Refractometer

[Randy Holmes-Farley]

Alfred:

Your issue sounds much more typical: swing arms that may be off as opposed to a refractometer that is off, although one cannot be sure which of yours is accurate.

In any case, I'm glad things look better.

 

[delafe]

Definately the swing arm. I did not take one (new) refractometers results as definative and had a friend bring his over. Both of them gave the same results and both were carefully calibrated.

I suspect that the rubber component of the swingarm hydrometer degrades or hardens over time and that is why we are seeing false readings. When I first purchased my swingarm, it gave very accurate readings (I compared it to a glass hydrometer as well as a refractometer)

In either case, if people are using the same swingarm for several years I would strongly recommend they compare their results with a friends refractometer and replace it once the results start to vary.

Regards,

-Alfred

 

[Randy Holmes-Farley]

FWIW, I tested some new swing arm hydrometers and they were not especially accurate even then:

Specific Gravity Measurement
http://www.advancedaquarist.com/issues/jan2002/chemistry.htm

 

[DaveBrader]

Just wanted to let everyone know, that Marine Depot never replied to my email to them about this issue. To me, that says more than if they did reply. It says they don't even want to get involved because of possible liability issues..

Dave

 

[Randy Holmes-Farley]

Thanks for the update, Dave.

That is disappointing.

 

[lakerfan]

HI Dave,

I apologize for not responding to your email, but i checked our servers and did not receive one from you from Dec 22 to today regarding the refactometers. Most of the emails we receive are actually answered in less than 24 hours. Any emails received by 6p.m. PST are answered on the same day, and emails sent through out the business day are actually answered in an average of less than 2 hours.

At any rate, this is the first we have heard of the problem with our branded refractometers. I actually used the sample myself and calibrated with both distilled and a 35 ppt solution we have and it read good against a vitalsine, JBJ's Digital unit and the lighted refractometer that we carry. We have contacted the manufacturer and are awaiting a response. We will keep you all updated as soon as possible.

Let us know if you have any other questions. I can be reached via email at customercare@marinedepot.com

Ben R.
Customer Service Manager
www.marinedepot.com

 

[DaveBrader]

Great Ben,

There is no way to tell how many of the refractometers might have this problem. It could have been one entire production run, or it could have been a small number within a production run.

As I said, the optics I believe are just fine. Once it is calibrated to a Solution of Known Salinity of 35, it works just fine. I have tested it against ten other refractometers now. This is certainly only a problem for those who trust the ZERO calibration with distilled water.

The part that I find interesting is that once it is calibrated to a Calibration Solution with a Salinity of 35, it still reads Zero for distilled water, even though when done in reverse and calibrated to Zero using distilled water, reads the Calibration Solution with a Salinity of 40.

What that means to me is that there is some "SLOP" at the ZERO point at the calibration mechanism that is set by the calibration screw. And, that "SLOP" does not exist when calibrating to a much higher Salinity, as in the Calibration Solution used.

The fact is, the problem does exist in at least three refractometers we know of for sure because of the posts in this thread. How many more might be affected is anyones guess...

I am perfectly happy with my Refractometer, and have no desire to replace it. I just feel it is important to try to notify anyone who has an affected Refractometer of the correct way to get an accurate Calibration...

Thanks, Dave

 

[TheDrunkenClam]

This is an important thread to keep going, so I thought I would add my experience with the MD refractometer.

After reading this thread I was spooked by the refractometer I ordered a couple of weeks ago. I followed the instructions in the reefkeeper article for mixing a S=35 calibration solution. Two liter coke bottle, 1/4 cup + 1 teaspoon mortons, mix well.

I zeroed the refractometer with RO/DI water, then tested with the calibration solution. Result = 1.027. So basically right on (within normal variation).

I had ordered it right after Xmas, so either I got lucky, or they fixed the problem at the manufacturer.

It would probably be helpful to others to keep this watchlist going, to see if the production tolerances slip again.

Dave

 

[Sindjin]

I got one from MD 2 weeks ago. Read 1.025...same as my 9.00 swing arm.

 

[Randy Holmes-Farley]

I zeroed the refractometer with RO/DI water, then tested with the calibration solution. Result = 1.027. So basically right on (within normal variation).


:thumbsup:

I expect most peple will find that.

 

[victorh]

<a href=showthread.php?s=&postid=6621861#post6621861 target=_blank>Originally posted</a> by Randy Holmes-Farley
I zeroed the refractometer with RO/DI water, then tested with the calibration solution. Result = 1.027. So basically right on (within normal variation).


:thumbsup:

I expect most peple will find that.

Same here. Bought mine in December.

 

[steve the plumb]

I have my swing arm for over eight years and it works fine.I always rinse with water after use.I tested with my friends salinity meter(AM brand) and got the same results.I wasn't expecting to get good results I thought mine would be off so I am lucky it works well.