Temp calibration techniques?

[skein]

Many, many times we hear someone asking "what's your temp" and many, many times the answer is something like "we're showing 57* but I think my temp gauge is off..."

So is mine.

Anybody got some techniques we could use to determine how far off our gauges are? I know lots of us have different sounders, etc, but the problem seems to be pretty universal.

I think I'm gonna start bringing the floating thermometer from my swimming pool. It's frustrating to not know for sure -- or at least reasonably close.

Skein

[Bluefinn]

I tied a piece of mono to our outdoor thermomiter plunked it in the water at the dock.My Garmin unit reads 2.5 degrees colder then the outdoor one.I just add 2.5 to whatever my unit says.Garmin does not have a way to change the temp reding yet.

[Boatdog]

Some sensors can be unbolted from the boat, and put into a bucket of water while still connected to the head.

If that's the case with you, you'll also need a known accurate thermometer. Have them both measuring the same water at the same time to determine your 'offset'.

[Chromaflage]

One thing to keep in mind - there may not be a linear relationship between what your sonar reads and the actual temperature. It may be +/- .5 deg in colder water and +/- 2.5 deg. in warmer water (for example). Just a thought - have no idea about the reality of this, but I'm thinking very possible.

[Fast Water]

Originally Posted by Boatdog

Some sensors can be unbolted from the boat, and put into a bucket of water while still connected to the head.

If that's the case with you, you'll also need a known accurate thermometer. Have them both measuring the same water at the same time to determine your 'offset'.

Or use a known standard. A bucket of ice water (mostly ice) would be 33 to 34 degrees F.

Or use two or three thermometers and average the readings and compare to the boats reading.

Does the manual for the instrument have a +/- accuracy range?

[Elkiller]

I have two temp gauges. The one on my chartplotter is within a degree of the actual all the time but only reads in full degrees so it is often showing one degree high. My lowrance in dash gauge is two degrees low in water up to 59 degrees but is within a half degree in water over 62. It reads in tenths. I can't calibrate either one so I'm stuck memorizing all this jumbo or mounting a third but so many people are reporting the same results that I don't have any confidence that would help. Man with one watch always knows what time it is, man with two watches never knows.

[Pilar]

Ice in contact with water will be at exactly 32 degrees. This is because of a principle called latent heat of solidification or the freezing point of water. This relationship is so reliable it is a calibration standard at all calibration facilities. The boiling point of water at sea level is always 212 degrees. As long as water and steam are present in the same container it simply cannot be any other temperature. Latent heat of vaporization or the boiling point of water, another reliable standard.

Chromoflage brings up a good point in that instruments are accurate at a certain temp and may vary at different temps. You can use the ice/water to check your 'standard' thermometer. The way a Calibration facility does it is to use freezing and boiling points to verify accuracy over a wide range of temperatures. Once you know your standard is accurate then compare the two in the 50 to 60 degree range and get your offset.

Don't boil or freeze your sonar transducer.

[Slobes]

Originally Posted by Pilar

The way a Calibration facility does it is to use freezing and boiling points to verify accuracy over a wide range of temperatures.

Here in the lab we use ice water and liquid nitrogen, but I doubt your transducer would like that...

[skein]

That seems to be the deal; either the equipment/environment is beyond reach, or the redneck calibration method is too coarse. I bought a little digital thermometer last year and it lasted about 15 minutes in our ocean conditions. At least it was cheap.

I guess my pool thermometer will have to do.

Skein

[Jason S]

Originally Posted by Pilar

Ice in contact with water will be at exactly 32 degrees. This is because of a principle called latent heat of solidification or the freezing point of water. This relationship is so reliable it is a calibration standard at all calibration facilities. The boiling point of water at sea level is always 212 degrees. As long as water and steam are present in the same container it simply cannot be any other temperature. Latent heat of vaporization or the boiling point of water, another reliable standard.

Chromoflage brings up a good point in that instruments are accurate at a certain temp and may vary at different temps. You can use the ice/water to check your 'standard' thermometer. The way a Calibration facility does it is to use freezing and boiling points to verify accuracy over a wide range of temperatures. Once you know your standard is accurate then compare the two in the 50 to 60 degree range and get your offset.

Don't boil or freeze your sonar transducer.

Don't forget that the upper point will also vary based on your elevation if you are going to do a two point check on a "reference thermometer". Sea level water will be 212. At just 100 ft above sea level it will only be 209.7

It would be hard to fins a thermometer that will read from those but you can find 0-100 C Thermometers online for not that expensive and use those by converting to F.

[F] = [C] x 9/5 + 32

[Big Billy]

You could use a meat thermometer (pocket rocket) about $10, calibrate it in ice water 32 degrees and then figure a way to get it into and out of the salt water safely, they have a nut under neath them that you can turn to calibrate them, they also have the infrared one that you point and pull the trigger which will give you the surface temp but they are $100 or more

[Reel Knotty]

Originally Posted by Bluefinn

I tied a piece of mono to our outdoor thermonitor plunked it in the water at the dock.My Garmin unit reads 2.5 degrees colder then the outdoor one.I just add 2.5 to whatever my unit says.Garmin does not have a way to change the temp reding yet.

That is interesting. My Garmin seems to read 2.5 degrees colder as well...

[Bluefinn]

I would think it would be the transducer and not the unit.I do not know my transducer is a Airamar ss-164.I hope Garmin will come up with an update to calibrate the unit soon.My old Furuno was spot on accurate.

[WaveDancer]

Funny this topic has come up.

I recently found out that my displayed temperature was inaccurate and was faced with having to see about correcting it.

I own a dual display Furuno NavNet system and it has the ability to correct the temp readout by assigning an offset.

What I came up with was to bring a high quality laser temp sensor with me during my last outing on the water.

I then put out a downrigger ball just under the surface and left it there until the temp stabilized, about five minutes in my case.

I then used the downrigger ball temp reading as a calibration point and adjusted my systems offset as needed.

Pretty easy after finding the procedure to change the temp offset. (thank you very much Furuno cust support, #1 IMO)

With temperature being such an important factor in finding longfins, more and more of us will need to make sure our equipment is displaying correct temperatures.

WD.

[Woody]

I have a glass 0-100 C lab thermometer I can bring to the coast with me. I'll start packing it in my knife bag.

We can check the low end with the boat on the trailer and do a sea water check off shore.

(C x 1.8) + 32 = F

[ron m]

If our temp readings are going to vary much when the temps are much colder or much warmer, then I'm for going low tech. My son brought over a high quality thermometer and we got a bucket of water from near the back of the boat and measured the temp of the water in the bucket and did an offset based on that.
ron m

[Spindrifter]

Originally Posted by Reel Knotty

That is interesting. My Garmin seems to read 2.5 degrees colder as well...

Same here! Mine was reading 57.4 out where the TUNA! slaughter was going on at 45:48 x 125:00. Probably about 3 degrees too cool. Everywhere I have researched there is no way currently to calibrate the darn thing. I have this one
http://www.rocktheboatelectronics.com/html/25810.html

[sarmstrong]

MarcMc gave me this method while i was out on the watewr last week, On your run by the stonewall bank bouy take a look at your temp then reference that temp and time later online

[rblucky]

Ok this topic was single handedly responsible for me losing many nights of sleep.hahahaha.
But let me say this Temperature is all relative if your not sending ships to Mars!
I upgraded my furuno ff to a new digital and when I did the temp calibration was different.So seeing as I was to get involved with the offset I thought I would involve a pro.The people that sold it to me.I was told that I should get an infrared digital temp guage and set it to that. I didn't buy the cheap one of course so 149 bucks later I'm checking the temp of everything . With a +- .5% variation at 50% of the temp displayed I figure close enough. Well It opened a can of worms that went for months.First I checked to see that my transducer/display would read 32 deg with slush under the transducer I set the offset and OK . But I could not get a consistant temp between the 2 temp sensors on the boat (I have a speed and temp sns mounted at the rear helm station).And When I got to the water it was way off so then !@#$ Well to make a long story way shorter.The digital infrared hand held sensors in spite of what is talked about will NOT produce a repeatable good temp off the surface of water , always 3-4 deg higher. One cannot use the bait tank water and a thermometer because the hoses going in proximtiy of the engine compartment is way wamer from engine heat.
So after months of asking all these brainy types even one that was a geothermal engineer that ran the Guiesers in napa that had a federal temperature tester. Finally I have decided that in the real world ,,Remember I said temperature is relative ? Well if you can't get a bouy reading when you go by one take an average of 3-5 buddies and set your default at thier average and sleep well.At least you all will be in the neighborhood!!! It's my best advice ..TADAAH !
scotty

[Sallysea]

Just to add a touch of confusion. Terrafin tells me their temps may not be accurate either. The readings they get are only the top 1mm of depth.
Ever notice the daytime temps seem to be warmer than the night temps?
The problem is reflection.

[Fast Water]

Originally Posted by rblucky

.The digital infrared hand held sensors in spite of what is talked about will NOT produce a repeatable good temp off the surface of water , always 3-4 deg higher. scotty

IR probes can be difficult to use this way as they need to be emissivity corrected. The better guns will have an adjustment.

[Onokai]

Jim I bought a very accurate thermometer for medical use in air and water from the net- cost about 25$ then calibrated my furuno unit in air and water with it. Now when I hear my unit reads whatever I ignore that call. The other way is get next to a weather buoy that puts out temp readings and calibrate yours to that. Mark

[fishonjon]

Use Mcdonalds coffee its been the same ever since the lawsuit.

[Sea Jypzee]

I purchased a digital thermometer accurate to .1 degree from Englunds with a metal probe and water proof. Was about $25 or so as I recall.

I just stick it down in the water over the side of the boat, get a reading and calibrate the Furuno from that. It gives me a pretty accurate assessment. I may not be exactly on target, but if it puts me within a .5 degree range, I'm happy.