1. Electronic Data Collection
Colin S. Campbell Ph.D.
Research Scientist
Decagon Devices, Inc.

2. Outline Data collection for the early scientist
Progress toward modern field techniques
Converting electronics into information
Electrical Engineering meets the scientist
Assessing the requirements of a project
Making the right system choice

3. Field research: Quantify physical environment
Early pioneers in environmental biophysics
Howard Penman at Rothamsted Research Station
Manual readings or strip chart/disk recordings
Sleepless nights
Seminal paper on evapotranspiration
Champ Tanner at U. Wisconsin
Travel trailer

4. Changing world of measurements
There’s got to be a better way
All-nighters at research site not terribly popular
Miss fast changes or events with human sampling
No control of processes
Goals
Make unattended measurements
Store measurements for analysis later
Transform data into information and understanding

5. Requirements for field research
Possible needs
Sensors that generate electrical signals that can be correlated with environmental phenomena
System to read electronic signals and store them
Make decisions based on measurements
Control external systems based on analysis

6. Modern field research Sensors Data logger
No limit to parameters that can be measured
Passion for instrumentation design
Only challenge is to find correlations
Indirect measurements
Measuring one parameter and inferring the one of interest
Data logger
Basically glorified multimeter and oscilloscope
Repository for raw sensor output
Interprets electronic signals and stores them

7. Evolution of measurement: Temperature example
First automation by strip chart recorder
Change in temperature of bimetallic strip
Deflection calibrated to known temperatures
Temperature variation changed pen position
Ink recorded changes over time
Data evaluated by hand
Widely used

8. Conversion to an electrical signal: The thermocouple
Seebeck effect
Two dissimilar metals jointed together produce voltage potential when differentially heated
Potential related to temperature difference
Correlation (copper-constantan thermocouple) ~ 40 mV per oC
Measurement of minute voltage changes provides accurate temperature
Assuming know the temperature of one junction
Electrical measurement is accurate

9. Other measurement techniques: Temperature
Thermocouple limitations
voltage accuracy requirement
reference temperature
Alternatives
Thermistor, platinum resistance thermometer
Change electrical resistance with temperature
Diode
Voltage drop across a PN junction

10. Data loggers and sensors

11. Sensor signal types Four general types of electronic sensor output
Voltage
Probably the most common type
Includes thermocouples, radiation sensors, some anemometers, etc.
Current
Often used over long cable distances
Common to some measurement and control industries
Pulse or switch closure
Rain gauge, some anemometers, some soil moisture sensors, etc.
Digital
Typical of sensors measuring more than one parameter
Allows for more than one signal per input location

12. Data logger types Plug and play (P&P)
Decagon Em50, Em5b
Onset Hobo
CrossBow eKo
Measurement and Control Systems (MCS)
Campbell Scientific CR1000, 3000, etc.
DataTaker DT80
National Instruments LabView

13. Choosing a data logger: Things to consider
What electronic outputs do you need to measure?
Voltage, current, pulse, digital
How many sensors are you putting at each research site?
How often will you be storing a measurement?

14. Choosing a data logger: Things to consider
Will some measurements need to be made more often than others?
>10 Hz (i.e. eddy covariance)
1 minute (i.e. radiation)
Do you need to control anything with your system (lights, heater, valve, etc.)?
Do you have the time or resources to program and setup the system?

15. Choosing the right system
Control?
Std P&P Sensor?
MCS
User needs No
Yes

16. P&P MCS Limited Sensor numbers/types Extensive
User Needs
Sensor numbers/types
Limited
Extensive
Power (batteries/solar Panels)
Cost (data logger, enclosure, power)
Low cost
Feature rich
Instrument enclosure
Integrated
Custom
Expertise
Simple setup
Program
P&P
MCS

17. Choosing a data logger Plug-and-play data logger
Built for specific sensor measurements or specific sensor types
Allow only a minimum of configuration
Date/time
Measurement interval
Sensor type
Limited sensor inputs
Low flexibility for sensor types

18. Plug-and-play data loggers
Advantages
Fast configuration
Simple deployment
No/low programming complexity
Simple data collection and analysis
Straight-forward sensor integration
Low power consumption
Price
Disadvantages
Limited sensor types
Limited input ports
Little or no configurability
No event-based sampling
No/little external control

19. Choosing a data logger Measurement and control systems (MCS)
Build for general purpose measurement
Measure most types of voltage, current, pulse, and digital sensors
Highly configurable
Many different measurement and control option
Programming allows for multiple measurement intervals
On board data processing and decision making
High speed measurement
Expandable
Add additional sensor capacity
Accurate
May utilize high resolution signal processing for accuracy

20. Measurement and Control Systems
Advantages
Disadvantages
Configurability
Precision and accuracy
Programmability
Speed
Decision making and control
Data processing
Programming
Configuration
Installation and setup
Power

21. Characteristics to evaluate
Required resolution and range
Thermocouple
0.1o C resolution = 4 mV data logger resolution
50o C range = 2000 mV data logger range
Water content sensor
0.1% VWC ~ 1 mV data logger resolution
100% VWC ~ 1000 mV data logger range
Excitation
Many sensors require a voltage be provided to the sensor
Decagon EC-5 – 2.5 or 3V regulated
Gill WindSonic anemometer – 12V unregulated
Excitation requirements vary mV to 10s of volts
Many data loggers have limited excitation options

22. Characteristics to evaluate (cont.)
Analog to digital converter (ADC)
Voltage and current measurements are made by an ADC
Precision of ADC defines accuracy of the measurement
Defined by bits
i.e. 12 bit ADC  0 to 4095  2.5 V range  0.61 mV/bit
Obviously not good enough for the thermocouple, but good for VWC
24 bit ADC  0 to  2.5 V range  0.15 mV/bit
Good enough for thermocouples
Noise rejection
Multiple sources of ambient electrical noise
60 cycle from electricity, radio frequency

23. Data logger applications
Making the decision
Many choices available
Sometimes confusion trying to decide which one will work the best
Discuss some applications from personal experience
Caveat: Vast majority of my experience is with Decagon and Campbell Scientific data logger
Many other manufacturers that you may consider
Delta-T, Onset, DataTaker, Stevens, Unidata, etc.

24. Rice net carbon exchange
Conditional sampling
Stored 77 different outputs
CO2, H2O concentration (voltage output from IRGA)
Pyranometer, quantum sensor, net radiation (mV)
Water content (pulse count)
Rain gauge (pulse count)
3-D sonic anemometer (digital)
Data downloaded by cell phone (2.5 h away)
5 Marine batteries charged by 6-12V solar panels
2 CR10X dataloggers, 2 MUX, Relay driver
Flexibility, control, programmability, storage, communication

25. Turf grass watering Control based on distributed water content sensors
Turf field with pop-up sprinklers
Decision: things to consider
Control based on distributed water content sensors
VWC at several locations
Threshold values control solenoid values for sprinklers
P&P data logger
Easy to read VWC sensors
Fast installation
Low power requirements
Data easily collected and graphed over radio or cell phone
Often lack control capability
MCS
Required for system control
Large sensor input capacity

26. Distributed field analysis of physical and morphological interactions
Site description
System choice
37 ha research farm
Large topographical variation
Goal
Investigate water, temperature, and EC variation in relation to soil morphology
42 distributed profiles
Measurement at 5 depths
Plug-and-play logging system well suited for distributed networks
Small number of sensors at each site
Radio or cell phone communications
Fast setup
Low power use
No requirement for control or specialized sampling

27. Fast, simple plot measurements
Description
Considerations
Goal
Compare performance of drought tolerant cultivars
Requirements
Soil moisture, temperature in plots
Weather station parameter in central location
Simple deployment
P&P systems require no programming
No specialized sample timing or control
Self contained loggers require no enclosure setup or external power

28. Summary Data loggers simply measure and store electronic signals
Art of instrumentation is to dream up new ways or correlating electronics to science
Data logger choices are numerous
Carefully determine all experimental needs
Evaluate system specifications