HOBO U24 Conductivity Logger (U24-001) Manual
1-800-LOGGERS 3 www.onsetcomp.com
3. Verify the status. Click the status button on the toolbar and
observe that the temperature is near the actual
temperature.
4. Launch the logger with the correct range. Refer to the
specifications on page 1 for both calibrated and extended
ranges (the calibrated ranges are also printed on the logger
housing). The logger will not record readings outside of the
extended range selected. If in doubt on the range needed
for your deployment, or for environments with wide
fluctuations, select both ranges. This will shorten the
deployment duration from 18,500 samples to 14,400
samples per parameter (not logging battery voltage). See
the HOBOware User’s Guide or online help for details on
launching.
Note: Logging battery voltage is not essential because you can
check the battery using the Status screen at launch or readout
of the logger. Logging the battery voltage will reduce the
number of conductivity and temperature readings you can log.
Taking Calibration Readings
It is important to take temperature and conductivity calibration
readings with a portable conductivity meter at both the
beginning (launchtime) and end of a deployment (readout)
because these readings are necessary for data calibration and
to compensate for any measurement drift during deployment.
The conductivity calibration readings should be the actual
conductivity without temperature compensation (not in specific
conductance at 25°C), and should be recorded in a notebook
with the time and location of the reading. You will use these
readings in the HOBOware Conductivity Assistant to calibrate
the readings for the corresponding data series offloaded from
the logger.
There are three methods for obtaining accurate calibration
readings. The first method involves placing the meter’s probe
into the water next to the logger. The second method involves
placing the logger and meter probe in a field water sample in a
jar. In both methods, the conductivity meter probe must be
close to the data logger—but not touching—so that it is
measuring water at the same conductivity as the logger. The
third method involves taking a sample back to the office to
measure with a meter there.
If the conductivity in the water where the logger is deployed is
stable and it is easy to reach the logger, then you can obtain
calibration readings by placing the probe directly into the water
next to the logger. However, taking calibration readings some
locations, such as in wells, can be difficult because it may be
hard to get the meter probe next to the logger. In these
instances, you should fill a jar with a water sample from where
the logger is deployed to take the calibration readings. To
obtain the water sample from a well or stilling well, you can use
a bailer with a diameter that is small enough to fit down the
well.
Note: Some salt residue may remain on the logger from factory
calibration. Carefully rinse the logger in distilled water or clean
freshwater to remove any residual salt before taking your first
calibration readings.
Method 1:
Taking readings directly in the water (recommended for
locations with access for the field meter probe and with
conductivity that is stable)
1. If you have just deployed the logger, allow enough time for
the logger temperature to stabilize for the best accuracy
(approximately 15 minutes).
2. Gently tap the logger to remove any bubbles from the
surface. Tug the cable if you cannot reach the logger itself.
3. Measure the temperature and actual conductivity with the
field meter, making sure the meter probe readings stabilize
per the meter’s specification. Record the values, time, and
location of the readings in a field notebook for use later in
the HOBOware Conductivity Assistant.
Method 2:
Taking readings in a jar (recommended for readings in wells or
in water with rapidly changing conductivity, such as areas
with saltwater and freshwater mixing)
1. Take a sample of water in a jar that is large enough to hold
both the logger and the probe from a portable conductivity
meter, leaving an inch of space between the probe and the
logger. For wells, use a bailer to obtain the water sample.
2. Leave the logger and the meter probe submerged in this jar
of water long enough so they reach temperature
equilibrium and the logger has logged at least three
readings (allow at least 15 minutes for the best accuracy).
(Three readings are necessary because this will help you
identify which readings were taken while the logger is in the
jar.)
3. Measure the temperature and actual conductivity with the
field meter. Record the values, time, and location of the
reading in a field notebook for use later in the HOBOware
Conductivity Assistant.
4. When using the Conductivity Assistant, look for the spot in
the data where there are three similar readings in a row
and link the last of those readings to the meter reading.
(The time you noted may be slightly different than the
logger time so looking for the three similar readings will
help isolate the correct reading.) The Conductivity Assistant
uses that value to calibrate the specific conductance and
salinity readings for that data series.
Method 3:
Taking a sample back to the office in a sealable jar to measure
there (recommended for locations with conductivity that is
stable when you do not have a field meter or it is not
convenient to access the logger)
1. Place a sample of the water taken from next to the logger in
a jar and immediately seal it to ensure that none of the
water evaporates. This allows the specific conductance and
salinity of the sample to be maintained, which in turn
results in usable temperature and conductivity readings
when you measure it with the meter at a later time.
2. Write down the time you take the sample for use later in
the HOBOware Conductivity Assistant.
