APERA INSTRUMENTS / SX716 / AI461

Dissolved oxygen in the field.
A serviceable polarographic system.

SX716 pairs a DO500 polarographic oxygen probe with a dedicated handheld meter for dissolved oxygen and temperature checks. Read concentration in mg/L or ppm, or oxygen saturation in percent. Its backlit screen, 100-set memory and fitted carrying case support a practical field workflow.

Choose AI461 for routine dissolved oxygen measurements when you can maintain a membrane electrode and keep water moving across its tip. DO500 is polarographic, not the DO803 optical sensor. Polarization, electrolyte and membrane care are part of this method, not optional accessories.

Compensate for the water you are testing

DO500 contains temperature and salinity sensors. DO compensation is automatic over 0 to 45°C and 0 to 45 ppt; barometric pressure is entered manually over 66 to 200 kPa. The P3 example of 101.3 means kPa, not mbar. These corrections do not remove the need for calibration, clean sensors or adequate water movement.

See the reading and the instrument state

The LCD combines DO, temperature, unit and status symbols. A smile indicates a stabilized reading; M+ and RM distinguish saving from recall. The original manual diagram identifies these indicators. Its all-segment display is explanatory artwork, not a measured sample or a performance certificate.

Replace the membrane, not the whole workflow

The DO503 cap holds a sensitive membrane over the gold cathode and silver anode. DO502 inner solution completes the serviceable assembly. Keep spare caps clean and avoid touching their membrane faces. The kit includes the maintenance materials and a screwdriver; replacement frequency depends on condition, not a promised fixed service interval.

Know what this configuration supplies.

Aquaculture and surface-water rounds

Compare oxygen conditions in compatible pond, aquarium or surface-water samples. Let the probe approach sample temperature and maintain flow across the membrane. Record location and collection time separately so readings remain meaningful after on-meter recall.

Treatment and process-water spot checks

Use spot measurements to follow oxygen changes in general water solutions. DO500 consumes oxygen during measurement, so stagnant samples can read progressively lower. Suspended solids can foul the membrane; this is not a no-flow or maintenance-free process sensor.

Training with visible maintenance steps

The replaceable membrane, sleeve and original electrode figures make preparation and care easy to explain. A field reading does not establish potability, regulatory compliance or biological safety. Strong acidic or alkaline water and organic solutions are outside DO500’s listed suitable samples.

Polarize first.
Calibrate, then keep the water moving.

Connect DO500 to the powered meter and allow five minutes of polarization after every power-on. After changing the membrane cap or electrolyte, allow 30 minutes instead. The response specification is no more than 30 seconds to 90% response at 25°C, not a guarantee of a fully stable result in 30 seconds.

For routine 100% calibration, moisten the sleeve sponge with several drops of distilled water without making it drip. Insert the probe, tighten the sleeve cap and enter CAL. Allow three to five minutes, longer if unstable, then confirm only after stabilization. Keep calibration and sample temperatures within 10°C; for a larger difference, precondition the probe in sample water for about ten minutes.

Immerse above the temperature sensor and hold the probe at 45° to 75° to the water surface. In flowing water, wait for stability and swirl slowly if needed. In static water, keep swirling faster than 5 cm/s for one to five minutes and continue while recording. A large temperature difference requires more than three minutes. Stopping motion lets the electrode deplete nearby oxygen.

The specification also lists air-saturated water, but the detailed routine procedure uses water-saturated air in the sleeve. Optional zero calibration is intended for demanding work below 1.0 ppm. Follow the manual’s fresh sodium-sulfite solution, 15-minute polarization and acceptance checks. Arbitrary custom DO calibration points are not documented. Salinity is factory-calibrated; after electrode replacement, the P2 procedure uses separately purchased 12.88 mS/cm standard.

Keep the membrane clean.
Keep the sleeve sponge moist.

Between uses, protect DO500 in its calibration/storage sleeve with the sponge moist from a few drops of distilled water, not dripping. Do not fill this sleeve with pH KCl storage solution. Rinse the probe after testing and inspect the membrane and electrolyte for damage or bubbles. Keep the electrical connector clean and dry.

Replace a wrinkled, cracked or damaged membrane, or investigate slow response and obvious errors. Unscrew the cap, rinse the exposed electrode with distilled water and shake off excess. Wipe the gold cathode with clean tissue. Slowly add fresh DO502 to a new DO503 cap without bubbles, stand it on a table and screw the electrode vertically into it. Wipe expelled electrolyte, rinse and check again for bubbles; reassemble if necessary.

For a contaminated gold cathode, use DO504 polishing paper lightly along the curved gold surface, then clean, rinse and refill as instructed. Never brush the platinum-black salinity sensor; swirl it in pure water instead. Re-polarize after fresh electrolyte and recalibrate before measurement. Handle electrolyte with appropriate protection and consult its safety instructions.

Read the display. Check the measurement mode.

Use the physical controls for measurement, calibration and the documented record functions. Check units, temperature, calibration indicators and the selected parameter before assigning a result to a sample. Screen values in photographs are illustrative, not sample results. The model-specific record and output workflow is explained below.

Follow the exact parameter-specific calibration procedure, using the required standard, solution or calibration atmosphere. Temperature compensation does not make different sample temperatures, preparation methods or chemistry equivalent. Follow the model-specific meter and electrode instructions before extending the method to a new sample.

Save 100 sets.
Recall locally and keep a separate field log.

When the smile remains on screen, a short press of M+/RM stores the reading. SX716 holds up to 100 sets containing serial number, measurement value, unit and temperature.

A long press recalls the last saved record; use the review keys to browse. The manual’s delete operation in recall mode clears all saved data, so transcribe needed readings first. No date/time fields, real-time clock setting, timed automatic logging, USB, Bluetooth or PC-Link export workflow is documented for this model. “Data logging” here means operator-initiated save and recall.