Hanna Instruments Taiwan
The Hanna Advantage: A Worldwide Leader in Technology and Innovation 100% Quality  360 Value
Contact Hanna: +886-2-8797-2918
Hanna Instruments Worldwide
Customer Support: +1 (800) 426-6287

Advanced Dissolved Oxygen Benchtop Meter with Optical DO Probe (opdo®) - HI6421

HI6421 is a streamlined dissolved oxygen benchtop meter supplied with Hanna’s optical dissolved oxygen
probe (opdo®) and features a large touch screen display for fresh and saltwater measurements.


HI6421 is a streamlined benchtop meter with a large touch screen display, comprised of a housing and an integrated module designed for fresh and saltwater measurements of dissolved oxygen.

HI6421 includes Hanna’s HI7641133 optical dissolved oxygen probe (opdo®) that is based on the principle of fluorescence quenching. An immobilized Pt-based luminophore is excited by the light of a blue LED and emits a red light. As oxygen interacts with the luminophore it reduces the intensity and lifetime of the luminescence. The lifetime of the luminescence is measured by a photodetector and is used to calculate the dissolved oxygen concentration.

The probe is fitted with easy to use Smart Caps (HI764113-1) which lock in place and contain pre-loaded calibration coefficients that are automatically transmitted to the probe. The Smart Cap features an immobilized O₂ sensitive luminophore with rugged insoluble black oxygen permeable protective layer. Over time, the sensor’s optical components can age but are compensated for by using the reference signal to compensate the measuring path. As a result, the sensor provides accurate DO measurements over long periods of time without the need for frequent calibration. Concentration measured. Additional features include built-in methods and calculations for the measurement of BOD (Biological Oxygen Demand), OUR (Oxygen Uptake Rate), and SOUR (Specific Oxygen Update Rate). Pressure compensation is done automatically (built-in barometer) or users have the option to manually enter required value. Pressure is displayed in user-configurable units: mmHg, mbar, kPa, inHg, psi, atm.


Features at-a-glance

User interface

  • 7-inch capacitive touch screen with multi-touch support
  • Capacitive touch back, home and system menu keys
  • User-friendly icons and symbols allow users to easily navigate and interpret the instrument functions

The user can select between five different views:

  • Basic measurement configuration
  • Simple GLP with calibration information
  • Full GLP with electrode status and calibration point details
  • Live updated, interactive graph
  • Tabulated data with date, time, and notes


  • Measure %Sat, mg/L, ppm (DO); mg/L, ppm (BOD); mg/L (OUR); ppm, mg/L (SOUR)
  • Application-specific profiles allow quick and direct measurement without the need to update the
    sensor and system settings
  • Active log during measurement Measurement stability indicator (using the Stability Criteria setting)
  • Reading modes: direct and direct/auto-hold
  • Temperature compensation can be Automatic or set manually
  • Audible and/or alarm messages for measurements outside of predefined limits
  • Galvanic isolation for measurement


  • One or two points calibration at 0% and/or 100% saturation
  • Single point manual calibration in mg/L or % saturation using a reference method
  • Non-volatile memory saves data and settings


  • Data log collection of at least 1, 000, 000 data points (with time and date stamp)
  • Logging types: manual, automatic, auto-hold
  • Sample ID for manual and auto-hold data

Connectivity features & services

  • Transfer logged data ta USB thumb drive
  • Log files that include measurements and calibration data (as .csv file)
  • FTP and email for log export via Ethernet and Wi-Fi connection
  • USB type A for USB stick, keyboard, and printer
  • USB type C for USB stick and PC connection

Help section for meter guidance

  • Video support presentation of main functionalities

Ordering Information:

HI6421 is supplied with HI7641133 optical dissolved oxygen probe (opdo®); HI764060 electrode holder; capillary pipette; 24 VDC power adapter; USB-C to USB-A cable; probe quality certificate; quick reference guide with instrument quality certificate.


HI7641133 optical dissolved oxygen probe (opdo®)
HI764113-1 Smart cap with O-ring
HI764113-2 Calibration/storage vessel
HI764113-3 Stainless steel protective shield

Additional information

Weight 12.02 kg

Dissolved, Oxygen


SKU HI6421
Name Advanced Dissolved Oxygen Benchtop Meter with Optical DO Probe (opdo®) – HI6421
DO (HI7641133 Optical probe) Range 0.00 to 50.00 mg/L (ppm) concentration; 0.0 to 500.0 % saturation
DO (HI7641133 Optical probe) Resolution 0.01 mg/L (ppm); 0.1 % saturation
DO (HI7641133 Optical probe) Accuracy from 0.00 to 20.00 mg/L (ppm) 1.5 % of reading or ± 0.01 mg/L (ppm), whichever is greater from 20.00 to 50.00 mg/L (ppm) ±5 % of reading from 0.0 to 200.0 % saturation ± 1.5 % of reading or ± 0.1 %, whichever is greater from 200.0 to 500.0 % saturation ±5 % of reading
Barometric Pressure Range 450 to 850 mmHg; 600 to 1133 mBar; 60 to 133 kPa; 17 to 33 inHg; 8.7 to 16.4 psi; 0.592 to 1.118 atm
Barometric Pressure Resolution 1 mmHg; 1 mBar; 1 kPa; 1 inHg; 0.1 psi; 0.001 atm
Barometric Pressure Accuracy ±3 mmHg within ±15 % from the calibration point ±3 mmHg ±1 least significant digit
Temperature Range −20.0 to 120.0 °C −4.0 to 248.0 °F 253.0 to 393.0 K
Temperature Resolution 0.1 °C; 0.1 °F; 0.1 K
Temperature Accuracy ±0.2 °C; ±0.4 °F; ±0.2 K
DO Calibration Points One or two points automatic calibration at 100% (8.26 mg/L) and 0% (0 mg/L). Single point manual using a value entered by the user in % saturation or mg/L.
DO Calibration Standards 0 and 100% saturation
DO Calibration Reminder Disabled Daily: 0 m in. to 23 hours and 59 m in. Periodic: 1 m in. to 500 days, 23 hours and 59 m in.
Temperature Compensation Automatic or Manual
Salinity Compensation Automatic from 0 to 70 PSU (manually set) 0.0 to 70.0 % / 0.0 to 45.0 g/L / 0.0 to 42.0 psu
Reading Modes Direct Direct/Autohold
Reading Stability criteria Accurate Medium Fast
Reading Isopotential 7.000 or 4.010
Reading Sampling rate 1000 ms
DO Views Basic Measurement (DO, Temperature) Stability status
DO Views Simple GLP Basic view information Last calibration date, offset, average slope
DO Views Full GLP Simple GLP information and calibration point details
DO Views Table Measurements updated every second are displayed in table
DO Views Graph (Plot) Measurement versus time graph can be panned or zoomed (pinch-to-zoom technology)
Logging Type Automatic, Manual, Autohold
Logging Number of records 50 000 maximum per file Stores at least 1 000 000 data points per user
Logging Automatic interval 1, 2, 5, 10, 30 seconds / 1, 2, 5, 10, 15, 30, 60, 120, 150, 180 minutes
Logging Sample ID Incremental mode
Logging Export option .csv file format
Users Up to 9 users and the default administrator account
Connectivity USB-A 2 ports for keyboard input or USB thumb drive
Connectivity USB-C 1 port for PC connectivity and USB-C type thumb drive
Connectivity Wi-Fi & Ethernet FTP / Web server Log transfer and download Email
Connectivity RS232 Connecting peripherals
Power supply DC adapter 100-240AC to 24VDC 2.5A
Environment 0 – 50 °C / 32 – 122 °F / 273 – 323 K maximum 95% RH non-condensing
Dimensions 205 x 160 x 77 mm (8.0 x 6.2 x 3.0 “)
Weight 1.2 kg (26.5 lbs.)1


Advanced Dissolved Oxygen Benchtop Meter with Optical DO Probe (opdo®) – HI6421