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Onset HOBO MX2501 Bluetooth pH and Temperature Data Logger

  • Onset HOBO MX2501 Bluetooth pH and Temperature Data Logger
  • Onset HOBO MX2501 Bluetooth pH and Temperature Data Logger
  • Onset HOBO MX2501 Bluetooth pH and Temperature Data Logger
  • Onset HOBO MX2501 Bluetooth pH and Temperature Data Logger

Bluetooth pH and Temperature Data Logger

Part Number: MX2501

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  • Long-Term pH and Temperature Measurements in Estuaries, Lakes, Streams, Rivers and Oceans (Salt and Freshwater Environments)

  • Wireless Transmission of Recorded Readings to Phone or Tablet Using Bluetooth Smart LE Communications

  • 2.0 to 12.0 pH and 2C to 50C Measurement Ranges and +/-0.10pH and +/-0.2C Accuracy

  • User-Replaceable Lithium Battery with 1 Year Typical Life (1 Minute Sampling Rate and Bluetooth Always On)

  • Stores up to 43,300 Measured Readings with Date/Time Stamp if Bluetooth Communications Not Available

Includes pH Electrode and Lithium Battery. HOBOmobile App Available on the Apple Store (iOS) and Google Play (Android)

Special order - please allow 3-5 business days for this item to ship.


All Calibration Orders Have a 5 to 7 Business Day Lead Time
1 Year Calibration Due Date Unless Otherwise Specified


Onset HOBO® MX2501 Outdoor Bluetooth pH and Temperature Data Logger Specifications

Data Channels 1 Humdity Channel
1 Temperature Channel
pH Measurement Range: 2.0 to 12.0 pH (-512 to 512mV)
Accuracy: ±0.10 pH (±20 mV) units within ±10°C of Temperature at Calibration
Response Time: 1 Minute Typical to 90% at Constant Temperature in Stirred Water
Resolution: 0.01 pH (0.02 mV)
Temperature Measurement Range: -2°C to 50°C (28.4°F to 122°F)
Accuracy: ±0.2°C (±0.36°F)
Response Time: 7 Minutes Typical to 90% in Stirred Water
Resolution: 0.024°C at 25°C (0.04°F at 77°F)
pH Electorde Life 6 Months
Bouyancy Fresh Water:13.6g (0.48 oz) Negative
Salt Water:19.6g (0.69 oz) Negative
Waterproof Up to 40 Meters
Water Detection Water Conductivity Level to 10 S/cm or Greater is Necessary for Reliable Detection of Water. Deionized Water or Water Below 100 S/cm May Not Be Detected.
The Water Conductivity Circuit May Not Reliably Detect Water that Has Frozen Around the Electrodes.
Data Storage Capacity 43,300 Readings (When Bluetooth Communications Not Available)
Logging Mode Fixed Interval (Normal, Statistics) or Burst
Memory Mode Wrap when Full or Stop When Full
Start Modes Immediately, Push Button, Date & Time or Next Interval
Stop Modes Wrap When Data Storage Full, Push Button, Date & Time or After Set Interval
Sampling Rate 1 Second to 18 Hours (User-Specified)
Power Source AA 1.5 Volt Lithium Battery (User-Replaceable)
Battery Life Bluetooth Always On: 1 Year typical @ 1 Minute Sampling Rate
Bluetooth Off, Water Detect Enabled: 2 Years typical @ 1 Minute Sampling Rate
Bluetooth Always Off: 3 Years typical @ 1 Minute Sampling Rate
Note: Dependant Upon Environment, Operating Range, Logging Interval, Remaining Connected with the App, Excessive Downloads and Paging May Impact Battery Life
Time Accuracy ±1 Minute per Month 0°C to 50°C
Communications Type: Bluetooth Wireless
Wireless Data Standard: Bluetooth Smart (Bluetooth Low Energy, Bluetooth 4.0)
Transmission Range: Up to 30.5 Meters (100 ft) Line of Sight
Radio Power: 1 mW (0 dBm)
Software HOBOmobile 1.7 Software App for iOS and Android
Note: Bluetooth 4.0 is Required on your Mobile Device (Phone or Tablet)
OS Compatibility Android Phones and Tablets
iPhone, iPad, iPod Touch with iOS 7.1 or Later
Bluetooth 4.0 or Later
Operating Range Temperature: -2°C to 50°C (28.4°F to 122°F) - Non-Freezing
Standards Compliance CE, IP68
Environment Designed for Outdoor and Underwater Usage
Materials Data Logger:PVC Housing and Sensor End Cap, Polycarbonate Closure Caps and Mounting End Cap with a TPE Switch
pH Electrode: Plastic-Bodied with Pellon® Junctions and Gel Electrolyte, Glass pH Sensor Bulb
Weight 286.2 grams (9.46 oz.)
Dimensions 22.86 cm x 4.27 cm (9.0" x 1.68")

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  • Answer:

    Yes, this like most pH loggers and sensors typically need to have their pH electrode replaced somewhat regularly to ensure accurate readings.  With normal use Onset recommends replacing it every six months.   The electrode is available for purchase as a replacement item separately and shown on the right side of the webpage under "Related Products".   The part number is MX2500-ELECTRODE and it costs $115.  Here is a link to the page for it -



    It is also recommended that you calibrate the sensor before each use using a pH solution.  These are also listed on the page as accessory items however you are free to use any other pH solution you might already have.

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