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

Instrumentation: Test and Measurement Methods and SolutionsReference Designs and System Applications

2

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3

Today’s Agenda

Understand challenges of precision data acquisition in sensing applications 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 high

noise-free code resolution (CN0216, CN0102)

Applications selected to illustrate important design principles applicable to a variety of precision sensor conditioning circuits including MEMS

See tested and verified Circuits from the Lab® signal chain solutions chosen to illustrate design principles Low cost evaluation hardware and software available Complete documentation packages:

Schematics, BOM, layout, Gerber files, assemblies

Circuits from the Lab

Circuits from the Lab reference circuits are engineered and tested for quick and easy system integration to help solve today’s analog, 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

System Demonstration Platform (SDP-B, SDP-S)

The SDP (System Demonstration Platform) boards provide intelligent USB communications between many Analog Devices evaluation boards and Circuits from the Lab boards and PCs running the evaluation software

5

USB USB

EVALUATIONBOARD

SDP-BSDP-S

EVALUATIONBOARD

POWER 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)

Impedance Measurement Devices

Impedance measurement is a difficult signal processing task

Need to measure complex impedances, not just R, L, or C

Impedance conversion …is becoming more important in many

sensor/diagnostic related applications …is traditionally accomplished using

discrete solutions …usually requires a high level of

analog design skill to extract frequency responses of the unknown impedance

7

Impedance Measurement Challenge

Problem: How to analyze a complex

impedance How to control ADC sampling

frequency with respect to DDS output frequency (windowing vs. coherent sampling)?

How to manage component selection?

Must develop software to control DDS

Software required for FFT How to calculate error budget? What about temperature effects? Usually ends up consuming greater

board area and cost?

8

Excitation/Stimulus

Frequency Response

Analysis

Integrated Single-Chip Solution

AD5933

DDS Filter Buffer

ADC

VDD/2

DAC

Z(ω)

SCL

SDA

DVDDAVDDMCLK

AGND DGND

ROUT VOUT

AD5933RFB

VIN

05

324

-001

1024-POINT DFT

I2CINTERFACE

IMAGINARYREGISTER

REALREGISTER

OSCILLATOR

DDSCORE

(27 BITS)

TEMPERATURESENSOR

ADC(12 BITS) LPF

GAIN

AD5933/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 imaginary

data word Simple off-chip processing required to calculate

magnitude and phase

9

I2CINTERFACETO µC OR PC UNKNOWN

IMPEDANCE

EXCITATION FREQUENCY

REAL AND IMAGINARYCOMPONENTREGISTERS

DDS

ADJUSTABLEVOLTAGEEXITATION

CURRENT TOVOLTAGECONVERTER

10

CN0217: High Accuracy Impedance Measurements Using 12-Bit Impedance Converters Circuit features

Wide impedance range 12-bit accuracy Analog front end (AFE) for

impedance measurements less than 1 kΩ

Circuit benefits Self contained DDS excitation DSP for calculating DFT Complex impedance

measurements

Target Applications Key Parts Used Interface/Connectivity

MedicalConsumerIndustrial

AD5933AD8606

I2C (AD5933)USB (EVAL-AD5933EBZ)

50kΩ

50kΩ

50kΩ

50kΩ

RFB

20kΩ

20kΩ

47nF

ZUNKNOWN

VDD

VDD

VDD

+

+

−

−

A1

A2

A1, A2 ARE½ AD8606

1.48V

1.98V p-p

VDD/2

1.98V p-p

VDD/2

DAC

SCL

SDA

DVDDAVDDMCLK

AGND DGND

ROUT

VOUT

AD5933/AD5934RFB

VIN

1024-POINT DFT

I2CINTERFACE

IMAGINARYREGISTER

REALREGISTER

OSCILLATOR

DDSCORE

(27 BITS)

TEMPERATURESENSOR

TRANSMIT SIDEOUTPUT AMPLIFIER

ADC(12 BITS) LPF

GAIN

VDD VDD

CN0217 External AFE Signal Conditioning

External analog front end (AFE) allows impedance measurements 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)11

VDD = 3.3V

12

High Accuracy Performance from the AD5933/AD5934 with External AFE

30 35 40

FREQUENCY (kHz)

45 508160

8180

8200

8220

8240

8260

8280

IMP

ED

AN

CE

MA

GN

ITU

DE

(Ω

)

R3

IDEAL

09

915-

008

35

30

25

20

15

10

5

029.95 30.00 30.05 30.10 30.15 30.20

10.3Ω

30Ω

1µF

30.25

FREQUENCY (kHz)

MA

GN

ITU

DE

(Ω

)

09

915

-003

Magnitude Results For ZC = 10 kΩ||10 nF, RCAL = 1 kΩ

Magnitude Results For Low Impedance ZC = 8.21 kΩ, RCAL = 99.85 kΩ

ZC = 217.25 kΩ, RCAL = 99.85 kΩOne calibration using 99.85 kΩ resistor covers wide range

Allows low value impedancemeasurements

Tracks R||Cacross frequency

30 35 40

FREQUENCY (kHz)

45 50

IMP

ED

AN

CE

MA

GN

ITU

DE

(kΩ

)

R4

09

91

5-0

09213.5

214.0

214.5

21.50

215.5

216.0

216.5

217.0

217.5

218.0

218.5

IDEAL

500

0

1000

1500

2000

2500

3000

3500

4000

4 24 44 64 84 104

IMP

ED

AN

CE

MA

GN

ITU

DE

(Ω

)

FREQUENCY (kHz)

IDEALMEASURED

09

915

-011

13

Low RON SPDT CMOS Switch Used to Switch Between RCAL and Unknown Z

50kΩ

ZUNKNOWN RCAL

S1

D

S2

RFB

VDD

IN

ADG849

50kΩ

A1

A2

Use low RON CMOS switch for switching from unknown impedance to calibration resistor

RON = 0.5Ω

14

CN0217 Evaluation Board, EVAL-CN0217-EB1Z

Complete design files Schematic Bill of material PADs layout Gerber files Assembly drawing

PC

Unknown Z

USB

15

AD5933 Web Based Demonstration Tool

Web tool demo:

Enter different impedance types

Generate frequency sweep

Examine impedance plot

16

AD5933 Used with AFE for Measuring Ground-Referenced Impedance in Blood-Coagulation Measurement System

Ground-referencedUnknown Z

17

Blood Clotting Factor Measurements

Liquid Quality Impedance Measurement

18

CONDUCTANCE LIQUIDMEASUREMENT

SWITCHES

AFE

AD5933/AD5934

CONTROLLER

CALIBRATION IMPEDANCE

UNKNOWN IMPEDANCE

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 conditioning

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 technology for electronically measuring tilt

Good accuracy and bandwidth

Small board area

Low power

High reliability

Minimal out of plane sensitivity

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 kHz

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 available

23

ADXL-Family Micromachined iMEMS Accelerometers (Top View of IC)

FIXEDOUTERPLATES

CS1 CS1 < CS2= CS2

DENOTES ANCHOR

BEAM

TETHER

CS1 CS2

CENTERPLATE

AT REST APPLIED ACCELERATION

24

ADXL-Family iMEMS AccelerometersInternal Signal Conditioning

OSCILLATOR A1SYNCHRONOUSDEMODULATOR

BEAM

PLATE

PLATE

CS1

CS2

SYNC

0°

180°A2

VOUT

CS2 > CS1

AP

PL

IED

AC

CE

LE

RA

TIO

N

25

Using a Single Axis Accelerometer to Measure Tilt

X

0°

+90°

q1g

Acceleration

X

–90°

–1g

0°

+1g

+90°

Acceleration = 1g × sin q

q0g

–90°

Highest sensitivity between −45° and +45°

Ambiguous beyond ±90°

26

Single Axis vs. Dual Axis Acceleration Measurements

Output Acceleration vs. Angle of Inclination Output Acceleration vs. Angle of Inclination

Single Axis Dual Axis Sensitivity equal over entire 360° range

Removes ambiguity beyond ±90°

X-Axis

Y-Axis

27

ADXL203 Dual Axis Accelerometer

1 mg resolution for BW = 60 Hz

700 µA current @ 5 V

28

CN0189: Tilt Measurement Using a Dual Axis Accelerometer Circuit features

Dual axis tilt measurement 0.5° accuracy over 360° arc

Circuit benefits Single supply Low power Conditioning circuits for ADXL203

outputs

Target Applications Key Parts Used Interface/Connectivity

MedicalConsumerIndustrial

ADXL203AD8608AD7887

SPI (AD7887) SDP-S (EVAL-CN0189-SDPZ)USB (EVAL-SDP-CS1Z)

29

CN0189 Dual Axis Tilt Measurement Circuit

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 current

0.5 Hz BW

30

Output Error for arcsin(X), arccos(Y), andarctan(X/Y) Calculations

OUTPUT = 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 Axis Accelerometer (CN0189 Block Diagram)

ADXL203DUAL AXIS

ACCELEROMETER

AD8608 QUAD OP AMP

SIGNAL CONDITIONING

AD78872-CHANNEL

12-BIT, 125kSPS SAR ADC

SYSTEMDEMONSTRATION

PLATFORM(SDP)

EVAL-SDP-CB1Z

PC

USB

X

Y

X

Y

CN0189 EVALUATION BOARD (EVAL-CN0189-SDPZ)

CN0189 Dual Axis Tilt Measurement Hardware and Demonstration Software

32

SDP-S BOARD

POWER CONNECTOR

SOFTWARE 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)

34

Resistance-Based Sensor Examples

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

VO

R4

R1

R3

R2

VB

VOR

R RVB

RR R

VB

11 4

22 3

RR

RR

RR

RR

VB

14

23

114

123

AT BALANCE,

VO IFRR

RR

014

23

+ -

Wheatstone Bridge for Precision Resistance Measurements

36

Output Voltage and Linearity Error for Constant Voltage Drive Bridges

R R

R R+DR

R+DR

R+DR R+DR R+DR

R−DR R+DR R−DRR R

R R−DR

VB VB VB VB

VOVO VO

VO

(A) Single-ElementVarying

(B) Two-ElementVarying (1)

(C) Two-ElementVarying (2)

(D) All-ElementVarying

LinearityError:

VO:

0.5%/% 0.5%/% 0 0

VB

4

DRDR2R +

VB

2

DRDR2R +

VB

2

DR

R VB

DR

R

R

37

R R

R R+DR

R+DR

R+DR R+DR R+DR

R−DR R+DR R−DRR R

R R-DR

VOVO VO

VO

IB IB IB IB

VO:

LinearityError: 0.25%/% 0 0 0

IBR

4

DRDR4R +

IB2

DR IBDRIB

2DR

(A) Single-ElementVarying

(B) Two-ElementVarying (1)

(C) Two-ElementVarying (2)

(D) All-ElementVarying

R

Output Voltage and Linearity Error for Constant Current Drive Bridges

Kelvin (4-Wire) Sensing Minimizes Errors Due to Lead Resistance for Voltage Excitation

38

6-LEADBRIDGE

RLEAD

RLEAD

+SENSE

– SENSE

+FORCE

– FORCE

+

+

+VB

–

–

VO

39

4-LEADBRIDGE

RLEAD

+

–RLEAD

RSENSE

VREF

VO

I

I

II =

VREF

RSENSE

Constant Current Excitation alsoMinimizes Wiring Resistance Errors

40

ADC Architectures, Applications, Resolution, Sampling Rates

10 100 1k 10k 100k 1M 10M 100M 1G8

10

12

14

16

18

20

22

24

S-D

SAR

PIPELINE

INDUSTRIALMEASUREMENT

DATA ACQUISITION

HIGH SPEEDINSTRUMENTATION,VIDEO, IF SAMPLING, SOFTWARE RADIO

SAMPLING RATE (Hz)

APPROXIMATE STATE-OF-THE-ART

(2013)

RE

SO

LU

TIO

N

41

SAR vs. Sigma-Delta Comparison

Successive approximation (SAR) Fast settling, ideal for multiplexing Data available immediately after

conversion (no "pipeline" delay) Easy to use (minimal programming) Requires external in-amp Has 1/f noise (need lots of

external filtering) Analog filter can be difficult

Sigma-Delta Digital filter limits settling More difficult to use (some

programming required) Some have internal PGA Some have chopping (removes

1/f noise) Internal digital filter (removes

power line noise) Oversampling relaxes requirement

on analog filter

42

Sigma-Delta Concepts: Oversampling, Digital Filtering, Noise Shaping, and Decimation

fs

2

fs

Kfs

2

Kfs

KfsKfs

2

fs

2

fs

2

DIGITAL FILTER

REMOVED NOISE

REMOVED NOISE

QUANTIZATIONNOISE = q / 12 q = 1 LSBADC

ADCDIGITALFILTER

SDMOD

DIGITALFILTER

fs

Kfs

Kfs

DEC

fs

NYQUISTOPERATION

OVERSAMPLING+ DIGITAL FILTER+ DECIMATION

OVERSAMPLING+ NOISE SHAPING+ DIGITAL FILTER+ DECIMATION

A

B

C

DEC

fs

43

First-Order Sigma-Delta ADC

å ò +

_

+VREF

–VREF

DIGITALFILTER

ANDDECIMATOR

+

_

CLOCKKfs

VINN-BITS

fs

fs

A

B

1-BIT DATASTREAM1-BIT

DAC

LATCHEDCOMPARATOR(1-BIT ADC)

1-BIT,

Kfs

Ʃ-∆ MODULATOR

INTEGRATOR

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 cost

45

Typical Applications of High Resolution Sigma-Delta ADCs Process control

4 mA to 20 mA

Sensors Weigh scale Pressure Temperature

Instrumentation Gas monitoring Portable instrumentation Medical instrumentation

WEIGH SCALE

46

Precision Weigh Scales-Industrial and High Precision Commercial Laboratory scales

Process control Hopper scales Conveyor scales

Stock control Counting scales

Retail scales

47

Weigh Scale Product Definition

Capacity 2 kg

Sensitivity 0.1 g

Other features Accuracy 0.1 % Linearity ±0.1 g Temperature drift (±20 ppm at

10°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 Huntleigh 505H-0002-F070 Load Cell

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 Huntleigh 505H-0002-F070 Load Cell

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"

n n+1 n+2 n+3 n+4n–1n–2n–3n–4

NUMBER OFOCCURANCES

RMS NOISE

P-P INPUT NOISE

» 6.6 × RMS NOISE

OUTPUT CODE

“GROUNDED INPUT HISTOGRAM"

51

Performance Requirement – Resolution

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" Resolution

EffectiveResolution

= log2

Full-Scale RangeRMS Noise Bits

Noise-FreeCode Resolution = log2

Full-Scale RangeP-P Noise Bits

P-P Noise = 6.6 × RMS Noise

Noise-FreeCode Resolution

= log2Full-Scale Range6.6 × RMS Noise

Bits

= Effective Resolution – 2.72 Bits

log2 (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 high

speed ADCs with sine wave inputs:

ENOB = log2 (RMS value of FS sine wave/RMS noise) This should not be confused with "Effective Resolution"

Options for Conditioning Load Cell Outputs

54

+

−

+

−

+

−

+

−

+

−

A: EXTERNAL IN-AMP

B:DIFFERENTIAL INPUT ADCEXTERNAL IN-AMP (SEE CN0216)

C: DIFFERENTIAL INPUT ADCINTERNAL IN-AMP OR PGA(SEE CN0102)

ADCSAR or Σ-Δ

RG

RG

VCM

LOADCELL

LOADCELL

LOADCELL

IN-AMP

FUNNEL AMP (AD8475)

10mVFS

10mVFS

10mVFS

ADCSAR or Σ-Δ

ADCSAR or Σ-Δ

ADCΣ-ΔPGA

~12 NOISE-FREE BITS

FOR 10mV FS

~12NOISE-FREE BITS

FOR 10mV FS

15NOISE-FREE BITS

FOR 10mV FS

16NOISE-FREE BITS

FOR 10mV FS

SEE CN0251)

LOW NOISE OP AMPS

55

CN0216: Load Cell Signal Conditioning with Differential 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-scale

Target Applications Key Parts Used Interface/Connectivity

Load cellWeigh scales

AD7791ADA4528-1ADP3301

SPI (AD7791) SDP (EVAL-CN0216-SDPZ)USB (EVAL-SDP-CB1Z)

CN0216: Load Cell Conditioning with Differential Input ADC and External In-Amp

56

G = 375

FS = 10mV

FS = 3.75VINPUT RANGE = 10V p-p1 LSB = 10V/224 = 0.596µV

24-BITΣ-Δ ADC

BW = 4.3Hz DIFF BW = 8HzCM BW = 160Hz

57

CN0216 Noise Performance

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 Software

Complete design files Schematic Bill of material PADs layout Gerber files Assembly drawing

59

AD7190, 24-Bit Sigma-Delta ADC: Weigh Scale with Ratiometric Processing

IN+

IN-

OUT- OUT+

+5V

2mV/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 range

available from the AD7190 prevents the offset and full-scale error from overloading the 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 accurate

reference

Multiplexer

PGA

Calibrations Self calibration, system calibration, auto calibration

Chopping options No offset and offset drifts Minimizes effects of parasitic thermocouples

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-scale

Target Applications Key Parts Used Interface/Connectivity

Weigh scalesLoad cells

AD7190ADP3303

SPI (AD7190) USB (EVAL-AD7190EBZ)

EVAL-AD7190EBZ

62

CN0102 Precision Weigh Scale System

63

AD7190 Sinc4 Filter Response, 50 Hz Output Data Rate

64

AD7190 Noise and Resolution, Sinc4 Filter, Chop Disabled

For G = 128VREF = 5 V, FS = 80 mV p-p

17.5for 10 mV p-p

Only using 10 mV out of 80 mV range

65

CN0102 Load Cell Test Results, 500 Samples

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 bits Compared 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 Cell

EVAL-AD7190EBZ

Software Display

Complete design files Schematic Bill of material PADs layout Gerber files Assembly drawing

67 Tweet it out! @ADI_News #ADIDC13

What We Covered

Fundamentals of making complex impedance measurements using integrated 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 PGA

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Visit the Impedance Measurement Demo in the Exhibition Room

Measuring complex impedances with the AD5933

This demo board is available for purchase: www.analog.com/DC13-hardware

SOFTWARE OUTPUT DISPLAY

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Visit the Tilt Measurement Demo in the Exhibition Room

Measure tilt using the ADXL203 dual axis accelerometer

This demo board is available for purchase: www.analog.com/DC13-hardware

SDP-S BOARDSOFTWARE OUTPUT DISPLAY EVAL-CN0189-SDPZ

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Visit the Weigh Scale Demo in the Exhibition Room

Measure weights from 0.1 g to 2000 g

This demo board is available for purchase: www.analog.com/DC13-hardware

SOFTWARE OUTPUT DISPLAY

EVAL-CN0216-SDPZ

SDP BOARD

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Design Resources Covered in this Session

Design tools and resources:Name Description URL

AD5933/AD5934 Demonstration and Design Tool

Demonstrates impedance measurement using the AD5933/AD5934

http://designtools.analog.com/dt/ad593x/ad593x.html

CN0189 FMC-SDP Interposer and Evaluation Board/ Xilinx KC705 Reference Design

Using the EVAL-CN0189-SDPZ evaluation board, together with the Xilinx® KC705 FPGA board, the Xilinx Embedded Development Kit (EDK), and the Micrium µC-Probe run-time monitoring tool.

http://wiki.analog.com/resources/fpga/xilinx/interposer/cn0189

ADXL203 Simulink® Model

Simulink model http://www.analog.com/en/mems-sensors/mems-inertial-sensors/adxl203/products/tools-software-simulation-models/index.html?location=tools-software

CN0216 BeMicro FPGA

BeMicro FPGA for CN0216 with Nios driver

http://wiki.analog.com/resources/fpga/altera/bemicro/cn0216

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Design Resources Covered in this Session-2

Name Description URL

Signal Chain Designer

Complete engineering design environment

http://www.analog.com/scd

AD7190 Tools Tools, software, and simulation models

http://www.analog.com/en/analog-to-digital-converters/ad-converters/ad7190/products/tools-software-simulation-models/index.html?location=tools-softwareAD7887 Tools Tools, software, and

simulation 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, and

simulation modelshttp://www.analog.com/en/analog-to-digital-converters/ad-converters/ad7791/products/tools-software-simulation-models/index.html?location=tools-software

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Design Resources Covered in this Session-3

Ask technical questions and exchange ideas online in our EngineerZone® Support Community Choose a technology area from the homepage:

ez.analog.com Access the Design Conference community here:

www.analog.com/DC13community

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Selection Table of Products Covered Today

Part number Description

AD5933 1 MSPS, 12-bit impedance converter, network analyzer

AD8606 Precision, low noise, RRIO, CMOS op amp (dual)

ADG849 3 V/5 V CMOS 0.5 Ω SPDT switch in SC70

AD8221 Precision instrumentation amplifier

AD820 Single-supply, rail-to-rail, low power, FET input op amp

ADXL203 Precision ±1.7 g, ±5 g, ±18 g dual axis iMEMS accelerometer

AD8608 Precision, low noise, RRIO, CMOS op amp (quad)

AD7887 2.7 V to 5.25 V, micropower, 2-channel, 125 kSPS, 12-bit ADC in 8-lead MSOP

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Selection Table of Products Covered Today-2

Part number Description

AD7791 24-bit, single-channel, ultralow power, Ʃ-∆ ADC

ADA4528-1 5.0 V ultralow noise, zero-drift, RRIO, single op amp

ADP3301 High accuracy anyCAP® 100 mA low dropout linear regulator

ADP7190 4.8 kHz ultralow noise 24-bit Ʃ-∆ ADC with PGA

ADP3303 High accuracy anyCAP 200 mA low dropout linear regulator

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References-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 Range

Signal 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/CN0189

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References-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-063

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References-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-070

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References-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_applic

ations_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/prod

ucts/design-handbooks/cu_dh_designers_guide_to_instrumentation_amps/resources/fca.html