The YSI Pro20i Dissolved Oxygen Meter

About the YSI Pro20i Dissolved Oxygen Meter

YSI releases the new Pro20i handheld dissolved oxygen instrument for quick and accurate DO measurements in the field.

YSI-Pro20i.jpgThis newest addition to the Professional Series family of rugged handhelds features an integral (non-detachable) cable, making it the perfect replacement for the YSI 55 and 550A at a price point that is lower than other, full-featured, Professional Series instruments.

It’s been a year of change in the world of dissolved oxygen measurements with the discontinuation of the YSI 55 and 550A instruments that we know you loved. We discontinued the model 55 in February, 2016 and announced that the 550A will be discontinued in December, 2016. As always, YSI honors our commitment to support products for 5-years after their discontinuation date. 

The Pro20i is not just a replacement for the 55 and 550A, it’s an upgrade! It is rugged and designed for the field with IP-67 waterproof rating and 1-meter drop test. And, it is by far our easiest DO instrument to use with:

  • One touch calibration – simply press and hold the Cal button and let the instrument do the rest!

Calibration of the YSI Pro20 and Pro20i are the same. Simply press and hold the 'Cal' key for 3 seconds.

  • Fastest DO response time on the market
  • User replaceable electrodes
  • Easy-to-replace cap membranes
  • Simple key pad and user interface
  • One hand operation; easy-to-hold with slip-proof rubber over-molded case

With ease comes accuracy and the Pro20i is more accurate than the legacy handhelds with an accuracy of +/-0.2 mg/L compared to +/-0.3 mg/L.


Other improvements include:

  • Superior cable and longer warranty: 3 year instrument, 2 year on the cable
  • Choice of two electrodes:
    • Polarographic – 1 year warranty, requires 5 to 10 minute warm-up time
    • Galvanic – 6 month warranty, no warm-up required
  • Polyethylene membrane lowers stirring requirement by 50 to 75% compared to traditional membrane material
  • 50 data set memory
  • Internal barometer for more accurate measurements and quick calibration
  • Ability to display DO % Local
  • English, Spanish, German and French

To better compare the Pro20i with other Professional Series instruments, the Model 55, and the Model 550A, check out the updated YSI Professional Series Poster and the new YSI DO Instrument Selection Guide. Also check out the Pro20i webpage.

>> Download the Pro20i specifications sheet



Additional Blog Posts of Interest

Do You Know How to Select the Right Water Quality Instrument?

Rugged, Field-Proven Water Quality Meters | 3 Real Life Examples

Nonload Parameters in Surface Water | Dissolved Oxygen

Environmental Dissolved Oxygen Values Above 100% Air Saturation 

4 Responses to this article

I have a YSI 550A unit and I think the DO probe is shot. How much does a unit cost and how do I go about ordering it. I did not find the probe listed among the parts so tell me how to proceed. It seems to be an old model. quick question, how do I test to see if the unit itself is ok? Is there a self-test mode? thanks. RG


Raul - I sent your information to our Tech Support group and they will respond and help you out directly via your email. Thanks! (


Greetings We are water treatment company in Dubai we are looking for DO meter YSI pro 20 Best regards


Thank you for your interest in YSI products. Someone will be reaching out to you shortly to get you pricing/delivery info.


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