New Refractometer

[Jhead85]

Looking for a good reliable New Refractometer..my old one won't work right..tried to calibrate it using solution and rodi water and it says it's fine but using my buddy's and brothers my salinity was reading low so I know something is wrong with mine..any suggestions on a brand most of y'all use

[wangspeed]

I switched to the milwaukee digital and haven't looked back. Hanna rebrands the same one and adds like $80.

 

 

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Warren

[cpu933k]

I tried the milwaukee digital but couldn't get it to validate with the provided validation solution or with my 53mS solution. It was about 0.002 off, which I read is within its range of error. This is after multiple attempts with lights on, lights off, palm covering the well, etc. etc. Gave up and went back to my trusty manual ATC refractometer, which exactly validated the milwaukee validation solution, milwaukee calibration solution, and my 53 mS solution.

[Origami]

I have three refractometers. All are relatively inexpensive. The first refractometer that I got was from eBay and it worked just fine, and continues to work well today. The second is one that I picked up from a WAMASer several years back. It is from Marine Depot and it works well, too, and is reliable. The third was given to me from another WAMASer, when they found that they could not get a good reading from it. It was purchased from eBay. This particular one is unusual in that the two sides of the scale (ppt and sg) don't match up for our needs. It obviously isn't for our hobby, but is probably a brine or saline refractometer. Once you calibrate it for one side of the scale, though, it seems to hold. I always calibrate these with calibration fluid made for refractometers. (This is important - some calibration fluids are mixed to calibrate conductivity meters, some for specific gravity, and some for refractive index, and some for mulitple parameters.)

 

Note that refractometers are designed to measure REFRACTIVE INDEX. Basically, it's measuring how much light bends as it passes through the thin film of tank water. This is a physical property of the water and pretty much all the refractometer is doing is just displaying a shadow line that shifts depending upon the refractive index of the water. Inside, there's an optical prism that sits on a straight band of metal and a scale on the far end, and little else. Well, there is an calibration screw that can adjust the height of the prism so that you can set the shadow on a specific part of the scale when you calibrate the device. It's interesting to note that the scale that you look into does not give you refractive index. Most of the time it's ppt and specific gravity, both of which can vary when the composition of the fluid varies. In effect, what you're looking at in the scale is a mapping of refractive index into specific gravity and ppt of salt. This mapping is specific to certain solutions. For example, the winemaking industry and beermakers use refractometers to measure the sugar content of their brews. If this scale was designed for something else (saline, sugar, etc.), the accuracy that you get at one reading may not translate to the same accuracy at another reading somewhere else on the scale. But - on the plus side - as long as the refractometer can be calibrated, can hold calibration, and adjusts reasonably to temperature, the light passing through your calibration fluid, and later your tank water, should be the same every time. That is to say, the shadow should fall on the same place on the scale every time.

 

The Milwaukee digital refractometer basically measures where a shadow falls when light reflects off of the thin film of water - that is, it measures the critical angle. Same principle, except that it does it with a sensor instead of your eyes.

 

From what I've read, one of the easier ones to calibrate is the DD H2Ocean refractometer. Introduced a few years ago, the scale is designed explicitly for our hobby and can be calibrated using RO/DI or distilled water. Not all saline refractometers will give you the right reading on your tank water if you use RO/DI or distilled to calibrate them. This can be convenient because you don't need to have calibration fluid (that you trust is accurate) on hand. This refractometer costs a little more, but might be worth considering. For a little more, you can get the Milwaukee. Otherwise, a cheaper refractometer can do, but you should calibrate it and use the same side of the scale for your measurements.

[s2nhle]

Great. thank you Tom for sharing.