Issues with Milwaukee MA887 Refractometer

[Randy Holmes-Farley Verified Community Expert]

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.

 

[Patx]

strange reading too...
brand new m887.
2 calibration (new) fluid 1.026 pinpoint bottles.
calibrate whit the 0ppm milliwaukee fluid.

results: 1.028

i recalibrate whit ro/di

result:1.028

same temperature. 23.4c

 

[Randy Holmes-Farley Verified Community Expert]

strange reading too...
brand new m887.
2 calibration (new) fluid 1.026 pinpoint bottles.
calibrate whit the 0ppm milliwaukee fluid.

results: 1.028

i recalibrate whit ro/di

result:1.028

same temperature. 23.4c

The claimed accuracy is only +/- 0.002 specific gravity, so 1.028 is within specifications of 1.026.

MA887 Digital Refractometer for Seawater Measurements

The MA887 is an optical instrument that employs the measurement of the refractive index to determine the salinity of seawater

www.us.milwaukeeinstruments.com

 

[Pistondog]

strange reading too...
brand new m887.
2 calibration (new) fluid 1.026 pinpoint bottles.
calibrate whit the 0ppm milliwaukee fluid.

results: 1.028

i recalibrate whit ro/di

result:1.028

same temperature. 23.4c

Make sure the sample is at the same temp as the instrument. You might have to wait a minute or 2.

 

[Patx]

it was
calibrate whit 0ppm at 23,4c
test 1.026 at 23,4c
always 1.028.

i try 1.026 fluid at 21c too... (calibrated at 23,4c)
still 1.028...

i will probably keep my SG at 1.027... 1.028 on the m887...
last thing to test, home made 35ppt solution, by curiosity..

 

[tbasinger]

I worked in a jellyfish lab with about 85 2 liter tanks, I was constantly measuring salinity and had one of those, it was a lifesaver. It is mostly accurate. In my opinion people get way to obsessed with salinity measurements. As long as the change is gradual most species can tolerate a fairly wide range.

 

[Randy Holmes-Farley Verified Community Expert]

I worked in a jellyfish lab with about 85 2 liter tanks, I was constantly measuring salinity and had one of those, it was a lifesaver. It is mostly accurate. In my opinion people get way to obsessed with salinity measurements. As long as the change is gradual most species can tolerate a fairly wide range.

I agree with that, certainly. Reef aquarists are fortunate that the acceptable salinity range is quite wide.