Refractometer calibration/temperature question

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Randy Holmes-Farley

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A number of folks have told me that the ATC refractometer that they've gotten from you says it should be calibrated at 68 deg F.

What possible reason could there be for doing that?

If the ATC works, it won't matter what temp you use for calibration, and if it isn't working perfectly, you'd want to calibrate at the same temp that you measure.

Can you clarify what these directions mean?

TIA
 

Ericsch333

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Mine doesn't say that it says calibrate with solution that it came with.
 

Sully

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Are you speaking of the Deepwater ATC refractometer? Mine just says to calibrate with distilled water ( I used filtered water that I left out to get to room temp for 10 minutes or so). So far, I love the ease of use of this thing.
 

Kworker

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I've seen that in directions for ATC that calls for the calibration fluid I believe. It's also in the directions to the Red Sea one I picked up a couple of months ago.
 

Eienna

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It's not from BRS, but I was wondering about the temperature-of-calibration oddness too. Mine says 74F.
 

leptang

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To use a refractometer properly we must first understand the correct calibration procedure. If you look down the lens of most good refractometers you will see 20/20 printed on the screen. This means that it was originally calibrated with both pure water and sample water temperatures set at 20C and so in order to recalibrate the instrument properly you must use the same temperature for your calibration sample. What many people do not understand however is that it is the temperature of the instrument that should be at 20C and not the liquid as the few drops of sample water contains so little heat that it soon equilibrates to the same temperature as the refractometer body.
So with your refractometer at 20C, which is close to normal room temperature, you add a sample of distilled or RO water to the screen and use the adjustment screw to line up the blue marker with the zero salinity mark. This can now be used to measure the sample salinity accurately but only whilst the refractometer is still at 20C. Remember that even if your aquarium is running at say 27C (80.6F), the refractometer will always read as if it were at 20C.
If you have an auto temperature compensating model (ATC) you must still calibrate the unit at the calibration temperature of 20C however this version, once correctly set, will auto adjust for environments where the instrument warms or cools away from this temperature. Normally the range is 10-35C and is achieved by a small bimetallic strip in the body of the refractometer which responds to the change and moves the graduated scale accordingly. For this reason copper bodied refractometers are better than the lower cost plastic ones as they conduct the ambient temperature changes faster.
 

leptang

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A good way to get your refractometer to a correct calibration temperature. You can put the refractometer in a zip locked bag and squeeze the air out and place it in a bucket of water, then add ice to the water to cool it to the correct calibration temperature or add hot water if needed to raise the temperature. Then let the refractometer sit in the water to reach a equilibrium temp.
 

leptang

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So when the manufacture build a refractometer they test it to a sample of pure water at there calibration temperature and make a mark to where pure water sould reads at that temperature. Then they mark samples of know density on there refractometer at the same temperature. Water can expand and contact at temperatures, that means the colder the water the more dense it gets to it freezes and becomes a solid. If water get to hot it turns to gas and is far less dense. There for refraction of light threw a density of water changes.
But in my opinion using a measurement of density to gauge salinity is poor way to do it. the best way is to evaporate all the water and weigh the salt left behind. Which NSW is 35ppt (35 pounds per 1000). That is if all other elements like calcium, magnesium, carbonates are the correct amounts in NSW density will probably not be spot on..... but i dont worry to much about it. As currants and rain, evaporated water changes salinity of our oceans all the time. Close enough is how i look at it.
 
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Randy Holmes-Farley

Randy Holmes-Farley

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If you have an auto temperature compensating model (ATC) you must still calibrate the unit at the calibration temperature of 20C however this version, once correctly set, will auto adjust for environments where the instrument warms or cools away from this temperature. Normally the range is 10-35C and is achieved by a small bimetallic strip in the body of the refractometer which responds to the change and moves the graduated scale accordingly.

Thanks. I'm aware how they work, but it is that sentence of yours (above) that is both what they claim, and what makes no sense to me.

If the ATC works perfectly, then it will make no difference what temperature you calibrate at because the setting will be exactly the same regardless of temperature (within the range of the ATC). If that wasn't true, you wouldn't be able to read RO/DI water correctly after calibration.

If the ATC is not working perfectly, then you will never get the correct reading for your sample at a temperature other than the temperature you calibrated at.

Consequently, I think my directions for using a refractometer, whether ATC or not, will work in EVERY circumstance as well as the stated directions, and will work better in many circumstances (e.g., it is a brine refractometer or the ATC is not perfect or it is not an ATC refractometer). :)

These are my directions:

1. Calibrate using a 35 ppt seawater standard (not RO/DI water, unless it is a digital device that physically doesn't permit this). Set the reading to 35 ppt or sg = 1.0264, depending on what the scale reads.

2. Calibrate at the same room and refractometer temperature as you intend to make measurements.

3. Calibrate and measure using the same lighting source, since color changes may impact the result.
 
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Bulk Reef Supply

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Sorry we’re late to the party guys! It seems like the confusion here stems from the awkwardly worded instructions that are included with the refractometer. Basically the instructions are written for both the ATC model (which we sell) and the standard model without ATC (which we do not sell). From my understanding an initial calibration at 20 degrees Celsius (68°F) will give you the best possible starting point since it is the midpoint of the refractometer’s ATC operating range of 10-30 degrees Celsius. With that being said I contacted the manufacturer for further clarification and they confirmed our suspicion that as long as the body of the refractometer is between 10 and 30 Celsius, the ATC will work properly and give you an accurate result.

I would recommend calibrating your refractometer at a temperature as close to the temperature at which you will be using it. The temperature of your systems water will not affect the accuracy of the refractometer due to the fact that the body of the refractometer will not be significantly altered by the small amount of water applied to the measuring prism.
 

-Logzor

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If the body of the refractometer is 19C and my water is 27C would the refractometer cool the aquarium water down the room temperature?

Should you measure immediately or wait for the temperature to equalize?
 

Sully

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When they are talking about temp, they are referring to the temp of the Refractometer, not the temp of the water you are testing.

If the body of the refractometer is 19C and my water is 27C would the refractometer cool the aquarium water down the room temperature?

Should you measure immediately or wait for the temperature to equalize?
 

Eienna

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Sorry we’re late to the party guys! It seems like the confusion here stems from the awkwardly worded instructions that are included with the refractometer. Basically the instructions are written for both the ATC model (which we sell) and the standard model without ATC (which we do not sell). From my understanding an initial calibration at 20 degrees Celsius (68°F) will give you the best possible starting point since it is the midpoint of the refractometer’s ATC operating range of 10-30 degrees Celsius. With that being said I contacted the manufacturer for further clarification and they confirmed our suspicion that as long as the body of the refractometer is between 10 and 30 Celsius, the ATC will work properly and give you an accurate result.

I would recommend calibrating your refractometer at a temperature as close to the temperature at which you will be using it. The temperature of your systems water will not affect the accuracy of the refractometer due to the fact that the body of the refractometer will not be significantly altered by the small amount of water applied to the measuring prism.
Thank you for that :)
 

-Logzor

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When they are talking about temp, they are referring to the temp of the Refractometer, not the temp of the water you are testing.

I understand that but they're suggesting to calibrate the refractometer with the same temperature water that we would be testing. I've done this, where I float the calibration solution bottle in the aquarium because the solution says to calibrate at 77 degrees. If my refractometer itself is 65 degrees then won't it quickly cool the water down and impact calibration?

Perhaps I'm misinterpreting but I've had issues in the winter-time when my refractometer is cold due to the lower inside air temperature.
 
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Sully

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First let me say I'm new to refractometers. But, from what I've read and understand is works like this. The refractometer itself needs to be very close to 68 degrees (20 degrees Celsius) when you calibrate it. The solution temp doesn't matter (within reason, I wouldn't use water or solution that is extremely cold or hot. Room temp should work fine). Once you calibrate it, the refractometer temp only needs to be in the 10-30 degree Celsius range when you're testing the water source. Basically once calibrated if your using indoors it should be fine. If I'm wrong, hopefully someone will provide further clarification.

I understand that but they're suggesting to calibrate the refractometer with the same temperature water that we would be testing. I've done this, where I float the calibration solution bottle in the aquarium because the solution says to calibrate at 77 degrees. If my refractometer itself is 65 degrees then won't it quickly cool the water down and impact calibration?

Perhaps I'm misinterpreting but I've had issues in the winter-time when my refractometer is cold due to the lower inside air temperature.
 

-Logzor

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First let me say I'm new to refractometers. But, from what I've read and understand is works like this. The refractometer itself needs to be very close to 68 degrees (20 degrees Celsius) when you calibrate it. The solution temp doesn't matter (within reason, I wouldn't use water or solution that is extremely cold or hot. Room temp should work fine). Once you calibrate it, the refractometer temp only needs to be in the 10-30 degree Celsius range when you're testing the water source. Basically once calibrated if your using indoors it should be fine. If I'm wrong, hopefully someone will provide further clarification.

I believe salinity varies depending on water temperature, this is why calibration fluid states that it's 1.0265 @ 77 Degree Fahrenheit. My understanding was that the refractometer will automatically correct for this regardless of water temperature.

How does this work exactly and is this function dependent on the original calibration temperature?

This is why I moved to a conductivity meter, had nothing but trouble with my refractometer, especially during the winter months. Could never figure it out, I could place a sample and measure, it would result in a reading, I could leave that same sample sit for a few minutes and the reading would totally change. Maybe mine was broken.
 

Sully

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Log, At this point, I think the only way to get a sure answer to your questions would be to call the manufacturer directly. BRS petty much explained the same thing as I did. Maybe I'm not understanding your confusion. It is possible that you got a bad unit though.

The fact that you'd get two different readings after letting the sample sit for a few minutes would lead me to believe there was something wrong with the unit.
 
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Randy Holmes-Farley

Randy Holmes-Farley

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they confirmed our suspicion that as long as the body of the refractometer is between 10 and 30 Celsius, the ATC will work properly and give you an accurate result.

Thank you.

Happy reefing. :)
 
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