Onset HOBO MX, MX2501 User Manual

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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