Why New Milwaukee Refractometer has higher readings

[Jyetman]

Calibrated MA887 as to the instructions with distilled water. Tested with pinpoint salinity 53.0 calibration fluid. According to the bottle it should read 1.026 but digital reads 1.028? Not in direct light, wiped clean drip well and recalibrated numerous times same results what am I doing wrong?

[slief]

Not sure why you love creating duplicate threads but as I said in your other thread on the same subject...

Does the distilled water temp match that of the 53mS solution?

FWIW, If you read the specs on this tester, you would see that this tester is only accurate within .002 so at a 1.028 reading of 53mS (1.026) solution, you are within it's accuracy range. When you calibrate with fresh water, the accuracy decreases as the salinity increases. This is the same reason why it's not recommended to calibrate a refractometer with distilled water as opposed to 53mS solution.

I use the Pinpoint Salinity Monitor because it is calibrated with 53mS/1.026 solution and because you are calibrating with solution that matches natural seawater, it's more accurate for our purposes.
http://www.marinedepot.com/American_...TEMOID-vi.html

[Jyetman]

Originally Posted by slief

Not sure why you love creating duplicate threads but as I said in your other thread on the same subject...

Does the distilled water temp match that of the 53mS solution?

FWIW, If you read the specs on this tester, you would see that this tester is only accurate within .002 so at a 1.028 reading of 53mS (1.026) solution, you are within it's accuracy range. When you calibrate with fresh water, the accuracy decreases as the salinity increases. This is the same reason why it's not recommended to calibrate a refractometer with distilled water as opposed to 53mS solution.

I use the Pinpoint Salinity Monitor because it is calibrated with 53mS/1.026 solution and because you are calibrating with solution that matches natural seawater, it's more accurate for our purposes.
http://www.marinedepot.com/American_...TEMOID-vi.html

Since you can't remove posts I just decided to place this in the lighting and equipment section where it belongs sorry.

So can I calculate if the 53.0 solution reads 1.028 my tank reading of 1.025 is actually 1.023 is this a correct assumption?

[slief]

Originally Posted by Jyetman

Since you can't remove posts I just decided to place this in the lighting and equipment section where it belongs sorry.

So can I calculate if the 53.0 solution reads 1.028 my tank reading of 1.025 is actually 1.027 is this a correct assumption?

If 1.026 solution reads 1.028 then your tank would be approx 1.025 if the meter is showing 1.027.

That is an approximation as temperature of the solution you calibrate with (distilled water) vs temp of the tank water can also impact the accuracy despite the meters temperature compensation.

Have you tried calibrating with RODI water and then test the 53mS solution to compare the results? Might be worth a try to see if the accuracy changes for the better.

[Jyetman]

Originally Posted by slief

If 1.026 solution reads 1.028 then your tank would be approx 1.025 if the meter is showing 1.027.

That is an approximation as temperature of the solution you calibrate with (distilled water) vs temp of the tank water can also impact the accuracy despite the meters temperature compensation.

Have you tried calibrating with RODI water and then test the 53mS solution to compare the results? Might be worth a try to see if the accuracy changes for the better.

Ok will give that a try when I can get some only have a RO system. Thank You

[Jyetman]

Okay the ambient temperature in my apartment is up from 75 to 76.2 degrees. Performed another calibration and tested 53 solution now getting a reading of 1.027 is this result from a different temperature? Thought the unit is suppose to be temperature compensated?

[slief]

Originally Posted by Jyetman

Okay the ambient temperature in my apartment is up from 75 to 76.2 degrees. Performed another calibration and tested 53 solution now getting a reading of 1.027 is this result from a different temperature? Thought the unit is suppose to be temperature compensated?

Despite the unit having temperature compensation, calibration solution should be at or near the same temp as your tank temps for most accurate results. This is especially true when calibrating with fresh water like RODI or distilled water. The same holds true for the tester. It too should be room temp as a colder tester will cool the water which impacts specific gravity. This is because specific gravity varies depending on water temps. When you calibrate using fresh water, temps can have more of an impact on accuracy at the range of natural salt water. When I calibrate my refractometer or my Pinpoint monitor, I always make sure my 53mS calibration solution is at room temp or tank temps depending on the difference in ambient temp vs tank temps. This insures best accuracy.

Per your instruction manual:
If the temperature of the sample differs significantly from the temperature of the instrument, wait approximately 1 minute to allow thermal equilibration.

[Jyetman]

Can I use Milwaukee Electrode Rinse Solution for calibration? I have one solution pak and its the only thing in my place that reads Deionized water?

[NSimpkins]

I was having the same problem. I called Milwaukee and they said the ATC compensates to the environment temperature not the other way around. Meaning that it will measure your tank sample at current ambient temp of the room. I offset this by holding my hand over the chamber until it is the temp of my tank. From doing that I get pretty accurate readings. Same with the calibration fluid. I put my bottle of 35 ppt in a ziplock so it didn't accidently leak then put in my sump for an hour. Did the same with my distiller water and all readings were accurate.

Hope that helps.

[Jyetman]

Originally Posted by NSimpkins

I was having the same problem. I called Milwaukee and they said the ATC compensates to the environment temperature not the other way around. Meaning that it will measure your tank sample at current ambient temp of the room. I offset this by holding my hand over the chamber until it is the temp of my tank. From doing that I get pretty accurate readings. Same with the calibration fluid. I put my bottle of 35 ppt in a ziplock so it didn't accidently leak then put in my sump for an hour. Did the same with my distiller water and all readings were accurate.

Hope that helps.

I tried your method and at tank temperature the calibration 53 is 1.027 which is closer. Thanks feel a little better.

[Jyetman]

On the 53 calibration bottle what does the + or - 1 % at 77 F mean? Doesn't this mean I need to calibrate the machine when it reads 77 F ???

[NSimpkins]

When I was talking to Milwaukee the rep who was very nice said that their machine is an approximation. Having to do over I probably would get a pinpoint checker or put the money towards apex with salinity module and probe.

As to your specific question. Due to temp changes it is meant to calibrate to that reading at that temperature. You can do the same method and get the unit to read 77. Good news is most tank temps are in that ballpark so shouldn't be much fluctuation from 77 to your 78-80 tank temp

[Jyetman]

Bump

[Jyetman]

This is what I received from Milwaukee Tech Support. Does it make sense?

Most "validation" liquids for refractometers are made from Sodium Chloride [NaCl ] @ 99% - one of the providers of this on the internet is Sybon Scientific and there are others. The problem with their solution is that it is designed for Salinity validation not for Seawater. Their solution is Sodium Chloride [NaCl ] @ 99% and seawater is made up of Sodium Chloride [ NaCl ] @ 97% and Potassium Chloride [ KCl ] @ 2% and Other Trace Minerals Salts @ 1% and that 3% makes a huge difference.

That pinpoint standard is used for Conductivity probes and is made to read and measure for NaCl and not Seawater. Trying to use a EC/TDS probe for seawater gives the probe an automatic 3% read deviation out of the box and then there is the accuracy variation on all EC units ( see your specifications listing on your EC unit ) -- Most EC unit will state this at 1% "accuracy" or 2% "variation" at read which means at 32000 ppm you have a +/- accuracy of 600ppm if your unit is a 2% unit ( 1200ppm swing ) and 300ppm if it is a 1% unit ( 600ppm swing ). Combine that lack of accuracy with the proceeding 3% NaCL vs Seawater and you have a huge variation using a meter to measure seawater. It simply cannot be done accurately.

The only way to validate you unit is with a seawater validation solution kit which, you should have received with your unit. If you did not get this validation kit we will be happy to send to you at no charge -- what is your address?

Bryan