YSI offers several models of field Dissolved Oxygen (DO) meters.  Below, I have listed the different models and their features and benefits.

DO200:  The DO200 is part of YSI's "Eco-Sense" product group.  It features a detachable cable from the display/meter and #5908 screw-on P/E cap membranes.  The DO200 is the entry level DO meter and is well suited for use in education, aquariums, and fishing.  The DO200 is splash-proof, but not submerisble.  It is calibrated using water-saturated air and by inputting the local elevation.  Cables are available in 4 and 10 meter lengths (~12 ft. & 33 ft.).  The DO200 has a factory warranty of 1 year on the meter, cable & probe. YSI has a BOD probe that works with this meter.  So it can be used both in the field and in the lab.  In fact, it's the least expensive BOD set-up I've seen. The DO200 meter is sold separately from the cable - so be sure to order a DO200 meter and DO200 cable/probe.  We offer the DO200 with 4 meter cable for $400.

Model 55: The Model 55 has been on the market for many years now and is commonly used in waste-water treatment and aquaculture.  The meter is rugged and durable and the 6 ea. AA batteries will power the instrument for over 100 hours of "on-time".  The Model 55 uses #5775 teflon stretch type membranes.  It is splash-proof, but is not submersible.  It is calibrated by using water-saturated air and by inputting the local elevation.  This model has an optional detachable cable connection and comes with cables in 12, 25 & 50 ft. lengths.  The Model 55 comes with a 1 year warranty on meter, cable & probe.  We sell the Model 55 meter with 12 ft. cable for $560.

Model 550A:  In my opinion, the Model 550A is the best value of these three meters.  If you are a professional or need a rugged field meter, I think the 550A is the only way to go.  The 550A has the following advantages:  3 year warranty on display (1 year on cable & probe); User-replaceable DO Probe Module;  #5908 screw-on P/E cap membranes; Submersible display; and water-saturated air or air-saturated water calibration function.  The 550A is bulkier & heavier than the Model 55, but I think it is more field-rugged.  It is powered from 4 ea. C cell batteries which provides over 400 hours of "on" time.  There is no detachable cable option for this meter.  Cables come in 12, 25, 50 & 100 ft. lengths.  We sell the Model 550A meter with 12 ft. cable for $645.   

Model 550 -- this meter was discontinued a few years ago and replaced with the 550A.   

Models 52/58:  We still offer these meters, but have had few requests for them over recent years.  The 52 & 58 have the versatility of being used both in the lab (BOD) & in the field.  The 52 & 58 tend to be too costly to justify -- since a customer can usually purchas a field DO meter and a lab DO meter for essentially the same price.  Why have both field & lab measurements tied to the same meter?  If it goes down, then neither data can be collected.  The 52 & 58 meters are sold separately from the cable and probes. 

Please inquire if you have a question about these meters or visit our eBay store "The Water Monitor" to purchase these meters.