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-dened 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 ofoad 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 difcult 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 specic 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 difcult 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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A water level logger’s sensor
and analog-to-digital (ADC) converter both contribute to error. The error from the ADC
can be just as signicant as
sensor error.
Accuracy for typical loggers over temperature
2. Understanding Accuracy
When evaluating water level accuracy, you’ll want answers to the following
questions:
• What is the system level accuracy? For non-vented loggers, the system
accuracy is the sum of the water level logger’s error plus the barometric pressure logger’s error. The barometric pressure error is often overlooked, but
needs to be included. On the other hand, vented water level loggers or sensors are measuring the differential pressure directly, so there is just the one sensor measurement error to include.
Does the accuracy specied relate only to the logger’s sensor,
or to the entire logger? A water level logger’s sensor and
analog-to-digital (ADC) converter both contribute to error. The
error from the ADC can be just as signicant as sensor error. For this reason, you’ll want to conrm with the manufacturer that the specied accuracy refers to the entire measurement
rather than just the sensor. To realize a 0.01-foot water level resolution requires at least a 12-bit ADC with a 30 psi water level
sensor. Likewise, you should make sure the barometric logger’s accuracy specication includes all sources of error.
Does the accuracy specication apply across the full-calibrated measurement range of the logger? The accuracy a water level logger can achieve at the high or low end of a given range may be far different from the accuracy at the
middle of the range. For this reason, it’s important to nd out if the logger’s accuracy specication refers to a single point or the entire measurement range.
Knowing the full-range accuracy of a water level logger will give you assurance that the logger will meet your accuracy requirements.
• Do temperature variations cause additional error outside of the accuracy spec? Some water level loggers are not able to effectively compensate for temperature changes, which cause incorrect pressure readings. For this
reason, it’s important to nd out if error that results from temperature changes is included in the accuracy specication, or if there is a separate error term that
must be added. Data loggers with reduced overall mass will equilibrate more quickly to changing temperature conditions to increase dynamic response
during changing conditions. The response-time specications will indicate how
quickly the logger will equilibrate.
• Is drift important? The pressure sensors in water level loggers will drift over time. Whether or not you need to be concerned about drift depends on your application. Drift is important in cases when absolute pressure values are needed, or if there are no recent reference level or depth measurements available. This may be the case if a water level logger is deployed for more than one year and no reference-level readings are taken during that
deployment. Otherwise, drift is not a signicant factor since it will be offset by
regular (i.e. monthly) manual reference-level readings. Regardless of whether drift will affect your data, it is a good idea to ask the logger manufacturer for
drift specications.
In addition to these questions, be sure to ask the manufacturer if the logger’s accuracy has been veried or measured against NIST-traceable standards. Some companies offer NIST-traceable calibration certicates as verication of the
accuracy of each logger.
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3. Software features that really matter
Just as water level loggers can vary considerably from model to model, so too can the graphing & analysis software or app that accompanies them.
From a general standpoint, it’s a good idea to look for something that’s highly intuitive, so the learning curve is minimal. You’ll also want to be able to quickly and easily perform tasks such as conguring loggers, and ofoading, graphing, and sharing data.
The software features you’ll want to consider depend on where the software is being used. For software being used in the eld, look for capabilities related to deploying loggers and ofoading data. For software being used to analyze data in your ofce, look for more powerful analysis
capabilities.
In terms of specic features, here are some you’ll want to consider,
depending on where you will be using it:
• Time-saving launch features – If you will be launching many loggers
at once, look for software that allows you to congure the logging parameters once, and then use those settings to congure all of the
loggers for the deployment. Not only does this save time, it also helps to
ensure that all loggers are congured the same. For example, you may want to congure a group of loggers to all start at the same time and
with the same logging rate.
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The software should enable you to quickly and easily perform tasks such as
conguring loggers, and ofoading, graphing, and
sharing data.
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Barometric compensation (for loggers that don’t include integrated barometric pressure compensation) – To convert a non-vented logger’s
pressure readings to barometrically-corrected water level values, make sure the logger software has a barometric compensation utility. These tools typically allow you to enter reference level, water density, and other values into a dialogue box, and then automatically perform the pressure­to-water level conversion.
• Multi-logger graphing – When monitoring water levels at multiple sites, it is often advantageous to be able to view and analyze data from each water level logger on a single graph. Be sure to ask the manufacturer about this capability.
• Easy data export – Because water level data often needs to be incorporated into other software programs, such as spreadsheets or modeling programs,
make sure you’re able to quickly and
easily export data in a range of data formats.
• Project save and recall – While the ability to save and recall projects may seem like a basic feature of any logger software package, the reality is that many do not support this capability. Since data analysis typically involves a number of steps, including merging
multiple data les together, converting
pressure readings to water level units,
and formatting charts, you’ll want to be sure that the logger’s software allows you
to save your work so you can easily recall it and add to it in the future.
HOBOware graph showing U20 temperature in red, and water level at two points along a stream in blue and green.
HOBOware’s Barametric Compensation
Assistant
HOBO U20-001-01 water level logger
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4. Buying vs. renting
In the past, the relatively high price of water level loggers has prevented many hydrologists from purchasing their own supply of loggers. Many have chosen to rent loggers instead. While renting can be a convenient option for short-term deployments, it is important to be aware that the price of water level loggers has decreased to the point where purchasing is more cost-effective for many applications.
If you provide hydrology or groundwater services, owning an inventory of water
level loggers may give you a competitive edge, since you’ll be able to waive
additional equipment rental fees for your customers.
5. Connecting to the Logger
Data loggers with wireless connection to a mobile device offer the convenience
of not having to take a laptop into the eld, while still being able to view data and change conguration settings in the eld, if needed. Wireless loggers with Bluetooth Low Energy (BLE) technology provide the additional benet
of not having to physically access the logger to push a button to activate communication, as earlier versions of Bluetooth require.
Loggers that rely on mechanical plug-in connectors can be damaged by water in
the eld and cause logger failures. Water level loggers with an optical interface that is completely sealed within the logger’s housing eliminate the possibility of
water-related damage and/or failures.
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For loggers with an optical interface, you will need an optical base station to connect the logger to a computer. The best option for connecting to the computer is a direct USB interface. Some older loggers use serial communications to the logger, and use a serial-to-USB converter to allow them to be connected to USB. Because the loggers still are using serial communications internally, their data
ofoad speeds are limited to the slower serial speeds, and they require special
drivers to be installed on the computer.
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Other informational resources available from Onset:
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Data Logger Basics
In today’s data-driven world of satellite uplinks, wireless
networks, and the Internet, it is common to hear the terms “data
logging” and “data loggers” and not really have a rm grasp of
what they are.
Most people have a vague idea that data logging involves electronically collecting measurements of key environmental parameters, such as temperature, relative humidity, or energy
use. They’re right, but that’s just a small view of what data
logging is.
Choosing a Conductivity Logger
Whether you are selecting a conductivity logger for the rst time
or have experience measuring conductivity, this paper can help you determine the type of logger that best suits your needs. It
highlights the ve most important considerations in selecting
and deploying a conductivity logger: measurement range and accuracy, other factors that affect accuracy, ease of deployment
and ofoad, software capabilities, and cost of ownership.
Robust, low-cost data loggers for stream temperature, ow intermittency, and relative
conductivity monitoring
Underwater Temperature Loggers: Considerations For Selection & Deployment
This paper offers guidance and tips on selecting and deploying water temperature loggers. Three main phases of operation
are discussed: conguration & launch, deployment, and data
retrieval & analysis.
Deploying Weather Stations: A Best Practices Guide
From the tropics to the poles, climate, agriculture and other researchers rely on unattended research-grade, data logging weather stations. For example, the US Department of Agriculture uses weather stations to study anything from molecular plant pathology to forest management. Non­government groups, such as universities, use weather stations to study a wide array of subjects including how glacial activity affects air temperature. Additionally, commercial companies depend on weather stations to conduct businesses.
Our new best-practices guide, Weather Station Deployment
Techniques, shares eld-proven tips and techniques for installing research-grade weather stations in the eld. A range
of topics are discussed, including weather station site location,
sensor placement, system conguration, and cable protection.
Water temperature and stream ow intermittency are critical parameters inuencing aquatic ecosystem health. Low-cost
temperature loggers have made continuous water temperature
monitoring relatively simple but determining stream ow timing
and intermittency using temperature data alone requires
signicant and subjective data interpretation.
Monitoring Wetlands with Data Loggers: A Best Practices Guide
Wetlands act as a natural lter for polluted water and thus
play an essential role in water quality protection. They serve
as oodwater storage to help minimize erosion, and create a habitat for many sh and wildlife.
While a variety of factors have decreased the number of wetlands in the U.S. by half since 1950, many organizations are
restoring wetlands back to their original ourishing ecosystems.
To ensure success, it is necessary to monitor wetland factors such as water level, temperature, and rainfall.
This guide shares eld-proven best practices for conguring,
launching and deploying portable data loggers in wetland monitoring applications. A range of data logger types is covered, and tips are provided on logger installation and maintenance.
Access our full resources library at: www.onsetcomp.com/learning
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About Onset
Onset is a world leader in data loggers. Our HOBO data logger products are used around the world in a broad range of monitoring applications, from verifying the performance of green buildings and renewable energy systems to agricultural and coastal research.
Based on Cape Cod, Massachusetts, Onset has been designing and manufacturing its HOBO data loggers on
site since the company’s founding in 1981.
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Sales (8am to 5pm ET, Monday through Friday) Email sales@onsetcomp.com Call 508-759-9500 In US call toll free 800-564-4377 Fax 508-759-9100
Technical Support (8am to 8pm ET, Monday through Friday) Email loggerhelp@onsetcomp.com Call 508-759-9500 In US call toll free 877-564-4377
Onset Computer Corporation 470 MacArthur Blvd. Bourne, MA 02532
Copyright© 2015, Onset Computer Corporation. All information in this document is subject to change without notice. Onset and HOBO are registered trademarks of Onset Computer Corporation. All other trademarks are the property of their respective owners. All rights reserved. Printed in the USA. Lit. No. MKT1128-1015
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