Hey guys I just want your opinion, I got a digital thermometer and I also have the regular thermometer that you find at any pet store, the one that is made of glass with a red line in the middle.. My question is which is better? The digital thermometer reads at 76.4 and the regular thermometer reads between 79-80. So which one you guys think its reading right?
Digital thermometer or regular thermometer?
- Thread starter waz1234
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ag09g
New member
This probably won't help much, but I have two regular thermometers in the same tank only inches apart. One reads 75 and the other reads 78. Not saying this means all of them are bad, but I'd probably trust a digital over my normals since clearly one of them (or both??) are not giving accurate readings.
Biocubehqi
New member
With a thermometer:hammer:
dkeller_nc
New member
With regards to accuracy, neither an inexpensive digital aquarium thermometer nor the inexpensive alcohol-filled glass thermometers can be relied upon for really accurate readings.
If you really, really want accuracy, you will need to purchase a calibrated, laboratory-grade thermometer. These are generally not inexpensive - perhaps $40 USD or so. The mercury types are ideal because once calibrated at the factory, they will never need calibrating again. However, because using a glass, mercury-filled thermometer has the obvious hazard of breakage and leaking of the mercury, you want to use it to determine the offset of an inexpensive digital thermometer that you will use in the aquarium.
If you really, really want accuracy, you will need to purchase a calibrated, laboratory-grade thermometer. These are generally not inexpensive - perhaps $40 USD or so. The mercury types are ideal because once calibrated at the factory, they will never need calibrating again. However, because using a glass, mercury-filled thermometer has the obvious hazard of breakage and leaking of the mercury, you want to use it to determine the offset of an inexpensive digital thermometer that you will use in the aquarium.
MondoBongo
Obligate Feeder Obsessed
You can check the calibration of a therm with a pretty good degree of accuracy by using it in a 50/50 ice and water bath. It should read around 32F with crushed ice.
That should give you a good idea of who is more accurate.
That should give you a good idea of who is more accurate.
try one of these. http://www.hannainst.com/usa/prods2.cfm?ProdCode=HI 98509&id=011008
I checked it against an oral mercury thermometer and it's extremely close. I use this to calibrate my digital controller.
I checked it against an oral mercury thermometer and it's extremely close. I use this to calibrate my digital controller.
Just FYI, digital and regular thermometers are allowed to be +/- 3 degrees. If you want one that is more accurate, you will need to purchase a laboratory grade thermometer as stated above or you can use a thermometer used by appliance (fridge, oven) technicians. They tend to use infrared thermometers. You just point it at the water a it gives you the reading. This can be a little inaccurate too because you re either testing the glass or the top of the water, which is getting cooled as it evaporates.
Use 3-4 different devises. Rely on the controller probe and triple check it every day w/ the other therms.
I use a Neptune and DA probes on the same tank, if they are not w/in 0.2 degrees F, then I know something is wrong.
If you do not possess controllers, use 2 alcohol thermometers--don't depend on a battery powered device.
I use a Neptune and DA probes on the same tank, if they are not w/in 0.2 degrees F, then I know something is wrong.
If you do not possess controllers, use 2 alcohol thermometers--don't depend on a battery powered device.
dkeller_nc
New member
Doing a triple point check on a thermometer is sometimes useful to determine if they're way out of whack, but I'd be cautious about interpreting a thermometer/temp measuring device as "accurate" at reef tank temperatures even if it's extremely close to 32 deg F in an ice bath.
The reason is that a triple point check (water vapor, ice and water in thermal equilibrium) is only a single point. So having your thermometer read accurately at that point establishes its accuracy at that temperature, but you've no way to tell if it will be accurate at a temperature relatively far away from that point (in this case, 75 - 80 deg F).
By the way, one caveat to doing an triple-point cal check is that the water that makes up the ice as well as the water the ice is being mixed with needs to be fairly low in dissolved substances. If your tapwater is less than 300 ppm TDS or so, the error introduced from freezing point depression from the dissolved substances will be pretty minor, but the error gets larger as the concentration of dissolved substances go up.
MondoBongo
Obligate Feeder Obsessed
this is excellent advice. the more accurate the calibration the better.
truth be told the ice bath method of therm calibration is something i picked up long ago when i was working as a chef. :lol:
in the OP's case it might be good enough to let him know who is way off, but i like your calibration method much more.
dkeller_nc
New member
Don't let me give you the wrong impression - doing a triple point check has a lot of value, it's just that it's a "necessary but not totally sufficient" test for accuracy. For example, if the temp measuring device in question is showing 45 deg F in a water/ice bath, it's probably junk and needs to be replaced (or recalibrated if it's a digital device). If it shows close to 32 deg F, then I'd characterize the result as "probably OK, but not sure how far off it is at tank temperatures".
The problem comes in when a hobbyist wants to get a second temperature close to the measurement point intent. Highly accurate machines exist to provide a temperature environment at 77 deg F, but that's not something a typical hobbyist has available to him or her.
Ideally, one would want a large-scale precision mercury thermometer that has a NIST-traceable temperature calibration certificate to compare the test device to. One can buy such a thermometer for about $40 - $200 depending on brand/accuracy/precision.
But I would certainly get why a hobbyist would be reluctant to spend that kind of dough just to check a $10 digital aquarium thermometer. So here's an alternative idea that I've used before to get reasonably close:
Wait until your local weather is clear and stable (little wind, not raining, etc...). Go outside with your temperature measurement device that you want to test and in the early morning or late evening (time of day is minimize local environment heating by the sun) and place the temp device such that it's at least 4 feet high over a grassy surface in the shade. Record your temperature measurement device's reading, and access your local NOAA weather station's temperature reading at approximately the same time (a cell phone with a web browser works wonderfully for this).
The comparison of the two readings (the NOAA weather station and your device) will tell you whether your device is accurate to within about 2 degrees F. To increase the accuracy of this comparison even further, you can do several such comparisons over a few days or hours.
