Instrumentation: Test and Measurement Methods and Solutions - VE2013
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Transcript of Instrumentation: Test and Measurement Methods and Solutions - VE2013
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