Maintenance; Verifying Accuracy; Battery Information - Hobo MX Series Manual

Maintenance

The logger requires the following periodic maintenance to
ensure optimal operation:
• Protect the logger. This logger can be damaged by shock.
Always handle the top end and sensor end with care. The
sensors may lose their calibrated accuracy or can be
damaged if dropped. Use proper packaging when
transporting or shipping the logger.
Important: Do not attempt to open the sensor end
housing! Unscrewing the nose cone of the sensor end will
cause serious damage to the pressure sensor and logger
electronics. There are no user serviceable parts inside the
sensor end. Contact Onset Technical Support if the sensor
end requires servicing.
• Periodically inspect the logger for biofouling. Biological
growth on the face of the pressure sensor will impact 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.
• Be careful of solvents. Check a materials-compatibility
chart against the wetted materials listed in the
Specifications table before deploying the logger in
locations where untested solvents are present. The logger
has Viton and Buna-N O-rings, which are sensitive to polar
solvents (acetone, ketone), ammonia, chlorine, and brake
fluids. The sensor is housed in an acetal end cap. Acetal is
resistant to most solvents, fuels, and lubricants.
Compensating for Drift
All pressure sensors drift over time. The drift for the pressure
sensors and electronics in the logger is less than 0.5% FS (worst
case) per year. In most applications, drift is not a significant
source of error because the offset created by any drift is zeroed
out when you enter the reference water level in the app at the
beginning of each deployment. In effect, you are re-zeroing the
sensor each time you apply a reference reading to the data file.
Pressure sensor drift matters more when absolute pressure
values are needed, or if there are no recent reference level or
depth measurements available. For example, if the logger is
deployed for one year and no new reference level readings are
taken during the deployment, it is possible that the sensor
could have drifted as much as 0.5% FS by the end of the
deployment.
It is possible to determine the actual amount of drift during a
deployment if a reference level is taken at the beginning and
the end of a long-term deployment. The results of applying the
two different reference levels (once at the beginning of the
data file and again at the end of the data file) can be compared.
Any difference between the files indicates the amount of
sensor drift (assuming accurate reference levels). See Reading
Out the Logger for changing the reference water level in the
data file.
1-508-759-9500 (U.S. and International)
1-800-LOGGERS (U.S. only)
HOBO MX Water Level Logger (MX2001-0x) Manual

Verifying Accuracy

You can check the differential accuracy of the logger for water
level measurements by deploying the logger's sensor end at
two depths and comparing the difference in level readings in
the data files. When verifying the accuracy this way, be sure to
allow the sensor's temperature to stabilize at each depth.
You can check the absolute pressure accuracy by using the two
pressure sensors in the logger. Pull up the sensor end that is in
the water so that both the absolute and differential sensors are
in the air. Check the differential pressure with the app. The
differential pressure should be zero or less than the sum of the
error for the two sensors.

Battery Information

The logger requires two user-replaceable AA 1.5 V alkaline
batteries for operation at the extreme ends of the logger
operating range. Expected battery life varies based on the
ambient temperature where the logger is deployed, the logging
or sampling interval, frequency of offloading and connection to
the mobile device, number of channels that are active, alarm
duration, use of burst mode or statistics logging, and battery
performance. New batteries typically last 1 year with logging
intervals greater than 1 minute. Deployments in extremely cold
or hot temperatures, a logging interval faster than 1 minute, or
a sampling interval faster than 15 seconds can impact battery
life. Estimates are not guaranteed due to uncertainties in initial
battery conditions and operating environment.
To install or replace the batteries:
1. Before changing the batteries, stop the logger and offload
any data.
2. Disconnect the cable.
3. Unscrew the end cap on the top end. Push the board out
from the cable end and then pull out the printed circuit
board.
4. Remove old batteries and wipe the contacts with a lint-free
cloth to clean any debris. Apply a small amount of fresh
dielectric grease to the contacts and the battery terminals
on the new batteries.
5. Insert two AA batteries observing polarity as shown on the
board. A slight curvature in the printed circuit board is
normal when the batteries are installed. Reinsert the board.
Remove board and install batteries
11
Unscrew end cap
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