Onset MX2001 User Manual
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Choosing a Water Level Logger:
5 Things You Should Know
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Introduction
As the demand for water resources continues to grow in the United States and
abroad, the ability to assess the impact of urban development and agriculture on
water resources is more important than ever. To meet this growing demand, water
resource managers, engineers, and hydrologists have a greater need to monitor
groundwater and surface water levels with water level data loggers in order to
document baseline and changing water levels over time.
Water level loggers typically incorporate built-in micro-processors, pressure
sensors, and battery power in a rugged enclosure designed for long-term
underwater deployment. They can be deployed and left unattended for months at
a time, collecting water level data at user-dened intervals and storing it digitally
into logger memory. By operating in a continuous 24/7 monitoring mode, water
level loggers eliminate many of the hassles of manual data collection, and facilitate
monitoring of multiple locations at the same time.
Water level loggers also automate the process of archiving and reporting data.
Hydrologists can simply ofoad the logger data to a mobile device or computer
and easily create detailed graphs or data les. The charts can be easily printed
for documentation purposes, while the electronic data can be shared with other
programs or archived.
While water level loggers have become the data collection instrument of choice
for an increasing number of hydrologists, the myriad of product choices available
today can make it difcult to determine which product is right for your application.
Whether you have previous experience with water level logging, or are just getting
started, this report can help you choose the right products for your needs. It points
out the ve most important considerations to keep in mind, and offers tips on
specic features.
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1. Barometric Compensation
There are two primary types of water level loggers – vented and non-vented.
Vented loggers include a built-in vent tube that enables the loggers to
automatically compensate for atmospheric pressure changes. By equalizing these
changes on both sides of the pressure sensor, a well-designed and maintained
vented water level logger can provide high-accuracy water level data.
Non-vented loggers do not use vent tubes. Instead, these loggers can be
barometrically compensated using a barometric pressure logger and a simple
software function to perform the mathematics. Barometric pressure values can
also be obtained from weather stations within a 10-mile radius.
Now there’s also a type of non-vented logger that incorporates both an in-water
sensor and a barometric pressure sensor.
Keep in mind that while vented loggers have the potential to provide the greatest
accuracy, they also have a number of limitations that can cause problems and
result in bad data and/or data loss. These limitations include:
• Vented loggers are bulkier than non-vented loggers, which makes them
more difcult to transport and deploy.
• Most vented loggers require the use of desiccants for moisture protection,
which increases the amount of maintenance that’s required and therefore
the total cost of ownership of the logger. And condensation buildup can
lead to accuracy problems.
Non-vented with two loggers
GROUND LEVEL
BAROMETRIC
PRESSURE
LOGGER
SUSPENSION
CABLE
WATER LEVEL
WATER LEVEL
LOGGER
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• When monitoring water containing contaminants, vent tubes with
contaminant-resistant material must be used, which adds to the cost of
the logger, as does the decontamination process that’s required before the
logger can be redeployed.
• Vented loggers lack exibility when it comes to deploying them at various
depths. Cables cannot be lengthened without sending them back to the
supplier, and shortening requires delicately coiling the cable without
creating any kinks.
• If the end of the vented logger cable is inundated by rising water,
all subsequent data are compromised due to unknown pressure
compensation dynamics during the ood event.
These limitations highlight the
Vented
advantages of non-vented loggers,
which are more compact, require
minimal maintenance, can be easily
Vented cable
Logger
deployed in wells of varying depths,
and are not affected by ood water.
The new non-vented logger that
incorporates two sensors offers the
additional advantage of providing
water level data directly, with no
need for post-processing.
Sensor
Excess vent cable
has to be looped
around a 1/2” pipe
Non-vented with integrated
barometric sensor
GROUND LEVEL
LOGGER WITH
BAROMETRIC
PRESSURE
SENSOR
COMMUNICATION
SUSPENSION
CABLE
WATER LEVEL
WATER LEVEL
SENSOR
Protective
well pipe
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