HOBO U20 Water Level Logger Manual
1-800-LOGGERS 6
www.onsetcomp.com
Redeploying the Logger
If you are redeploying the logger, you must first make sure that
it is launched. If you used the HOBO Waterproof Shuttle to
offload data, the shuttle automatically performs a synchronized
relaunch of the logger so that data is logged on the same
measurement intervals. If you wish to change the launch
settings, you must launch the logger using HOBOware Pro.
The existing suspension can be reused as long as the water
level logger remained in the water and the barometric logger
remained out of the water for the entire test interval. Take a
new reference reading with the date and time as described in
Collecting Data
. Record this information in your field notebook
to use later to calibrate your data, which will zero out any drift
error.
Processing Data using
Barometric Pressure Data
To determine water level using barometric pressure data, use
the
Barometric Compensation Assistant
in HOBOware Pro, as
described below.
If you are using barometric pressure data from a HOBO weather
station, you can use the data file as if it were U20 barometric
data. For data from sources other than Onset products, see
Barometric Data from Other Sources
below.
1.
In HOBOware Pro, open the water depth data file. The
Plot
Setup
window appears.
2.
Uncheck all boxes except
Abs. Pressure
.
3.
Run the Barometric Compensation Assistant.
a.
Click the
Process
button.
b.
Select the water density box that best describes the
water that you are measuring or enter the actual water
density.
c.
Check the
Use a Reference Water Level
box and enter
the reference water level that you measured at the
beginning of the deployment.
d.
Select the date and time from the pull-down menu that
is closest to the recorded date/time for the
measurement. If you measured the depth before
deployment because of pipe size, then select a
date/time after the start of the deployment.
e.
Check
Use Barometric Data file
.
f.
Click the
Choose
button. This will allow you to select the
data file to use for barometric pressure compensation.
g.
Select and open the data file.
h.
Click the
Create New Series
button. A new Plot Setup
window appears.
4.
Select the
Water Level
box and any other series that you
want plotted. Click the
Plot
button to obtain a plot of the
resulting water level data.
Measurement Error
Measurement error can be caused by manual measurement
error, sensor drift, or change in the suspension cable length.
To quantify measurement error (which is ideally zero), compare
the calculated water level at the end of the plot with the water
level measured just before you removed the water level logger.
Barometric Data from Other Sources
Third Party Weather Station or Barometric Logger
If you choose to use barometric pressure from a third party
weather station or barometric logger, you need to convert the
date, time, and pressure data to a text file with special header
requirements. For information on how to set up the text file,
see the HOBOware Help or User Guide. It is easiest to do this
work in EXCEL and then save it as a text file.
Online Weather Station
If you choose to use barometric pressure from an online
weather station, such as the National Weather Service, the
measured barometric pressure is modified to be at sea level.
This sea level pressure is useable since all pressure offsets are
zeroed when you enter the reference measurement.
In the Barometric Compensation Assistant, when you select the
Barometric Data File, select the text file that you generated.
HOBOware Pro will ask for the data format and data separation
characters (tab or comma) and then import the barometric
data.
Maintenance
Protecting the Logger
Important:
Do not attempt to open the logger housing!
Unscrewing the metal nose cone of the logger will cause
serious damage to the pressure sensor and logger electronics.
There are no user serviceable parts inside the case. Contact
Onset technical support if your logger requires servicing.
This logger can be damaged by shock.
Always handle the
logger with care. The logger may lose its calibrated accuracy or
be damaged if it is dropped. Use proper packaging when
transporting or shipping the logger.
Biofouling
Periodically inspect the logger for fouling. Biological growth on
the face of the pressure sensor will throw off the pressure
sensor’s accuracy. Organisms that grow inside the sensor nose
cone and on the sensor itself can interfere with the sensor’s
operation and eventually make the sensor unusable. If the
deployment area is prone to biofouling, check the logger
periodically for marine growth.
Solvents
Check a materials-compatibility chart before deploying the
logger in locations where untested solvents are present.
The logger is shipped with Viton O-rings installed. Viton has an
excellent resistance to most solvents and is suitable for
deployments in water that contain a mixture of most fuels,
solvents and lubricants. However, the Viton O-rings are
sensitive to polar solvents (acetone, ketone), ammonia, and
brake fluids.
