U26 Dissolved Oxygen Logger

A low-cost data logger for measuring concentrations of oxygen in lakes, streams and rivers

The HOBO U26 combines the high accuracy, robust performance of industry-leading RDO® Basic (Rugged Dissolved Oxygen) sensor technology with an easy-to-maintain design.

  • Affordable, high performance dissolved oxygen (DO) monitoring with 0.2 mg/L accuracy
  • Optical DO sensor technology for long-lasting calibration with less maintenance
  • Dissolved Oxygen Assistant software corrects for measurement drift from fouling; provides salinity-adjusted DO concentrations and percent saturation
  • Optical USB interface for high-speed, reliable data offload
  • Easy-to-replace DO sensor cap lasts six months


NOTE: If you need to measure DO in saltwater environments, salinity or conductivity measurements are required. If you need DO in Percent Saturation, barometric pressure data is required, which can be logged with a HOBO Water Level Logger (U20-001-04).



  • Sensor Type: Optical
  • Measurement Range: 0 to 30 mg/L; Calibrated Range: 0 to 20 mg/L; 0 to 35°C
  • Accuracy: 0.2 mg/L up to 8 mg/L; 0.5 mg/L from 8 to 20 mg/L
  • Resolution: 0.02 mg/L
  • Response Time: To 90% in less than 2 minutes
  • DO Sensor Cap Life: 6 months, cap expires 7 months after initialization
  • Temperature Measurement: -5 to 40°C; non-Freezing
  • Temperature Accuracy: 0.2°C
  • Temperature Resolution: 0.02°C
  • Memory: 21,700 sets of DO and temperature measurements (64 KB total memory)
  • Battery: 3.6 V lithium battery; factory replaceable; Battery Life 3 years (at 5 minute logging)
  • Depth Rating: 100 m
  • Wetted Materials: Black Delrin®, PVC, EPDM o-rings, silicone bronze screws; rated for saltwater use
  • Size: 39.6 mm diameter x 266.7 mm length; Weight 464 g


About the manufacturer

Based on Cape Cod, Massachusetts, Onset has been designing and manufacturing its data loggers and monitoring solutions on site since the company's founding in 1981. Specialising in miniature, battery powered solutions, Onset data loggers are exceptional quality and value, ranging from indoor to outdoor and underwater applications. HOBO® data logger and weather station 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.


Alliance for Coastal Technologies Performance Verfication Statement for the U26

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DO datalogger brochure

File Size 225KB   Filename onset_hobo_u26_dissolved_oxygen_data_loggers-1.pdf   Download

DO technology backgrounder

File Size 776KB   Filename do-technology-backgrounder_-_new.pdf   Download

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