Instrumentation: Test and Measurement Methods and Solutions Reference Designs and System Applications

Walt Kester, Applications Engineer, Greensboro, NC, US

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

3

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

EVALUATION BOARD

SDP-B SDP-S EVALUATION

BOARD

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

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

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

0532

4-00

1

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

I2C INTERFACE TO µC OR PC UNKNOWN

IMPEDANCE

EXCITATION FREQUENCY

REAL AND IMAGINARY COMPONENT REGISTERS

DDS

ADJUSTABLE VOLTAGE EXITATION

CURRENT TO VOLTAGE CONVERTER

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

10

Target Applications Key Parts Used Interface/Connectivity Medical Consumer Industrial

AD5933 AD8606

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

0991

5-00

1

I-V

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

High Accuracy Performance from the AD5933/AD5934 with External AFE

12

30 35 40FREQUENCY (kHz)

45 508160

8180

8200

8220

8240

8260

8280

IMPE

DA

NC

E M

AG

NIT

UD

E (Ω

)

R3

IDEAL

0991

5-00

8

35

30

25

20

15

10

5

029.95 30.00 30.05 30.10 30.15 30.20

10.3Ω

30Ω

1µF

30.25FREQUENCY (kHz)

MA

GN

ITU

DE

(Ω)

0991

5-00

3

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 kΩ One calibration using 99.85 kΩ resistor covers wide range

Allows low value impedance measurements

Tracks R||C across frequency

30 35 40FREQUENCY (kHz)

45 50

IMPE

DA

NC

E M

AG

NIT

UD

E (k

Ω)

R4

0991

5-00

9213.5

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

IMPE

DA

NC

E M

AG

NIT

UD

E (Ω

)

FREQUENCY (kHz)

IDEALMEASURED

0991

5-01

1

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

13

50kΩ

ZUNKNOWN RCAL

S1

D

S2

RFB

VDD

IN

ADG849

50kΩ

A1

A2

0991

5–01

3

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

RON = 0.5Ω

CN0217 Evaluation Board, EVAL-CN0217-EB1Z

14

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

PC

Unknown Z

USB

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

16

Ground-referenced Unknown Z

Blood Clotting Factor Measurements

17

Liquid Quality Impedance Measurement

18

CONDUCTANCE LIQUID MEASUREMENT

SWITCHES

AFE

AD5933/ AD5934

CONTROLLER

CALIBRATION IMPEDANCE

UNKNOWN IMPEDANCE

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

19

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

20

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

21

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

22

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

23

FIXED OUTER PLATES

CS1 CS1 < CS2 = CS2

DENOTES ANCHOR

BEAM

TETHER

CS1 CS2

CENTER PLATE

AT REST APPLIED ACCELERATION

ADXL-Family iMEMS Accelerometers Internal Signal Conditioning

24

OSCILLATOR A1 SYNCHRONOUS DEMODULATOR BEAM

PLATE

PLATE

CS1

CS2

SYNC

0°

180° A2

VOUT

CS2 > CS1

APPL

IED

AC

CEL

ERAT

ION

Using a Single Axis Accelerometer to Measure Tilt

25

X

0°

+90°

θ 1g

Acceleration

X

–90°

–1g

0°

+1g

+90°

Acceleration = 1g × sin θ

θ 0g

–90° Highest sensitivity between

−45° and +45°

Ambiguous beyond ±90°

Single Axis vs. Dual Axis Acceleration Measurements

26

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

ADXL203 Dual Axis Accelerometer

27

1 mg resolution for BW = 60 Hz

700 µA current @ 5 V

CN0189: Tilt Measurement Using a Dual Axis Accelerometer

28

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 Medical Consumer Industrial

ADXL203 AD8608 AD7887

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

CN0189 Dual Axis Tilt Measurement Circuit

29

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

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

30

OUTPUT = arcsin(X)

OUTPUT = arccos(Y)

OUTPUT = arctan(X/Y)

Error increases at ±90°

Error increases at 0°

Uniform error distribution

CN0189 Dual Axis Tilt Measurement Hardware and Demonstration Software

32

SDP-S BOARD

POWER CONNECTOR

SOFTWARE OUTPUT DISPLAY EVAL-CN0189-SDPZ

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

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

Resistance-Based Sensor Examples

34

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

VO

R4

R1

R3

R2

VB

VOR

R RVB

RR R

VB=+

−+

11 4

22 3

=−

+

+

RR

RR

RR

RR

VB

14

23

1 14

1 23

AT BALANCE,

VO IF RR

RR

= =0 14

23

+ -

Wheatstone Bridge for Precision Resistance Measurements

35

Output Voltage and Linearity Error for Constant Voltage Drive Bridges

36

R R

R R+∆R

R+∆R

R+∆R R+∆R R+∆R

R−∆R R+∆R R−∆R R R

R R−∆R

VB VB VB VB

VO VO VO VO

(A) Single-Element Varying

(B) Two-Element Varying (1)

(C) Two-Element Varying (2)

(D) All-Element Varying

Linearity Error:

VO:

0.5%/% 0.5%/% 0 0

VB 4

∆R ∆R 2 R +

VB 2

∆R ∆R 2 R +

VB 2

∆R R

VB ∆R R

R

R R

R R+∆R

R+∆R

R+∆R R+∆R R+∆R

R−∆R R+∆R R−∆R R R

R R−∆R

VO VO VO VO

IB IB IB IB

VO:

Linearity Error: 0.25%/% 0 0 0

IBR 4

∆R ∆R 4 R +

IB 2

∆R IB ∆R IB 2

∆R

(A) Single-Element Varying

(B) Two-Element Varying (1)

(C) Two-Element Varying (2)

(D) All-Element Varying

R

Output Voltage and Linearity Error for Constant Current Drive Bridges

37

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

38

6-LEAD BRIDGE

RLEAD

RLEAD

+SENSE

– SENSE

+FORCE

– FORCE

+

+

+VB

–

–

VO

4-LEAD BRIDGE

RLEAD

+

– RLEAD

RSENSE

VREF

VO

I

I

I I = VREF

RSENSE

Constant Current Excitation also Minimizes Wiring Resistance Errors

39

ADC Architectures, Applications, Resolution, Sampling Rates

40

10 100 1k 10k 100k 1M 10M 100M 1G 8

10

12

14

16

18

20

22

24

Σ - ∆

SAR PIPELINE

INDUSTRIAL MEASUREMENT

DATA ACQUISITION

HIGH SPEED INSTRUMENTATION, VIDEO, IF SAMPLING, SOFTWARE RADIO

SAMPLING RATE (Hz)

APPROXIMATE STATE - OF - THE - ART (2013)

RES

OLU

TIO

N

SAR vs. Sigma-Delta Comparison

41

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

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

42

fs

2 fs

Kfs 2

Kfs

Kfs Kfs 2

fs 2

fs 2

DIGITAL FILTER REMOVED NOISE

REMOVED NOISE

QUANTIZATION NOISE = q / 12 q = 1 LSB ADC

ADC DIGITAL FILTER

Σ∆ MOD

DIGITAL FILTER

fs

Kfs

Kfs

DEC

fs

NYQUIST OPERATION

OVERSAMPLING + DIGITAL FILTER + DECIMATION

OVERSAMPLING + NOISE SHAPING + DIGITAL FILTER + DECIMATION

A

B

C

DEC

fs

First-Order Sigma-Delta ADC

43

∑ ∫ +

_

+VREF

–VREF

DIGITAL FILTER

AND DECIMATOR

+

_

CLOCK Kfs

VIN N-BITS

fs

fs

A

B

1-BIT DATA STREAM

1-BIT DAC

LATCHED COMPARATOR (1-BIT ADC)

1-BIT, Kfs

Ʃ-∆ MODULATOR

INTEGRATOR

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

44

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

45

WEIGH SCALE

Precision Weigh Scales-Industrial and High Precision Commercial

46

Laboratory scales Process control Hopper scales Conveyor scales

Stock control Counting scales

Retail scales

Weigh Scale Product Definition

47

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”)

Characteristics of Tedea Huntleigh 505H-0002-F070 Load Cell

48

Full load 2 kg

Sensitivity 2 mV/V

Excitation 5 V

Other features Impedance 350 Ω Total error 0.025% Hysteresis 0.025% Repeatability 0.01 Temperature drifts 10 ppm/°C Overload 150%

Four strain gages

Characteristics of Tedea Huntleigh 505H-0002-F070 Load Cell

49

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”

Input-Referred Noise of ADC Determines the "Noise-Free Code Resolution"

50

n n+1 n+2 n+3 n+4 n–1 n–2 n–3 n–4

NUMBER OF OCCURANCES

RMS NOISE

P-P INPUT NOISE

≈ 6.6 × RMS NOISE

OUTPUT CODE

“GROUNDED INPUT HISTOGRAM"

Performance Requirement – Resolution

51

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

Definition of "Noise-Free" Code Resolution and "Effective" Resolution

52

Effective Resolution

= log2 Full-Scale Range

RMS Noise Bits

Noise-Free Code Resolution = log2

Full-Scale Range P-P Noise Bits

P-P Noise = 6.6 × RMS Noise

Noise-Free Code Resolution

= log2 Full-Scale Range 6.6 × RMS Noise

Bits

= Effective Resolution – 2.72 Bits

log2 (x) = log10 (x)

log10 (2) =

log10 (x)

0.301

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"

53

Options for Conditioning Load Cell Outputs

54

+

−

+

− +

−

+

−

+

−

A: EXTERNAL IN-AMP

B: DIFFERENTIAL INPUT ADC EXTERNAL IN-AMP (SEE CN0216)

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

ADC SAR or Σ-Δ

RG

RG

VCM

LOAD CELL

LOAD CELL

LOAD CELL

IN-AMP

FUNNEL AMP (AD8475)

10mV FS

10mV FS

10mV FS

ADC SAR or Σ-Δ

ADC SAR or Σ-Δ

ADC Σ-Δ PGA

~12 NOISE-FREE BITS

FOR 10mV FS

~12 NOISE-FREE BITS

FOR 10mV FS

15 NOISE-FREE BITS

FOR 10mV FS

16 NOISE-FREE BITS

FOR 10mV FS

SEE CN0251)

LOW NOISE OP AMPS

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

55

Target Applications Key Parts Used Interface/Connectivity Load cell Weigh scales

AD7791 ADA4528-1 ADP3301

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 = 3.75V INPUT RANGE = 10V p-p 1 LSB = 10V/224 = 0.596µV

24-BIT Σ-Δ ADC

BW = 4.3Hz DIFF BW = 8Hz CM BW = 160Hz

CN0216 Noise Performance

57

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

CN0216 Evaluation Board and Software

58

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

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

59

IN+

IN-

OUT- OUT+

+5V

2mV/V SENSITIVITY

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.

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

60

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

61

Target Applications Key Parts Used Interface/Connectivity Weigh scales Load cells

AD7190 ADP3303

SPI (AD7190) USB (EVAL-AD7190EBZ)

EVAL-AD7190EBZ

CN0102 Precision Weigh Scale System

62

AD7190 Sinc4 Filter Response, 50 Hz Output Data Rate

63

AD7190 Noise and Resolution, Sinc4 Filter, Chop Disabled

64

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

17.5 for 10 mV p-p

Only using 10 mV out of 80 mV range

CN0102 Load Cell Test Results, 500 Samples

65

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

CN0102 Evaluation Board and Load Cell

66

EVAL-AD7190EBZ

Software Display

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

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

67

Tweet it out! @ADI_News #ADIDC13

Visit the Impedance Measurement Demo in the Exhibition Room Measuring complex impedances with the AD5933

68

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

SOFTWARE OUTPUT DISPLAY

Tweet it out! @ADI_News #ADIDC13

Visit the Tilt Measurement Demo in the Exhibition Room

69

Measure tilt using the ADXL203 dual axis accelerometer

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

SDP-S BOARD SOFTWARE OUTPUT DISPLAY EVAL-CN0189-SDPZ

Tweet it out! @ADI_News #ADIDC13

Visit the Weigh Scale Demo in the Exhibition Room

70

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