Onset U26-001 Operating Manual

HOBO® Dissolved Oxygen Logger (U26-001) Manual

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The HOBO Dissolved Oxygen logger is a standalone logger that uses RDO® Basic Technology
to measure dissolved oxygen (DO). The logger has an optical sensor that provides 0.2 mg/L
accuracy. The logger also features an easily replaceable sensor cap and an integrated
temperature sensor. Using HOBOware® software for logger setup and a HOBO Waterproof
Shuttle for quick data offload, this logger is easy to deploy in both freshwater and saltwater
environments making it an ideal tool for environmental impact studies as well as ecological
and oceanographic research. Using the data offloaded from the logger, the HOBOware
Dissolved Oxygen Assistant can calculate percent saturation and salinity-adjusted DO
concentration as well as correct for measurement drift from fouling (additional meter or
logger measurements required).

Specifications

HOBO Dissolved Oxygen Logger with

Included Calibration Boot and
Sponge (Shown Wet in Photo)

HOBO Dissolved
Oxygen Logger

U26-001

Included Items:

• Dissolved Oxygen
Sensor Cap

• Protective Guard

• Calibration Boot and

Sponge

Required Items:

• Coupler (COUPLER-2-C)
with USB Optic Base
Station (BASE-U-4) or
HOBO Waterproof Shuttle
(U-DTW-1)

• HOBOware Pro 3.3.1 or
later

Accessories:

• Replacement Dissolved
Oxygen Sensor Cap
(U26-RDOB-1)

• Anti-Fouling Guard
(U26-GUARD-2)

• Sodium Sulfite
(U26-CAL-SOL)

You May Also Need:

• For salt water, salinity or
conductivity measurements
are required; HOBO
Conductivity/Salinity
Logger (U24-002-C)
recommended

• For percent saturation,
barometric pressure is
required; HOBO Water
Level Logger (U20-001-0x
or U20L-0x) recommended

Dissolved Oxygen

Sensor Type Optical (dynamic luminescence quenching)

Measurement Range 0 to 30 mg/L

Calibrated Range 0 to 20 mg/L; 0 to 35°C (32 to 95°F)

Accuracy ±0.2 mg/L up to 8 mg/L; ±0.5 mg/L from 8 to 20 mg/L

Resolution 0.02 mg/L

Response Time To 90% in less than 2 minutes

DO Sensor Cap Life 6 months (cap expires 7 months after initialization)

emperature

Temperature Measurement/
Operating Range

Temperature Accuracy 0.2°C (0.36°F)

Temperature Resolution 0.02°C (0.04°F)

Response Time To 90% in less than 30 minutes

Logger

Memory 21,700 sets of DO and temperature measurements (64 KB total

Logging Rate 1 minute to 18 hours

Time Accuracy ±1 minute per month at 0 to 50°C (32 to 122°F) (see Plot A)

Battery 3.6 V lithium battery; factory replaceable

Battery Life 3 years (at 5 minute logging)

Download Type Optical

Depth Rating 100 m (328 ft)

Buoyancy Salt water: 178 g (6.27 oz) negative

Wetted Materials Black Delrin®, PVC, EPDM o-rings, silicon bronze screws; rated

Size 39.6 mm diameter x 266.7 mm length (1.56 x 10.5 inches);

Weight 464 g (16.37 oz)

Environmental Rating IP68

-5 to 40°C (23 to 104°F), non-freezing

memory); logging stops when memory fills

Fresh water: 185 g (6.52 oz) negative

for saltwater use

mounting hole 7.88 mm (0.31 inches)

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

Plot A: Time Accuracy

15603-J MAN-U26x

HOBO Dissolved Oxygen Logger (U26-001) Manual

Logger Components and Operation

Communications Cap/Lanyard

Temperature Sensor

(Inside Logger Housing)

Protective Guard

DO Sensor

Communications Cap/Lanyard. This removable cap protects
the optical communications window. An LED in the
communications window of the logger confirms logger
operation. When the logger is logging, the LED blinks once
every four seconds. The LED also blinks when the logger is
recording a sample. When the logger is awaiting a start because
it is configured to start “At Interval,” “On Date/Time,” or “Using
Coupler,” the LED blinks once every eight seconds until logging
begins. See Connecting the Logger to a Computer or
Waterproof Shuttle for details on using the communications
window.

Mounting Hole. Use the hole on the communications cap to
mount the logger. See Deploying the Logger for more
information.

Alignment Notch for Coupler. Use this notch to align the
coupler when communicating with the logger. See Connecting
the Logger to a Computer or Waterproof Shuttle for more
information.

DO Sensor. This optical sensor measures dissolved oxygen using
RDO® Basic Technology. It is shipped with a red dust cap that
must be replaced with a green sensor cap that lasts for six
months plus a one-month grace period. See Installing the
Sensor Cap for more details.

Protective Guard. This removable guard protects the DO
sensor. Unscrew it to install or replace the sensor cap as
needed. See Installing the Sensor Cap for more details.

Temperature Sensor. This built-in sensor (not visible in
diagram) measures temperature.

WARNING: This logger can be damaged by mechanical

shock. Always handle the logger with care. The logger may be
damaged if it is dropped. Use proper packaging when
transporting or shipping the logger.

Do not attempt to open the logger case or sensor housing.
Disassembling of the logger case or sensor housing will cause
serious damage to the sensor and logger electronics. There are
no user-serviceable parts inside the case. Contact Onset
Technical Support at 1-800-LOGGERS (1-800-564-4377) or an
authorized Onset dealer if your logger requires servicing.

Alignment Notch

for Coupler

Mounting

Hole

Installing the Sensor Cap

The logger ships with a replaceable sensor cap that provides six
months of continuous use. Once the cap is initialized, an
internal clock within the logger will count down until the sensor
cap expiration date. When the sensor cap expires, you will need

).

to replace it with a new cap (U26-RDOB-1

The sensor cap is
intended for six months of actual deployment, but the
expiration date is seven months from the date the cap was
initialized. This allows for any time needed between launching
the logger and physically deploying as well as extra time in case
you are not able to get the logger after exactly six months of
deployment. To install the sensor cap:

1. Unscrew the protective guard covering the DO sensor (see

diagram at left).

2. Remove the red dust cap that protects the sensor during

shipping.

3. Take the green sensor cap out of the canister.

4. With the flat part of the DO sensor pointing down and the

green sensor cap oriented with the arrow up, slide the sensor
cap over the sensor until it snaps in place. The cap should be
snug against the logger housing without any gaps. (If you see a
gap, the protective guard installed in the next step will close
the gap by pushing the sensor cap down into place.)

Sensor cap with arrow
positioned up; slide over DO
sensor until it snaps in place

DO sensor, flat
side down

5. Screw the external protective guard back on until tight.

IMPORTANT: The sensor cap expires 7 months (to the day)
after it has been initialized. The logger will record a value of ­888 mg/L at each logging interval after the cap has expired.
Initialization occurs automatically when the cap is installed
while the logger is logging. You can also initialize it from the
Status window in HOBOware or when using the Lab Calibration
tool. To see when the sensor cap expires after being initialized,
check the Status in HOBOware for the expiration date. The cap
also has a shelf life; check the “Install By” date printed on the
canister.

Connecting the Logger to a Computer or
Waterproof Shuttle

To connect the logger to a computer, use either the Optic USB
Base Station (BASE-U-4) or HOBO Waterproof Shuttle (U-DTW-

1) with a coupler (COUPLER2-C). To launch and read out the
logger in the field, use one of these three methods:

• Laptop computer with Optic USB Base Station (BASE-U-4)
and coupler (COUPLER2-C)

• HOBO Waterproof Shuttle (U-DTW-1, Firmware Version

3.2.0 or later) and coupler (COUPLER2-C)

1-800-LOGGERS 2 www.onsetcomp.com