This paper highlights results from Onset's tests of the HOBO Water Level logger
and comparable loggers from two competitors. Vendors specify water
level data loggers in different ways, and we felt it would be valuable
to compare accuracy under identical test conditions. All loggers tested
have a 30-ft measurement range. Our testing concluded that while the
data loggers have similar accuracy at a fixed temperature, the HOBO
Water Level Logger had significantly better accuracy when there were
changing temperatures. See the detailed test results below.
Vendor's Specified Accuracy:
| Product | Specified Accuracy | Qualifications |
| HOBO® Water Level Logger | ±0.015 ft |
over the factory-calibrated range 0 to 40 °C (32 to 104 °F) |
| Competitor 1 | ±0.016 ft |
with automatic temperature compensation, but no range specified |
| Competitor 2, Model A | ±0.033 ft |
over the factory-calibrated range 0 to 40 °C (32 to 104 °F) |
| Competitor 2, Model B | ±0.016 ft |
over the factory-calibrated range 0 to 40 °C (32 to 104 °F) |
Accuracy at a Constant Temperature
We tested the water level loggers in a constant temperature environment
to collect data for accuracy deviation over a range of depths.
The HOBO® Water Level logger
performed well in this test. The worst case error for the HOBO logger
was 0.013 feet, while the worst case errors for the competitive loggers
were 0.016, 0.027 and 0.029 feet respectively.
Temperature Compensation Accuracy
Accurate performance over temperature is particularly important for
applications with varying water temperatures, such as streams, wetlands
and tidal areas. We tested the water level loggers for accuracy across a
range of temperatures.
The worst case error for the HOBO® Water Level logger
in this test was 0.010 feet, while the worst case errors for the
competitive loggers were 0.100, 0.023 and 0.077 feet respectively.
The HOBO was within its accuracy specification across the full range of
temperatures tested, measuring 10 times more accurately than the
Competitor 1 logger at 35 °C.
Barometric Pressure Logger Accuracy
We tested the HOBO® Water Level Logger's
barometric pressure sensor against dedicated barometric pressure
loggers from both competitors. The graph below shows the stability of
the HOBO Water Level logger's sensor over the same range of barometric
pressure as those dedicated loggers.
Measuring accurately over temperature is particularly important for
barometric pressure loggers, since air temperatures can vary widely.
When tested, the HOBO logger had accuracy similar to that of the two
competitors' dedicated barometric pressure loggers when tested at a
constant temperature.
For the temperature test, the HOBO and Competitor 2 had similar accuracy
(0.0085 and 0.0095 feet of error respectively), while the logger from
Competitor 1 had over twice as much error (0.0215 feet).
Other Advantages of the HOBO Water Level Logger:
The HOBO Water Level Logger has Guaranteed Accuracy
Onset guarantees the accuracy performance of HOBO U20 Water Level
Loggers by providing a 3-point calibration certificate with every
logger, showing measured accuracy versus a NIST-traceable standard.
The HOBO Water Level Logger uses a Robust Sensor
The HOBO U20 Water Level Logger
uses a ceramic sensor, while Competitor 1's logger uses a stainless
steel sensor. Stainless steel sensor diaphragms are the thickness of
aluminum foil and are sensitive to any kind of shock. Even the shock
from hitting water too hard can be enough to damage this type of
diaphragm. Stainless steel sensors can also be damaged in freezing
water, while ceramic sensors survive and continue to operate once the
water thaws. Ceramic sensors are also suitable for use in salt water,
while stainless steel sensors will corrode. Competitor 1's logger
housing is protected by a zirconium coating; however, if scratched, this
will actually increase the corrosion of the underlying stainless steel.
For loggers that will be deployed in a corrosive environment, the best
option is the titanium version of the HOBO Water Level Logger.
The HOBO Water Level Logger has a Factory-replaceable Battery
The competitive loggers' batteries are not replaceable. Although the
competitive loggers claim a 10-year battery life, when they are used at
fast sampling rates or at higher temperatures, their batteries can be
depleted in months vs. years.
The HOBO Water Level Logger is part of the HOBO System
The HOBO Water Level Logger works seamlessly with other components in
the HOBO System, including the HOBO waterproof shuttle for easy field
offload and HOBOware software, well-known for its powerful graphing and
analysis capabilities.
The HOBO Water Level Logger uses reliable optic communications
The completely sealed housing and optic communications in the HOBO Water
Level Logger provide a reliable, easy way to offload data quickly to
either the HOBO Waterproof Shuttle or a computer. Other loggers require
additional mechanical connectors and spring-loaded pins for offloading,
which can become corroded. The system uses USB communication to the
computer for fast and convenient data offload.
Easy Import of Barometric Pressure Data
The HOBOware Barometric Compensation Assistant accepts barometric data from another HOBO Water Level Logger, a HOBO Weather Station or HOBO Micro Station, or text data from a nearby weather station.
HOBO Loggers are Proven in Field Use
Used in more than one million deployments worldwide, HOBO data loggers
have earned a reputation for reliable operation in harsh field
conditions.
Data File Compatibility
HOBOware software is compatible with all HOBO Water Level Logger files
and allows import of data from other manufacturers' water level loggers
as well.
The HOBO Water Level Logger is the Best Value
The HOBO Water Level Logger
provides accurate and reliable measurements at an affordable price.
This logger not only offers 0.01 foot accuracy over a full temperature
range, but its all-metal sensor mounting provides the dimensional
stability necessary for repeatable measurements. Plus, the 13 foot model
provides the highest accuracy among affordably priced water level
loggers making it ideal for applications with less than 13 feet of
change, such as wetlands. And, to ensure top-quality construction, the
HOBO Water Level Logger is manufactured in-house following IPC 610 Class
2 specifications. You can be sure with the HOBO Water Level Logger that
your investment will last for years to come.
Return to U20 Series HOBO Water Level Loggers
