Instruction Manual

HOBO MX pH and Temperature Logger (MX2501) Manual
U.S. and International Sales: 1-508-759-9500 5 www.onsetcomp.com
Notes:
• The date of the last calibration, the slope and offset
values, and the buffers used for the calibration are listed
under the Deployment Information in the Configuration
screen for reference.
• Once a logger is connected to the app, a notice appears if
the last calibration is more than seven days old prompting
you to recalibrate the logger. Although you can postpone
the calibration, we recommended you recalibrate the
logger before configuring it.
• If the status message during calibration indicates the
reading is invalid or it never stabilizes, try the following:
 Make sure the sensor is in the correct buffer solution or
try rinsing the sensor and restarting the calibration. If
the problem persists, clean the sensor (see Maintaining
the Logger) and inspect it to make sure it is not
damaged. Note: There could be microcracks on the
glass bulb of the electrode that may not be visible to
the human eye.
 Remove the sensor from the calibration solution and
clean it (see Maintaining the Logger). Restart the entire
calibration process.
 Wait longer to see if it stabilizes, keeping in mind that a
pH electrode has a 6-month typical maximum life and
may produce unstable readings if it is older than 6
months. The slope and offset values that are provided
are the best indication for the condition of the
electrode. A healthy electrode has a slope between
85% and 100% and an offset between ±30 mv.
 If the reading reported in app is acceptable for your
deployment even though it is reported as unstable, you
can tap Stop and then Confirm and proceed with the
calibration.
• You can calibrate the logger while it is logging. After the
calibration is saved, any new data logged uses the new
calibration. Data logged before the new calibration was
saved uses the old calibration data. If you do not want
data in a single file to be based on more than one
calibration, then stop the logger and read it out. You can
then calibrate it and reconfigure it.
• pH values of calibration buffers and samples vary
depending on their temperature. It is important that the
logger is calibrated in buffers that have the same
temperature as that of the sample. To do this, you must
use buffers that have known values at different
temperatures. The app automatically compensates for
temperature variances from 25°C (77°F) based on the
actual temperature-dependent pH value (from the chart
below) of buffers and samples.
Temperature
°C °F
pH 4.01
Buffer
pH 7.00
Buffer
pH 10.00
Buffer
0 32 4.01 7.12 10.31
5 41 4.00 7.09 10.24
10 50 4.00 7.06 10.17
15 59 4.00 7.04 10.11
20 68 4.00 7.02 10.05
25 77 4.01 7.00 10.00
Temperature
°C °F
pH 4.01
Buffer
pH 7.00
Buffer
pH 10.00
Buffer
30 86 4.01 6.99 9.95
35 95 4.02 6.98 9.92
40 104 4.03 6.97 9.88
45 113 4.04 6.97 9.85
Configuring the Logger
Use the app 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 HOBOconnect User’s Guide.
1. Remove the logger from water. If the logger was previously
configured with Bluetooth Always Off, press the switch on
the logger to wake it up. If you are working with multiple
loggers, pressing the button also brings the logger to the
top of the list in the app.
2. Tap Devices and then tap the logger tile in the app to
connect to the logger.
3. Tap Configure & Start to configure the logger.
4. Tap Name and type a name for the logger (optional). If you
do not enter a name, the app uses logger serial number as
the name.
5. Tap Group to add the logger to a group (optional).
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
uses 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 begins:
• On Save. Logging begins immediately after
configuration settings are saved.
• On Next Interval. Logging begins at the next even
interval as determined by the selected logging interval.
• On Button Push. Logging begins when you press either
the Start/Stop logging button on the logger for 3 seconds
or start logging with the app.
• On Date/Time. Logging begins at a date and time you
specify. Select the Date and Time.
8. Tap Stop Logging and select the options for when logging
ends:
• Never Stop (Overwrites Old Data). The logger does not
stop at any predetermined time. The logger continues
recording data indefinitely, with newest data overwriting
the oldest.
• On Date/Time. The logger stops logging on a specific
date and time that you specify.
• 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. For
example, select 30 days if you want the logger to log data
for 30 days after logging begins.
• Stop When Memory Fills. The logger continues recording
data until the memory is full.