Hanna Instruments Australia
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Sales: (03) 9769 0666   |    Mon to Fri: 8:30am – 5:00pm
Hanna Instruments Australia
Sales: (03) 9769 0666   |    Mon to Fri: 8:30am – 5:00pm

Advanced Dissolved Oxygen Benchtop Meter - HI6421



Prices include GST. Not all items are in stock. Call 03 9769 0666 to confirm.

HI6421 and HI6421P are streamlined benchtop meters with a large touch screen display, comprised of a housing and an integrated module designed for fresh and saltwater measurements of dissolved oxygen.

  • 7-inch Color Display
  • 800 x 480p Resolution
  • Capacitive Multi-touch Screen and Keys
  • Ethernet and Wi-Fi Connection
  • USB type A & type C


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

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 a 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 for the measuring path. As a result, the sensor provides accurate DO measurements over long periods of time without the need for frequent calibration.

Advanced Dissolved Oxygen Meter with Polarographic DO Probe

HI6421P includes the HI764833 polarographic probe. Slim and versatile, this probe covers a wide range of dissolved oxygen and has a built-in thermistor temperature sensor that compensates for temperature variations. The slim design allows for convenient measurement in test tubes and Biological Oxygen Demand (BOD) bottles.

Durable and robust, the probe features a platinum cathode and Ag/AgCl anode assembly. Accurate and with a fast response time, readings are not flow dependent.

The probe is fitted with durable (PTFE), oxygen permeable, screw on membrane caps. Caps are filled with electrolyte and easily installed on the probe.

Concentration measurements are automatically compensated for barometric pressure, temperature, and salinity. Barometric pressure and temperature are automatically measured and compensated. Salinity is automatically compensated by setting manually the salinity concentration of the water being measured.

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.

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.

Five Intuitive 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


  • 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/autohold
  • 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

Zero Oxygen Calibration Solution

When performing a DO calibration, it is important that the correct standards are used. We include some starter solution to get you going. HI7040L is a bi-component zero oxygen solution designed so you can quickly calibrate to 0% oxygen concentration.



  • Data log collection of up to 1,000,000 data points (with time and date stamp)
  • Logging types: manual, automatic, autohold
  • Sample ID for manual and autohold data

Connectivity Features & Services

  • Transfer logged data to a 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

Smart Cap Technology

Automatic Cap Recognition

Hanna’s Smart Caps feature a built-in RFID reader that is able to store important data, including manufacture date and first-use date for increased traceabilty.

Longer Life

Smart Caps last one year from the date of first use. Your meter will automatically count down from initialization and will have your meter remind you when it has expired with an on-screen message.

Aligned Right Every Time

An alignment key ensures that your Smart Cap is on correctly every time.

Specification Name Detail
SKU HI6421
DO Range HI6421 - HI7641133 Optical probe: 0.00 to 50.00 mg/L (ppm) concentration; 0.0 to 500.0% saturation
HI6421P - HI764833 Polarographic probe: 0.00 to 90.00 mg/L (ppm) concentration; 0.0 to 600.0% saturation
DO Accuracy (@25˚C/77˚F) HI6421 - HI7641133 Optical probe: 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
HI6421P - HI764833 Polarographic probe: ±1.5 % of reading ±1, least significant digit
DO Resolution HI6421 - HI7641133 Optical probe: 0.01 mg/L (ppm); 0.1% saturation
HI6421P - HI764833 Polarographic probe: 0.01 mg/L (ppm); 0.1% saturation
DO Calibration DO optical:
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 polarographic:
Automatic-two points / User standard-single point
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 Probe HI6421: HI7641133 Optical probe
HI6421P: HI764833 Polarographic probe
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 Approximately 1.2 kg (26.5 lbs.)
Warranty 2 years

HI6421-02 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.

HI6421P is supplied with HI764833 polarographic probe; 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.

All prices are inclusive of GST and not all items are stock items, if you require an immediate solution please send an email to sales@hannainst.com.au or call us on (03) 9769 0666.

Free standard delivery: We offer free delivery within Australia on orders over $100, typically arriving within 5 to 7 days. Delivery times may vary depending on the courier service and the recipient's location. Free shipping is not available with other offers or discounts.

Same-day despatch: Place your order before 1 PM Monday to Friday for same-day despatch. Delivery times may vary depending on the courier service and the recipient's location. Subject to stock availability.

Please note that we do not offer shipping to PO Box addresses.

Additional information

Weight 1.2 kg