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Product Characterization
Through Data Logging
April 3, 2002
presented by:
Bill Griffith
DAC Back to Basics
Product
characterization
through data logging
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to edit
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• Why perform product characterization
• Data logging system overview
•
•
•
•
•
•
•
Sensors
And, how to make
better
Signal Conditioning
measurements!
Multiplexing / Switching
Analog to Digital Converter
PC Connectivity
An example of characterizing a power supply
Questions and answers
Page 2
What is Product Characterization
The to
use
ofMaster
measurements
on a product or
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design to verify proper operation
• Does it meet design goals?
• Does it meet standards (UL,CUL,CSA,
•
•
•
•
GS/TUV,CE, etc.)?
Is it reliable?
Can it be manufactured ?
Is it energy efficient?
Is the product safe?
Page 3
Automated test can
collect more data and
will have more
repeatable results
Product Characterization
Some
examples
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•
•
PC board / Components
• Life / Durability tests
• Operation vs. temp and humidity
• Noise, accuracy, gain checks
• Incoming value screening
Temperature is
Battery Tests
the most common
measurement• Charge / Discharge rates
typically changes
• Life test
slowly
• Temperature Rise
Page 4
Product Characterization
Some
more
examples
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• Mechanical Enclosures
•
•
•
Heat rise, hot spots
Cooling effectiveness
Air flow
•
Environmental tests (extreme
temp and humidity)
Standards (UL, CE, etc.)
Specification development through margin analysis
Reliability - Vibration, Stress
Tests
• Whole Product
•
•
•
Page 5
Why Product Characterization
Temperature
can affect
reliability
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•
•
•
Reliability
• Changes in temperature create mechanical stress
• Strain will lead to failure
• Possible safety issues
Temperature changes can occur during power up or
thermal gradients caused by hot spots
Hot spots can be caused by:
• Components
•
Dead air spots
Page 6
Why Product Characterization
Temperature
can affect
performance
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•
•
Performance
• A change in temperature can cause frequency drift
• In addition, voltage can change with temperature
• Temperature can affect energy efficiency
Solutions - reduce differences
in temperature
• Add vents
• Add fan - optimize design
(size, cost, quiet operation,
power consumption,
magnetic flux)
Page 7
Hitachi has developed
what it says is the first
water cooled laptop.
The machine has no
fan to cool its CPU.
Why Product Characterization
An example
of product
characterization
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• Power Supply - unique challenges
•
•
Smaller transformer often more desirable
• drawbacks include less efficiency and more
heat
• Transformers create more heat at lower
frequencies
Measurement challenges
• Magnetic flux and RF energy can interfere with
temperature measurements
• Parts maybe grounded creating potential ground
loops with instruments used to measure
temperature
Page 8
Why Product Characterization
Product characterization is the process of using electrical
and physical measurements to gain insight and improve
a design
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• Most common measurements include:
•
•
•
•
•
•
Temp, DCV, Current, ACV, Frequency, and Events
Measurement characteristics include:
Multiple inputs: typically < 20 channels
Relatively slow reading rates: ~ 1 channel/sec
Standalone or PC-connected: Most analysis done
in a PC
Data storage: Electronic memory or documented
on paper
Page 9
Data Logger System Architecture
Overview
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Signal
Transducer
Multiplexer
Conditioning
Digital
Multimeter
(DMM)
Display
Analysis &
Reporting
SCAN
A/D
MON
VIEW
28.32 C
Consider PC connectivity
- Cables
- Adapters
- SW
Page 10
Data Logger System - Transducers
Physical
parameter
to electrical
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Physical Parameters
•
•
•
•
•
•
•
Temperature
Flow
Pressure
Strain
Position
Weight
Speed
Electrical Signals
Transducer
•
•
•
•
•
•
dc Volts
ac Volts
dc current
ac current
Resistance
Frequency
Choose the correct sensor
Mount it correctly
Position it correctly
Page 11
Data Logger System - Transducers
Temperature
background
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•
•
How is heat transferred
• Glass is a poor conductor
• Gap reduces conduction
• Metallization reflects radiation
• Vacuum reduces convection
Thermal mass
• Don’t let the measuring device
change the temperature of
what you are measuring
• Response time is a function of
the mass of the sensor and
the mass of object being
measured
Page 12
Dewar
Sensor
Data Logger System - Transducers
Making
temperature
measurements
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•
•
•
•
•
What is your normal temperature?
97.6 98.6 99.6
36.5 37 37.5
Thermometer resolution, accuracy
Contact time
Thermal mass of tongue,
thermometer
Human error in reading
Page 13
Data Logger System - Transducers
Thermocouples
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•
Need accurate, sensitive
measurements--
•
J-type thermocouple
at room temp = < 1 mV
•
A 1C change at 0C =
50.38 V
To see a 0.1C change
in a J-type TC at 0C,
your instrument must
be able to resolve
down to 5 V.
•
Page 14
Metal A
Metal B
+
VAB
-
• Good junction
•Thermal shunting
• Noise and leakage
current
•Thermocouple specs
• Calibration of TC
Data Logger System - Transducers
Thermocouples
Gradient
Click
to edit Master -subtitle
styleTheory
•
•
•
•
The wire is the sensor, not
the junction
Heating one end of a wire
creates a voltage Vax
The voltage is a non-linear
function dependent on wire
type and the temperature
difference from one end of
the wire to the other
The Seebeck coefficient (e)
is used to quantify the
voltage that is created
Page 15
+
TX
VAX Metal A TA
Metal B

Tx
VAB = eAdT +
Ta
TB

+
VAB
-
Tb
eBdT
Tx
Data Logger System - Transducers
Thermocouples
Gradient
Click
to edit Master -subtitle
styleTheory
•
If a “thermocouple junction”
is made with two wires of the Tx
same metal - what voltage
would the TC produced (VAB)?
a) 2*VAX - twice the gradient
voltage of metal A
b) No voltage
c) Can’t determined without
knowing the temperature
difference
d) Can’t determine without
knowing the metal type
Page 16
+
VAX Metal A Ta
Metal A
Tb
+
VAB
-
Data Logger System - Transducers
A modern
data logger
make it easy to
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style
make measurements
•
•
We are taking a deeper look at how measurements are
made - a lot of the details are handled by the data
logger
The architecture that we have presented makes it
possible to connect any type of transducer to any
channel.
• Simply setup the data logger with the type of
transducer and channel information
• The data logger will make the necessary
measurements, conversions and display the
correct results in scientific units
Page 17
Data Logger System - Transducers
Moretoinformation
is available
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• For more details on making temperature
measurements - see application note 290.
• Having a good understanding
of transducers will allow us
to make better measurements
• In order to make good
measurements - care has to
be taken
Page 18
Data Logger System - Transducers
Thermocouples
Gradient
Click
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styleTheory
•
•
•
+
If a thermocouple was
made of a single metal
Metal A the TC would
produce zero volts
Two different metals are
combined to create a TC
How do you measure a
TC?
Tx
VAX Metal A Ta
Metal B
Tx
Metal A
Metal B
Page 19
Tb
+
VAB
-
Metal C
+
V
Metal C
Data Logger System - Transducers
Thermocouples
How tostyle
measure a TC
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• Create a reference
•
•
•
•
Metal A
junction
Tx V
X
Measure Tref using
Metal B
thermistor
Lookup Vref for TC at
Tref
reference junction
Compute
Vx=V+Vref
Compute Vx = V+Vref
Solve for Tx using Vx
Metal C
+
V
Metal C
Vx
Vref
V
o
0 Tref
Tx
Data Logger System - Transducers
Thermocouples
Common
Click
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styleTypes
mV
E
Platinum T/Cs
Base Metal T/Cs
60
K
J N
40
20
T
0
500
RS
1000
2000
Page 21
deg C
Data Logger System - Transducers
Thermistor
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•
Rlead
Better accuracy and more
expensive
•
•
•
•
Absolute temperature
A common thermistor
type has 5000  at
25C with 4%/ C
Rtemp
Rlead
+
Rmeas
-
Often physically small
mass
• Won’t cause thermal
1C = 200 
loading
10  of lead resistance • A large measurement
would cause a .05 C
current will cause self
error
heating
Page 22
Data Logger System - Transducers
RTDto- Resistance
Temperature
Detector
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•
+ Vlead RTDs
• Absolute measurement
Rlead
RTD
• Accurate measurement
Rtemp
• A common RTD has 100
Rlead
 at 0C with .385 / C
• 10  of lead resistance
+ Vlead would cause a 26 C
error
• Avoid self heating, a 5 mA current source
would create 2.5 mW of power in our RTD.
• At 1 mW/ºC, that is an error of 2.5/ºC
Page 23
DMM
i
+
V
-
R=V/i
Data Logger System - Transducers
RTDto- Four
wire ohm
measurement
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DMM
Rlead
I=0
RTD
Rlead
i
Rtemp
+ V=Vtemp=i*Rtemp
V
-
Rlead
I=0
Rlead
Page 24
Rtemp=V/i
• For more R=V/i
information on 4wire ohm
measurements see
application note
1389-2
Data Logger System - Transducers
IC -to
Temperature
sensor
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• Linear change in voltage or
current with change in
temperature
• 10 mV/K (voltage IC)
•
Room temp approx. 3V
with a 10mV/°C change
OR
•
•
•
1 A/K (current IC)
Need an external power
source
Absolute measurement
Page 25
+
10mv/K V
temp v
-
• Have limited
temperature range <
150 C
• Fairly large mass
Data Logger System - Transducers
Temperature
sensors
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IC
Thermocouple
+ Most accurate + High output
+ High output
+ Wide variety
+ Most Stable
+ Fast
+ Most linear
+ Cheap
+ Fairly linear
+ 2-wire meas.
+ Inexpensive
+ Wide T. range
- Expensive
- Very nonlinear - Limited variety + No self-heating
- Slow
- Limited range - Limited range
RTD
Thermistor
- Hard to measure
- Needs I source- Needs I source - Needs V source - Relative
temperature only
-Self heating
- Self-heating
- Self-heating
- Nonlinear
-4-wire meas. - Fragile
- Special
Absolute temperature sensors
connectors
Page 26
Data Logger System - Transducers
Polling
Question
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• Your designing an electronic device and have
included an IC temperature sensor in your
design and want to verify the accuracy of the
IC sensor - what type of sensor would you use
with your data logger to make the
measurement?
A) Thermocouple
B) RTD
C) Thermistor
D) IC Sensor
Page 27
Data logger System Architecture
Overview
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Signal
Transducer
Multiplexer
Conditioning
Digital
Multimeter
(DMM)
Display
Analysis &
Reporting y
SCAN
A/D
V
V
Wiring errors
Page 28
MON
VIEW
28.32 C
Data Logger System - Wiring Errors
Thermocouple
wires
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subtitle style
Small diameter
measurement
wires
•
Long rugged extension wires
Possible problem
Extension wires are less
expensive, more rugged, but
have slightly different
temperature curves than the
thermocouple
Page 29
• Keep the junction
of the extension
wire and the
thermocouple wire
near room
temperature
Data Logger System - Wiring Errors
Common
Click
to edit Mode
MasterErrors
subtitle style
Metal A
H
L
Metal B
Icom
ZH
DMM
ZL
• Common mode errors create a •Make Z as large as
L
current into both the high and
the low measurement paths
possible
•Avoid connections to
• Typically caused by a difference grounds
in grounds
Page 30
Data Logger System - Wiring Errors
Normal
Mode
Errors
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magnetic
coupling
V
Inorm
DMM
Reduce the size of the
• Normal mode noise
measurement loop
introduces a current that is - twisted pair wire
in the same direction as the - move measurement hardware
measurement current
closer to the source
• Magnetic flux or RF energy - run measurement wires
perpendicular to high current
are common sources of
wires
normal mode errors
Page 31
Data Logger System - Wiring Errors
Normal
Mode
Errors
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Electrostatic noise
Inorm
DMM
ZL
• Large ZL is important
to avoid capacitance
coupling through tip of
thermocouple
Shielding will provide an
alternative path for
electrostatic energy
- Only ground one end
Page 32
Data logger System Architecture
Overview
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Signal
Transducer
Multiplexer
Conditioning
Digital
Multimeter
(DMM)
Display
Analysis &
Reporting y
SCAN
A/D
V
V
Page 33
MON
VIEW
28.32 C
Data Logger - Signal Conditioning
Signal
Conditioning
- Examples
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to edit
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style
•
Convert signal to be
compatible with system
• Thermocouple
reference junction
•
•
•
•
•
Filter
Strain gauge bridge
completion circuit
Shunt resistor for
indirect current meas.
Amplifier / Attenuator
AC converter
Page 34
Metal A
Metal C
Metal B
Metal C
+
V
-
Isothermal
Reference
Junctions
+
V
-
I
Data Logger - Signal Conditioning
Filter
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magnetic
coupling
V
•
•
Inoise
Reduce noise that has been
coupled into the signal
“normal mode error”
Allow for filter settling time
Page 35
I < Inoise
Include lead and
switch resistance, plus
lead and switch
capacitance
when calculating
settling time
Data logger System Architecture
Overview
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Signal
Transducer
Multiplexer
Conditioning
Digital
Multimeter
(DMM)
Display
Analysis &
Reporting y
SCAN
DMM
V
V
Page 36
MON
VIEW
28.32 C
Data Logger System - Multiplexing
Multiplexing
- Examples
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subtitle style
H
H
H
L
L
L
H
H
H
L
L
L
H
H
H
L
L
L
H
H
H
L
L
L
1-wire, 4:1 MUX
2-wire, 4:1 MUX
Page 37
4-wire, 2:1 MUX
Data Logger System - Multiplexing
Switch
characteristics
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Typical
Voltage
Offset
Speed
Life
Armature
300 V
1A
3 µV
1
60 ch/s
10 M
Reed
300 V
50 mA
16 V
1 mA
300 V
1A
6 µV
1
25 µV
1 k
3 µV
3
MAX
FET
Solid
State
Page 38
500 ch/s
10 M
100k ch/s Infinite
200 ch/s
Infinite
Data logger System Architecture
Overview
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Signal
Transducer
Multiplexer
Conditioning
Digital
Multimeter
(DMM)
Display
Analysis &
Reporting y
SCAN
DMM
V
V
Page 39
MON
VIEW
28.32 C
Data Logger System - DMM
DMMto- Digital
Multimeter
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subtitle style
H Amplifier, attenuator
L
and shunt resistors
for current
AC RMS
Current Source for
resistance
A/D
Converter
ZL
Control and reading memory
• Reduce the complexity of signal condition
•
•
May only need one RMS converter
May not need additional attenuation and
amplifiers in signal conditioning
Page 40
Data Logger System - DMM
Normal
Mode
Errors
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to edit
Master
subtitle style
magnetic
coupling
Inorm
A/D Converter
When using an integrating A/D
the integration period will be
introduces a current that is set to line frequency
in the same direction as the
- Use at least 1 PLC to
measurement current
reject noise
- Higher frequency noise
•An integrating A/D can be
will be integrated and reduced
used to reduce normal
along with power line noise
• Normal mode noise
mode noise
Page 41
Data Logger System - DMM
Integrating
A/D Converter
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subtitle style
•
•
V
Normal mode noise is
Vnoise
typically generated by large
currents that have the same
VTemp
1 PLC
frequency as line frequency 2 PLC
integrating over one Power
NPLC
Line Cycle will make Vnoise=0
Can trade off reading rate
(speed) for resolution
T
• 1 line cycle = 60 rdgs/s
• 10 line cycles = 6 rdgs/s
Page 42
Data Logger System - DMM
Measurement
Characteristics
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• Resolution - How many bits or
digits the ADC/system produces
• Repeatability - How consistent
results are reading-to-reading
• Accuracy
Relative accuracy statistical determination of error
(deviation from norm)
Absolute accuracy statistical determination of error
from a traceable source
Page 43
Data logger System Architecture
Overview
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to edit Master subtitle style
Signal
Transducer
Multiplexer
Conditioning
Digital
Multimeter
(DMM)
SCAN
DMM
MON
VIEW
Display
Analysis &
Reporting
28.32 C
System error is a sum of
the error from each
component
- avoid noise sources!
Page 44
Data Logger System - Reporting Tasks
Common
tasks
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to edit reporting
Master subtitle
style
•
•
•
•
•
Quickly setup data logger
• Self guiding menus
Make sure that you are collecting valid data
• Verify setup / possibly monitor a channel
• Set limits and alarms
Upload results to PC
• Create final reports in Microsoft
applications
Use away from bench
• Display viewing angle
• Bright in multiple lighting conditions
Save channel setups and easily modify
Page 45
Data Logger System- Reporting Tasks
PC Connectivity
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• Connecting to data logger
•
•
•
•
RS-232
USB
LAN
GPIB
•
•
•
Easy to use
Create documentation
Compatible with Microsoft Office Apps
• Software
Page 46
Data Logger System - Reporting Tasks
Creating
reports
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•
•
•
Typically report results in
Microsoft Office applications;
Excel, Word, or PowerPoint
Need a way to cut and paste
graphical data into these
office applications easily
Could create a program or
use an off-the-shelf
application designed for the
task
Page 47
Data Logger System - Reporting Tasks
UsingtoRS-232
/ USB
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subtitle style
•
•
•
Although a common
interface RS-232 has a
couple of drawbacks
• RS-232 can be slow
• Can be difficult to find
the correct cable
USB has become prevalent
and addresses the common
problems of RS-232
USB to GPIB converters have made it possible to take
advantage of USB and create an opportunity to take
advantage of portable computers away from the bench
Page 48
Data Logger System - Reporting Tasks
UsingtoLAN
connectivity
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•
•
LAN connectivity has several
advantages
• Fast - although not tuned
for measurement data like
GPIB
• Can be used over long
distances
• Allows resources to be
shared
LAN to GPIB converters can
take advantage of LAN
capability
Page 49
Data Logger System - Reporting Tasks
PC Software
Summary
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subtitle style
Software Create
Report
Data
logger
SW
Make 1st Flexibility
Reading
Cost
Low product
specific
Free to
$300
Textual
Time
Time
language intensive intensive
Great
$300 to
$1,000
T&M
graphical Medium
language
Great
$600 to
$1,400
Quick
Quick
Medium
Page 50
Data Logger System - Reporting Tasks
PC Connectivity
Summary
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to edit Master subtitle
style
Interface Common Common Speed Distance Cost
to PC
to Instr.
Short
$0 to
Low
Yes
Need an Medium
Short
adapter
$500
Yes
Need an Fast
adapter
Long
$1100
Fast
Short
$400 to
$600
RS-232
Yes
USB
LAN
GPIB
Need an
adapter
Yes
Yes
Low
Page 51
Data Logger System Demo
OEMto
Power
Supplysubtitle
Characterization
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style
• Specified an OEM power supply to speed
product development. Requirements include:
• 100 Vac - 240 Vac +/- 10% line voltage
• Characterize temperature measurements in
critical areas
• Voltage stability under full load
• Voltage regulation under low line voltage
Page 52
Data Logger System Demo
OEMto
Power
Supplysubtitle
Characterization
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style
• Test setup
•
•
•
•
Data acquisition / switch unit connected to:
• Four temperature measurements using
T-type thermocouples
• Four dc voltage measurements
A PC with USB/GPIB converter
Data logger software
Create a report, Temperatures vs. Time,
Voltage vs. Time
Page 53
Data Logger System Demo
OEMto
Power
Supplysubtitle
Characterization
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style
• Getting Started
•
•
•
•
Use front panel of DAC system to quickly
verify voltage and temperature setup
The PC and SW is used to automate the
measurements over time
Varied line voltage manually
The data logger screen images were then
cut and pasted into a Microsoft Word
document for the final report
Page 54
Data Logger System Demo
Power
Test subtitle style
Click
to Supply
edit Master
SCAN
A/D
Vab 
Vcd 
Vef Page 55
MON
VIEW
28.32 C
Summary - System Accuracy
Click to edit Master
Signal subtitle style Analog-toTransducer
Transducer
errors
Conditioning
Thermal
gradient
Multiplexer
Thermal EMF /
Offsets
Display
digital
converter
DMM - offset,
noise, linearity,
resolution,
accuracy
SCAN
Additional
cable
errors
A/D
MON
VIEW
28.32 C
Data logger
temperature
conversion
algorithm
Ref transducer accuracy
System accuracy is the sum of the measurement errors
for each component
Page 56
Summary
Modern
Data
loggersubtitle
- Can help
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to edit
Master
style
•
•
•
Data logger may include PC cables and software
Data logger will make thermocouple measurements
easy - built-in conversion routines, reference junction,
reading storage, monitor data from display
Data logger may specify system accuracy - to
determine complete error add transducer error
• For our example the data logger specifies the
system error for a T-type TC as 1oC. The TC has an
error of 1oC or .75% which ever is greater. So the
total error is 2oC
Work to minimize external
sources of error
Page 57