Onset U20-001-04-TI, HOBO U20 User Manual

HOBO® U20 Water Level Logger
(Part # U20-001-04-Ti)

Inside this package:

• HOBO U20 Water Level Logger

• Calibration certificate

The HOBO Water Level Logger is designed to measure water level in wells,
rivers, streams, lakes, estuaries, and tidal areas. The logger uses a
maintenance-free absolute pressure sensor and features a durable titanium
housing and ceramic pressure sensor. The logger uses precision electronics to
measure pressure and temperature. Using a reference water level, the
HOBOware

®

software automatically converts the pressure readings into
water level readings. Furthermore, the software supports compensation for
temperature, fluid density, and barometric pressure. The logger has enough
memory to record over 21,700 combined pressure and temperature
measurements.

The logger uses an optical USB communications interface (USB-Optic Base

Doc #11219-A, MAN-U20-001-04-Ti
Onset Computer Corporation

Thank you for purchasing a HOBO data logger. With
proper care, it will give you years of accurate and
reliable measurements.

Station, Part # BASE-U-4, with COUPLER2-B) for launching and reading
out the logger. The optical interface allows the logger to be offloaded without
breaking the integrity of the seals. The USB compatibility allows for easy
setup and fast downloads.

HOBOware software is also required for logger operation. Visit
www.onsetcomp.com for compatible software.

Specifications

Pressure Sensor

Operation range

Factory calibrated range 69 to 145 kPa (10 to 21 psia), 0° to 40°C (32° to 104°F)
Burst pressure 310 kPa (45 psia) or 18 m (60 ft) depth

Water level accuracy*

Raw pressure accuracy**
Resolution < 0.014 kPa (0.002 psi), 0.14 cm (0.005 ft) water
Pressure response time 90% < 1 second
Thermal response time (90%)† Approximately 10 minutes in water to achieve full temperature compensation of the pressure sensor

* With accurate reference water level measurement and Barometric Compensation Assistant data
** Absolute pressure sensor accuracy includes all pressure drift, temperature, and hysteresis-induced errors
† Maximum error due to rapid thermal changes is approximately 0.5%

Temperature Sensor
Operation range -20° to 50°C (-4° to 122°F)
Accuracy 0.37°C at 20°C (0.67°F at 68°F), see Plot A
Resolution 0.1°C at 20°C (0.18°F at 68°F) (10-bit), see Plot A
Response time (90%) 3.5 minutes in water (typical)
Stability (drift) 0.1°C (0.18°F) per year
Logger
Real-time clock ± 1 minute per month 0° to 50°C (32° to 122°F)
Battery 2/3 AA, 3.6 Volt Lithium, factory-replaceable
Battery life (typical use) 5 years with 1 minute or greater logging interval

Memory (non-volatile)

Dimensions

Weight Approximately 140 g (4.8 oz)
Wetted materials Titanium, Viton® o-rings, acetyl cap, ceramic sensor

Shock/drop Logger is sensitive to shocks. Handle with care and avoid any impact. Always use proper packaging when shipping the logger.

Logging interval

Launch modes Immediate start and delayed start

Offload modes Offload while logging; stop and offload

Battery indication Battery voltage can be viewed in status screen and optionally logged in datafile. Low battery indication in datafile.

0 to 145 kPa (0 to 21 psia); approximately 0 to 4 m (0 to 13 ft) of water depth at sea level, or 0 to 7 m (0 to 23 ft) of
water at 3,000 m (10,000 ft) of altitude

Typical error - 0.075% FS, 0.3 cm (0.01 ft) water
Maximum error - 0.15% FS, 0.6 cm (0.02 ft) water

0.3% FS, 0.43 kPa (0.063 psi) maximum error

2

Accuracy Resolution

1.5

1

Accuracy/ Resoluti on (°C)

0.5

64K bytes memory (approx. 21,700 pressure and temperature
samples)

2.46 cm (0.97 inches) diameter, 15 cm (5.9 inches) length;
mounting hole 6.3 mm (0.25 inches) diameter

0

-20 0 20 40

Temperature (°C)

Plot A

Fixed-rate or multiple logging intervals, with up to 8 user-defined logging intervals and durations; logging intervals from 1
second to 18 hours. Refer to HOBOware software manual.

The CE Marking identifies this product as complying with the relevant directives in the European Union (EU).

© 2006 Onset Computer Corporation
Part #: MAN-U20-001-04-Ti, Doc #: 11219-A

HOBO U20 Water Level Logger

Connecting the logger

The HOBO Water Level Logger requires a coupler (Part #
COUPLER2-B) and USB Optic Base Station (Part # BASE-U-4) or
HOBO Waterproof Shuttle (Part # U-DTW-1) to connect to the
computer.

1. Install the logger software on your computer before proceeding.

2. Follow the instructions that came with your base station or shuttle
to attach the base station or shuttle to a USB port on the computer.

3. Unscrew the black plastic end cap from the logger by turning it
counter-clockwise.

4. Attach the coupler to the base station or shuttle, then insert the
logger into the coupler with the flat on the logger aligned with the
arrow on the coupler label. Gently twist the logger to be sure that it
is properly seated in the coupler (it should not turn).

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 and excessive marine growth on the logger will

compromise 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.

• 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.

− The black acetyl cap is provided to help protect the

communications window. Acetyl is resistant to most solvents,
fuels, and lubricants.

− The polycarbonate communications window is sealed as an

additional barrier to water and dirt entering the logger housing.

5. If you are using the HOBO Waterproof Shuttle, briefly press the
coupler lever to put the shuttle into base station mode.

6. If the logger has never been connected to the computer before, it
may take a few seconds for the new hardware to be detected by the
computer.

7. Use the logger software to launch the logger.

8. You can check the logger’s status, read out the logger while it
continues to log, stop it manually with the software, or let it record
data until the memory is full.

Refer to the software user’s guide for complete details on launching,
reading out, and viewing data from the logger, including multiple
logging intervals and barometric compensation.

Important: USB communications may not function properly at
temperatures below 0°C (32°F) or above 50°C (122°F).

Note: The logger consumes significantly more power when it is

“awake” and connected to a base station or shuttle. To conserve
power, the logger will go into a low-power (sleep) mode if there has
been no communication with your computer for 30 minutes. To wake
up the logger, remove the logger from the coupler, wait a moment,
then re-insert the logger.

Note: The first time you launch the logger, the deployment number
will be greater than zero. Onset launches the loggers to test them prior
to shipping.

Protecting the logger

• Important! Do not attempt to open the logger housing!

Unscrewing the titanium nose cone of the logger will cause serious
damage to the pressure sensor and logger electronics. There are no

Operation

A light (LED) in the communications window of the logger confirms
logger operation. The following table explains when the logger blinks
during logger operation:

When: The light:

The logger is logging Blinks once every one to four seconds (the

The logger is awaiting a start
because it was launched in
Start At Interval or Delayed
Start mode

shorter the logging interval, the faster the
light blinks); blinks when logging a
sample

Blinks once every eight seconds until
logging begins

Sample and event logging

The logger can record two types of data: samples and events. Samples
are the sensor measurements recorded at each logging interval (for
example, the pressure every minute). Events are independent
occurrences triggered by a logger activity, such as Bad Battery or Host
Connected. Events help you determine what was happening while the
logger was logging.

The logger stores 64K of data, and can record over 21,700 samples of
pressure and temperature.

Barometric Compensation

The HOBO Water Level Logger records absolute pressure, which is
later converted to water level readings by the software. In this
application, absolute pressure includes atmospheric pressure and water
head. Atmospheric pressure is nominally 100 kPa (14.5 psi) at sea
level, but changes with weather and altitude.

Left uncompensated, barometric variations could result in errors of

0.6 m (2 ft) or more. To compensate for barometric pressure changes,
you can use another HOBO Water Level Logger as a barometric
reference. The 0-4 m (0-13 ft) HOBO Water Level Logger
(U20-001-04) is a good barometric reference due to its smaller range,

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