General Description & Intended Use 6
4. GENERAL DESCRIPTION & INTENDED USE
HI6421 is an advanced benchtop meter with a capacitive display, comprised of a housing and an integrated
dissolved oxygen (DO) measurement module.
Compact and easy to operate, HI6421 is delivered either with HI7641133 optical dissolved oxygen (opdo
®
)
probe or HI764833 polarographic probe. When delivered with polarographic probe meter ordering code is HI6421P.
Designed for fresh and saltwater measurements of dissolved oxygen, the system responds to a complex range
of measurement and monitoring requirements, providing accuracy, reproducibility, and reliability.
HI7641133 optical DO probe (with HI764113‑1 Smart Cap) provides accurate DO
measurements over long periods of time reducing the need for frequent calibration. The
Smart Cap, pre‑loaded with calibration coefficients, includes the immobilized O
2
sensitive
luminophore with rugged, insoluble black oxygen permeable protective layer.
The principle of operation is based on the principle of fluorescence quenching and features
an immobilized Pt‑based luminophore that is excited by the light of a blue LED and emits
a red light. Dissolved oxygen quenches this excitation. When there is no oxygen present,
the lifetime of the signal is the greatest; as oxygen hits the sensing surface, the lifetime
becomes shorter.
The intensity and lifetime are inversely proportional to the amount of oxygen present; 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. This is, in turn,
reported by the meter as % saturation or mg/L of dissolved oxygen.
HI764833 polarographic probe features a platinum cathode and Ag/AgCl anode assembly, and a built‑in
temperature sensor that compensates for temperature variations. The probe is fitted with a PTFE screw cap
membrane that separates the probe’s cathode and anode from the sample being measured. Oxygen diffuses
across the membrane and interacts with the polarographic system to produce a current proportional to oxygen
concentration.
The cap is filled with HI7041 electrolyte and screwed on to the probe.
Probe connection to the unit is secured through a DIN connector.
The meter is supplied with an electrode holder that has a flexible arm. The holder can be mounted quickly and
provides secure support for electrodes while taking measurements in sample containers.
This benchtop meter supports:
• USB type A – support for USB drive, printer (standard or thermal), keyboard
• USB type C – support for USB drive, PC connection
The user can select between five different views.
• Basic measurement configuration
• Simple GLP with calibration information
• Full GLP with probe status and
calibration details
• Live updated, interactive graph
• Tabulated data with date, time, and notes
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