Aimed at hydrologists, ecologists, water works professionals and others who need to record changing water levels, this 45-minute webinar will examine a range of topics, including: -Choosing the right water level monitoring product for your application -Demystifying water level logger accuracy specifications -Deploying water level loggers in the field: field-proven methods and techniques

1. Critical Success Factors in
Water Level Monitoring
May 16, 2006
Presenters:
Richard Kaiser, Onset Engineer and Water
Level/Flow Monitoring Specialist
Nick Lowell, Onset Chief Engineer
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2. Topics for Discussion
I. Considerations in choosing a pressure-based
water level logger
 Comparing specifications
 Vented vs. non-vented
 Materials
 Software & communications
II. Deployment tips and considerations
 In water wells
 In streams, lakes, estuaries, channels and
wetlands
III. Questions
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3. Choosing a Water Level Logger
Demystifying Accuracy Specifications
Total Error: .4% (typical)
Does the specified accuracy
relate to the sensor or entire
logger? Sensor 0.1%
• Potential sources of logger
accuracy errors: ADC/Voltage
reference 0.1%
– Sensor error
– ADC/Voltage reference
– Temperature error
Thermal 0.1%
– Case/Sensor mounting
• Barometric pressure
Case/
Sensor 0.1%
mounting
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4. Choosing a Water Level Logger
Choosing a Logger
Demystifying Accuracy Specifications
Do sensor accuracy
specifications reflect real-
world effects such as:
ACCURACY TEST
• Single point vs. entire 35
pressure range 30
25
• Linearity
PSI
20
• Repeatability 15
10
• Hysteresis 5
11/17/2005 11/17/2005 11/17/2005 11/17/2005 11/17/2005 11/17/2005 11/17/2005
13:40 13:48 13:55 14:02 14:09 14:16 14:24
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5. Choosing a Water Level Logger
Demystifying Accuracy Specifications
Do temperature variations
cause additional error TEMP DEPTH ERROR at 20 PSIA
outside the accuracy spec?
FIGURE 2
0.1000
DEPTH ERROR (% of FS)
0.0500
• Temperature changes affect 0.0000
all pressure-based sensors -0.0500
HOBO U20
EXAMPLE
• Compensation for temp -0.1000
changes required -0.1500
• Temp should be stabilized
-0.2000
0 10 20 30 40
prior to reference
TEMPERATURE C
measurement
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6. Choosing a Water Level Logger
Demystifying Accuracy Specifications
What is the impact of drift errors?
LARGE DRIFT ERROR EXAMPLE
• All pressure sensors drift over time 17
• Important in long-term deployments 16.5
where no recent reference 16
PSI
measurements are available 15.5
• Drift is quantifiable through manual 15
measurements at beginning and end of 14.5
12/9/04 12/19/04 12/29/04 1/8/05 1/18/05 1/28/05 2/7/05
deployments DATE / TIME
ACTUAL DRIFT ERROR
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7. Choosing a Water Level Logger
Demystifying Accuracy Specifications
Logger calibration and testing
considerations:
• Has the logger been calibrated and
tested against NIST-traceable
standards?
• Has the logger been factory-calibrated
over multiple points?
– 1-point eliminates offset errors
– 2-point eliminates offset and gain
errors
– Multi-point eliminates offset, gain
and linearity errors
– Pressure/temperature calibration
ensures accuracy when
temperature changes
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8. Choosing a Water Level Logger
Vented vs. Non-Vented
High-level considerations:
• All pressure-based readings
require barometric compensation
• Vented loggers rely on built-in
vent tubes
• Non-vented loggers use
Vented logger
barometric pressure data from
external source
Non-vented logger
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9. Choosing a Water Level Logger
Vented vs. Non-Vented
Vented Loggers Non-Vented Loggers
• Highest accuracy possible • Easy to deploy
• More expensive • Fewer maintenance issues
• Significant • Barometric pressure data
reliability/maintenance issues required
- Problems from condensation
• Theoretically not as accurate
- Wider-range sensor to measure
- Must be above flood level
same depths
- Bulky, hard to transport, conceal
- Error potential with separate
- Easily damaged, hard to clean
barometric pressure measurement
- Requires desiccant replacement
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10. Choosing a Water Level Logger
Logger Materials Considerations
• Will the environment corrode the
logger?
• Will the logger and/or vent tube
contaminate the well water? (is
it easy to clean?)
• Could the logger be frozen in
ice?
• Is there a temperature extreme?
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11. Choosing a Water Level Logger
Logger Materials Considerations
Housing: 316 stainless steel is suitable for many applications (stable, non-
corrosive, non-contaminating)
Titanium is recommended in salt water or other corrosive
environments
Sealed bladder is an alternative option
Must also consider other wetted materials such as o-rings, end
caps, and vent tubes
Sensor: Stainless steel sensors are common but can be damaged by
improper handling, shock, corrosion or expansion of
freezing water
Properly-mounted ceramic sensors are more robust and not damaged
by freezing, corrosion or shock
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12. Choosing a Water Level Logger
Communications Considerations
• Does the logger offer a USB or serial
interface?
• Is the interface optical or mechanical?
• Is real-time data necessary?
• How often do loggers need to be offloaded?
• What are the options for data offload?
- Bring logger back to PC
- Take laptop into the field
- Data shuttle
- Telemetry
• Will the logger need to be removed or is
there an access cable option?
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13. Choosing a Water Level Logger
Software Considerations
• Is the software easy-to-use
and intuitive?
- Set up
- Readout and Level
Conversion
- Plotting
- Data Export
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14. Choosing a Water Level Logger
Software Considerations
Set-up
• Is logger setup
intuitive and
repeatable?
• What sampling
modes are available?
- Multiple user-defined
logging intervals
- Logarithmic sampling
- Event based
• How do I synchronize
multiple loggers?
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15. Choosing a Water Level Logger
Software Considerations
Readout and
converting pressure
to water level
• Is readout fast and
reliable?
• Can I enter my own fluid
density?
• How do I enter a
reference level?
• Can I import barometric
pressure files from other
loggers or local weather
stations? (Not required
for vented loggers.)
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16. Choosing a Water Level Logger
Software Considerations
Plotting
• Can I get a quick preview
view of the data?
• Is the plot format easy to
manipulate?
• Does the software allow for
plotting of multiple series?
• Can I easily do
min/max/average data
filtering?
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17. Choosing a Water Level Logger
Software Considerations
Data Export
• How do I export data from the
logger software to my
groundwater modeling software
package?
• Does the export function allow for
flexibility in data formats?
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18. Choosing a Water Level Logger
Deployment Tips and Considerations
In general…
• Use stranded, stainless-steel wire
that will not stretch or kink
during deployment
(www.onsetcomp.com/water_level_tech_notes)
• Use Teflon-coated wire where
ease-of-cleaning is important
• Be careful lowering the logger
into water to avoid sensor shock
• Always take reference
measurements to optimize
accuracy
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19. Choosing a Water Level Logger
Deployment Tips and Considerations
Water Well Deployments
• Deploy logger, wait 10 minutes for
temperature stabilization, take
manual measurement
• Synchronize PC and field clocks
• Take manual measurement before
removing or offloading logger to
check for drift
• Take additional manual measurement
at redeployment
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20. Choosing a Water Level Logger
Deployment Tips and Considerations
Deployments in streams,
lakes, estuaries, channels
and wetlands
• Typically, build a stilling well with
PVC schedule 40 conduit and slotted
pipe
• Take manual measurement at fixed
lake or stream location, record date
and time
• Repeat manual measurements at
beginning and end of each
deployment
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21. Choosing a Water Level Logger
Deployment Tips and Considerations
Stilling Well Examples
For more information see www.onsetcomp.com/water_level_tech_notes
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22. Choosing a Water Level Logger
Deployment Tips and Considerations
General Deployment Tips
• Be sure to log temperature as well as
pressure for accurate temperature
compensation
• Consider mounting logger in pipe within
well
• Deploy barometric pressure logger in
area where temperature fluctuations
are minimal, such as in a well
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23. Questions and Discussion
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24. Thank You!
For additional information, contact:
Richard Kaiser, Onset Computer Corp.
richard_kaiser@onsetcomp.com
Nick Lowell, Onset Computer Corp.
nick_lowell@onsetcomp.com
www.onsetcomp.com/webinar/waterlevel
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