Onset S-LWA Specifications

Leaf Wetness Smart Sensor (S-LWA-M003) Manual

The leaf wetness smart sensor is designed to work with HOBO® stations with its plug-in
modular connector. All calibration parameters are stored inside the smart sensor, which
automatically communicates configuration information to the station without the need for any
programming, calibration, or extensive setup. Unlike other leaf wetness sensors, the HOBO leaf
wetness smart sensor does not require any painting or coating—it is ready to use.

Specifications

Measurement Range 0 (dry) to 100% (wet)

Sensor Type Capacitive grid

Interchangeability Between
Sensors (Over the Range
10–90% Wet)

Repeatability ±5%; see Note 1

Leaf Wetness Smart
Sensor

S-LWA-M003

Items Included:

• Mounting bracket

• U-bolt

• Tie wraps

Resolution

Stability (Drift)

Service Life 3 years in typical growth conditions

Operating Temperature Range -40°C to 70°C (-40°F to 158°F)

Environmental Rating Weatherproof

Sensor Construction Materials PVC housing, epoxy potting compound, nylon grommet, FR-4 circuit

Bracket Materials PVC mounting bracket, UV-stable nylon cable ties, zinc dichromate

Bits per Sample 8

Number of Data Channels* 1

Measurement Averaging Option No

Dimensions Sensor grid: 4.7 cm x 5.1 cm (1.8 in x 2.0 in)

Weight (Sensor and Cable) 127 g (4.5 oz)

Weight (Including Mounting
Bracket)

Cable Length Available 3.0 m (9.8 ft)

Length of Smart Sensor
Network Cable*

* A single station can accommodate 15 data channels and up to 100 m (328 ft) of smart sensor cable (the digital

communications portion of the sensor cables).

Note 1 Given the nature of the sensor design and sensor operating frequency, the system has inherent susceptibilities to

Radio Frequency signals. The repeatability specification when subjected to certain RFI environments, such as
those outlined in IEC 61000-4-3 and IEC 61000-4-6, may be significantly reduced.

The system level repeatability will be particularly affected when placed in an electric field of 3 V/m or greater in
the 150 KHz to 1000 MHz range. RFI mitigation practices and physical deployment changes may reduce the
system susceptibility. If deployments are planned in high RFI energy environments, Onset recommends on-site
testing to determine system level repeatability.

±10%

0.59%

< ±5% per year (in typical growth conditions)

board, PVC cable jacket

plated steel U-bolts

Housing: 12.2 cm length x 1.8 cm diameter (4.8 in x 0.7 in)
Mounting bracket: 20 cm x 3 cm x 0.5 cm (8 in x 1.3 in x 0.2 in)

290 g (10.2 oz)

3.0 m (9.8 ft)

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

9826-E MAN-S-LWA

Leaf Wetness Smart Sensor (S-LWA-M003) Manual

Mounting

Placement and Mounting Considerations

• In most applications, the sensor should be mounted in
whichever direction will prolong wetness the longest. For
example, in the Northern hemisphere, orienting the sensor
to face northwest will minimize exposure to solar radiation in
the morning and maximize morning dew exposure.

• The leaf wetness sensor can be tilted to any angle. As the
angle becomes steeper, water will run off the sensor more
easily, reducing the amount of time the sensor stays wet. The
exact angle used is a function of the type of vegetation of
interest. Onset recommends using an angle of more than 15
degrees from horizontal to prevent puddles from forming on
the sensor.

• The leaf wetness bracket can also be mounted to the cross
arm (M-CAA or M-CAB).

• Be sure to secure the sensor cable with cable ties to protect
the cable from damage. Wires should be bound tightly to the
mast to help protect them from getting damaged in severe
weather.

• Do not mount the sensor within two feet of the station case.

• Refer to the station manual and Tripod Setup Guide for more

information regarding setting up stations.

Operation

The leaf wetness smart sensor measures the percentage of the
sensor grid that is wet. A completely dry sensor will record 0%
wetness, while a measurement of 100% wetness corresponds
to the sensor being completely covered with a thin layer of
water.

After prolonged exposure to very hot and wet environments,
the sensor may return to only 1 to 3% wet when dried out, but
given a day or two in a warm, dry environment, the sensor will
recover and return to zero when dry.

IMPORTANT: Do Not Paint the Sensor.

Unlike most other leaf wetness sensors, the leaf wetness smart
sensor is ready to use and should not be coated. Some
manufacturers of leaf wetness sensors recommend painting
their sensors with a flat latex paint to improve the sensor’s
characteristics. These manufacturers supply their sensors
uncoated and require the user to paint it.

Do not coat the HOBO leaf wetness smart sensor. Onset’s
sensor is preconditioned and factory calibrated. Although it is
certainly possible to alter the response of the sensor by
painting it, applying any sort of coating will only reduce its
sensitivity.

Bracket Mounting

Onset recommends that you mount the leaf wetness smart
sensor using the included bracket as shown in the figure below.
To mount the sensor using the bracket:

1. Use the U-bolt to secure the bracket to any 2.5 to 4 cm (1 to

1.6 inch) diameter mast.

2. Use two cable ties to secure the sensor to the bracket. Do
not fully tighten the cable ties.

3. Note that one side of the sensor surface has a visible grid.
The grid side should be facing upwards. Typically the sensor
is mounted at an angle of 15 to 45 degrees from horizontal.

4. Once the desired angle has been set, pull the cable ties tight
and cut off the tag ends.

5. Secure the sensor communications cable with cable ties
between the sensor and data logger.

Typical Mounting of the Leaf Wetness Smart Sensor

Connecting the Sensor to a Station

To connect the sensor to a station, stop the station from
logging and insert the smart sensor’s modular jack into an
available smart sensor port on the station. See the station
manual for details on operating stations with smart sensors.

Calibration

The leaf wetness smart sensor should be field calibrated to
determine the wet/dry transition point. Various types of
vegetation will have varying transition points. The best practice
is to install a station and the leaf wetness smart sensor in the
study area and, while logging data, directly observe the plants
to record the time of day that the vegetation makes the
transition from wet to dry. Read out the station to determine
the percent wetness when the wet/dry transition was
observed. In most cases, this is the value that will best
represent the wet/dry transition point for your study. You will
need to retain this value for use with any third-party software.

Maintenance

The sensor is a capacitive sensor and is less sensitive to
contamination than resistive sensors. However, dust, dirt or other
contaminants on the sensor will retain moisture and that will
ultimately affect the sensor’s performance. You should
periodically inspect the sensor and gently clean the sensor grid
once per year with a non-abrasive rag, mild soap, and fresh water.

Verifying Accuracy

It is recommended that you check the functionality of the Leaf
Wetness smart sensor annually. If the sensor is not providing
accurate data, it may be damaged or broken. If you are unsure
of accuracy, send the smart sensor back to Onset for testing.
Contact Onset or your place of purchase for a Return
Merchandise Authorization (RMA) number and associated costs
before sending it.

1-800-LOGGERS (564-4377) • 508-759-9500
www.onsetcomp.com • [e-mail]

© 2010–2015 Onset Computer Corporation. All rights reserved. Onset and HOBO are trademarks or
registered trademarks of Onset Computer Corporation. All other trademarks are the property of
their respective companies.

9826-E MAN-S-LWA