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Instrumentation: Test and Measurement Methods and Solutions (Design Conference 2013)

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Tilt Measurement: …

Tilt Measurement:
Tilt measurement is fast becoming a fundamental analysis tool in many fields including automotive, industrial, and healthcare. Navigation, vehicle dynamic control, building sway indication and motion detection systems all rely on this simple, cheap, and precise way of angle monitoring. MEMs accelerometers are ideally suited to inclination measurement than other methodologies. This session will address the challenges encountered when designing a dual-axis tilt sensor using a MEMs accelerometer including measurement resolution, signal conditioning, single- vs.
dual-axis, angle computation, and calibration.

Impedance Measurement: The measurement of complex impedance is widely used across industrial, commercial, automotive, healthcare, and consumer markets, and can include applications such as proximity sensing, inductive transducers, metallurgy and corrosion detection, loudspeaker impedance, biomedical, virus detection, blood coagulation factor, and network impedance analysis. This session will cover the concepts, approaches, and challenges of performing complex impedance measurements, and will present a system-level solution for impedance conversion.

Weigh Scale Measurement: Most common industrial weigh scale applications use a bridge-type load-cell sensor, with a voltage output that is directly proportional to the load weight placed on it. This session examines the basic parameters of a bridge-type load-cell sensor, such as the number of varying elements, impedance, excitation, sensitivity (mV/V), errors, and drift. It will also discuss the various components of the signal conditioning chain and present solutions with high dynamic range.

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  • 1. Instrumentation: Test andMeasurement Methods and SolutionsReference Designs and System Applications
  • 2. Legal Disclaimer Notice of proprietary information, Disclaimers and Exclusions Of WarrantiesThe ADI Presentation is the property of ADI. All copyright, trademark, and other intellectual property andproprietary rights in the ADI Presentation and in the software, text, graphics, design elements, audio and all othermaterials originated or used by ADI herein (the "ADI Information") are reserved to ADI and its licensors. The ADIInformation may not be reproduced, published, adapted, modified, displayed, distributed or sold in anymanner, in any form or media, without the prior written permission of ADI.THE ADI INFORMATION AND THE ADI PRESENTATION ARE PROVIDED "AS IS". WHILE ADI INTENDS THE ADIINFORMATION AND THE ADI PRESENTATION TO BE ACCURATE, NO WARRANTIES OF ANY KIND ARE MADEWITH RESPECT TO THE ADI PRESENTATION AND THE ADI INFORMATION, INCLUDING WITHOUT LIMITATIONANY WARRANTIES OF ACCURACY OR COMPLETENESS. TYPOGRAPHICAL ERRORS AND OTHERINACCURACIES OR MISTAKES ARE POSSIBLE. ADI DOES NOT WARRANT THAT THE ADI INFORMATION ANDTHE ADI PRESENTATION WILL MEET YOUR REQUIREMENTS, WILL BE ACCURATE, OR WILL BEUNINTERRUPTED OR ERROR FREE. ADI EXPRESSLY EXCLUDES AND DISCLAIMS ALL EXPRESS AND IMPLIEDWARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT OFANY THIRD PARTY INTELLECTUAL PROPERTY RIGHTS. ADI SHALL NOT BE RESPONSIBLE FOR ANY DAMAGEOR LOSS OF ANY KIND ARISING OUT OF OR RELATED TO YOUR USE OF THE ADI INFORMATION AND THE ADIPRESENTATION, INCLUDING WITHOUT LIMITATION DATA LOSS OR CORRUPTION, COMPUTERVIRUSES, ERRORS, OMISSIONS, INTERRUPTIONS, DEFECTS OR OTHER FAILURES, REGARDLESS OFWHETHER SUCH LIABILITY IS BASED IN TORT, CONTRACT OR OTHERWISE. USE OF ANY THIRD-PARTYSOFTWARE REFERENCED WILL BE GOVERNED BY THE APPLICABLE LICENSE AGREEMENT, IF ANY, WITHSUCH THIRD PARTY.©2013 Analog Devices, Inc. All rights reserved.2
  • 3. Today’s AgendaUnderstand challenges of precision data acquisition in sensingapplications Complex impedance measurements over a wide range (CN0217) Tilt measurements over full 360° range using dual axis low-g iMEMS®accelerometers (CN0189) Weigh scale signal conditioning and digitization of low level signals with highnoise-free code resolution (CN0216, CN0102)Applications selected to illustrate important design principlesapplicable to a variety of precision sensor conditioning circuitsincluding MEMSSee tested and verified Circuits from the Lab® signal chain solutionschosen to illustrate design principles Low cost evaluation hardware and software available Complete documentation packages: Schematics, BOM, layout, Gerber files, assemblies3
  • 4. Circuits from the Lab Circuits from the Lab reference circuits are engineered andtested for quick and easy system integration to help solve today’sanalog, mixed-signal, and RF design challenges.4 Evaluation board hardwareDesign files and software Windows evaluation software Schematic Bill of material PADs layout Gerber files Assembly drawing Product device drivers
  • 5. System Demonstration Platform (SDP-B, SDP-S) The SDP (System Demonstration Platform) boards provide intelligent USBcommunications between many Analog Devices evaluation boards andCircuits from the Lab boards and PCs running the evaluation software5USB USBEVALUATIONBOARDSDP-BSDP-SEVALUATIONBOARDPOWER POWER SDP-S (USB to serial engine based) One 120-pin small footprint connector Supported peripherals: I2C SPI GPIO SDP-B (ADSP-BF527 Blackfin® based) Two 120-pin small footprint connectors Supported peripherals: I2C SPI SPORT Asynchronous parallel port PPI (parallel pixel interface) Timers
  • 6. Impedance Measurement ApplicationsConsumer and biomedical markets High end biomedical equipment Resistivity/conductivity of biomedical tissues Medical sample analysis Consumer Medical sample analysis (e.g., glucose)Industrial and instrumentation markets Electro impedance spectrometry Corrosion analysis Liquid condition analysis Sensor interface (sensor impedance changes with some external event)6
  • 7. Impedance Measurement DevicesImpedance measurement is adifficult signal processing taskNeed to measure compleximpedances, not just R, L, or CImpedance conversion …is becoming more important in manysensor/diagnostic related applications …is traditionally accomplished usingdiscrete solutions …usually requires a high level ofanalog design skill to extract frequencyresponses of the unknown impedance7
  • 8. Impedance Measurement ChallengeProblem: How to analyze a compleximpedance How to control ADC samplingfrequency with respect to DDSoutput frequency (windowingvs. coherent sampling)? How to manage componentselection? Must develop software tocontrol DDS Software required for FFT How to calculate error budget? What about temperature effects? Usually ends up consuming greaterboard area and cost?8Excitation/StimulusFrequency ResponseAnalysisIntegratedSingle-ChipSolutionAD5933DDS Filter BufferADC
  • 9. VDD/2DACZ(ω)SCLSDADVDDAVDDMCLKAGND DGNDROUT VOUTAD5933RFBVIN05324-0011024-POINT DFTI2CINTERFACEIMAGINARYREGISTERREALREGISTEROSCILLATORDDSCORE(27 BITS)TEMPERATURESENSORADC(12 BITS)LPFGAINAD5933/AD5934 Impedance Converter 1 kΩ to 10 MΩ impedance range 12-bit impedance resolution 100 kHz maximum excitation frequency Adjustable voltage excitation User programmable frequency sweep Single frequency capability 1 MSPS SAR ADC (AD5933) DFT carried out at each frequency point Manual calibration routine Single-chip solution with internal DSP Output at each frequency is real and imaginarydata word Simple off-chip processing required to calculatemagnitude and phase9I2CINTERFACETO µCOR PCUNKNOWNIMPEDANCEEXCITATIONFREQUENCYREAL AND IMAGINARYCOMPONENTREGISTERSDDSADJUSTABLEVOLTAGEEXITATIONCURRENT TOVOLTAGECONVERTER
  • 10. CN0217: High Accuracy ImpedanceMeasurements Using 12-Bit Impedance ConvertersCircuit features Wide impedance range 12-bit accuracy Analog front end (AFE) forimpedance measurements lessthan 1 kΩCircuit benefits Self contained DDS excitation DSP for calculating DFT Complex impedancemeasurements10Target Applications Key Parts Used Interface/ConnectivityMedicalConsumerIndustrialAD5933AD8606I2C (AD5933)USB (EVAL-AD5933EBZ)
  • 11. 50kΩ50kΩ50kΩ50kΩRFB20kΩ20kΩ47nFZUNKNOWNVDDVDDVDD++−−A1A2A1, A2 ARE½ AD86061.48V1.98V p-pVDD/21.98V p-pVDD/2DACSCLSDADVDDAVDDMCLKAGND DGNDROUTVOUTAD5933/AD5934RFBVIN1024-POINT DFTI2CINTERFACEIMAGINARYREGISTERREALREGISTEROSCILLATORDDSCORE(27 BITS)TEMPERATURESENSORTRANSMIT SIDEOUTPUT AMPLIFIERADC(12 BITS)LPFGAINVDD VDD09915-001I-VCN0217 External AFE Signal Conditioning External analog front end (AFE) allows impedancemeasurements below 1 kΩ The solution is based on the AD8605/AD8606 op amp Excitation stage: low Output Z (<1 Ω) up to 100 kHz Receive stage: low bias current (<1 pA)11VDD = 3.3V
  • 12. High Accuracy Performance from theAD5933/AD5934 with External AFE1230 35 40FREQUENCY (kHz)45 508160818082008220824082608280IMPEDANCEMAGNITUDE(Ω)R3IDEAL09915-0083530252015105029.95 30.00 30.05 30.10 30.15 30.2010.3Ω30Ω1µF30.25FREQUENCY (kHz)MAGNITUDE(Ω)09915-003Magnitude Results For ZC = 10 kΩ||10 nF, RCAL = 1 kΩMagnitude Results For Low Impedance ZC = 8.21 kΩ, RCAL = 99.85 kΩZC = 217.25 kΩ, RCAL = 99.85 kΩOne calibrationusing 99.85 kΩresistorcoverswide rangeAllows lowvalueimpedancemeasurementsTracks R||Cacross frequency30 35 40FREQUENCY (kHz)45 50IMPEDANCEMAGNITUDE(kΩ)R409915-009213.5214.0214.521.50215.5216.0216.5217.0217.5218.0218.5IDEAL500010001500200025003000350040004 24 44 64 84 104IMPEDANCEMAGNITUDE(Ω)FREQUENCY (kHz)IDEALMEASURED09915-011
  • 13. Low RON SPDT CMOS Switch Used to SwitchBetween RCAL and Unknown Z13Use low RON CMOSswitch for switchingfrom unknown impedanceto calibration resistorRON = 0.5Ω
  • 14. CN0217 Evaluation Board, EVAL-CN0217-EB1Z14 Complete design files Schematic Bill of material PADs layout Gerber files Assembly drawingPCUnknown ZUSB
  • 15. AD5933 Web Based Demonstration ToolWeb tool demo: Enter differentimpedance types Generate frequencysweep Examine impedanceplot15
  • 16. AD5933 Used with AFE for Measuring Ground-Referenced Impedance in Blood-CoagulationMeasurement System16Ground-referencedUnknown Z
  • 17. Blood Clotting Factor Measurements17
  • 18. Liquid Quality Impedance Measurement18CONDUCTANCELIQUIDMEASUREMENTSWITCHESAFEAD5933/AD5934CONTROLLERCALIBRATIONIMPEDANCEUNKNOWNIMPEDANCE
  • 19. Precision Tilt Measurements Fundamentals of iMEMS (micro electro mechanical systems)accelerometers Single axis tilt measurements Dual axis tilt measurements for better accuracy (CN0189) Signal conditioning19
  • 20. Why Use Accelerometers to Measure Tilt? Pendulums/potentiometers wear out Accuracy and bandwidth is limited Reliability is lower Takes up a large area Out of plane sensitivity/mechanical interference MEMS accelerometers are the latest proven technologyfor electronically measuring tilt Good accuracy and bandwidth Small board area Low power High reliability Minimal out of plane sensitivity20
  • 21. Applications of iMEMS AccelerometersTilt or inclination Car alarms Patient monitorsInertial forces Laptop computer disc drive protection Airbag crash sensors Car navigation systems Elevator controlsShock or vibration Machine monitoring Control of shaker tables Data loggers to determine events/damageADI accelerometer full-scale g-range: ±2g to ±100gADI accelerometer frequency range: DC to 1 kHz21
  • 22. Tilt Measurements Using Low g AccelerometersNeed accuracy over full 360° arcOutput error less than 0.5°Single-supply operationLow powerCN0189 illustrates the signal chain solution Accelerometer signal conditioning Easy to use SAR ADC Low power, single supply Hardware, software, and design files available22
  • 23. ADXL-Family Micromachined iMEMSAccelerometers (Top View of IC)23FIXEDOUTERPLATESCS1 CS1 < CS2= CS2DENOTES ANCHORBEAMTETHERCS1 CS2CENTERPLATEAT REST APPLIED ACCELERATION
  • 24. ADXL-Family iMEMS AccelerometersInternal Signal Conditioning24OSCILLATOR A1SYNCHRONOUSDEMODULATORBEAMPLATEPLATECS1CS2SYNC0°180°A2VOUTCS2 > CS1APPLIEDACCELERATION
  • 25. Using a Single Axis Accelerometer toMeasure Tilt25X0°+90°q1gAccelerationX–90°–1g0°+1g+90°Acceleration = 1g × sin qq0g–90° Highest sensitivity between−45 and +45 Ambiguous beyond 90
  • 26. Single Axis vs. Dual Axis AccelerationMeasurements26Output Acceleration vs. Angle of Inclination Output Acceleration vs. Angle of InclinationSingle Axis Dual Axis Sensitivity equal over entire 360° range Removes ambiguity beyond ±90°X-AxisY-Axis
  • 27. ADXL203 Dual Axis Accelerometer27 1 mg resolution for BW = 60 Hz 700 µA current @ 5 V
  • 28. CN0189: Tilt Measurement Using a Dual AxisAccelerometer28Circuit features Dual axis tilt measurement 0.5° accuracy over 360° arcCircuit benefits Single supply Low power Conditioning circuits for ADXL203outputsTarget Applications Key Parts Used Interface/ConnectivityMedicalConsumerIndustrialADXL203AD8608AD7887SPI (AD7887)SDP-S (EVAL-CN0189-SDPZ)USB (EVAL-SDP-CS1Z)
  • 29. CN0189 Dual Axis Tilt Measurement Circuit29AD7887 ADC■ 12-bit, 125 kSPS SAR■ 850 µA current @ 5 V AD8608 Quad Op Amp■ 65 µV input offset voltage■ 1 pA input bias current■ 4 mA quiescent current0.5 Hz BW
  • 30. Output Error for arcsin(X), arccos(Y), andarctan(X/Y) Calculations30OUTPUT = arcsin(X)OUTPUT = arccos(Y)OUTPUT = arctan(X/Y)Error increases at ±90°Error increases at 0°Uniform error distribution
  • 31. Tilt Measurement Using Dual AxisAccelerometer (CN0189 Block Diagram)31ADXL203DUAL AXISACCELEROMETERAD8608QUAD OP AMPSIGNALCONDITIONINGAD78872-CHANNEL12-BIT, 125kSPSSAR ADCSYSTEMDEMONSTRATIONPLATFORM(SDP)EVAL-SDP-CB1ZPCUSBXYXYCN0189 EVALUATION BOARD (EVAL-CN0189-SDPZ)
  • 32. CN0189 Dual Axis Tilt Measurement Hardwareand Demonstration Software32SDP-S BOARDPOWER CONNECTORSOFTWARE OUTPUT DISPLAYEVAL-CN0189-SDPZ Complete design files■ Schematic■ Bill of Material■ PADs layout■ Gerber files■ Assembly drawing
  • 33. Precision Load Cell (Weigh Scales) Wheatstone bridge solutions Low level signal conditioning issues High common-mode voltage with respect to signal voltage Weigh scale system requirements Understanding noise-free code resolution ΣΔ ADC vs. SAR ADC High performance instrumentation amp solution (CN0216) High resolution ΣΔ integrated solution (CN0102)33
  • 34. Resistance-Based Sensor Examples34Strain gages 120 Ω, 350 Ω, 3500 ΩWeigh scale load cells 350 Ω to 3500 ΩPressure sensors 350 Ω to 3500 ΩRelative humidity 100 kΩ to 10 MΩResistance temperature devices (RTDs) 100 Ω, 1000 ΩThermistors 100 Ω to 10 MΩ
  • 35. VOR4R1R3R2VBVORR RVBRR RVB11 422 3 RRRRRRRRVB1423114123AT BALANCE,VO IFRRRR 01423+ -Wheatstone Bridge for Precision ResistanceMeasurements35
  • 36. Output Voltage and Linearity Error for ConstantVoltage Drive Bridges36R RR R+DRR+DRR+DR R+DR R+DRR−DR R+DR R−DRR RR R−DRVB VB VB VBVOVO VOVO(A) Single-ElementVarying(B) Two-ElementVarying (1)(C) Two-ElementVarying (2)(D) All-ElementVaryingLinearityError:VO:0.5%/% 0.5%/% 0 0VB4DRDR2R +VB2DRDR2R +VB2DRRVBDRRR
  • 37. R RR R+DRR+DRR+DR R+DR R+DRR−DR R+DR R−DRR RR RDRVOVO VOVOIB IB IB IBVO:LinearityError:0.25%/% 0 0 0IBR4DRDR4R +IB2DR IB DRIB2DR(A) Single-ElementVarying(B) Two-ElementVarying (1)(C) Two-ElementVarying (2)(D) All-ElementVaryingROutput Voltage and Linearity Error for ConstantCurrent Drive Bridges37
  • 38. Kelvin (4-Wire) Sensing Minimizes ErrorsDue to Lead Resistance for Voltage Excitation386-LEADBRIDGERLEADRLEAD+SENSE– SENSE+FORCE– FORCE+++VB––VO
  • 39. 4-LEADBRIDGERLEAD+–RLEADRSENSEVREFVOIIII =VREFRSENSEConstant Current Excitation alsoMinimizes Wiring Resistance Errors39
  • 40. ADCArchitectures, Applications, Resolution, Sampling Rates4010 100 1k 10k 100k 1M 10M 100M 1G81012141618202224S-DSARPIPELINEINDUSTRIALMEASUREMENTDATA ACQUISITIONHIGH SPEEDINSTRUMENTATION,VIDEO, IF SAMPLING,SOFTWARE RADIOSAMPLING RATE (Hz)APPROXIMATESTATE-OF-THE-ART(2013)RESOLUTION
  • 41. SAR vs. Sigma-Delta Comparison41Successive approximation(SAR) Fast settling, ideal for multiplexing Data available immediately afterconversion (no "pipeline" delay) Easy to use (minimal programming) Requires external in-amp Has 1/f noise (need lots ofexternal filtering) Analog filter can be difficultSigma-Delta Digital filter limits settling More difficult to use (someprogramming required) Some have internal PGA Some have chopping (removes1/f noise) Internal digital filter (removespower line noise) Oversampling relaxes requirementon analog filter
  • 42. Sigma-Delta Concepts: Oversampling, DigitalFiltering, Noise Shaping, and Decimation42fs2fsKfs2KfsKfsKfs2fs2fs2DIGITAL FILTERREMOVED NOISEREMOVED NOISEQUANTIZATIONNOISE = q / 12q = 1 LSBADCADCDIGITALFILTERSDMODDIGITALFILTERfsKfsKfsDECfsNYQUISTOPERATIONOVERSAMPLING+ DIGITAL FILTER+ DECIMATIONOVERSAMPLING+ NOISE SHAPING+ DIGITAL FILTER+ DECIMATIONABCDECfs
  • 43. First-Order Sigma-Delta ADC43  +_+VREF–VREFDIGITALFILTERANDDECIMATOR+_CLOCKKfsVINN-BITSfsfsAB1-BIT DATASTREAM1-BITDACLATCHEDCOMPARATOR(1-BIT ADC)1-BIT,KfsƩ-∆ MODULATORINTEGRATOR
  • 44. Sigma-Delta ADC Architecture BenefitsHigh resolution 24 bits, no missing codes 22 bits, effective resolution (RMS) 19 bits, noise-free code resolution (peak-to-peak) On-chip PGAsHigh accuracy INL 2 ppm of full-scale ~ 1 LSB in 19 bits Gain drift 0.5ppm/°CMore digital, less analog Programmable balance between speed  resolutionOversampling and digital filtering 50 Hz/60 Hz rejection High oversampling rate simplifies antialiasing filterWide dynamic rangeLow cost44
  • 45. Typical Applications of High ResolutionSigma-Delta ADCsProcess control 4 mA to 20 mASensors Weigh scale Pressure TemperatureInstrumentation Gas monitoring Portable instrumentation Medical instrumentation45WEIGH SCALE
  • 46. Precision Weigh Scales-Industrial andHigh Precision Commercial46Laboratory scalesProcess control Hopper scales Conveyor scalesStock control Counting scalesRetail scales
  • 47. Weigh Scale Product Definition47Capacity 2 kgSensitivity 0.1 gOther features Accuracy 0.1 % Linearity ±0.1 g Temperature drift (±20 ppm at10°C ~ 30°C) Data rate 5 Hz to 10 Hz Power (120 V AC) Dimensions (7.5” × 8.6” × 2.6”) Qualification (“legal for trade”)
  • 48. Characteristics of Tedea Huntleigh505H-0002-F070 Load Cell48Full load 2 kgSensitivity 2 mV/VExcitation 5 VOther features Impedance 350 W Total error 0.025% Hysteresis 0.025% Repeatability 0.01 Temperature drifts 10 ppm/°C Overload 150%Four straingages
  • 49. Characteristics of Tedea Huntleigh505H-0002-F070 Load Cell49 Full load 2 kg Sensitivity 2 mV/V Excitation 5 V VFS = VEXC × Sensitivity VFS = 5 V × 2 mV/V = 10 mV VCM = 2.5 V Full-scale voltage 10 mV Proportional to excitation “Ratiometric”
  • 50. Input-Referred Noise of ADC Determines the"Noise-Free Code Resolution"50n n+1 n+2 n+3 n+4n–1n–2n–3n–4NUMBER OFOCCURANCESRMS NOISEP-P INPUT NOISE 6.6 × RMS NOISEOUTPUT CODE“GROUNDED INPUTHISTOGRAM"
  • 51. Performance Requirement – Resolution51Required: 0.1 g in 2 kg # Noise free counts = full-scale/p-p noise in g # Noise free counts = 2000 g/0.1 g = 20,000 20,000 counts VFS = 10 mV at 5 V excitation V P-P NOISE < VFS/# counts VP-P NOISE < 10 mV/20,000 = 0.0005 mV 0.5 µV p-p noise VRMS NOISE  VP-P NOISE/6.6 VRMS NOISE  0.5 µV/6.6 = 0.075 µV 75 nV RMS noise Noise-free bits = log2( VFS/VP-P NOISE) Noise-free bits = log10(VFS/VP-P NOISE) / log10(2) Noise-free bits = log10(10 mV/0.0005 mV)/0.3 Noise-free bits = 14.3 (minimum) 14.3 bits p-p in 10 mV range: Bits RMS = log10( VFS/VRMS NOISE)/log10(2) Bits RMS = log10( 10 mV/0.000075)/0.3 17.0 bits RMS in 10 mV range
  • 52. Definition of "Noise-Free" Code Resolution and"Effective" Resolution52EffectiveResolution= log2Full-Scale RangeRMS Noise BitsNoise-FreeCode Resolution= log2Full-Scale RangeP-P NoiseBitsP-P Noise = 6.6 × RMS NoiseNoise-FreeCode Resolution= log2Full-Scale Range6.6 × RMS NoiseBits= Effective Resolution – 2.72 Bitslog2 (x) =log10 (x)log10 (2)=log10 (x)0.301
  • 53. Terminology for Resolution Based on Peak-to-Peak and RMS NoisePeak-to-peak noise: Noise-free code resolution Noise-free bits Flicker-free bits Peak-to-peak resolutionRMS noise: Effective resolution RMS resolution The term "Effective Number of Bits" (ENOB) applies to highspeed ADCs with sine wave inputs:ENOB = log2 (RMS value of FS sine wave/RMS noise)This should not be confused with "Effective Resolution"53
  • 54. Options for Conditioning Load Cell Outputs54+−+−+−+−+−A:EXTERNAL IN-AMPB:DIFFERENTIAL INPUT ADCEXTERNAL IN-AMP(SEE CN0216)C:DIFFERENTIAL INPUT ADCINTERNAL IN-AMP OR PGA(SEE CN0102)ADCSAR or Σ-ΔRGRGVCMLOADCELLLOADCELLLOADCELLIN-AMPFUNNELAMP (AD8475)10mVFS10mVFS10mVFSADCSAR or Σ-ΔADCSAR or Σ-ΔADCΣ-ΔPGA~12NOISE-FREE BITSFOR 10mV FS~12NOISE-FREE BITSFOR 10mV FS15NOISE-FREE BITSFOR 10mV FS16NOISE-FREE BITSFOR 10mV FSSEE CN0251)LOW NOISEOP AMPS
  • 55. CN0216: Load Cell Signal Conditioning withDifferential Input ADC and External In-AmpCircuit features Gain of 375 low noise in-amp 15.3 noise-free bits of resolutionCircuit benefits Precision load cell conditioning Zero-drift in-amp Single +5 V operationInputs 10 mV full-scale55Target Applications Key Parts Used Interface/ConnectivityLoad cellWeigh scalesAD7791ADA4528-1ADP3301SPI (AD7791)SDP (EVAL-CN0216-SDPZ)USB (EVAL-SDP-CB1Z)
  • 56. CN0216: Load Cell Conditioning withDifferential Input ADC and External In-Amp56G = 375FS = 10mVFS = 3.75VINPUT RANGE = 10V p-p1 LSB = 10V/224 = 0.596µV24-BITΣ-Δ ADCBW = 4.3Hz DIFF BW = 8HzCM BW = 160Hz
  • 57. CN0216 Noise Performance57 Data rate = 9.5 Hz VP-P NOISE = 159 counts × 0.596 µV = 94.8 µV VFS = 3.75 V Noise-free counts = VFS / VP-P NOISE= 3.75 V/94.8 µV= 39,557 Noise-free bits = log2(39,557)= 15.3 bits
  • 58. CN0216 Evaluation Board and Software58Complete design files Schematic Bill of material PADs layout Gerber files Assembly drawing
  • 59. AD7190, 24-Bit Sigma-Delta ADC: Weigh Scalewith Ratiometric Processing59IN+IN-OUT- OUT++5V2mV/VSENSITIVITYLoad cell:■ 2 mV/V typically => with +5 V excitation, full-scale signal from load cell = 10 mV.AD7190■ With VREF = 5 V, gain = 128, full-scale signal = ±40 mV (80 mV p-p).■ 12.5% of range used by load cell signal (10 mV ÷ 80 mV = 0.125).■ The load cell has an offset (~50%) and full-scale error (~±20%). The wider rangeavailable from the AD7190 prevents the offset and full-scale error from overloadingthe AD7190.■ Ratiometric operation eliminates need for external voltage reference.
  • 60. AD7190 Sigma-Delta System On-Chip FeaturesAnalog input buffer options Drives Σ-Δ modulator, reduces dynamic input currentDifferential AIN, REFIN Ratiometric configuration eliminates need for accuratereferenceMultiplexerPGACalibrations Self calibration, system calibration, auto calibrationChopping options No offset and offset drifts Minimizes effects of parasitic thermocouples60
  • 61. CN0102: Precision Weigh Scale SystemCircuit features Integrated solution with PGA 16.8 noise-free bitsCircuit benefits Single supply Optimized for weigh scalesInputs 10 mV full-scale61Target Applications Key Parts Used Interface/ConnectivityWeigh scalesLoad cellsAD7190ADP3303SPI (AD7190)USB (EVAL-AD7190EBZ)EVAL-AD7190EBZ
  • 62. CN0102 Precision Weigh Scale System62
  • 63. AD7190 Sinc4 Filter Response, 50 Hz OutputData Rate63
  • 64. AD7190 Noise and Resolution, Sinc4Filter, Chop Disabled64For G = 128VREF = 5 V,FS = 80 mV p-p17.5for10 mV p-pOnly using 10 mV out of 80 mV range
  • 65. CN0102 Load Cell Test Results, 500 Samples65System resolution with load cell connected Load cell: full-scale output = 10 mV (2 mV/V sensitivity, VEXC = 5 V) Measured RMS noise = 12 nV at 4.7 Hz data rate (G = 128) Measured peak-to-peak noise = 88 nV Noise-free counts = {full-scale output/peak-to-peak noise}= 10 mV/88 nV = 113,600 Noise-free resolution: log2 (113,600) = 16.8 bitsCompared to 17.5 bits for AD7190 alone If a 2 kg load cell is used, resolution is 2000 g/113,600 = 0.02 g
  • 66. CN0102 Evaluation Board and Load Cell66EVAL-AD7190EBZSoftware Display Complete design files Schematic Bill of material PADs layout Gerber files Assembly drawing
  • 67. Tweet it out! @ADI_News #ADIDC13What We CoveredFundamentals of making complex impedance measurements usingintegrated solutions (CN0217) Applications Extending the range of measurement using analog front end circuit Measurement results and applicationsTilt measurements using dual axis accelerometers (CN0189) Applications Advantages of dual axis vs. single axis Accelerometer conditioning circuitsPrecision load cells (weigh scales) (CN0216, CN0102) Applications and requirements Bridge fundamentals Sigma-delta ADC fundamentals Noise considerations and definition of noise-free code resolution Solution using external in-amp Solution using integrated PGA67
  • 68. Tweet it out! @ADI_News #ADIDC13Visit the Impedance Measurement Demo in theExhibition RoomMeasuring complex impedances with the AD593368This demo board is available for purchase:www.analog.com/DC13-hardwareSOFTWARE OUTPUT DISPLAY
  • 69. Tweet it out! @ADI_News #ADIDC13Visit the Tilt Measurement Demo in theExhibition Room69Measure tilt using the ADXL203dual axis accelerometerThis demo board is available for purchase:www.analog.com/DC13-hardwareSDP-S BOARDSOFTWARE OUTPUT DISPLAY EVAL-CN0189-SDPZ
  • 70. Tweet it out! @ADI_News #ADIDC13Visit the Weigh Scale Demo in the ExhibitionRoom70Measure weights from0.1 g to 2000 gThis demo board is available for purchase:www.analog.com/DC13-hardwareSOFTWARE OUTPUT DISPLAYEVAL-CN0216-SDPZSDP BOARD
  • 71. Tweet it out! @ADI_News #ADIDC13Design Resources Covered in this SessionDesign tools and resources:71Name Description URLAD5933/AD5934Demonstration andDesign ToolDemonstrates impedancemeasurement using theAD5933/AD5934http://designtools.analog.com/dt/ad593x/ad593x.htmlCN0189 FMC-SDPInterposer andEvaluation Board/Xilinx KC705Reference DesignUsing the EVAL-CN0189-SDPZevaluation board, together with theXilinx® KC705 FPGA board, the XilinxEmbedded Development Kit (EDK),and the Micrium µC-Probe run-timemonitoring tool.http://wiki.analog.com/resources/fpga/xilinx/interposer/cn0189ADXL203 Simulink®ModelSimulink model http://www.analog.com/en/mems-sensors/mems-inertial-sensors/adxl203/products/tools-software-simulation-models/index.html?location=tools-softwareCN0216 BeMicroFPGABeMicro FPGA for CN0216with Nios driverhttp://wiki.analog.com/resources/fpga/altera/bemicro/cn0216
  • 72. Tweet it out! @ADI_News #ADIDC13Design Resources Covered in this Session-272Name Description URLSignal ChainDesignerComplete engineeringdesign environmenthttp://www.analog.com/scdAD7190 Tools Tools, software, andsimulation modelshttp://www.analog.com/en/analog-to-digital-converters/ad-converters/ad7190/products/tools-software-simulation-models/index.html?location=tools-softwareAD7887 Tools Tools, software, andsimulation modelshttp://www.analog.com/en/analog-to-digital-converters/ad-converters/ad7887/products/tools-software-simulation-models/index.html?location=tools-softwareAD7791 Tools Tools, software, andsimulation modelshttp://www.analog.com/en/analog-to-digital-converters/ad-converters/ad7791/products/tools-software-simulation-models/index.html?location=tools-software
  • 73. Tweet it out! @ADI_News #ADIDC13Design Resources Covered in this Session-373Ask technical questions and exchange ideas online in ourEngineerZone® Support Community Choose a technology area from the homepage: ez.analog.com Access the Design Conference community here: www.analog.com/DC13community
  • 74. Tweet it out! @ADI_News #ADIDC13Selection Table of Products Covered Today74Part number DescriptionAD5933 1 MSPS, 12-bit impedance converter, network analyzerAD8606 Precision, low noise, RRIO, CMOS op amp (dual)ADG849 3 V/5 V CMOS 0.5 Ω SPDT switch in SC70AD8221 Precision instrumentation amplifierAD820 Single-supply, rail-to-rail, low power, FET input op ampADXL203 Precision ±1.7 g, ±5 g, ±18 g dual axis iMEMS accelerometerAD8608 Precision, low noise, RRIO, CMOS op amp (quad)AD7887 2.7 V to 5.25 V, micropower, 2-channel, 125 kSPS, 12-bit ADC in8-lead MSOP
  • 75. Tweet it out! @ADI_News #ADIDC13Selection Table of Products Covered Today-275Part number DescriptionAD7791 24-bit, single-channel, ultralow power, Ʃ-∆ ADCADA4528-1 5.0 V ultralow noise, zero-drift, RRIO, single op ampADP3301 High accuracy anyCAP® 100 mA low dropout linear regulatorADP7190 4.8 kHz ultralow noise 24-bit Ʃ-∆ ADC with PGAADP3303 High accuracy anyCAP 200 mA low dropout linear regulator
  • 76. Tweet it out! @ADI_News #ADIDC13References-1Circuit Notes CN0217, Impedance Measurements www.analog.com/CN0217 CN0189, Tilt Measurements www.analog.com/CN0189 CN0216, Precision Weigh Scale, External In-Amp www.analog.com/CN0216 CN0102, Precision Weigh Scale, Internal PGA www.analog.com/CN0102 CN0251, A Flexible 4-Channel Analog Front End for Wide Dynamic RangeSignal Conditioning www.analog.com/CN0251 CN0260, Oversampled SAR ADC with PGA www.analog.com/CN0260 CN0189, 4 mA to 20 mA Loop-Powered Pressure Sensor Transmitter www.analog.com/CN018976
  • 77. Tweet it out! @ADI_News #ADIDC13References-2Mini Tutorials MT-004, ADC Input Noise www.analog.com/MT-004 MT-021, Successive Approximation (SAR) ADCs www.analog.com/MT-021 MT-022, Sigma-Delta ADC Basics www.analog.com/MT-022 MT-023, Sigma-Delta ADC Advanced Concepts www.analog.com/MT-023 MT-061, In-Amp Basics www.analog.com/MT-061 MT-062, Two Op Amp In-Amp www.analog.com/MT-062 MT-063, Three Op Amp In-Amp www.analog.com/MT-06377
  • 78. Tweet it out! @ADI_News #ADIDC13References-3Mini Tutorials MT-064, In-Amp DC Errors www.analog.com/MT-064 MT-065, In-Amp Noise www.analog.com/MT-065 MT-066, In Amp Bridge Circuit Error Analysis www.analog.com/MT-066 MT-069, In-Amp Overvoltage Protection www.analog.com/MT-069 MT-070, In-Amp Input RFI Protection www.analog.com/MT-07078
  • 79. Tweet it out! @ADI_News #ADIDC13References-4Reference Books Sensor Signal Conditioning www.analog.com/sensor_signal_conditioning Analog-Digital Conversion http://www.analog.com/library/analogDialogue/archives/39-06/data_conversion_handbook.html Op Amp Applications http://www.analog.com/library/analogDialogue/archives/39-05/op_amp_applications_handbook.html Linear Circuit Design http://www.analog.com/library/analogDialogue/archives/43-09/linear_circuit_design_handbook.html Instrumentation Amplifier Handbook http://www.analog.com/en/specialty-amplifiers/instrumentation-amplifiers/products/design-handbooks/cu_dh_designers_guide_to_instrumentation_amps/resources/fca.html79

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