I was reading an article comparing the D-D Seawater Refractometer to the new Red Sea Seawater Refractometer explaining that the Red Sea would be more accurate in our reef tanks because it is calibrated at 77 degrees vs. the D-D that is calibrated at 72 degrees. The article stated that 77 degrees is closer to the temps reef tanks normally run thus the higher accuracy. Since both are ATC, I must not understand the auto compensation feature. I assumed that the compensation would correct for temperature differences within a reasonable range to give a true reading. What am I missing or is it just advertising hype?
Explain the ATC in Refractometers
- Thread starter Mark426
- Start date
Misleading hype (IMO).
If a refractometer is ATC, and is properly made, it shouldn't matter what temperature you choose to read it at or calibrate it at, as long as you are withing the range of its ATC capabilities. Having the standard and the water read at the same temp is a reasonable idea (minimzing the impact of a potentially not completely accurate ATC capability), but that will end up being room temp anyway, not the tank temp.
Some claim you need to calibrate at a certain temp, but that never made any sense to me.
Use a 35 ppt (sg = 1.0264 standard) to minimize all such concerns.
This has more:
Refractometers and Salinity Measurement
http://reefkeeping.com/issues/2006-12/rhf/index.php
If a refractometer is ATC, and is properly made, it shouldn't matter what temperature you choose to read it at or calibrate it at, as long as you are withing the range of its ATC capabilities. Having the standard and the water read at the same temp is a reasonable idea (minimzing the impact of a potentially not completely accurate ATC capability), but that will end up being room temp anyway, not the tank temp.
Some claim you need to calibrate at a certain temp, but that never made any sense to me.
Use a 35 ppt (sg = 1.0264 standard) to minimize all such concerns.
This has more:
Refractometers and Salinity Measurement
http://reefkeeping.com/issues/2006-12/rhf/index.php
Hi David,
I comment on that in the link (third paragraph):
It turns out that refractive index is highly dependent on temperature. When using a refractometer that does not account for this effect, temperature changes can be a large source of errors. Most liquid materials expand slightly when heated and shrink when cooled. For a given material, light can pass through it more easily when it is expanded, so the index of refraction falls when materials are warmed. However, the magnitude of this effect is different for every material, and refractometers must somehow take this into account.
Handheld refractometers account for temperature by employing a bimetal strip inside them. This bimetal strip expands and contracts as the temperature changes. The bimetal strip is attached to the optics inside the refractometer, moving them slightly as the temperature changes. This movement is designed to exactly cancel temperature's effects on refractive index, and generally does a very good job IF the refractometer is designed to cancel out the temperature effects of the specific material being analyzed.
Because many refractometers are designed to use aqueous (water) solutions, the bimetal strip can be designed to account for the change in refractive index of aqueous solutions, although it may not be perfect in some situations because salts and other materials in the water can change temperature's effects on refractive index by a small extent (possibly to a larger extent for very concentrated solutions, like 750% sugar in water, but seawater is not in that category). Other details of this compensation may cause it to be imperfect (for example, the bimetallic strip provides a linear correction while the true temperature effect may be nonlinear), but those issues are beyond the scope of this article, and in general automatic temperature compensation (ATC) is a very useful attribute for aquarists using refractometers.
I comment on that in the link (third paragraph):
It turns out that refractive index is highly dependent on temperature. When using a refractometer that does not account for this effect, temperature changes can be a large source of errors. Most liquid materials expand slightly when heated and shrink when cooled. For a given material, light can pass through it more easily when it is expanded, so the index of refraction falls when materials are warmed. However, the magnitude of this effect is different for every material, and refractometers must somehow take this into account.
Handheld refractometers account for temperature by employing a bimetal strip inside them. This bimetal strip expands and contracts as the temperature changes. The bimetal strip is attached to the optics inside the refractometer, moving them slightly as the temperature changes. This movement is designed to exactly cancel temperature's effects on refractive index, and generally does a very good job IF the refractometer is designed to cancel out the temperature effects of the specific material being analyzed.
Because many refractometers are designed to use aqueous (water) solutions, the bimetal strip can be designed to account for the change in refractive index of aqueous solutions, although it may not be perfect in some situations because salts and other materials in the water can change temperature's effects on refractive index by a small extent (possibly to a larger extent for very concentrated solutions, like 750% sugar in water, but seawater is not in that category). Other details of this compensation may cause it to be imperfect (for example, the bimetallic strip provides a linear correction while the true temperature effect may be nonlinear), but those issues are beyond the scope of this article, and in general automatic temperature compensation (ATC) is a very useful attribute for aquarists using refractometers.
Thanks Randy. I thought it HAD to be advertising hype or I my IQ was slowly converging with my age.
:lol:
:thumbsup:
Happy Reefing.
:lol:
:thumbsup:
Happy Reefing.
