Identifying noise in daq webinar rp3 171027 (1)

Identifying and
Overcoming Noise
in Data Acquisition
Richard Patterson
Product Manager

2
Copyright © Yokogawa Meters & Instruments Corporation
KRISTIN PORCHÉ
Marketing Specialist
Yokogawa Corporation of America
Newnan, GA
kristin.porche@us.yokogawa.com
1-800-888-6400 ext. 12345678
tmi.yokogawa.com
Host & Panelist

3
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Recorded
Presentation
A recording of this presentation will be posted under
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Select and send all questions to “Panelist” during
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5
RICHARD PATTERSON
Product Manager
Yokogawa Corporation of America
Newnan, GA
richard.patterson@us.yokogawa.com
1-800-888-6400 ext. 2537
tmi.yokogawa.com
Presenter

6
Overview
Data acquisition overview
Quantization noise
Internal A/D noise
Power line noise
Time skew
Aliasing noise
Common mode noise
Radiated noise (EMI)
Application example

7
Data Acquisition
Application Space Overview

8
Data Acquisition Applications by Rate
DC-1kHz
Temperature, pressure,
Static load, displacement
Production monitoring
Power line monitoring
1kHz-100kHz
Mechanical Electronics
Sound and Vibration
Automotive, Aerospace
100kHz-20MHz
Electrical performance
Digital, timing, pattern I/O
Consumer electronics
20MHz-1GHz +
Component design
RF, Microwave
PC-based (PCI, USB or PCIe; most PC-
centric)
Pro: low cost, multi-function, bus throughput
Con: little/no signal conditioning,
often multiplexed, poor noise immunity
Benchtop (least PC-centric, DL850E/350)
Pro: separate/isolated power, portable,
better quality measuring hardware,
built-in functions (firmware) and datalogging
Con: less channel density, higher initial cost,
large footprint, slower for automation
PC-based External (SL1000, MX100, GM10)
Pro: most scalable, better quality measurement HW,
fast performance and integrated software for PC automation,
lower cost, high bus speed, high channel density

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DAQ Signal Types
Analog Input
■  DC/AC Voltages
■  Sensors
•  Accelerometer, ICP Microphone
•  Strain Gage, Load Cell
•  RTD, Thermistor, Resistance
Analog Output
DC, function generation, arbitrary,
sweeping
Digital Input/Output TTL/CMOS, static & buffered
Timing Measurements
Event counting, delay, period, frequency,
tachometer, encoder, time stamps

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Analog Input Applications
Low Speed Monitoring and Recording High Speed Single Shot
■  Machine monitoring
■  Process monitoring
■  Certification testing
■  Reliability testing
■  Startup/shutdown monitoring
■  Electrical response
■  Device characterization
■  Sweep testing
■  Destructive/explosion testing

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Analog Input Applications
Combination: High Speed Continuous Monitoring
■  Streaming, circular buffer, FIFO buffer
■  In-vehicle/flight, high energy physics, real-time monitoring of multi-hour tests

12
Block Diagram of a Data Acquisition Setup
Sensor Cable Analog Input Chain
■  Filters
■  Amplifiers
■  Multiplexer
■  Isolation
ADC Analysis
■  Built-in processor
■  PC
■  Storage

13
Block Diagram of a Data Acquisition Setup
Sensor Cable Analog Input Chain
■  Filters
■  Amplifiers
■  Multiplexer
■  Isolation
ADC Analysis
■  Built-in processor
■  PC
■  Storage

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Sources of Noise

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Most commonly affects:
■ Low-voltage measurements
•  Thermocouple measurements
•  Ripple measurements
•  Small details
■ High-speed (on 8-bit scopes)
Source 1: Quantization Noise

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Principle of Quantization Noise
Decimal System (Base 10) Binary System (Base 2)
■  Used by humans
■  Number of Digits
■  1 digit = 0-9 [10 counts]
■  2 digits = 00-99 [100 counts]
■  3 digits = 000-999 [1000 counts]
■  Counts = 10↑𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑑𝑖𝑔𝑖𝑡𝑠 
■  Used by Analog-Digital converters
■  Number of Bits
■  1 bit = 0↓2 −1↓2 [2 codes]
■  2 bits = 00↓2 −11↓2  [4 codes]
■  3 bits = 000↓2 −111↓2  [8 codes]
■  counts = 2↑𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑏𝑖𝑡𝑠 
8 bit A/D = 2↑8  = 256
16 bit A/D = 2↑16  = 65536
Binary (8 bits)
Output Code
Decimal (raw) Voltage (scaled)
00000000 0 -10V
00000001 1 -9.921875
00000010 2 -9.84375
00000011 3 -9.765625
00000100 4 -9.6875
00000101 5 -9.609375
… … …
11111111 255 +10V

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Principle of Quantization Noise
■ Bit Resolution determines how many counts (codes) exist across the full scale
■ A Least Significant Bit (LSB) is the smallest voltage change that can be measured
•  1 LSB = = 𝑅 𝑎𝑛𝑔𝑒/𝐶𝑜𝑢𝑛𝑡𝑠  𝑜𝑟 𝑅 𝑎𝑛𝑔𝑒/2↑𝑏𝑖𝑡𝑠 𝑜𝑓 𝑟𝑒𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛  
•  8 bit LSB: 10 𝑉 −(−10 𝑉)/2↑8   = 20 𝑉/256 = 78.125 mV
•  12 bit LSB: 10 𝑉 −(−10 𝑉)/2↑12   = 20 𝑉/4096  = 4.883 mV
Goal Maximize use of all the “codes”
b0
b1
b2
b3
b4
b5
b6
b7
A/DPGIA
+10V
-10V
Full scale
1 LSB

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Typical Quantization Noise Solution
■ Digital software filter (poor)
■ SW Filter used: Sharp, Lowpass, fcutoff = 2% *fsample, 88th order

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Hardware solution: Match the ADC range, or increase the bit depth
Quantization Noise Solution
b0
b1
b2
b3
b4
b5
b6
b7
A/DPGIA
b0
b1
b2
b3
b4
b5
b6
b7
A/DPGIA
b0
b1
b2
b3
b4
b5
b6
b7
A/DPGIA

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AC Coupling
■ The DC offset is wasting some of the range of the ADC
■ Use AC Coupling to eliminate the DC component
Must Use
±2V Range
Due to DC
Offset
Enable AC/DC
Coupling
Circuit, allowing
use of a lower
Range
(±100mV)

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Source 2: A/D Internal Noise
■ Noise described by printed specifications
■ Main factors contributing to internal noise
•  Nonlinearity of the A/D converter itself (differential &
integral nonlinearity)
•  PGIA & A/D block – gain and offset
•  Thermal effects and thermal stability of the entire digitizer
•  Frequency response
■ Accuracy specifications are highly inconsistent

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Source 2: A/D Internal Noise
Various Specifications
Improving A/D Internal Noise
■ Accuracy (gain and offset)
■ Absolute accuracy
■ Signal to noise ratio (SNR)
■ Effective number of bits (ENOB)
■ Noise floor (dB)
■ Spurious free dynamic range (SFDR)
■ Higher precision digitizer
■ Control environmental temperature
■ Reduce the bandwidth
Measurement
Range
Accuracy
±50 mV ±(0.15% of rdg + 0.5 mV)
±100 mV ±(0.15% of rdg + 0.5 mV)
±200mV ±(0.15% of rdg + 0.5 mV)
±500 mV ±(0.05% of rdg + 0.5 mV)
±1 V ±(0.05% of rdg + 0.7 mV)
±2 V ±(0.05% of rdg + 1.4 mV)
±5 V ±(0.05% of rdg + 3.5 mV)
±10 V ±(0.05% of rdg + 7 mV)
±20 V ±(0.05% of rdg + 14 mV)
±50 V ±(0.05% of rdg + 35 mV)

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Source 3: Power Line Noise
■ “Pick Up” or “Hum”
■ Conducted or radiated
■ 50/60/400Hz
■ Inexpensive switching power supplies cause “spikes”
Clean Signal Signal with Power Line Noise

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Integrating A/D Converter
■ Integrating A/D converters quantize by time rather than by voltage
■ Better linearity and accuracy, no missing codes
■ Best low speed solution (DMM use case)
■ Eliminate random and sine wave noise
Normal Sampling For Integration-type A/D
Time
Voltage
Signal with power
supply noise
Voltage corresponding to the
value after the conversion
Time
Voltage
Signal with power
supply noise
Voltage corresponding to the
value after the conversion

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Other Power Line Noise
■ Moving average (compare to your input signal speed)
■ Power line filters
■ Isolated input to data acquisition hardware

26
Source 4: Time Skew
■ Is your data acquisition system/module Multiplexing?
■ Differential measurements can have time skew between + and – terminals
(pseudo-differential)
Actual Signal Measured Signal

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Principle of Time Skew
Multiplexing Sampling Simultaneous Sampling
Ch1
Ch2
Ch3
Ch4
…
channel clock [inter-channel skew]
scan clock
Ch1
Ch2
Ch3
Ch4
…
A/D
converter
Analog mode
multiplexer
PGIA
Calibration Dither
Acquisition
control
Acquisition
memory
Ch1
Ch2
Ch3
Ch4
ATT PGA
LPF
ADC
Programmable gain amp
Isolation
FilterCh1
Ch2
Ch3

28
CH1 – CH2 = 0 CH1 – CH2 ≠ 0
Missing peaks (green channel)
False phase difference

29
Source 5: Aliasing Noise
■ Aliasing or fold-over distortion
■ Occurs when higher frequency content exists beyond the sampling
bandwidth

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Principle of Aliasing
Any analog signal or
non-sinusoidal waveform =
sine waves of various:
■ Amplitudes
■ Frequencies
■ Phases
Fourier Transform
fmax
𝑓(𝑥)=∫−∞↑∞▒Ϝ(𝑘) 𝑒↑2 𝜋𝑖𝑘𝑥   𝑑𝑘
f(t)=a↓0 +a↓1  cos( 𝜔↓0 t)+b↓1  sin( 𝜔↓0 t)+a↓2  cos(2 𝜔↓0 t)+b↓2  sin(2 𝜔↓0 t) +…

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Red trace is actual signal, Green dots are measured values
Original waveform with 20 samples per
period (fs = 20 f0)
period (fs = 5 f0)
period (fs = 2 f0)

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“Perfect” example
fs = 16 samples/sec
Adequately sampled
■ f0 = 1 Hz
■ fN= 8 Hz
Near “Nyquist frequency” or sampling bandwidth
■ fN = ½ fs = 8 Hz
■ f0 = 7 Hz
Above “Nyquist frequency” or sampling bandwidth
■ fN = ½ fs = 8 Hz
■ f0 = 11Hz
■ In this case we should see a flat line
■ Instead we see the aliased

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■  More realistic example
■  Original signal
•  3 Hz content, 1Vpp
•  50 Hz content, 0.2Vpp
■  Aliased noise
at 5 Hz
■  Sampled at 55 Hz
■  (fN = ½ fs = 27.5 Hz)
■  F=ABS(1*55-50)=5 Hz

34
Effect of Aliasing
Some Signals (i.e. a sawtooth wave)
have infinite harmonics
If the fundamental frequency of the
sawtooth wave is f0, and we sample
at 20*f0, what happens?
f(t)=∑n=1↑∞▒2(−1)↑n+1 /n  
sin⁠(nt) 
=2sin⁠(t)−sin⁠(2t)+2/3 sin⁠(3t)−
1/2 sin⁠(4t)+2/5 sin⁠(5t)…     
Result = increased noise floor

35
Aliasing Solution
■ A Hardware filter (low pass) eliminates fold-over distortion
■ Set the filter frequency close to Nyquist frequency (½ fs)
■ The filter must reside in hardware – software filters are ineffective
•  Because the aliased signals are lower than the Nyquist frequency
•  External HW filter is an option, some sources use SW-selectable,
HW built into instrument
1.0
0
0.5
f = Cutoff frequency
3 dB
Increasing frequency f

36
Reconstructing the Signal
■ In theory, the reconstructed waveform must not possess any frequency content >=
sampling frequency
■ To perfectly reconstruct, bandwidth limit the re-creation/output
•  Cutoff frequency = Nyquist frequency
■ You can also use curve fitting to approximately reconstruct the signal
•  Linear interpolation, sinusoidal interpolation, spline
■ In practice, most engineers do not reconstruct waveforms prior to analysis!
■ Therefore, apply a Practical over-sampling criteria fsample > 5x fmax

37
Source 6: Common Mode Noise
■  Original signal with no common mode
■  Signal with Common mode input to a
pseudo-differential device
■  Saturating the input with common mode
■  Signal with Common mode measured by
isolated digitizer
*Noise depends on CMRR
■  Signal with Common mode noise greater
than digitizer specification

38
Principle of Common Mode Voltage
■ Voltage difference between sensor “ground” and instrument ground
■ Can cause permanent damage to measurement hardware
+
Power
supply
-
Power
supply
Instrument
Analog ground
Sensor
5V
0+Vcm
Vcm+5
Power ground
Vcm

39
Common Mode noise is noise occurring in-phase on both wires of a
differential measurement
■ It could be radiated or conducted
■ The design of the amplifier going in to the ADC can reject this – never perfect
■ Slight DC offset or impedance mismatch between + and – makes it worse
■ Measure CMRR in dB
Common Mode Noise

40
Ground Loops
■ Return paths for current referred to as “ground”
■ Occurs when more than one ground connection path exists
between devices
DAQ
Ground path through building
or earth ground
DUT or sensor
Ground path through shield
or negative terminal of SE
measurement

41
Ground Loops
Three ways ground loops cause
equipment problems
Loop is an antenna, especially
for AM signals and EMI1
High-energy transients g
circuit ground2
Ground loops can cause common-
mode noise on power systems3

42
Common Mode Solution
■ Isolation Barriers
•  Prevents ground loops and negates common mode voltage
■ Safety: keeps high voltage/current away from people and equipment
■ Integrity: rejects unwanted voltages from affecting measurement accuracy
Instrument
Power
supply
Isolation
barrier
Isolation
amplifier
Sensor
+V
Vcm
Normal
mode signal

43
Common Mode Solution
■ Built-in Isolation Systems
■ Four isolation specifications
to consider
•  [V1] Channel-to-ground isolation
•  [V2] Module-to-module isolation
(in a modular system)
•  [V3] Channel-to-channel isolation
•  [V4] Transient overvoltage
protection (or maximum
withstand voltage)
Module A
Module B
V2
V3
V1
V4

44
Channel to Earth Isolation
■ [V1] Channel-to-ground isolation
■ Accessible parts of instrument are
safe
■ Prevents ground loops and common
mode noise
Isolation Barrier
Analog
Module
A
Analog
Module
B
Analog
Module
C
Backplane
Module A
Module B
V2
V3
V1
V4

45
Module to Module Isolation
■ [V2]
■ Each module is isolated from each other
■ Provides noise immunity and overvoltage
protection
Module A
Module B
V2
V3
V1
V4

46
Channel to Channel Isolation
■ [V3] Channel-to-Channel isolation
■ Provides channel to channel
protection from:
•  Crosstalk
•  High energy transients
Module A
Module B
V2
V3
V1
V4

47
Source 7: Radiated Noise (EMI)
■ Certain environments are especially
prone to noise:
•  Industrial or manufacturing facilities
•  Power engineering labs (supplies, UPS, etc.)
•  Motor or drive companies
•  High energy physics laboratories
■ Emission sources
•  Fluorescent lighting (120 Hz sinusoidal)
•  Bipolar power supplies
•  Internal components of desktop PC
•  Crosstalk (other sensors, particularly
active sensors)
■ Manifest as common mode and normal
mode voltage

48
Reducing EMI Noise Effects
■  Faraday Cage
■  Shield Cabling
•  Use standard shielded cable types (coaxial/
BNC, twisted pair)
•  Use an external cable shield around each
sensor-to-digitizer cable
•  Tie the cable shield to ground on only one side
•  Consider optical connections when feasible
■  Shield the Digitizer Module (vendor)
■  Shield the Station or Chassis (vendor)
■  Shield the Rack

49
Reducing EMI Noise Effects
■  Ribbon cables
■  Unshielded terminal blocks
■  Many digitizer instruments have
direct connections (clamp
terminals, NDIS, BNC)
■  Use true differential hardware
with isolation
■  4-20 mA current signals

50
Elements of a Noise Minimizing Digitizer
Acquisition
control
Acquisition
memory
Ch2
Ch3
Ch4
ATT PGA
LPF
ADC
Filter
Isolation
Element Purpose
BNC connection Radiated noise
Attenuation Quantization noise
PGA Quantization noise
Low pass filter Anti-aliasing
High resolution ADC Quantization noise
Simultaneous sampling Time skew
Isolation barrier Common mode noise
Shielded hardware EMI

51
Application Example: Fuel Cell Impedance Testing
When a cell is used for a long time, its
impedance will increase. This causes a
degradation or inefficiency.
By measuring the fuel cell impedance, we
can verify the electrical nature of the
internal configuration of the fuel cell.
Current Density (Output Current from Cell)
Conductor Resistance of electrode
Reaction Resistance at Anode side
Reaction Resistance at Cathode side
Electrolyte Resistance
OutputVoltagefromCell
1.03V
(Theoretical)
Anode Side Cathode Side
Reaction Resistance
Electric Bilayer
Capacitance
Solution
Resistance Fuel Cell Equivalent Circuit

52
Application Example: Fuel Cell Impedance Testing
Hydrogen flow
Hydrogen outlet
Air(Oxygen) flow
Water and air outlet
Electric load DC
component
Electric load AC
component
DC voltage(cell voltage) (Optional)
switch box
Measured load current
AC voltage(ripple)
Key Requirements
■  Isolated output
■  Isolated input
■  High resolution, 16 bit
■  AC/DC coupling
■  Programmable gain
■  Hardware filtering
■  Simultaneous sampling

53
Isolated DAQ Instruments
Scope Corder Series
■  1000 Vrms isolation
■  100 MS/s high-speed sampling
■  12-bit A/D resolution
■  Complete built-in isolation system
Parallel/
serial
converter
AMP A/D
Laser
driver
Detection
amp
Parallel/
serial
converter
Detection
amp
Laser
driver
Input
terminal Data
Converter clock
LD PD
PD LD
Optical fiber
Isolated via optics

54
100 MS/s High-
Speed Isolation
Module
10 MS/s High-
Speed Isolation
Module

55
High-Speed PC Based
SL1000 Series
■ 12 types of input modules
for measuring:
•  Voltage
•  Strain
•  Temperature
•  Acceleration
•  Frequency
■ 1000 Vrms isolation
■ 100 MS/s high-speed sampling
Install modules
into unit
Connect
to PC
Start acquisition
software
Unit and modules
automatically
recognized
Select unit
and module
Start
measurement
Power
On

56
Summary – What We Hope We Did
■ Data acquisition overview
•  Applications by speed and signal types
-  Low speed monitoring and recording, high
speed single shot, repetitive waveform
monitoring, memory blocks (sequential store),
high speed continuous monitoring
■ Quantization noise
•  Vertical resolution, LSB, gain
■ Internal A/D noise
•  What do accuracy specifications mean and
how do they reflect the noise
characteristics of the DAQ hardware?
■ Power line noise
•  Filtering, integrating A/D
■ Time skew
•  Inter channel skew, and simultaneous
sampling
■ Aliasing noise
•  Nyquist theory, sampling rate/interval and
frequency spectrum, AAF
■ Common mode noise
•  Ground loops, common mode, isolation
■ Radiated noise (EMI)
•  Crosstalk, DAQ product shielding, cable
shielding
■ Application example
•  Fuel cell impedance measurements

57
Questions?

58
Questions
If you have any questions for one of these
Webinar Topics, please send them to the
below e-mail. I will try to answer them
during the Webinar or directly afterwards.
webinarwednesdays@us.yokogawa.com

59
Thank You
for Attending

Identifying noise in daq webinar rp3 171027 (1)

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