HOBO® MX pH and Temperature Logger (MX2501) Manual
The HOBO MX pH and Temperature logger is designed for long-term monitoring of pH in
aquatic systems. With a replaceable pH electrode and anti-fouling copper guard, this durable
logger can be deployed in both fresh salt water environments. This logger is Bluetooth® Low
Energy-enabled logger for wireless communication with a mobile device. Using the
HOBOmobile® app, you can easily calibrate and configure the logger, download logged data to
your phone or tablet, or automatically upload the data to HOBOlink® for further analysis. You
can also configure the logger to calculate statistics, set up alarms to trip at specific thresholds,
or enable burst logging in which data is logged at a faster interval when sensor readings are
above or below certain limits.
HOBO MX pH and
Temperature Logger
MX2501
Included Items:
• pH electrode in solution
• Electrode storage solution
and cap
• Anti-fouling copper guard
Required Items:
• HOBOmobile app
• Device with iOS and
Bluetooth
Accessories:
• Calibration beaker
(MX2500-CAL-BKR)
• Calibration kit with three
250 mL bottles of pH 4.01,
7.01, and 10.01 solution
(MX2500-CAL-KIT)
• pH 4.01 calibration
solution, 250 mL (MX2500CAL-4)
• pH 7.01 calibration
solution, 250 mL (MX2500CAL-7)
• pH 10.01 calibration
solution, 250 mL (MX2500CAL-10)
• Electrode cleaning solution
(MX2500-CLEAN-SOLN)
• Replacement pH electrode
(MX2500-ELECTRODE)
• Replacement end cap
(MX2500-END-CAP)
• Replacement anti-fouling
copper guard (MX2500GUARD)
• Additional electrode
storage solution (MX2500STORE-SOLN) and cap
(MX2500-STORE-CAP)
Specifications
pH Sensor
in pH in mV
Range 2.00 to 12.00 pH -1,000 to 1,000 mV
Accuracy ±0.10 pH ±0.2 mV
Resolution 0.01 pH 0.5 mV
Temperature Sensor
Range -2° to 50°C (28.4° to 122°F)
Accuracy ±0.2°C (±0.36°F)
Resolution 0.04°C (0.072°F)
Logger
Operating Range -2° to 50°C (28.4° to 122°F)
Waterproof To 40 m (131.2 ft)
Water Detection Water conductivity level of 100 µS/cm or greater necessary for reliable
Radio Power 1 mW (0 dBm)
Transmission Range Approximately 30.5 m (100 ft) line-of-sight
Wireless Data Standard Bluetooth Low Energy (Bluetooth Smart)
Logging Rate 1 second to 18 hours
Logging Modes Fixed interval (normal, statistics) or burst
Memory Modes Wrap when full or stop when full
Start Modes Immediate, push button, date & time, or next interval
Stop Modes When memory full, push button, date & time, or after a set logging
Time Accuracy ±1 minute per month 0° to 50°C (32° to 122°F)
Battery Type One AA 1.5 Volt, user replaceable
Battery Life 1 year typical at 25°C (77°F) with logging interval of 1 minute and
pH Electrode Life 6 months
Memory 152 KB (43,300 measurements, maximum)
detection of water. Deionized water or water below 100 µS/cm may not
be detected.
The water conductivity circuit may not reliably detect water that has
frozen around the electrodes, i.e. below 0°C (32°F).
period
Bluetooth Always Off disabled in software.
2 years typical at 25°C (77°F) with logging interval of 1 minute and
Bluetooth Off Water Detect enabled in software.
3 years typical at 25°C (77°F) with logging interval of 1 minute and
Bluetooth Always Off enabled in software.
Faster logging intervals and statistics sampling intervals, burst logging,
remaining connected with the app, excessive downloads, and paging may
impact battery life.
22511-1
Specifications (continued)
Full Memory Download Time Approximately 60 seconds; may take longer the further the device is
Dimensions 22.86 x 4.27 cm (9.0 x 1.68 inches)
Weight 268.2 g (9.46 oz)
Wetted Materials PVC housing and sensor guard, polycarbonate end caps and mounting
Environmental Rating IP68
Logger Components and Operation
HOBO MX2501 MX pH and Temperature Logger Manual
from the logger
end with a TPE switch, plastic pH electrode
The CE Marking identifies this product as complying with all relevant
directives in the European Union (EU).
See last page
Anti-Fouling
Copper
Guard
End Cap
Sensor
Guard
Temperature
Sensor
pH Electrode
Anti-Fouling Copper Guard: Use this guard to protect the pH
electrode when deploying the logger in flowing water. Do not
use when the logger is in still water or when the probe is in
storage solution (see Deploying and Mounting the Logger).
End Caps: There are two end caps that are screwed on to the
sensor end and the mounting end of the logger.
Sensor Guard: This is a protective guard for the sensor end of
the pH electrode.
Temperature Sensor: This temperature sensor is located at the
base of the sensor guard.
Water Detection Screws: These two screws can detect the
presence of water. This allows you to configure the logger in a
power-saving mode in which Bluetooth advertising is active
only when the logger is removed from water. See Configuring
the Logger for details. Note: The logger will check for the
presence of water every 15 seconds when the Bluetooth Off
Water Detect power-saving mode is selected.
pH Electrode: This is the electrode that is plugged into the
logger. The clear, plastic end is the pH sensor and must always
be in storage solution when not deployed in water. This
electrode must be replaced every 6 months.
Logger Housing: This is the main body of the logger.
Battery Holder: This is where one AA battery is installed under
a battery strap (see Battery Information).
Reed Switch: This is used in conjunction with the magnetic
switch on the mounting end of the logger.
LEDs: The blue LED blinks every 4 seconds when the logger is
logging (unless Show LED is disabled as described in Configuring
the Logger). The blue LED blinks every 8 seconds if the logger is
waiting to start logging because it was configured to start “On
Button Push” or with a delayed start. The red LED blinks every 4
Water Detection Screw
(one of two)
Logger Housing
Battery Holder
LEDs (Not
Visible)
Reed Switch
Mounting
Hole
Magnetic Switch
(not visible)
seconds when an alarm is tripped (unless the Show LED option
is disabled). The blue and red LEDs will blink once when you
press the magnetic switch to wake up the logger or will blink
four times when you press the switch to start or stop logging. If
you select Page Logger LED in the HOBOmobile app, the red
LED will be illuminated for 5 seconds.
Magnetic Switch: This switch next on the mounting end of the
logger (not visible in the diagram) acts as a button and works in
conjunction with the reed switch. Press this button for 3 seconds
to start or stop the logger when it is configured to start or stop
“On Button Push” (see Configuring the Logger). Press this button
for 1 second to wake up the logger (if configured with Bluetooth
Always Off as described in Configuring the Logger).
Mounting Hole: Use the hole on the mounting end of the
logger to attach it to a cable or cord for deployment (see (see
Deploying and Mounting the Logger).
Installing the pH Electrode in the Logger
The logger is shipped with the pH electrode uninstalled and the
the plastic end housing the pH sensor in storage solution as
shown.
Important: The pH sensor must be kept in storage solution
when not being calibrated or deployed in water. The gel
surrounding the sensor will dry out after 10 minutes if the pH
sensor is not submersed in storage solution, calibration
solution, or water.
pH electrode
End Cap
pH sensor in
storage
solution
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HOBO MX pH and Temperature Logger (MX2501) Manual
To install the pH electrode in the logger:
1. Unscrew the end cap over the sensor end of the logger.
Unscrew this
end cap
2. Pull the sensor guard straight out from the logger housing
without twisting it.
Pull this sensor
guard straight
out
3. Remove the pH electrode from the shipping bottle and
insert the pH sensor into the sensor guard as shown.
Push the sensor through this
end of the guard
Gently push the pH electrode into the guard until the clear
plastic is fully seated in the sensor guard as shown.
Do not twist or turn the sensor guard as you push the pH
electrode straight into position.
Notch in line with groove
Push the sensor guard until the notch is fully seated in the
groove as shown.
Notch fully seated in groove
5. Screw the end cap back on this end of the logger and then
screw the storage solution cap on as shown.
pH electrode fully seated in guard
pH sensor visible through
window in guard
4. Plug the pH electrode into the logger, using the tab as a
guide to make sure it is installed in the correct orientation
with the notch in the guard fitting into small groove in the
logger housing.
Groove in logger
housing
Tab oriented up with
groove and notch
Notch
End cap reinstalled
Storage solution cap
installed
6. Unscrew the cap on the storage solution bottle. Insert the
sensor guard into the bottle and screw the cap that is
installed on the guard onto the bottle.
Insert
sensor
guard into
storage
solution
Important: Do not install the copper anti-fouling guard in the
sensor guard while the pH sensor is in the storage solution. The
copper in the guard can affect the properties of the storage
solution.
Screw the
cap
attached to
the logger
onto the
bottle with
the storage
solution.
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HOBO MX pH and Temperature Logger (MX2501) Manual
7. Keep the sensor in the storage solution as shown until you
are ready to calibrate it and deploy the logger.
Downloading HOBOmobile and
Connecting to a Logger
Install the HOBOmobile app to connect to and work with the
logger.
1. Download the HOBOmobile app from the App Store®.
2. Open the app and enable Bluetooth in the device settings if
prompted.
3. Press the button on the logger to wake it up.
4. Tap the HOBOs icon at the bottom of the screen. Tap the
logger in the list to connect to it.
If the logger does not appear in the list or if it is having trouble
connecting, follow these tips:
• Make sure the logger is “awake” by pressing the start
button. The alarm and status LEDs will blink once when
the logger wakes up. You can also press the button a
second time to bring it to the top of the list if you are
working with multiple loggers.
• Make sure the logger is within range of your mobile
device. The range for successful wireless communication
is approximately 30.5 m (100 ft) with full line-of-sight.
• If there are several loggers in the area, move the logger
to a location with fewer loggers. Interference can
sometimes occur when numerous loggers are in one
location.
• If your device can connect to the logger intermittently or
loses its connection, move closer to the logger, within
sight if possible.
• If the logger appears in the list, but you cannot connect
to it, close HOBOmobile and power cycle the mobile
device. This forces the previous Bluetooth connection to
close.
Once connected to the logger you can select one of the
following actions:
• Configure. Select logger settings and load them onto the
logger to start logging. See Configuring the Logger.
• Readout. Download logger data. See Reading Out the
Logger.
• pH Calibration. Calibrate the logger following the
instructions in the app.
• Full Status Details. Check the battery level and view the
configuration settings currently selected for the logger.
• Start Logging. Select this option to begin logging (if the
logger is configured to start “On Button Push” as
described in Configuring the Logger).
• Stop Logging. Stop the logger from recording data. This
overrides any Stop Logging settings described in
Configuring the Logger.
• Page Logger LED. Press and hold this option to illuminate
the logger LEDs for 5 seconds.
• Logger Password. Select this to create a password for the
logger that will be required if another mobile device
attempts to connect to it. To reset a password, connect
to the logger, tap Set Logger Passkey, and select Reset to
Factory Default. You can also press the button on the
logger for 10 seconds to reset a password.
Update Firmware. When new logger firmware is
available, this action appears in the list. Select it and
follow the instructions on the screen. A logger readout
will be completed automatically at the beginning of the
firmware update process. If the connection is lost
between the logger and the mobile device during the
firmware update, a Firmware Update Pending Status
displays for the logger in the HOBOs list. Connect to
the logger and select Restore Logger (or Update
Firmware if that option is available) to continue
updating the firmware.
Important: Before updating the firmware on the
logger, check the remaining battery level by selecting
Full Status Details and make sure it is no less than 30%.
Make sure you have the time to complete the entire
update process, which requires that the logger remains
connected to the device during the upgrade.
• Force Offload. This may appear if an error was
encountered when loading configuration settings. Select
this to offload all the data on the logger before
reconfiguring it.
Calibrating the Logger
The logger needs to be calibrated for accurate pH readings. You
can calibrate the logger using a 4.01, 7.01, and 10.01 buffer. It
is recommended that you calibrate the logger immediately
before deploying it.
Important: The pH sensor must be kept in storage solution
when not being calibrated or deployed in water. The gel
surrounding the sensor will dry out after 10 minutes if the pH
sensor is not submersed in storage solution, calibration
solution, or water.
1. Open HOBOmobile and tap the HOBOs icon.
2. Find the logger in the list and tap it to connect to it. If the
logger was previously configured with Bluetooth Always
Off, press the switch on the logger to wake it up. If the
logger was previously configured with Bluetooth Off Water
Detect and it is deployed in water, remove it from water.
3. Tap pH Calibration.
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HOBO MX pH and Temperature Logger (MX2501) Manual
4. Follow the instructions in the app.
5. Once calibrated, follow the instructions in the next section
for Configuring the Logger.
Configuring the Logger
Use HOBOmobile to set up the logger, including selecting the
logging options, configuring alarms, and other settings. These
steps provide an overview of setting up the logger. For
complete details, see the HOBOmobile User’s Guide.
1. Open HOBOmobile and tap the HOBOs icon.
2. Find the logger in the list and tap it to connect to it. If the
logger was previously configured with Bluetooth Always Off,
press the switch on the logger to wake it up. If the logger
was previously configured with Bluetooth Off Water Detect
and it is deployed in water, remove it from water. If you are
working with multiple loggers, pressing the button also
brings the logger to the top of the list (and the logger name
will turn green). Note that the current sensor readings are
displayed even when the logger is not logging.
3. Once connected, tap Configure.
• On Date/Time. Logging will begin on a date and time you
specify. Select the Date and time and tap Done.
Tap Done in the Start Logging screen.
8. Tap Stop Logging and select the options for when logging
will end.
a. Choose one of two memory options:
• When Memory Fills. The logger will continue recording
data until the memory is full.
• Never (Wrap When Full). The logger will continue
recording data indefinitely, with newest data
overwriting the oldest. This option is not available if
the Logging Mode is set to Burst (see Burst Logging).
b. Select On Button Push if you want to be able to stop
logging by pushing the button on the logger for 3
seconds. Note that if you also choose On Button Push for
the Start Logging option, then you will not be able to stop
logging until 30 seconds after logging begins.
c. Select one of the following time options for when to stop
logging:
• Never. Select this if you do not want the logger to stop
at any predetermined time frame.
• On Date/Time. Select this if you want the logger to
stop logging on a specific date and time. Select the
date and time and then tap Done.
4. Tap Name and type a name for the logger up to 20
characters (optional). Tap Done. If no name is selected, the
logger serial number is used as the name.
5. Tap Group to add the logger to the Favorites group, an
existing custom group, or create a new group name with up
to 20 characters (optional). Tap Done.
6. Tap Logging Interval and choose how frequently the logger
will record data unless operating in burst logging mode (see
Burst Logging). Note: If you configure an alarm, the logger
will use the logging interval you selected as the rate to
check for alarm conditions (alarms are not available if burst
logging is configured). See Setting up Alarms for more
details.
7. Tap Start Logging and select when logging will begin:
• Now. Logging will begin immediately after tapping Start
in the Configure screen.
• On Next Logging Interval. Logging will begin at the next
even interval as determined by the selected logging
interval.
• On Button Push. Logging will begin once you press the
button on the logger for 3 seconds.
• After. Select this if you want to control how long the
logger should continue logging once it starts. Choose
the amount of time you want the logger to log data
and then tap Done. For example, select 30 days if you
want the logger to log data for 30 days after logging
begins.
d. Tap Done in the Stop Logging screen.
Select the sensor measurement types that will be logged:
9.
temperature and pH. You can also set up alarms to trip
when a sensor reading rises above or falls below a specified
value. See Setting up Alarms for details on enabling sensor
alarms.
10. Tap Logging Mode. Select either fixed interval logging or
burst logging. With fixed interval logging, the logger records
data for all enabled sensors and/or selected statistics at the
logging interval selected (see Statistics Logging for details
on choosing statistics options). In burst mode, logging
occurs at a different interval when a specified condition is
met. See Burst Logging for more information. Tap Done.
11. Enable or disable Show LED. If Show LED is disabled, the
alarm and status LEDs on the logger will not be illuminated
while logging (the alarm LED will not blink if an alarm trips).
You can temporarily turn on LEDs when Show LED is
disabled by pressing the button on the logger for 1 second.
12. Select the power saving mode, which determines when the
logger will “advertise” or regularly send out a Bluetooth
signal for the phone or table to find via HOBOmobile.
• Bluetooth Always Off. The logger will only advertise
during logging when you push the switch on the logger.
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This will wake up the logger when you need to connect to
it. This option uses the least battery power.
• Bluetooth Off Water Detect. The logger will not
advertise when the presence of water is detected. Once
the logger is removed from the water, advertising will
automatically turn on, thereby not requiring you to push
the switch to wake up the logger when you need to
connect to it. This option preserves some battery power.
Note: The logger will check for the presence of water
every 15 seconds when this is option is selected.
• Bluetooth Always On. The logger will always advertise.
You will never need to push a switch to wake up the
logger. This option uses the most battery power.
13. Tap Start in the upper right corner of the Configure screen
to load the settings onto the logger.
Logging will begin based on the settings you selected. See
Deploying and Mounting the Logger for details on mounting
and see Reading Out the Logger for details on downloading.
Setting up Alarms
You can set up alarms for the logger so that if a sensor reading
rises above or falls below a specified value, the logger alarm
LED will blink and an alarm icon will appear in the app. This can
alert you to problems so you can take corrective action.
To set an alarm:
1. Tap the HOBOs icon and tap the logger to connect to it. . If
the logger was configured with Bluetooth Always Off
enabled, push the switch on the logger to wake it up. If the
logger was configured with Bluetooth Off Water Detect and
is currently underwater, remove it from the water.
2. Once connected, tap Configure.
HOBO MX pH and Temperature Logger (MX2501) Manual
7. Select either Cumulative or Consecutive Samples. If you
select Cumulative Samples, then the alarm will trip when
the time the sensor is out of range over the course of the
deployment is equal to the selected duration. If you select
Consecutive Samples, then the alarm will trip when the
time the sensor is continuously out of range is equal to the
selected duration. For example, the high alarm for
temperature is set to 85°F and the duration is set to 30
minutes. If Cumulative is selected, then an alarm will trip
once a sensor reading has been at or above 85°F for a total
of 30 minutes since the logger was configured; specifically,
this could be 15 minutes above 85°F in the morning and
then 15 minutes above 85°F again in the afternoon. If
Consecutive is selected, then an alarm will trip only if all
sensor readings are 85°F or above for a continuous 30minute period.
8. Tap Done and repeat steps 3–8 for the other sensor if
desired. Note that when both alarms are configured, an
alarm is raised when either sensor is in an alarm condition.
9. Back in the Configure screen, select one of the following
options to determine how the alarm indications are cleared:
• Logger Reconfigured. The alarm indication will display
until the next time the logger is reconfigured.
3. In Sensor & Alarm Setup, tap an enabled sensor.
4. Enable the High Alarm if you want an alarm to trip when the
sensor reading rises above the high alarm value. Drag the
slider to the reading that will trip the alarm or tap the value
field and type a specific reading. In the example, an alarm
will trip when the temperature rises above 85°F.
5. Enable the Low Alarm if you want an alarm to trip when the
sensor reading falls below the low alarm value. Drag the
slider to the reading that will trip the alarm or tap the value
field and type a specific reading. In the example, an alarm is
configured to trip when the temperature falls below 32°F.
Note: The actual values for the high and low alarm limits are
set to the closest value supported by the logger.
6. Under Raise Alarm After, select the duration before an
alarm is tripped and tap Done in the Alarm Duration screen.
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• Sensor in Limits. The alarm icon indication will display
until the sensor reading returns to the normal range
between any configured high and low alarm limits.
10. Tap Start in the Configure screen to load the alarm settings
onto the logger if you are ready to start.
When an alarm trips, the red logger LED blinks every 4 seconds
(unless Show LED is disabled), an alarm icon appears in the app,
and an Alarm Tripped event is logged. The alarm state will clear
when the readings return to normal if you selected Sensor in
Limits in step 9. Otherwise, the alarm state will remain in place
until the logger is reconfigured.
Notes:
• Alarm limits are checked at every logging interval. For
example, if the logging interval is set to 5 minutes, then
the logger will check the sensor readings against your
configured high and low alarm setting every 5 minutes.
• The actual values for the high and low alarm limits are set
to the closest value supported by the logger. For
example, the closest value to 85°F that the logger can
HOBO MX pH and Temperature Logger (MX2501) Manual
record is 84.990°F and the closest value to 32°F is
32.043°F. In addition, alarms can trip or clear when the
sensor reading is within the specified resolution. This
means the value that triggers the alarm may differ
slightly than the value entered. For example, if the High
Alarm is set to 75.999°F, the alarm can trip when the
sensor reading is 75.994°F (which is within the specified
resolution).
• When you read out the logger, alarm events can be
displayed on the plot or in the data file. See Logger
Events.
Burst Logging
Burst logging is a logging mode that allows you to set up more
frequent logging when a specified condition is met. For
example, a logger is recording data at a 5-minute logging
interval and burst logging is configured to log every 30 seconds
when the temperature rises above 85°F (the high limit) or falls
below 32°F (the low limit). This means the logger will record
data every 5 minutes as long as the temperature remains
between 85°F and 32°F. Once the temperature rises above
85°F, the logger will switch to the faster logging rate and record
data every 30 seconds until the temperature falls back to 85°F.
At that time, logging then resumes every 5 minutes at the
normal logging interval. Similarly, if the temperature falls below
32°F, then the logger would switch to burst logging mode again
and record data every 30 seconds. Once the temperature rises
back to 32°F, the logger will then return to normal mode,
logging every 5 minutes. Note: Sensor alarms, statistics, and the
Stop Logging option “Wrap When Full” are not available in
burst logging mode.
To set up burst logging:
1. Tap the HOBOs icon and tap the logger to connect to it. If
the logger was configured with Bluetooth Always Off
enabled, push the switch on the logger to wake it up. If the
logger was configured with Bluetooth Off Water Detect and
is currently underwater, remove it from the water.
2. Once connected, tap Configure.
3. Tap Logging Mode and then tap Burst Logging.
4. Tap a sensor under Burst Sensor Limits.
5. Enable High Limit if you want burst logging to occur when
the sensor reading rises above a specific reading. Drag the
slider to the reading that will trigger burst logging or tap the
value field and type a specific reading. In this example, the
logger will switch to burst logging when the temperature
rises above 85°F.
slider to the reading that will trigger burst logging or tap the
value field and type a specific reading. In the example, the
logger will switch to burst logging when the temperature
falls below 32°F.
7. Tap Done and repeat steps 4–7 for the other sensor if
desired.
8. Tap Burst Logging Interval and select an interval faster than
the logging interval. Keep in mind that the faster the burst
logging rate, the greater the impact on battery life and the
shorter the logging duration. Because measurements are
being taken at the burst logging interval throughout the
deployment, the battery usage is similar to what it would be
if you had selected this rate for the normal logging interval.
Tap Done.
9. Tap Done to exit the Logging Mode screen.
10. Tap Start in the Configure screen to load the burst settings
onto the logger if you are ready to start.
Notes:
• The high and low burst limits are checked at the burst
logging interval rate whether the logger is in normal or
burst condition. For example, if the logging interval is set
to 1 hour and the burst logging interval is set to 10
minutes, the logger will always check for burst limits
every 10 minutes.
• If high and/or low limits have been configured for more
than one sensor, then burst logging will begin when any
high or low condition goes out of range. Burst logging will
not end until all conditions on all sensors are back within
normal range.
• The actual values for the burst logging limits are set to
the closest value supported by the logger. For example,
the closest value to 85°F that the logger can record is
84.990°F and the closest value to 32°F is 32.043°F.
• Burst logging can begin or end when the sensor reading is
within the specified resolution. This means the value that
triggers burst logging may differ slightly than the value
entered. For example, if the high limit for a temperature
alarm is set to 75.999°F, burst logging can start when the
sensor reading is 75.994°F (which is within the specified
resolution).
• Once the high or low condition clears, the logging
interval time will be calculated using the last recorded
data point in burst logging mode, not the last data point
recorded at the normal logging rate. For example, the
logger has a 10-minute logging interval and logged a data
point at 9:05. Then, the high limit was surpassed and
burst logging began at 9:06. Burst logging then continued
until 9:12 when the sensor reading fell back below the
high limit. Now back in normal mode, the next logging
interval will be 10 minutes from the last burst logging
point, or 9:22 in this case. If burst logging had not
occurred, the next data point would have been at 9:15.
6. Enable Low Limit if you want burst logging to occur when
the sensor reading falls below a specific reading. Drag the
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A New Interval event is created each time the logger
•
enters or exits burst logging mode. See Logger Events for
details on plotting and viewing the event. In addition, if
the logger is stopped with a button push while in burst
logging mode, then a New Interval event is automatically
HOBO MX pH and Temperature Logger (MX2501) Manual
logged and the burst condition is cleared, even if the
actual high or low condition has not cleared.
Statistics Logging
During fixed interval logging, the logger records data for
enabled sensors and/or selected statistics at the logging
interval selected. Statistics are calculated at a sampling rate you
specify with the results for the sampling period recorded at
each logging interval. The following statistics can be logged for
each sensor:
• The maximum, or highest, sampled value,
• The minimum, or lowest, sampled value,
• An average of all sampled values, and
• The standard deviation from the average for all sampled
values.
For example, a logger is configured with both the temperature
and pH sensors enabled, and the logging interval set to 5
minutes. The logging mode is set to fixed interval logging with
Normal and all four statistics enabled and with a statistics
sampling interval of 30 seconds. Once logging begins, the logger
will measure and record the actual temperature and pH sensor
values every 5 minutes. In addition, the logger will take a
temperature and pH sample every 30 seconds and temporarily
store them in memory. The logger will then calculate the
maximum, minimum, average, and standard deviation using the
samples gathered over the previous 5-minute period and log
the resulting values. When reading out the logger, this would
result in 10 data series (not including the mV series): two
sensor series (with temperature and pH data logged every 5
minutes) plus eight maximum, minimum, average, and standard
deviation series (four for temperature and four for pH with
values calculated and logged every 5 minutes based on the 30second sampling).
To log statistics:
1. Tap the HOBOs icon and tap the logger to connect to it. If
the logger was configured with Bluetooth Always Off
enabled, push the switch on the logger to wake it up. If the
logger was configured with Bluetooth Off Water Detect and
is currently underwater, remove it from the water.
2. Once connected, tap Configure.
3. Tap Logging Mode and then select Fixed Interval Logging.
4. Select Normal to record the current reading for each
enabled sensor at the logging interval shown at the top of
the screen. Do not select this if you only want to log
statistics.
5. Select the statistics you want the logger to record at each
logging interval: Maximum, Minimum, Average, and
Standard Deviation (average is automatically enabled when
selecting Standard Deviation). Statistics will be logged for all
enabled sensors. In addition, the more statistics you record,
the shorter the logger duration and the more memory is
required.
6. Tap Statistics Sampling Interval and select the rate to use
for calculating statistics. The rate must be less than, and a
factor of, the logging interval. For example, if the logging
interval is 1 minute and you select 5 seconds for the
sampling rate, then the logger will take 12 sample readings
between each logging interval (one sample every 5 seconds
for a minute) and use the 12 samples to record the resulting
statistics at each 1-minute logging interval. Note that the
faster the sampling rate, the greater the impact on battery
life. Because measurements are being taken at the statistics
sampling interval throughout the deployment, the battery
usage is similar to what it would be if you had selected this
rate for the normal logging interval.
7. Tap Done.
8. Tap Done again to exit the Logging Mode screen.
9. Tap Start in the Configure screen to load the statistics
settings onto the logger if you are ready to start.
Setting a Password
You can create an encrypted password for the logger that will
be required if another phone or tablet attempts to connect to
it. This is recommended to ensure that a deployed logger is not
mistakenly stopped or purposely altered by others. This
password uses a proprietary encryption algorithm that changes
with every connection.
To set a password:
1. Tap the HOBOs icon and connect to the logger.
2. Tap Logger Password.
3. Type a password up to 10 characters.
4. Tap Save.
Only the phone or tablet used to set the password can then
connect to the logger without entering a password; all other
mobile devices will be required to enter the password. For
example, if you set the password for the logger with your tablet
and then try to connect to the device later with your phone,
you will be required to enter the password on the phone but
not with your tablet. Similarly, if others attempt to connect to
the logger with different devices, then they would also be
required to enter the password. To reset a password, connect
to the logger, tap Set Logger Passkey, and select Reset to
Factory Default or press the button on the logger for 10
seconds.
Reading Out the Logger
To offload data from the logger:
1. Open HOBOmobile.
2. If the logger was configured with Bluetooth Always On,
continue to step 3.
If the logger was configured with Bluetooth Always Off,
press the button on the logger for 1 second to wake it up.
If the logger was configured with Bluetooth Water Detect
and it is deployed in water, remove it from the water.
3. Tap the HOBOs icon and tap the logger to connect to it.
4. Once connected, tap Readout.
5. Tap the Data Files icon to view a mini-graph of the
downloaded data.
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HOBO MX pH and Temperature Logger (MX2501) Manual
6. Tap the mini-graph to view a larger version of the graph or
to share the file. See the HOBOmobile User’s Guide for
details on viewing graphs and sharing data.
Data can also be uploaded automatically to HOBOlink, Onset’s
web-based software. Tap the Settings icon to enable the
HOBOlink Upload Data option (this requires a HOBOlink
account at www.hobolink.com). See the HOBOmobile User’s
Guide for more details on this setting and see the HOBOlink
help for details on working with data in HOBOlink.
Logger Events
The logger records the following internal events to track logger
operation and status. To plot events in HOBOmobile, tap a
mini-graph and then tap . Select the events you wish to plot
and then tap again. You can also view events in shared or
exported data files.
Internal Event Name Definition
Host Connect
Started The logger started logging.
Stopped The logger stopped logging.
Calibration End The pH calibration ended.
Calibration Cancel The pH calibration was cancelled.
Calibration Values
Calibration Buffers
Alarm
Tripped/Cleared
New Interval The logger has switched to logging at the
Water Detect The logger has been placed in water or
Low Power The battery level dropped below 2.3 V.
Safe Shutdown The battery level dropped below a safe
The logger was connected to the mobile
device.
The values set during the pH calibration
process.
The buffers used during the pH calibration
process.
An alarm has occurred because the
reading was outside the alarm limits or
back within range. Note: Although the
reading may have returned to a normal
range during logging, an alarm cleared
event will not be logged if the logger was
set up to maintain alarms until
reconfigured.
burst logging rate or back to the normal
rate.
removed from water.
operating voltage and the logger
performed a safe shutdown.
Deploying and Mounting the Logger
Important: The pH sensor must be kept in storage solution
when not being calibrated or deployed in water. The gel
surrounding the sensor will dry out after 10 minutes if the pH
sensor is not submersed in storage solution, calibration
solution, or water. Do not remove the pH sensor from the
storage solution until you are ready to deploy the logger.
Follow these guidelines when deploying the logger:
• Use the copper anti-fouling guard when deploying the
logger in moving water. Do not use the copper guard
when the pH sensor is being calibrated, placed in storage
solution, or deployed in still water as the copper can
affect the properties of those liquids. To install the
copper guard, insert it into the sensor guard over the pH
sensor as shown below.
The windows in the copper guard should line up with the
windows in the sensor guard as shown below.
• Attach a nylon cord or other strong cable to the
mounting hole to deploy the logger.
• The logger should be appropriately weighted, secured,
and protected depending on water conditions and
desired measurement location.
Maintaining the Logger
Periodically inspect the logger for biofouling. To clean the
logger housing, rinse the logger in warm water. Use a mild
dishwashing detergent if necessary. Do not use harsh
chemicals, solvents, or abrasives.
Use electrode cleaning solution (MX2500-CLEAN-SOLN) to clean
the pH electrode.
Battery Information
The logger requires one user-replaceable AA 1.5 V alkaline or
lithium battery. With a logging interval of 1 minute and at 25°C
(77°F), battery life is 1 year with Bluetooth Always On selected, 2
years with Bluetooth Off Water Detect selected, and 3 years with
Bluetooth Always Off selected. Expected battery life varies based
on the ambient temperature where the logger is deployed, the
logging interval, the frequency of connections, downloads, and
paging, and the use of burst mode or statistics logging.
Deployments in extremely cold or hot temperatures or a logging
interval faster than 1 minute can impact battery life. Estimates
are not guaranteed due to uncertainties in initial battery
conditions and operating environment.
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HOBO MX pH and Temperature Logger (MX2501) Manual
To install or replace the battery:
1. Unscrew the end cap on the mounting end of the logger.
Unscrew
the end
cap
Use mounting
tab to pull out
battery holder
2. Use the mounting tab to pull the top end with the battery
out from the logger. Use a flat-head screwdriver inserted
through the mounting hole for leverage.
3. Use a flat-head screwdriver to pop out the battery strap
holding the battery in place.
Insert flat-head screwdriver and
pop out battery strap
4. Remove the battery and install a new one, observing
polarity.
5. Place the battery strap back in place, using the notches in
the holder to align it.
Push the mounting tab until the notch is fully seated in the
groove as shown.
7. Screw the end cap back.
Notch fully seated in groove
WARNING: Do not cut open, incinerate, heat above 85°C
(185°F), or recharge the lithium battery. The battery may
explode if the logger is exposed to extreme heat or conditions
that could damage or destroy the battery case. Do not dispose
of the logger or battery in fire. Do not expose the contents of
the battery to water. Dispose of the battery according to local
regulations for lithium batteries.
Notch to align battery strap
6. Reinstall the top end, using the tab as a guide to make sure
it is installed in the correct orientation with the notch in the
guard fitting into small groove in the logger housing.
Groove in logger housing
Tab oriented up with
groove and notch
Notch
Do not twist or turn the top end as you push it into position.
Notch in line with groove
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HOBO MX pH and Temperature Logger (MX2501) Manual
Federal Communication Commission Interference Statement
This equipment has been tested and found to comply with the limits for a Class B digital device, pursuant to Part 15 of the FCC Rules. These limits are designed to provide
reasonable protection against harmful interference in a residential installation. This equipment generates uses and can radiate radio frequency energy and, if not installed and
used in accordance with the instructions, may cause harmful interference to radio communications. However, there is no guarantee that interference will not occur in a
particular installation. If this equipment does cause harmful interference to radio or television reception, which can be determined by turning the equipment off and on, the user
is encouraged to try to correct the interference by one of the following measures:
• Reorient or relocate the receiving antenna
• Increase the separation between the equipment and receiver
• Connect the equipment into an outlet on a circuit different from that to which the receiver is connected
• Consult the dealer or an experienced radio/TV technician for help
This device complies with Part 15 of the FCC Rules. Operation is subject to the following two conditions: (1) This device may not cause harmful interference, and (2) this device
must accept any interference received, including interference that may cause undesired operation.
FCC Caution: Any changes or modifications not expressly approved by the party responsible for compliance could void the user's authority to operate this equipment.
Industry Canada Statements
This device complies with Industry Canada license-exempt RSS standard(s). Operation is subject to the following two conditions: (1) this device may not cause interference, and
(2) this device must accept any interference, including interference that may cause undesired operation of the device.
Avis de conformité pour l’Industrie Canada
Le présent appareil est conforme aux CNR d'Industrie Canada applicables aux appareils radio exempts de licence. L'exploitation est autorisée aux deux conditions suivantes : (1)
l'appareil ne doit pas produire de brouillage, et (2) l'appareil doit accepter tout brouillage radioélectrique subi, même si le brouillage est susceptible d'en compromettre le
fonctionnement.
To comply with FCC and Industry Canada RF radiation exposure limits for general population, the logger must be installed to provide a separation distance of at least 20cm from
all persons and must not be co-located or operating in conjunction with any other antenna or transmitter.
KC Statement
해당 무선설비는 전파혼신 가능성이 있으므로 인명안전과 관련된 서비스는 할 수 없음
Translation:
The service related to human safety is not allowed because this device may have the possibility of the radio interference.
NCC Statement
經型式認證合格之低功率射頻電機，非經許可，公司、商號或使用者均不得擅自變更頻率、加大功率或變更原設計之特性及功能。
低功率射頻電機之使用不得影響飛航安全及干擾合法通信；經發現有干擾現象時，應立即停用，並改善至無干擾時方得繼續使用。前項合法通信，指依電信法規定作
業之無線電通信。低功率射頻電機須忍受合法通信或工業、科學及醫療用電波輻射性電機設備之干擾。
Translation:
Article 12
Without permission granted by the NCC, any company, enterprise, or user is not allowed to change frequency, enhance transmitting power or alter original characteristic as well
as performance to an approved low power radio-frequency device.
Article 14
The low power radio-frequency devices shall not influence aircraft security and interfere with legal communications. If found, the user shall cease operating immediately until no
interference is achieved. The said legal communications means radio communications is operated in compliance with the Telecommunications Act. The low power radiofrequency devices must be susceptible with the interference from legal communications or ISM radio wave radiated devices.
1-800-LOGGERS (564-4377) • 508-759-9500
www.onsetcomp.com/support/contact
© 2018 Onset Computer Corporation. All rights reserved. Onset, HOBO, and HOBOlink are registered
trademarks of Onset Compute r Corporation. App Store is a service mark of Apple Inc. Bluetooth and Bluetooth
Smart are registered trademarks of Bluetooth SIG, Inc. All other trademarks are the property of their
respective companies.
Patent #: 8,860,569 22511-1
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