Manufacturer: YSI
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The YSI 550A dissolved oxygen meter features a waterproof IP-67, impact-resistant case and innovative field-replaceable DO electrode modules.

Measure temperature and dissolved oxygen simultaneously using highly accurate thermistors and YSI's proven polarographic technology for dissolved oxygen. The fastest DO response times on the market.

Measurements are fast and easy with one-hand operation, an easy-to-use backlit display, automatic push-button calibration, and a weighted, quick-sinking probe. The YSI550A DO has a built-in calibration chamber, low-battery indicator, direct salinity, and altitude compensation. The instrument provides simultaneous readings of oxygen and temperature. Dissolved oxygen readings are automatically compensated for temperature.

Screw-on cap membranes make membrane changes easier than ever. The PE membranes are also faster responding and require far less flow dependence.

The replaceable electrode decreases any down time due to old or damaged electrodes. Simply unscrew the old electrode, replace it with a new one, and calibrate! No need to send it in or to replace the whole cable assembly.

Key Features

  • Field-replaceable DO electrode modules
  • Screw-on cap membranes
  • IP-67 case
  • Over 2000 hours battery life
  • Calibrate in either mg/L or % saturation


  • 12, 25, 50, or 100- foot lengths


  • Push-button, built-in calibration chamber


  • CE
  • IP-67
  • High-impact resistance


  • 11.9 cm width x 22.9 cm length (4.7"  x 9")


  • Large, backlit


  • Fresh, sea, or polluted water

Parameter Compensation

  • Automatic temperature compensation for dissolved oxygen
  • Automatic salinity compensation with manual salinity input from 0-70 ppt for dissolved oxygen
  • Altitude compensation for calibration


  • 4 alkaline C-cells
  • Over 2000 hours at 25° C
  • Low battery indicator on display

Weight with Batteries

  • 0.91 kg (2 lbs)
Sensor Type
Range Accuracy Resolution
Dissolved Oxygen (%) Steady-state Polarographic 0 to 500% air saturation 0 to 200%: ±2% of reading or 2% air saturation, whichever is greater; 200 to 500%: ±6% of reading 0.1% air saturation or 1%; selectable
Dissolved Oxygen (mg/L) Polarographic 0 to 50 mg/L 0 to 20 mg/L: ± 0.3 mg/L or 2% of reading, whichever is greater; 20 to 50 mg/L: ±6% of reading 0.01 mg/L or 0.1 mg/L; selectable
Temperature Thermistor -5 to 45°C ±0.3°C 0.1°C