reef Posted October 10, 2005 Report Share Posted October 10, 2005 http://www.trademe.co.nz/structure/auction_detail.asp?id=37486095 Quote Link to comment Share on other sites More sharing options...
cookie extreme Posted October 10, 2005 Report Share Posted October 10, 2005 ACCURACIES Temperature 1C Salinity 2ppt Specific gravity 0.002 S.G not that great in accuracy for the price! Quote Link to comment Share on other sites More sharing options...
reef Posted October 10, 2005 Author Report Share Posted October 10, 2005 It is bettter than most meters, i think even more accurate than a refractometer. Quote Link to comment Share on other sites More sharing options...
suphew Posted October 10, 2005 Report Share Posted October 10, 2005 The guy is selling PH and temp meters to, but the best of all his sales.... Potato gun! range 200+ meters :lol: Quote Link to comment Share on other sites More sharing options...
Ira Posted October 11, 2005 Report Share Posted October 11, 2005 Refractometers should be able to measure much better than .002 That's when your water's actually 1.026 it could be reading 1.024-1.028. That's EASILY within the range of a refractometer. Quote Link to comment Share on other sites More sharing options...
Brianemone Posted October 11, 2005 Report Share Posted October 11, 2005 wouldnt it be that your water is 1.025 and its reading 1.023-1.027 Quote Link to comment Share on other sites More sharing options...
Ira Posted October 11, 2005 Report Share Posted October 11, 2005 Same thing. Quote Link to comment Share on other sites More sharing options...
Brianemone Posted October 11, 2005 Report Share Posted October 11, 2005 duh, i just re-read your post :roll: Quote Link to comment Share on other sites More sharing options...
HelifaxNZ Posted October 11, 2005 Report Share Posted October 11, 2005 I bought one from Ebay. Me and Jetskisteve tested it out and found his refractometer showed 1.026 and my digital to be 1.023. Temperature was accurate and it automatically adjusts to the temperature. So we're none the wiser which one was better. The digital came with salt water to calibrate the unit, and it was slightly out, but not so much to make that much of a difference. My conclusion is for the convenience, the digital is good. Quote Link to comment Share on other sites More sharing options...
reef Posted October 11, 2005 Author Report Share Posted October 11, 2005 interesting, the refractometer will be out by a bit as there is a formula that you have to use to get the correct reading, i have to find the link and post it. here is some info i found The important points are the following. 1. ATC on a refractometer is very different from ATC on a pH meter. The portable refractometer has no electronic components. It does not measure temperature. The compensation is achieved through simple optical elements. 2. It is the temperature of the refractometer (which is the ambient temperature) that is important, not the temperature of the sample. In fact, the sample temperature is the refractometer temperature because a drop of sample quickly attains the refractometer temperature. 3. It is essential that the refractometer with ATC by nulled at 68 F (20 C). [Nulled means setting zero point with a drop of distilled water.] For example, I nulled a refractometer with ATC at 77 F and had an error of about 10% at 25 Brix. I then nulled the same unit at 68 F and the error was zero. Our units are nulled correctly by the manufacturer and should not need to be adjusted. If you need to renull the unit, you will need to get as close to 68F as possible. I have found that anywhere between 66-70 F gives very good accuracy. Also, bear in mind that you must accurately determine the temperature, i.e, you must have an accurate thermometer. 4. ATC covers 10-30 C, 50-86 F. Quote Link to comment Share on other sites More sharing options...
reef Posted October 11, 2005 Author Report Share Posted October 11, 2005 so after reading that the electronic could be more accurate. Quote Link to comment Share on other sites More sharing options...
chimera Posted October 11, 2005 Report Share Posted October 11, 2005 i tested my (aquamedic) refractometer with RO/DI water, temperature adjusted to the same as my tank (25 degrees) I found it read 1.000 EXACTLY. interesting that the ATC side of it is based on the temperature of the refractometer, makes sense I suppose as you're only using a drop of water which is so small it would adjust to the temp of the refractometer fairly quickly anyway Quote Link to comment Share on other sites More sharing options...
reef Posted October 11, 2005 Author Report Share Posted October 11, 2005 I think that is why there is a correction formula that we have to find, i have seen it somewhere, So to get it close to the tank water we will have to heat up the refractometer to tank temp to give a more accurate salinity. Quote Link to comment Share on other sites More sharing options...
Ira Posted October 11, 2005 Report Share Posted October 11, 2005 I thought the whole point of it being ATC was that you wouldn't need any kind of correction? Quote Link to comment Share on other sites More sharing options...
reef Posted October 11, 2005 Author Report Share Posted October 11, 2005 refractomers are designed for brix, not seawater. Quote Link to comment Share on other sites More sharing options...
Feelers Posted October 11, 2005 Report Share Posted October 11, 2005 200+ meters, spud guns are awsome, once fired a beer bottle 400 meters. We managed to time an apple fired straight up and worked out it must have left the barrel at 487kph. Then when we were firing it off the deck the back end blew out and smashed through a window....... I digress.......... How accurate do you guys need these things? I also thought reefers often went with lower than sea salinity. Apparently full strength is very important for an octopus, but I cant afford on of these, what about those stick on dial-ly things? How much for a run of the mill standard hydrometer? Quote Link to comment Share on other sites More sharing options...
reef Posted October 11, 2005 Author Report Share Posted October 11, 2005 How much for a run of the mill standard hydrometer Generally they are not accurate at all; some are so far out that most problems will alway stem back to incorrect salinity. Refractometers are quite good but could still be out as they are not designed for seawater so there is a correction formula that needs to be applied if you want it spot on. Quote Link to comment Share on other sites More sharing options...
lduncan Posted October 11, 2005 Report Share Posted October 11, 2005 Refractometers are quite good but could still be out as they are not designed for seawater so there is a correction formula that needs to be applied if you want it spot on. I don't think that is correct. Refractometers are made for measuring density of liquids, based on the refractive index. There are two types of refractometers. Automatic Temperature Compensation (ATC) - They should be calibrated to 0 using distilled water at the temperature they are usually used at. The scale within the prism is floating allowing it to automatically move with changes in temperature of the device. (I think it uses the expansion and contraction of metal strips with temperature). The second type does not have a floating scale, and doesn't automatically compensate for temperature changes. It is calibrated at a specified temperature (could be 20 degrees, depends on manufacturer) for optimum accuracy. Because the optical density of liquids changes with temperature, the angle the light refracts also changes. So if measurements at made at 26 degrees, when the refractometer is calibrated at 20 degrees, you need to use a formula to adjust for the change in refraction angle, to get a true salinity reading. I'd say that a refractometer is generally going to be more accurate than most other electronic measurements. Quote Link to comment Share on other sites More sharing options...
reef Posted October 11, 2005 Author Report Share Posted October 11, 2005 What i have read says that they are not designed for seawater and that there is a correction formula. that is what most of the information states. I am not saying that the refractometer is way off , it stands to reason that when you read it off the refractometer that it is reading it at a lower temp as the refractometer is going to cool the water when you put a drip on it. As temp rises then salinity drops. so when you read the refractometer the temp will drop the sample to the salinity will read higher. here it is again The important points are the following. 1. ATC on a refractometer is very different from ATC on a pH meter. The portable refractometer has no electronic components. It does not measure temperature. The compensation is achieved through simple optical elements. 2. It is the temperature of the refractometer (which is the ambient temperature) that is important, not the temperature of the sample. In fact, the sample temperature is the refractometer temperature because a drop of sample quickly attains the refractometer temperature. 3. It is essential that the refractometer with ATC by nulled at 68 F (20 C). [Nulled means setting zero point with a drop of distilled water.] For example, I nulled a refractometer with ATC at 77 F and had an error of about 10% at 25 Brix. I then nulled the same unit at 68 F and the error was zero. Our units are nulled correctly by the manufacturer and should not need to be adjusted. If you need to renull the unit, you will need to get as close to 68F as possible. I have found that anywhere between 66-70 F gives very good accuracy. Also, bear in mind that you must accurately determine the temperature, i.e, you must have an accurate thermometer. 4. ATC covers 10-30 C, 50-86 F. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.