Milwaukee MA887 digital refractometer, give it a minute and different readings?

[nim6us]

So this one has been itching at me a while but thought I’d finally ask it to the group.

I’ve got a MA887, the green one, and I noticed when I put the water in and take a reading in PPT I get one number but if I forget to empty it and out of curiosity read the sample 10 minutes later I get a different reading. It’s always seems to be 1ppt difference so not that concerning. I always calibrate and do my water test in the same way meaning the information I’m working from is at least consistent. However I just wondered if anyone had the same experience? And for bonus points which reading is likely to be more accurate? Maybe on for @Randy Holmes-Farley

 

[JMSKI333]

I’d recommend comparing it up against other salinity tests or testing it up against confirmed calibration solution. If it reads those accurately then I wouldn’t worry. A few drops of water can evaporate pretty quickly altering salinity.

 

[TankCandy]

I wonder if it's the temperature difference as the sample cools down. Curious to see what you find. I have been looking into one of these.

 

[leighton.bingham]

I have one of those and it does the same thing. I end up taking three different samples and go with the highest of the two. Its not perfect but its pretty close.

 

[nim6us]

It’s tough because I have been using calibration fluid and even with that depending on the time left in the well the results fluctuate.

Regarding temperature from my understanding that’s only a factor for SG where PPT isn’t affected by temp.

I found a great video from Treasure Corals where they were doing a comparison on testers and he stumbled into the same issue I’m describing.


I’ve since done experiment on my DT water. I pressed read immediately and then read the same sample again every 1 minute for 6 minutes. I did this with 3 different samples to compare the data, so 18 total readings. And the result was the same on all 3 samples.

From reading the sample immediately up to the first 2 minutes the results were fluctuating. BUT after from the 3 minute mark to the 6 minute mark the results were rock solid.

The conclusion for me; I’m going to continue to calibrate once a month and when I take a sample I’ll wait 3 minutes before taking a reading. I’m sure there’s a million holes in my theory mostly because Milwaukee says in their instructions there’s a plus or minus range of TWO whole PPT.

 

[Waters]

I have found that I have to calibrate before every reading and let the sample sit for at least a minute.....then I get consistent readings that match my other refractometers.

 

[Acros]

I let the water sample sit for a minute (not longer), so that the temp settles to somewhat stable.

I also have 2 MA887, I always use both at the same time for redundancy. Once both meters read 1.026 (which it does 99% of times), I consider salinity to be ok.

 

[Randy Holmes-Farley Verified Community Expert]

I agree that it may be a temperature issue.

This copy and paste to here is from your other post I responded to:

Regarding temperature from my understanding that’s only a factor for SG where PPT isn’t affected by temp.

I found a great video from Treasure Corals where they were doing a comparison on testers and he stumbled into the same issue I’m describing.


I’ve since done experiment on my DT water. I pressed read immediately and then read the same sample again every 1 minute for 6 minutes. I did this with 3 different samples to compare the data, so 18 total readings. And the result was the same on all 3 samples.

From reading the sample immediately up to the first 2 minutes the results were fluctuating. BUT after from the 3 minute mark to the 6 minute mark the results were rock solid.

The conclusion for me; I’m going to continue to calibrate once a month and when I take a sample I’ll wait 3 minutes before taking a reading. I’m sure there’s a million holes in my theory mostly because Milwaukee says in their instructions there’s a plus or minus range of TWO whole PPT.

That first statement is somewhat confusing as written.

It is true that ppt doesn’t change with temp, but it is also true that sg also hardly changes with temp.

BUT, refractive index, which this device is measuring, changes alot with temperature. Hence, if temperature is not bring correctly accounted for by the device, the readings will be off, regardless of the units of measure reported.

 

[G Santana]

I have one of those and it does the same thing. I end up taking three different samples and go with the highest of the two. Its not perfect but its pretty close.

This is exactly what I do with mine!!!