Comparing the YSI Model 55 to the Pro20i and Pro20

May 18, 2017
This video compares the new Pro20i and the Pro20 to the 55.

Hi, my name is Chris Cushman and I'm an Assistant Product Manager at YSI. Today, I would like to introduce you to some replacement options for the YSI Model 55 Dissolved Oxygen Instrument.

The Model 55 has been around since 1993 and we discontinued it in 2016. So, 23 years of service for the Model 55.

Now, as far as replacement options for the Model 55, there are two that I would consider to be direct replacement options. One is called the Pro20 Instrument. It is similar to the Model 55, it uses an electrochemical dissolved oxygen sensor. 

However, there are quite a few differences between the Pro20 and the Model 55.

There's also the Pro20i that is available. It is similar to the Pro20 and as far as the differences between the Pro20 and Pro20i, the Pro20i has a built-in cable, so an integral cable, which reduces the cost of the instrument compared to the Pro20.

As far as some key differences between the Model 55 and both of our Pro20’s.

One, the Model 55 used a stretch membrane style of membrane. So, that's where you had to actually stretch the membrane over the sensor. And it was a lot more cumbersome of an install for the membrane, whereas with the Pro20 styles, these all have a cap that has the membrane already pre-stretched. So, you simply install the cap over the sensor. It makes installation of that membrane so much easier. It's definitely one of the biggest differences that you'll notice between the 55 and the Pro20 and Pro20i.

Second, it's easier to operate, the Pro20 and Pro20i. So, the Pro20 and Pro20i feature a CAL key. Rather than having to go through the menu structure of the Model 55 in order to calibrate, there's a CAL key right on the menu or right on the keypad. To quick-calibrate the Pro20, you just simply press and hold it for three seconds. So, as far as the easy use, the Pro20 and Pro20i are much easier to calibrate.

Also, there are more cable options with the Pro20 and Pro20i. With the Pro20i, cables go up to 10 meters. With Pro20, cables actually go up to 100 meters. And with the 55, they were restricted to about 15 meters in length. With the Pro20, you can also get a lab BOD, a cable, and a sensor assembly. So, that way, you can take it into the lab and measure in the lab and with the 55, you can’t do that.

Now, while I'm on the topic of cables, the 55 also has a built-in cable just like the Pro20i does. The Pro20i and the 55 are the most alike when it comes to cable. So, Pro20i is more of the direct replacement. It also has a cost that's very similar to the 55. So, I would consider the Pro20i to be more of the direct replacement for the 55.

Another difference between the 55 and the Pro20 and Pro20i is that as far as the sensing technology itself, the sensors have a little bit higher accuracy, but definitely, a much wider measurement range. And also, with the sensor caps that are available with the Pro20 and Pro20i, the membrane material that those sensing caps are made out of is a little bit different than the membrane material used on the model 55. This newer membrane material allows for faster response time and less stirring. So, therefore, you don't have to stir as much in the sample. And since you don't have to stir as much, it's gonna give you a little bit more reliable results because you don't have to focus on stirring it so much in the sample. So, the membrane material on the Pro20 and Pro20i definitely have some advantages over the 55.

Finally, another difference and a major difference between them is that the Pro20 and Pro20i are a lot more rugged. They have a three-year handheld meter warranty whereas the warranty on the Model 55 is only a two-year warranty. Also, it's easier to see in the field. So, the display is improved, and also, the cables have a two-year warranty versus a one-year warranty on the Model 55.

So, those are some of the key differences between the Model 55 and then the Pro20 and Pro20i. If you have any questions about them, please feel free to contact YSI.

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