YSI Pro20i Dissolved Oxygen Instrument

Instrument, cables, probes/sensors included.

Dissolved oxygen and temperature handheld instrument with integral cable. The Pro20i is a direct replacement for the model 55 and 550A dissolved oxygen instruments.

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Easy to use, rugged and reliable, the YSI Pro20i provides everything you need in a handheld instrument for the measurement of dissolved oxygen. User-friendly and convenient calibration routine and 50 data set memory. A true field instrument with IP67 waterproof, rubber over molded case, and 1-meter drop tests ensure durability to provide years of sampling even in the harshest field conditions.

Features Include:

  • Integral (i.e. built-in) cable with 1- 4- 10-m field cable; user-replaceable DO sensors
  • One Touch Cal allows for easy DO calibrations within 3 seconds with the press of a button. Automatic barometric pressure compensation.
  • Quick response times; 95% response time in approximately 8 seconds with standard membrane (fastest response time on the market)
  • Stores 50 data sets; no need to write down data
  • Large graphic, backlit display and glow in the dark keypad
  • A true field instrument – the display is visible when wearing polarized sunglasses
  • Tough. IP-67, impact-resistant, waterproof case. Waterproof with and without the battery cover
  • Rubber over molded case provides extra durability
  • Multiple languages: English, Spanish, French, and German
  • 3-year instrument; 2-year integral cable; 1-year polarographic sensors; 6-month galvanic sensor warranty


Cable Options 1- 4- 10-m lengths (3.28, 13.1, 32.8 ft.)
Certifications RoHS, CE, WEEE, IP-67 waterproof, 1-meter drop test
Languages English, Spanish, German, French
Memory 50 data sets
Power 2 alkaline C-cells providing ~400 hours of battery life (without backlight); low battery indicator when 1 hour is left

8.3 cm width x 21.6 cm length x 5.6 cm depth (3.25 in. x 8.5 in. x 2.2 in.)


3-year instrument; 2-year cable; 1-year polarographic sensors; 6-month galvanic sensors

Weight 475 grams (1.05 lbs.) (with batteries)




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