Refractometer

"Boomer" wrote in message ...
About 95 % of the expensive refracts, $200-$300, only go to 1 ppt

Thanks, so why people say refracts are so acurate and reliabe?
People can get acuracy 0.001 sg with cheap Deep Six swing arm.

Are we paying more just to have a convenience of refractometer?

There is less error involved with a refract. I have yet seen a Deep-Six that is even close
to what it should read. Swing arms units also have a habit of collecting salt deposits on
the swing arms and pin, which can cause very low readings. Thus, they need to be soaked in
vinegar every month to remove such deposits. Floating hydrometers have the issue of temp
compensation, where most in this hobby seem to get lost. Refracts are much more accurate
out of the box. However, they are also in error but we can compensate for that. For the
last couple of months Randy and I have been colleting data so he could redo the old DIY
calibration solutions from months ago. We knew something was wrong with them and we wanted
something reefers could make easily for a DIY calibration solution. The first ones we had
were to low. In short your refract reads 1.5 ppt to low. So if you want a salinity of 35
ppt (3..5 %), on your refract, it needs to read 36.5, which equals 35 ppt NSW. Refracts
from the factory are not calibrated to seawater but NaCl, which does not have the same RI
( Refractive Index) as NSW. You can read all about it here. It just came out the other day
:-)

http://reefkeeping.com/issues/2004-06/rhf/index.htm

--
Boomer

Want to talk chemistry ? The Reef Chemistry Forum
http://www.reefcentral.com/vbulletin/index.php

Want to See More ?
Please Join Our Growing Membership
www.coralrealm.com

If You See Me Running You Better Catch-Up
"Pszemol" wrote in message ...
: "Boomer" wrote in message
...
: About 95 % of the expensive refracts, $200-$300, only go to 1 ppt
:
: Thanks, so why people say refracts are so acurate and reliabe?
: People can get acuracy 0.001 sg with cheap Deep Six swing arm.
:
: Are we paying more just to have a convenience of refractometer?

"Boomer" wrote in message ...
There is less error involved with a refract. I have yet seen a Deep-Six that is even close
to what it should read. Swing arms units also have a habit of collecting salt deposits on
the swing arms and pin, which can cause very low readings. Thus, they need to be soaked in
vinegar every month to remove such deposits. Floating hydrometers have the issue of temp
compensation, where most in this hobby seem to get lost. Refracts are much more accurate
out of the box. However, they are also in error but we can compensate for that.

Looking at the scale of mine refractometer with divisions for 34 and 35 ppt so close
to each other and comparing wide scale of swing arm with a centimeter between 34 and 36
is it hard to believe refractometers are "much more accurate"... But I will take your word.

Also, would you agree that Coralife statement of +/-0.001 SG accuracy of their
DEEP SIX is not true if you say +/- 1ppt refractometer is "much more accurate"?

For the
last couple of months Randy and I have been colleting data so he could redo the old DIY
calibration solutions from months ago. We knew something was wrong with them and we wanted
something reefers could make easily for a DIY calibration solution. The first ones we had
were to low.

I will wait then... thanks. But now I remember I have a postal scale with 1g acuracy...
It should give me acurate enough result for the calibration.

In short your refract reads 1.5 ppt to low. So if you want a salinity of 35
ppt (3..5 %), on your refract, it needs to read 36.5, which equals 35 ppt NSW. Refracts
from the factory are not calibrated to seawater but NaCl, which does not have the same RI
( Refractive Index) as NSW. You can read all about it here. It just came out the other day
:-)

Thank you.
So it looks like people adjusting their tanks to a refractometer reading 35 ppt
are really using sea water with less than 34 ppt of salt in it... Adding on top
of it +/- 1ppt manufacturer stated measurement error margin we could be off by
more than 2.5 ppt if we do not correct NaCl offset... Sounds very pessimistic :-)

"Also, would you agree that Coralife statement of +/-0.001 SG accuracy of their
DEEP SIX is not true if you say +/- 1ppt refractometer is "much more accurate"?"

If you went out and bought 10 of each the refracts would be 9 out of 10, right on for a 35
ppt NaCl solution. The Deep-Six, 9 out of 10 would be all over the place.

" We knew something was wrong with them and we wanted
something reefers could make easily for a DIY calibration solution. The first ones we had
were to low."

AND

"I will wait then... thanks. But now I remember I have a postal scale with 1g accuracy...
It should give me accurate enough result for the calibration.""

You don't have to wait it has already been done go back and re-read the other post, that
is the new one. I gave a link to it.

" Adding on top
of it +/- 1ppt manufacturer stated measurement error margin we could be off by
more than 2.5 ppt if we do not correct NaCl offset..."


They are rarely off that much. What that means is that they guaranteed no more than that.
Even a $250 NIST certified hydrometer is + / - .001. Even the $ 600 fiberoptic
refract , for SEAWATER is only +/- 1 ppt. If you want to get accurate you need a
conductivity meter starting a + $400 to get it to 0.1 ppt.

If you use our stds. you will know exactly where you are at, with the refract and
Deep-Six


Boomer

Want to talk chemistry ? The Reef Chemistry Forum
http://www.reefcentral.com/vbulletin/index.php

Want to See More ?
Please Join Our Growing Membership
www.coralrealm.com

If You See Me Running You Better Catch-Up
"Pszemol" wrote in message ...
: "Boomer" wrote in message
...
: There is less error involved with a refract. I have yet seen a Deep-Six that is even
close
: to what it should read. Swing arms units also have a habit of collecting salt deposits
on
: the swing arms and pin, which can cause very low readings. Thus, they need to be
soaked in
: vinegar every month to remove such deposits. Floating hydrometers have the issue of
temp
: compensation, where most in this hobby seem to get lost. Refracts are much more
accurate
: out of the box. However, they are also in error but we can compensate for that.
:
: Looking at the scale of mine refractometer with divisions for 34 and 35 ppt so close
: to each other and comparing wide scale of swing arm with a centimeter between 34 and 36
: is it hard to believe refractometers are "much more accurate"... But I will take your
word.
:
: Also, would you agree that Coralife statement of +/-0.001 SG accuracy of their
: DEEP SIX is not true if you say +/- 1ppt refractometer is "much more accurate"?
:
: For the
: last couple of months Randy and I have been colleting data so he could redo the old
DIY
: calibration solutions from months ago. We knew something was wrong with them and we
wanted
: something reefers could make easily for a DIY calibration solution. The first ones we
had
: were to low.
:
: I will wait then... thanks. But now I remember I have a postal scale with 1g acuracy...
: It should give me acurate enough result for the calibration.
:
: In short your refract reads 1.5 ppt to low. So if you want a salinity of 35
: ppt (3..5 %), on your refract, it needs to read 36.5, which equals 35 ppt NSW.
Refracts
: from the factory are not calibrated to seawater but NaCl, which does not have the same
RI
: ( Refractive Index) as NSW. You can read all about it here. It just came out the other
day
: :-)
:
: Thank you.
: So it looks like people adjusting their tanks to a refractometer reading 35 ppt
: are really using sea water with less than 34 ppt of salt in it... Adding on top
: of it +/- 1ppt manufacturer stated measurement error margin we could be off by
: more than 2.5 ppt if we do not correct NaCl offset... Sounds very pessimistic :-)

"Boomer" wrote in message ...
They are rarely off that much. What that means is that they guaranteed no more than that.
Even a $250 NIST certified hydrometer is + / - .001. Even the $ 600 fiberoptic
refract , for SEAWATER is only +/- 1 ppt. If you want to get accurate you need a
conductivity meter starting a + $400 to get it to 0.1 ppt.

I am surprised with the amount of money this kind of ohm-meter costs...
Is the electrode so expensive? The meter itself should be dirt cheap.

If you use our stds. you will know exactly where you are at, with the refract and
Deep-Six

Good idea.

The probes are cheap, it is the meter that is expensive. Go here for a look :-)

www.coleparmer.com

Type in Conductivity in the search window. The click on Conductivity , then Portable
Meters

--
Boomer

Want to talk chemistry ? The Reef Chemistry Forum
http://www.reefcentral.com/vbulletin/index.php

Want to See More ?
Please Join Our Growing Membership
www.coralrealm.com

If You See Me Running You Better Catch-Up
"Pszemol" wrote in message ...
: "Boomer" wrote in message
...
: They are rarely off that much. What that means is that they guaranteed no more than
that.
: Even a $250 NIST certified hydrometer is + / - .001. Even the $ 600 fiberoptic
: refract , for SEAWATER is only +/- 1 ppt. If you want to get accurate you need a
: conductivity meter starting a + $400 to get it to 0.1 ppt.
:
: I am surprised with the amount of money this kind of ohm-meter costs...
: Is the electrode so expensive? The meter itself should be dirt cheap.
:
: If you use our stds. you will know exactly where you are at, with the refract and
: Deep-Six
:
: Good idea.

"Boomer" wrote in message ...
The probes are cheap, it is the meter that is expensive. Go here for a look :-)

www.coleparmer.com

Type in Conductivity in the search window. The click on Conductivity ,
then Portable Meters

Do not understand these prices... Why is it so expensive? )
The only reason which I could guess is "not mass produced".
There is less electronics in this kind of meter than in
a $20 multimeter from Walmart... What a strange world )
I need to make this kind of meter myself :-))

Pszemol wrote:
Looking at the scale of mine refractometer with divisions for 34 and 35 ppt so close
to each other and comparing wide scale of swing arm with a centimeter between 34 and 36
is it hard to believe refractometers are "much more accurate"... But I will take your word.

Also, would you agree that Coralife statement of +/-0.001 SG accuracy of their
DEEP SIX is not true if you say +/- 1ppt refractometer is "much more accurate"?

A measurement tool is more PRECISE if it can measure to a greater number
of significant digits. The Deep Six is a more precise measuring device.

A measurement tool is more ACCURATE if it can come closer to the true
value of whatever it is you're measuring. The refractometer is more
accurate.

From this, hopefully it's clear that it does no good to be more precise
if the instrument is not accurate. We use refractometers because they
are fairly accurate. Unfortunately, they are not very precise.

Eric

Good posting Eric,
In my work we've used the terms resolution capability versus accuracy,
but they mean exactly what you have defined as precise versus accuracy,
Mike
"Eric" wrote in message
...
Pszemol wrote:
Looking at the scale of mine refractometer with divisions for 34 and 35
ppt so close
to each other and comparing wide scale of swing arm with a centimeter
between 34 and 36
is it hard to believe refractometers are "much more accurate"... But I
will take your word.

Also, would you agree that Coralife statement of +/-0.001 SG accuracy of
their
DEEP SIX is not true if you say +/- 1ppt refractometer is "much more
accurate"?

A measurement tool is more PRECISE if it can measure to a greater number
of significant digits. The Deep Six is a more precise measuring device.

A measurement tool is more ACCURATE if it can come closer to the true
value of whatever it is you're measuring. The refractometer is more
accurate.

From this, hopefully it's clear that it does no good to be more precise
if the instrument is not accurate. We use refractometers because they
are fairly accurate. Unfortunately, they are not very precise.

Eric

"Eric" wrote in message ...
A measurement tool is more PRECISE if it can measure to a greater number
of significant digits. The Deep Six is a more precise measuring device.

A measurement tool is more ACCURATE if it can come closer to the true
value of whatever it is you're measuring. The refractometer is more
accurate.

From this, hopefully it's clear that it does no good to be more precise
if the instrument is not accurate. We use refractometers because they
are fairly accurate. Unfortunately, they are not very precise.

:-)
I guess I understand the difference between precision and accuracy, and it
looks to me, a good accuracy is not worth anything without a good precision...

A meter cannot be more accurate than 1ppt if it is not precise to a single ppt.
Highly compressed scale on the refractometer hardly guarantee 1 ppt
precission, which means the accuracy is not better than 1ppt as well...

What refractometer gains on accuracy it looses on precission to swing arm.
I would risk the statement a nicely calibrated (checked with the standard)
swing arm could be more accurate than refractometer because of
its greater precision :-)