissner-Moran Corporation (New York, NY, 212-661-4600)--a privately-held, international, multi-industry holding company with 1998 revenues approaching $700 million--completed their acquisition of Optek Technology, Inc. (Carrollton, TX, 972-323-2200)--a manufacturer of custom optoelectronic, fiber-optic, and magnetic sensor products--for $25.50 per share in cash. On a fully-diluted basis, the value of the transaction is about $200 million.

"The combination of DKM's Wabash Technologies (Huntington, IN) and Optek brings together two leaders in their respective markets and creates opportunities for the customers, suppliers, and employees of both companies," stated Tom Felisi, Optek's chairman and CEO. "The combined entity will offer its customers access to a broad array of technologies and present future growth opportunities."

"Optek is a tremendous addition to our core holdings holdings and has all the features we look for in an acquisition," stated Robert R. Dyson, chairman and CEO of DKM.

It is envisioned that there are key opportunities for Wabash Technologies, Inc.--which is owned by DKM's Kearney-National, Inc. subsidiary, and produces customized sensors and actuators for the global automotive and off-road vehicle markets--and Optek to collaborate in the areas of product development, manufacturing, and sales of automotive (e.g., magnetic) sensors. Moreover, Optek's other products (e.g., optoelectronic sensors for non-automotive applications) represent a new growth arena for DKM.

Robert Kosobucki, vice president, strategic marketing at Optek, told SBD that there are key synergies between Optek and Wabash Technologies in terms of their respective sensor products and markets. He noted that Wabash Technologies has secured a large automotive business for magnetic (e.g., variable reluctance) sensors, which affords Optek access to a broader customer base. Optek's Hall effect, magnetoresistive, and optoelectronic semiconductor sensing capabilities dovetail with and augment Wabash's magnetic sensor offerings; and Wabash can take advantage of Optek's active semiconductor sensor manufacturing capabilities. Moreover, Optek's fiber-optic products for automotive and commercial networking applications represent a growth area for DKM.

Kosobucki added that the combination of Optek and Wabash offers a wider range of solutions for customers, and that the combined companies have the ability to supply a full range of sensors for position and speed applications throughout the vehicle. A very smooth unification is underway; and Wabash and Optek are working on approaches (including new packaging technologies) for driving-down sensor costs, while maintaining performance and quality. The Optek Sensor Group will retain the Optek and Wabash Technologies brands and will market these products as a unified entity.

Over the years, DKM has completed scores of acquisitions, as platform investments and as strategic add-ons for their subsidiaries. In contrast to leveraged-buyout firms, DKM invests only its own capital, with a long-term time horizon. DKM's philosophy is to keep its purchased entities intact and operating autonomously.

Platform acquisitions typically have revenues exceeding $50 million, operating income of over $5 million, excellent track records, experienced management, and significant and sustainable market positions. The sole criterion for a strategic or add-on purchase is the way an acquisition complements and enhances the prospects of an existing business. Strategic acquisitions completed with the active participation of core company management since mid-1996 accounted for nearly 20% of DKM's 1998 revenue.

Kearney-National, Inc.--a manufacturer of sophisticated sensors and actuators for the global automotive, industrial, and electronics markets with revenues in excess of $220 million--is comprised of the following operations: Wabash Technologies; Wabash Control Products (Wabash, IN); Coto Technology; Spectrol Electronics (Ontario, CA); and Hapco (Abingdon, VA).

In 1981, Kearney-National acquired Wabash (whose origins hark back to 1946); and the latter's name was changed to Wabash Electrical Components Group. In 1988, the Kearney/Wabash name was changed to Wabash Magnetics, a Kearney-National Company. In 1992, Wabash Magnetics was separated into two operating groups: Automotive Products; and Control Products.

In 1998, Kearney-National restructured their business units and formed Wabash Technologies Corp., focusing on the automotive component business. The divisions include Wabash Technologies--Huntington, Los Angeles (Ontario, CA), Mexico, Detroit Technology Center (Southfield, MI), Advanced Technology Center (Los Angeles), England, Slovakia, and Japan.

Wabash Technologies is purportedly the largest independent, high-volume manufacturer of custom electrical/electronic/magnetic devices in the U.S. The company specializes in sensors for proximity, position, and speed, along with fuel injection stators and actuators. Wabash Technologies is one of the largest independent coil manufacturers worldwide. Daily production output currently exceeds 30,000 wound sensors, 185,000 wound coils, and 500,000 insert-molded sub-assemblies.

Wabash Technologies is a major supplier to automotive manufacturers, using variable reluctance, Hall effect, and Wabash's new magnetoresistive sensing technologies. The company's sensor capabilities, moreover, include resistive and eddy current technologies.

Applications for Wabash Technologies' sensors include camshaft and crankshaft position sensing for ignition, fuel, and variable valve timing; early synchronization and misfire detection; sensing transmission input and output shaft speeds to support electronically-controlled shift strategies; wheel speed sensing in ABS and vehicle stability management systems; throttle position sensing; pedal position sensing for electronic (drive-by-wire) throttle control; EGR (exhaust gas recirculation) valve position sensing; transmission speed input selector for controlling the shifting of the transmission (i.e, the quadrature output signals from an incremental encoder are sent to the on-board computer, which tells transmission the desired direction and speed for the vehicle); HVAC blower speed control resistors/relay resistor modules; and fluid level measurement (fuel cards and fluid level senders).

Wabash Technologies' non-contacting rotary position sensors (NCRPS)--which combine Hall effect core semiconductor technology, proprietary magnetic circuitry, and custom signal conditioning electronics--provide a highly repeatable, fast-response linear output signal for shaft rotary position applications (e.g., throttle position, pedal position, suspension height).

Wabash's RPS 1036 rotary position sensor--developed to operate under harsh environmental conditions--is suitable for such applications as transmission position, steering angle, gear lever position, pedal position, suspension level, and throttle position.

Wabash Technologies offers resistive and non-contacting sensing technologies for throttle position sensing applications. The former uses the company's custom-developed inks and ceramic substrates to produce a durable element system. Wabash has developed is own Hall effect core semiconductor technology--which provides longevity and enhanced performance in tough environments--to incorporate into TPS applications. The company notes that throttle position sensor technology is required for all fuel injected engine applications; and this function can often be employed on diesel fuel pumps, ranging from passenger cars to luxury vehicles.

Wabash Technologies' sealed rotary position sensor (SRPS), designed to meet off-road and automotive vehicle sensing requirements, addresses such applications as throttle position, transmission position, two and four steering angle, clutch and accelerator pedals, gearshift position, plough height position, lever position. The design can be specified with a shaft and lever, rendering it suitable for other applications, such as suspension level, valve position, and air conditioning.

Wabash's patented Silver-in-Glass® technology uses standard thick-film processes to fabricate the element and create the necessary processes for the encoder. A layer of glass is fused to the ceramic substrate, and a layer of conductive silver is partially embedded into the glass layer. The conductor and glass form the on/off pattern that will provide the electrical on/off output. When kiln-fired during the manufacturing process, the conductive silver sinks into the glass, forming a smooth switching surface. The encoder's switching function displays very low roll-off/roll-on. This capability leads to very low contact bounce, which is useful in the design of the associated electrical circuitry.

The thick-film manufacturing technique, moreover, allows secondary safety and security circuits to be added at minimal additional cost; i.e., a manual operating lever could operate an encoder circuit, while simultaneously engaging an independent enabling switch circuit on the same encoder disk.

Wabash Technologies is a major provider of fluid cards that use proprietary thick-film technology, shipping over 2,000,000 units annually. In their fluid cards, which utilize a thick-film cermet materials on a ceramic card, durable and chemically-resistant glass is combined with semiconductors at low cost and good resistance stability. Wabash possess the technology to supply the entire fluid level sender unit. Their fluid cards and fluid level senders are able to provide an output that is linear to the volume of fluid in the tank, despite the shape of the fluid tank; and such products can withstand five million wiping cycles.

Wabash Technologies is a key supplier of automotive engine position sensors; and their product offerings for this application area include variable reluctance, Hall effect, and magnetoresistive systems. Wabash's engine timing sensor customers include Ford, GM Powertrain, Toyota, Honda, and Cummins.

Wabash Technologies offers a variety of anti-lock brake sensors for the automotive/truck industry, including externally-mounted variable reluctance sensors, and in-bearing sensors that use a patented concentric design with an integral connector. Their ABS sensor customers include Delphi Chassis and AlliedSignal.

Moreover, Wabash Technologies is a major supplier of transmission sensors to the automotive and heavy vehicle markets. Applications for their transmission sensors include input/output shaft speed, PRNDL (shift position), transmission speed, and continuously variable transmission (CVT) range.

Applications for the magnetoresistive and variable reluctance sensors offered by Wabash include ignition/engine timing, transmission speed, ABS/traction sensing, and position sensing. Applications for their Hall effect sensors include injection/engine timing, fuel injection timing, transmission/tachometer speed, ABS/traction sensing, throttle position, pedal position, rotary position, EGR valve position. Applications for Wabash's resistive sensors include HVAC modules/encoders, fuel level senders, pedal position, throttle position, rotary position, and EGR valve position.

Wabash Technologies' eddy current sensors have application in position and proximity sensing. Applications for their Silver-in-Glass sensing technology include fuel cards and contacting encoders.

Optek Technology, which acquired TRW's Electro-Optics Division circa 1988, designs and manufactures electronic components and assemblies that detect motion and position. The company utilizes optoelectronic and magnetic field sensing technologies to target non-standard applications that require specialized engineering and manufacturing expertise. Optek sells its products for end-use by OEMs in the office equipment, automotive, industrial, aerospace/defense, medical, and communications markets.

For the fiscal year ended October 30, 1998, Optek had net sales of $87,229,000 and net income of 13,004,000. The distribution of the company's sales by target market was: office equipment--$28.4 million; automotive--$26.6 million; industrial--$21.2 million; aerospace/defense--$5.0 million; medical--$4.4 million; and communications--$1.6 million.

Optek perceives the automotive industry to offer key growth opportunities, as an increasing number of sensors are being incorporated into vehicles to enhance fuel efficiency and emissions, boost passenger safety, and provide additional consumer options. Opportunities for Optek's integrated, application-specific sensor solutions (based on the company's expertise in magnetic, optoelectronic, and fiber-optic sensing technologies) are driven by government mandates for improved passenger safety and reduced emissions and by consumer demand for enhanced safety, performance, and functionality.

During 1998, sales of optoelectronic devices accounted for about 69% of Optek's net sales. The company's optoelectronic products consist of: infrared light-emitting and light-sensing semiconductor chips; discrete components (plastic or metal packages housing the light-emitting or light-sensing chips); assemblies, which combine the light-emitting and light-sensing discrete components in a single package to meet various electrical and/or mechanical specifications; and fiber-optic products, which use light-emitting and light-sensing technologies to transmit and receive light signals for data transmission through fiber-optic cables.

The light-emitting and light-sensing chips are core elements in Optek's optoelectronic products. LED chips emit light in response to an electrical charge. Optek manufactures light-emitting chips from gallium arsenide and gallium aluminum arsenide wafers via standard semiconductor manufacturing techniques. Light sensors, which can be used to sense and relay the signal produced by an LED, are semiconductor chips that convert light into electrical signals. Optek uses standard silicon semiconductor manufacturing processes to produce light-sensitive chips from polished silicon slices.

During 1992, Optek began production of Hall effect magnetic field sensing devices, which are now supplied for such automotive applications as camshaft and crankshaft sensors for ignition timing, theft-deterrent ignition locks, and automatic van doors and seat belt latches. Optek's Hall effect camshaft and crankshaft sensors for ignition timing are used, for example, on the GM 3800 V-6 engine.

Optek's ongoing growth in the automotive arena was spearheaded in FY '98 by the successful implementation of their theft-deterrent sensor assembly on all GM trucks, vans, and SUVs for the first time. Optek supplies the Hall effect sensors for use in GM theft-deterrent ignition lock systems directly to Strattec Security. Optek will supply Hall effect sensors for use in a theft-deterrent system developed by HUF of Germany, which will be used in GM Saturn vehicles. Non-automotive applications for Optek's Hall effect sensors include gas pumps, elevator doors, space applications, and office equipment.

Optek is vertically integrated and is capable of producing the elements incorporated into its magnetic sensor assemblies and optoelectronic products. The company produces its own Hall effect sensor chips through processes and techniques that are similar to those utilized for manufacturing their light-sensing chips. Optek purchases MR sensor chips from Emcore Corporation (Somersett, NJ) (Nasdaq: EMKR), which has been licensed to use certain patented technology pertaining to the manufacture of such chips. The MR sensor chips are mounted into discrete components that are incorporated into custom assemblies.

Optek and Emcore have maintained an ongoing collaboration in the automotive arena; i.e., Optek packages and adds value to Emcore's indium antimonide (InSb) MR (magnetoresistive) die for automotive applications. Emcore supplies InSb MR sensor die, based on technology developed by General Motors, to GM for such applications as crankshaft position sensing for ignition timing. To meet its production demand, GM licensed the InSb sensor design it developed to Emcore, which has developed and enhanced the MR position sensors for commercial applications.

In November 1998, Optek and Emcore Corporation reported the formation of Emtek Sensors L.L.C., a limited liability company headquartered in Carrollton, TX, which is jointly owned by Emcore and Optek. Emcore L.L.C. leverages the strengths of each partner to enhance the functionality and design flexibility of products presently available in the automotive market, and develop new, high-performance products for emerging consumer and industrial markets.

Emtek's InSb MR sensors are targeted at a wide range of speed and position sensing applications in the industrial (e.g., downhole oil drilling), consumer electronics, and automotive (e.g., active wheel speed sensing for anti-lock braking/traction control, transmission speed sensing, crankshaft and camshaft position/speed sensing) sectors. Initially, Emtek offers seven new MR sensor products that utilize InSb compound semiconductor die, produced by Emcore, and Optek's value-added packaging.

Emtek's initial product line consists of sensor packages containing either a dual element InSb MR die, a single element InSb MR die, or two single element InSb MR die. Three basic package styles are available: a modified TO-92 (traditional Hall effect sensor package style) black, plastic package; an industry-standard surface mount (SOT 223) black, plastic package; and a black, plastic package incorporating an SmCo biasing magnet.

Optek, Emtek's initial key customer, will supply Emtek's InSb MR sensors for camshaft and crankshaft sensing on a V-8 engine under development by GM. Emtek's InSb MR sensors will also be used for crankshaft sensing on a newly developed GM premium V-8 engine.

Kosobucki indicated that magnetoresistive sensors are particularly beneficial for engine compartment (i.e., camshaft and crankshaft position sensing) and powertrain (transmission and transfer case gear speed sensing) applications.

In Magnetic Sensor Alternatives Attract Attention, Kosobucki, notes that variable reluctance (VR), Hall effect (HE), and magnetoresistive (MR) magnetic sensing technologies offer a palette of advantageous options for engine control (e.g., rotational speed and position sensing for precision timing of ignition and fuel injection). Moreover, "magnetoresistive technologies offer the latest and most capable sensing option for the increasing demands of engine control systems. As industry awareness and the use of MR sensors increases, it is believed that they will offer a very cost-effective alternative."

VR sensors, also known as inductive sensors, provide a beneficial low-cost alternative for rotational speed sensing over an intermediate range of speeds. HE sensors offer high accuracy and high reliability in position detection, in addition to speed sensing. MR sensors provide a larger signal than HE sensors (nearly 10 times the signal amplitude for a similar magnetic field change). The larger signal reduces the possibility of false signals, and provides higher accuracy angular position detection even at low speeds or zero speed.

VR sensors generate a small electric voltage with changes in a magnetic field. The typical VR sensor consists of a small magnetic metal pole around which a wire coil is wrapped. A permanent magnet is located at one end of the pole, and the other end is positioned close to the ferromagnetic target to be detected. In a typical configuration where teeth on a ring gear are sensed, the passing teeth or gaps, or varying reluctance, change the magnetic field density passing through the sensor coil, generating a small signal.

The VR sensor's output is a sinusoidal voltage, with an amplitude proportional to rotational speed and a frequency equal to the number of teeth passing per second. The VR sensor's performance is affected by the pole's dimensions, tooth and gap width, and the sensor-to-tooth distance. A typical sensor-to-tooth distance is less than 1mm.

VR sensors offer low cost, do not require power, and only require two wires to connect to the ECU (electronic control unit). However, since the amplitude of its output signal is proportional to rotational speed, a VR sensor will have a low speed limit below which its signal is too small to be useful. High noise can also reduce the usefulness of the VR sensor's signal at low signal amplitudes. Since the sensor coil is an inductor, the output signal will shift in phase proportional to the signal frequency. Signal amplitude and phase changes with speed pose a challenge when attempting to accurately detect the angular position of the target. However, high-impedance signal conditioning circuitry can be employed to minimize the phase shift.

The aforementioned article notes that the HE sensor for engine control (e.g., rotational speed and position sensing for precise ignition and fuel injection timing) is an active semiconductor device, which typically has a bipolar silicon semiconductor surface through which a 3-10 mA current is passed. HE sensors are often assembled in a back biasing configuration in which the North pole of a permanent magnet is attached to the backside of the Hall element. In this configuration, the magnetic field is perpendicular to the surface of the Hall element; and a voltage differential, which occurs across the surface of the Hall element perpendicular to the current flow, is detected as the output signal. The voltage differential across the Hall element is proportional to the magnetic field density through the element.

To obtain a high-quality signal, Hall effect sensors are positioned less than 1mm from the target. As in the VR sensing system, the alternating teeth and gaps in the target alter the magnetic flux density flowing through the Hall sensor, thereby changing the device's voltage signal output.

The differential magnetic comparator (DMC) configuration--which uses two closely spaced HE sensors and compares the difference in the signals between them--allows for detecting zero speed (which cannot be detected using single Hall sensors). One DMC Hall element is primarily adjacent to a target tooth, while the other is primarily adjacent to a gap. While the DMC configuration provides high accuracy and zero speed detection capability, installation tolerances are more critical with respect to the sensor-to-target distance and alignment. Moreover, DMC's are relatively more costly, due to the critical adjustments during their manufacture to ensure that the magnetic field is equally balanced over both Hall elements.

Hall effect sensors offer high accuracy and repeatability in detecting an edge on a target, which is essential for precise timing of ignition and fuel injection. Since Hall sensors are fabricated as bipolar semiconductor devices, it is possible to integrate additional processing functionality (e.g., amplification, temperature compensation, signal conditioning, logic switching) onto the same chip, allowing for direct connection to the ECU. To achieve the precise switching characteristics required for a specific engine application, the Hall component manufacturer can modify the Hall chip design in order to fine-tune the magnetic operate (BOP) and release (BRP) points. Since the Hall sensor's signals are less subject to change in amplitude or phase shift with rotational speed, such sensors are usable over a wider range of speeds.

MR sensors have a resistance which is proportional to magnetic field density. MR sensors for automotive engine applications often use indium antimonide as the sensing material. The MR sensor is configured so that the flux from a magnet passes perpendicularly through the MR element's surface. The MR sensor often shows the most change in resistance in the 2,000 to 3,000 gauss range, where the resistance changes about 500 ohms over that in the 1,000 gauss range. MR sensor elements can be designed to have particular resistance ranges for a selected magnetic flux density range.

Since MR elements are passive, circuitry is required to detect the resistance change. An ASIC (application-specific integrated circuit) can be utilized to detect the change in resistance, compensate for temperature changes, regulate the supply voltage, filter noise, amplify and condition the signal, and trigger the generation of logic-level signals at predetermined resistance points. The ASIC and magnet are assembled into an application-specific housing to address the mechanical requirements of the application.

The MR sensor can be configured with dual MR elements to generate differential analog signals. Using differential signals enhances noise immunity, and reduces the effects of variations in sensor-to-target distance, magnetic flux density, and time-related electrical parameter changes. The aforementioned article on magnetic sensing technologies for engine control notes that another advantage of a dual-element MR sensor is that irregularly spaced and sized target teeth can be used to accurately generate unique timing signals. Moreover, circuitry can be designed to generate quadrature signals, which can be utilized to detect the direction of rotation. In contrast to the Hall effect DMC, the placement of the back-biasing magnet is less critical, since laser trimmed resistors can be used to balance the signals from the dual MR elements.

MR sensors can provide rotational position sensing accuracy of +/0.5° and a repeatability of +/-0.025°, which is approximately twice as accurate as HE sensors. The sensor's high accuracy and repeatability can be highly valuable attributes for meeting the timing requirements of sophisticated engine designs. MR sensors can operate at up to 3mm from the target (or twice the distance of HE sensors), resulting in more mechanically robust installation tolerances and, therefore, reduced installation and warranty costs. MR sensors can cost slightly more than Hall sensors. However, the cost for MR sensors is expected to become comparable with that of HE sensors, as industry use of MR sensors increases.

The MR sensor's large signal and high accuracy allows for using a more sophisticated "mirrored" target--a ferromagnetic disc with two tracks, comprised of different tooth patterns, machined adjacent to each other on its circular surface or cylindrical edge. The tooth patterns on each adjacent track mirror each other; i.e., where a tooth occurs on one track, a gap occurs on the adjacent track. A dual-element MR sensor is positioned so that each element sees only one track, resulting in a signal that can be used to detect position and speed (including zero speed) with very high accuracy and repeatability, and good tolerance for mechanical variation. However, mirrored targets are relatively more expensive than gear or vane sensor/target configurations.

Optek notes that magnetic sensing technologies offer advantages over other sensing technologies in automotive engine applications, including their proven high reliability under harsh operating conditions. Magnetic field lines are able to penetrate the oil, moisture, and grit that accumulates in the engine environment. Recent advances in magnetic sensors and targets allow for meeting the higher-accuracy position detection requirements in new engine designs.

With respect to rotational speed and position sensing for ignition and fuel injection timing, the selection of the most cost-effective design approach is highly dependent on the application's requirements, particularly those for rotational position sensing accuracy and reliability. Additional factors impacting the selection of the magnetic sensing solution include tolerance to mechanical variation during installation and over time, the mechanical envelope for the target and sensor, and ease of installation, alignment, and calibration. Moreover, the overall cost goal must be met, which requires trade-offs among sensor cost, target cost, installation cost, and warranty cost.


 
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