Paul DuPuis Honeywell Military Avionics Division Louis Park, Minn

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Paul DuPuis Honeywell Military Avionics Division Louis Park, Minn

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Matchbook-Sized "Smart" Pressure Transducer Critical Applications
Paul DuPuis
Honeywell Military Avionics Division Louis Park, Minnesota 55416 (612)542-5965 Abstract:
Modern control systems strive attain peak efficiency minimize costs; reduce pollution; enhance safety. This applies throughout realm transducer applications-from electronic fuel injection systems today's cars, factory automation, high-performance aerospace applications. meet their end-application's performance goals, system designers have been ever tightening their requirements accurately measure relevant control variables. Currently, they often demand accuracies more than order magnitude better than that realizable using conventional measurement system architectures. This performance often specified under more severe environments too. application family "smart" digital transducers that solves those concerns meets requirements critical applications iscussed. features it's: Stability, Maintenance-free life, Accuracy, Reliability, Tractability. This device also tiny, power, able multiplex numerous transducers same -directional serial digital bus. transducers configured operate synchronously asynchronously with each other. It's Real! Since January 1990, Honeywell delivered over 2,000 LG-1237 matchbook-sized smart pressure transducers engine control systems. These flying recently introduced Airbus A340 destined other aircraft, both civil military. term "smart" used differentiate that this transducer internal intelligence form micro controller compared more traditional transducer implementations. This micro controller provides intelligence "smarts" interactive stand-alone decision making capability within transducer. This allows transducer dynamically adapt itself operating environment. also performs measurement, control, communication, computation, self test roles within transducer. Nine these transducers used second generation, full authority digital engine control system-the FADEC-II which controls each 31,200 thrust CFM56 engines A340. That engine made International Paris, France.
FADEC-II also used 95,000 pound thrust GE90 being developed.
Figure Matchbook-Sized LG-1237
Published conference proceedings presented "Sensors Expo", Chicago, September 1992. more information LG1237 Pressure Transducer, contact Honeywell 1-800-323-8295 visit website: www.pressuresensing.com find your local Honeywell representative.
FADEC-II uses these transducers sense pressure within engine's core stages external core. These LG-1237's provide pressure measurement feedback required engine's closed-loop control system. precise pressure measurements provided these transducers used FADEC-ll's internal algorithms both control engine's power output optimize efficiency. also provides mechanism detecting degraded performance required maintenance that occur result normal erosion; service damage such bird, hail, water ingestion; other factors affecting safety such icing nacelles. achieve this application's objectives, extremely stable, accurate, high resolution transducer required. This requires three ranges transducers. These have full scale pressure ratings 20,130, psia (750 psia GE90) 0.02% f.s. tightest accuracy point. This performance must maintained over year life. Conventional analog transducer-based system architectures typically able meet such stringent requirements when subject comprehensive system-level tolerance analysis.
Inside Story
meet these demanding application needs, team extra "aces" sleeve. extensive experience using piezoresistive silicon sensing elements comb ined with algorithmic correction repeatable error sources. This technology been used digital data computers (DADC) since 1970. They provide altitude, airspeed, mach number information pilot -through instrument displays -and autopilot -10, 747, 737,727, MD80 aircraft. Those DADC's however, more "macro," "bread box" size scale than "micro," matchbook scale required FADEC-II application. experience producing high volumes silicon piezoresistive pressure sensors. These used ST-3000 smart industrial transmitter (transducer) manufactured Honeywell's Industrial Automation Control (IAC) Division. Those primarily used petrochemical industry. This however, compatible with desired "matchbook" size; small "beer keg" -like package typical process control industry. sensors this application produced Honeywell's Solid State Electronics Center. PG-1052 ARINC Data Module (ADM) Airbus A320. That part distributed data/ inertial reference system (ADIRS) which eight remotely mounted ADM's send accurate pressure information processor that resides within main chassis. That processor then reduces pressure data into data parameters. that application, data computer separate entity been eliminated. These ADM's brick-sized device although early prototypes were same size shape can! challenge
Critical Application Requirements
challenging requirements this transducer are: Size: 2.25" 0.6"-the outline large matchbook Reliability: 150K minimum predicted MTBF Mil-Hdbk-217E category AUF-severe! Life/Long term stability: design life Accuracy: 0.02% (95% confidence) Rugged-severe vibration, shock, thermal media environments High pressure operation-to psia Frequency response: latency Cost: Competitive commercial programs Quality: certified military standards-extremely rigorous! Interface characteristics: node high speed serial digital bus-saves wiring Special features: Built-in-test Synchronized "snapshot" measurement multiple nodes-no measurement skew Pressure "simulation" capability-used system emulation.
"Ton" Technology Package!
Figure shows tiny size this device. Considering size device, very electronic components will mitigate risk, standard off-the-shelf components were used except custom piezoresistive sensor. Instead hardware, "packed" device with software -figuratively "ton" judging quantity documentation required meet both military civil airworthiness certification requirements.
Published conference proceedings presented "Sensors Expo", Chicago, September 1992.
more information LG1237 Pressure Transducer, contact Honeywell 1-800-323-8295 visit website: www.pressuresensing.com find your local Honeywell representative.
Will Ever Fail?
These transducers configured such that common device used both demanding military applications high-performance fighter engines commercial aircraft engines which less environmentally demanding more heavily utilized. development objectives this transducer provide predicted component reliability approximately 150K hours operation severe Airborne, Uninhabited, Fighter category Military Handbook 217E while maintaining full rated performance. That equates over years continuous operation -service lifetime exceeding years when evaluated that environment. represents application environment having severe combination shock, vibration, wide-range thermal cycling. This level component reliability-but long term stability-is similar that predicted ventional analog transducer implementations. Airborne, Uninhabited, Cargo (AUC) category, which more benign used airliners, reliability LG-1237 equates predicted year application life. When evaluated under ground, fixed (stationary) equipment (GF) category, predicted reliability equates failure-free years continuous operation.
part process defining method meet these stringent long term performance requirements, application overall system-level error analysis candidate "straw man" transducer configurations necessary. "conventional" analog transducer combined with remainder system which installed first evaluated baseline. block diagram that configuration shown Figure optimized "smart" transducer configuration LG1237 shown Figure comparison. elements affecting performance these system architectures follows: pressure sensing element "sensor" which converts pneumatic input into low-level electrical signal. front-end signal conditioning which converts low-level sensor output into both temperature linearity compensated high-level output signal that transmitted data acquisition interface. communication means over which analog data passes, this case wires. data acquisition conversion interface which converts analog signal back into digital signal usable micro computing element which implements control algorithms. Each these blocks characteristics which ultimately limit realizable end-system performance. Some more pronounced these error sources tallied Table
Development Philosophy
attain required level reliability, considering technical sophistication application, focused development philosophy. points are: concurrent engineering involving customer, systems, hardware, software, manufacturing, evaluation, quality. Minimize component count reduce power increase reliability. lowest power parts commensurate with required performance. (It's mostly CMOS.) MIL-qualified customer approved IC's discrete parts. Derate parts specs. attentive thermal management minimize power dissipation temperature rise within components.
Conventional Analog Data Acquisition
Transducer following relates conventional analog pressure measurement system implementation depicted Figure "transducer" represents component normally purchased user. incorporates both sensor signal conditioning functions within Within easily correctable sensor errors typically accomplished through series laser trims both passive active analog correction networks. These done both sensor attempt provide compensation function which complementary particular sensor error characteristic. complexity compensation networks varies depending magnitude compensatible errors, compensated temperature range, device's accuracy requirements. This compensation scheme compromise between circuit complexity (affecting cost stability), ease calibration without
Architectural Considerations
result transducer which significantly exceeds reliability requirements typically dissipates only 0.25 watts power.
Published conference proceedings presented "Sensors Expo", Chicago, September 1992. more information LG1237 Pressure Transducer, contact Honeywell 1-800-323-8295 visit website: www.pressuresensing.com find your local Honeywell representative.
interaction between laser trims (affecting yield), performance over operational pressure temperature envelope. best piezoresistive sensor based transducers utilizing laser-trim similar analog compensation networks usually have accuracy limitation about ±0.25% over +125°C (military) temperature range-before incorporation into system. remaining error sources uncompensatable ones plus uncompensatible residuals after laser-trim compensation. These residual thermal sensitivities non-linearities. Installation Into System When incorporated into system, other accuracy affecting factors become manifest. -system engineered interfaces noise main culprits. Interface Signals often overlooked factor having significant impact system error analog transducer implementation which fails provide ratiometric output. this ratiometric configuration, both pressure output signal transducer's internal voltage reference provided outputs often external reference input). having reference voltage output, mistracking between transducer's reference data acquisition system's voltage reference eliminated source error. Failing such configuration needlessly from f.s. additional error system tolerance capability-this depends accuracy stability internal voltage reference. Ratiometric outputs express transducer's output function dimensionless ratio signal voltage reference voltage. data acqu isition then treat transducer's reference voltage external reference input making more precise measurements. This three-wire measurement technique been utilized extensively precision analog instrumentation applications seldom applied fielded pressure transducer applications. Interface Wiring Noise induced analog signal transmission lines partially filtered input, typically lowpass, filter analog data acquisition portion
control system. That filtering must pass frequencies interest without significant attenuation phase shift; such would degrade dynamics control loop which installed point causing instability sluggish response. Along with ltered analog input signal rides transmission line induced noise within that same passband-it unavoidable this analog implementation. this implementation each transducer requires separate pair wires transmit analog data back data acquisition system. That make both material labor costs wiring large system quite expensive. aircraft applications that added wiring carries significant weight reliability penalty. Analog Digital Conversion Process data acquisition system's converter accuracy another error source. well related input multiplexer pass filters dynamically self calibrated. This will effectively correct thermal long term drift errors receiving transmission line. Most credible converting input voltage into digital equivalent. problem that, real world, those analog inputs containing analog pressure data least partially corrupted electrica induced noise transmission line. This cannot removed without compromising system dynamics. Analog Transducer System Performance Summary analog transducer system implementation having noise induced transmission line, ratiometric three-wire measurement technique, performance approaches that guaranteed transducer alone. those criteria simultaneously met, achievable transducer performance must determined case case basis. Deciphering transducer data sheet precisely what performance achievable rolling that into total system tolerance analysis immensely complicates task configuring control system. This result more expensive less than optimum trol system since tolerance allocations allocated part system (e.g. interface wiring noise) unnecessarily burden another portion system (e.g. transducer accuracy) order meet desired system-level tolerance budget.
Published conference proceedings presented "Sensors Expo", Chicago, September 1992. more information LG1237 Pressure Transducer, contact Honeywell 1-800-323-8295 visit website: www.pressuresensing.com find your local Honeywell representative.
Figure Conventional Analog Transducer System Implementation
Figure Smart Transducer System Implementation
Smart Transducer System Implementation
LG-1237 architecture optimized provide premium in-system performance. based Honeywell's long experience with algorithmic correction precision transducers. derive architecture, system-level error contributors were evaluated eliminated minimized through concurrent engineering. That insured that sensor, internal electronic hardware, internal software, interface characteristics user system took maximum synergistic advantage each function's capability. Minimizing component count non-compensatible sources error through this system-engineering approach have resulted device which able provide guaranteed in-system tolerance. That because critical sources error have been merged within smart transducer where they effectively managed eliminated.
Here's main categories error sources listed Table managed within LG-1237. Sensor: piezoresistive silicon sensor used this device. outputs voltage; typically hundred millivolts full scale. "raw" output piezoresistive pressure sensor significantly affected temperature, therefore, compensation those effects order. feature Honeywell's precision piezoresistive pressure sensors that they configured independently sense both pressure temperature -this temperature information will used later compensation process. magnitude thermal effect pressure measurement about f.s. before correction. Rather than complicate sensing element with thermal compensation networks laser trims, intent here keep sensing element repeatable stable over time making simple.
Published conference proceedings presented "Sensors Expo", Chicago, September 1992. more information LG1237 Pressure Transducer, contact Honeywell 1-800-323-8295 visit website: www.pressuresensing.com find your local Honeywell representative.
Table System-Level Sources Measurement Error
Source Measurement Error Sensor
Correctable Non-linearity Thermal sensitivities Null shift Span shift Linearity changes Zero-pressure offset 25°C) Full scale span 25°C) Non-correctable Hysteresis repeatability. Long-term drift, yrs. Pressure media influences Vibration acceleration influences Partial correction, 0.1% typ. Partial corr., 0.25 0.5% typ. Partial correction, 0.1% typ. 0.05 0.1% typical 0.2% typical Varies, 0.1% typical Varies, 0.05 to.2.5% Appl. dependent Appl. dependent .003 0.03 013% worst case 0.01% worst case <0.005% typical <0.03% <0.005% inclusive 0.002 0.1% typical <0.007% inclusive Partial correction, 0.1% typ.
Analog System Architecture
Smart Transducer Architecture (LG-1237)
Signal conditioning transducer):
Correctable Initial offset scale factor Thermal sensitivities Offset Scale factor Linearity Non-correctable Residual errors after correction Long-term component drift 0.002 0.1% typical 0.05 0.2% typical 0.1% typical 0.05 0.1% typical typical <0.005% typical <0.005% typical
Interface Susceptibility Data acquisition conversion:
Correctable rejectable Digital reception errors Noise Voltage reference mismatch System converter errors Non-correctable
0.01% typical
Inherent noise immunity
Partially filtered 0.02 0.01 Residuals 0.02 0.1%
Rejectable Minimal effect effect-does apply effect-does apply Multiple parity failures
RSS'd In-System Accuracy
±0.4
±0.02%
Published conference proceedings presented "Sensors Expo", Chicago, September 1992. more information LG1237 Pressure Transducer, contact Honeywell 1-800-323-8295 visit website: www.pressuresensing.com find your local Honeywell representative.
Signal Conditioning: signal conditioning, conversion data reduction sensor's output closely-coupled sensor itself. From error correction standpoint. treated essentially integral part sensor. This minimizes influence electrically induced noise data transmission line. This conversion technique gained wide acceptance compact disc players. output this converter processed micro controller. corrections have been applied converted data. approach removing compensatible errors used Honeywell does make laser trims other analog electrical adjustments. Instead, algorithmic "modeling" technique utilized. This advantage thermally stressing sensor when laser trims utilized. This algorithmic technique thereby offers ultimate long term stability since there added analog components involved which could change value fail over time. This compensation technique extremely flexible easily optimized since analog hardware involved-it literally requires only stroke pen-an automated that-which mathematically describes error correction algorithm applied. This technique demonstrated other Honeywell products have compensation range greater than three orders magnitude2. That degree correction excess what achievable through analog techniques. sensing element thus optimized long term stability-even apparent expense having slightly worse thermal non-linearity effects. Although slight, sensor error, thermal effects device's converter electronics also corrected this modeling algorithm. Other algorithms executed micro controller device take care digital filtering measured pressure data. This prevents aliasing data applied remainder control system. Built test functions which also executed micro controller provide both continuous special power-up checks validate integrity device. output accurate digital data engineering units. provides 0.02% accurate data confidence level.
LG-1237 outputs this data bi-directional serial digital format. contains data bits, four source identification bits, three built-in-test status bits, parity which validates data integrity. This information transmitted over high speed baud synchronous Kbaud asynchronous multi-node serial digital bus. Interface: Electrically, this CMOS compatible short interfaces, typically when installed subassembly within another piece equipment done FADEC-II. differential output RS-485-like configuration optionally available applications having external buses which subject EMI; that configuration utilizes twisted pair wiring. power, LG-1237 typically uses +5±0.5V +14±5V Data Acquisition: LG-1237 only requires UART, computer serial port, shift register, 8051 series micro controller interface with user system. analog signals involved this interface. fifteen these transducers networked together over single bus. Each transducer responds upon command when installation addressderived name called master. Since transducer's output data repeatedly read moderate rate, measurement measurement changes small, data transmission integrity checking with only parity sufficient most applications. Asynchronous Interface Communication This asynchronous interface provides ability Command read pressure measurements from uniquely specified transducers This "read pressure" command. Command read time-synchronized "snapshot" measurements entire network These "snapshot" "read snapshot" commands. Reset individual transducers entire network. "Reset, individual global" commands.
Published conference proceedings presented "Sensors Expo", Chicago, September 1992.
more information LG1237 Pressure Transducer, contact Honeywell 1-800-323-8295 visit website: www.pressuresensing.com find your local Honeywell representative.
Access each transducer's detailed test report generated built-in test functions. This "read virtual memory" command. asynchronous mode operation controlled three word asynchronous command which uniquely directed specific transducer broadcast entire network. Only quely directed commands evoke response onto bus. Synchronous Interface Communication -1237 also provides Mbaud high speed synchronous mode which chosen lieu asynchronous mode. This mode provides unidirectional output -only communication. interfaces easily with shift register 8051 receiving end; doesn't require intelligent master asynchronous mode. this mode transducers independently "strobed" access their data they utilize common strobe synchronize their measurements. Data, clock, busy signal output. When using common strobe, each device's data sequentially output onto time -slot which allocated unique installation address. synchronous mode output only consists pressure, status parity information which similar asynchronous "read pressure" command. Special Features special feature this device ability master command transducers make synchronized "snapshot" measurement -independent traffic. This mode particularly valuable evaluating relationships between multiple pressure points where time -skew normal single channel command response protocol objectionable. accomplish this synchronized measurement, master broadcasts "snapshot" command which acted upon devices. Each device then stores away current input measurement that instant. This stored measurement data available recall upon request transmitting unique "read snapshot" command each transducer whose information required.
Future Trends Pressure transducer users manufacturers both gain following this approac apparent that achieve optimum pressure transducer performance, multidisciplined system-engineering based overall architecture required rather than piecemeal building block approach. That allows optimization performance indices consistent with minimizing cost. That approach indeed "smart" provides: Stability, Maintenance-free life, Accuracy, Reliability, Tractability-its ease implementation into system. Instrument Society America SP50 Committee developing standard entitled "SP50 Field (draft) Standard. That device functional extension capability LG-1237. points future smart sensors transmitters. Acknowledgment: following people were instrumental development this "smart" transducer deserve mention: Eugenio Espiritu-Santo, George Smith, Jeff Siefke, Gordy Handberg, Jack Schuck, Mike Greenwood, Walt Posingies, Wendy McDonald, Katherine Thomas, Russ Johnson, Jack Hunger, Dave Gregg, Deborah Bailey, many others. References: Burns, DuPuis, P.," Microengineered Silicon Pressure Sensors," Proceedings IEEE Electro/International '91, York, York, April 1991. DuPuis, Novel Primary Data Quality Pressure Transducer," Proceedings IEEE National Aerospace Electronics Conference-NAECON, 20-24, 1985, 275-283. Instrument Society America Process Instrumentation Terminology, ANSI S51.1-1979, 1979. Instrument Society merica "SP50 Field Draft Standard", ISA/SP50-1992-236P, 1992. Najafi, Khalil, "Smart Sensors," Journal Micromechanics Microengineering, Vol. 1991, 86-102. Stefanides, E.J., 'Smart' Pressure Transducer Simplifies, Upgrades Cont Systems," Design News, November 1986. 86-89.
Published conference proceedings presented "Sensors Expo", Chicago, September 1992.
more information LG1237 Pressure Transducer, contact Honeywell 1-800-323-8295 visit website: www.pressuresensing.com find your local Honeywell representative.

Paul DuPuis Honeywell Military Avionics Division Louis Park, Minn

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