Heaters faulty?

[Kimberly4403]

So yesturday I brought myself a proper digital thermometer to test my tank temp with instead of using the cheap suction cap one... I have 2x 150watt heaters placed at either side of my 4 foot 285L tank and they are set to 28C however my digital thermometer reads 24-25C is my thermometer faulty or are my heaters not working properly??

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[LiterallyHydro]

Are you able to raise the temperature higher on the heater to bring the temperature where you want it? For me to set my tank's temperature to 78F I have to set the heater to around 85F.

 

[Bob Ellis]

The markings on the heater have rarely matched the tank temperature in my experience. What is important is knowing your thermometer is accurate and your heater will maintain a temperature whether or not that matches what its own dial says.

Most heaters I have bought have had a disclaimer saying to verify the temperature of the water with a thermometer and not rely on the knob on the heater for temperature verification.

 

[gsong321]

Titanium heaters are the only way to go! Set the temp and that is what you get...I've checked mine through several different means and it's always right on the money!

 

[Bob Ellis]

But you should always verify with a thermometer so for my money if the heater is consistent I'm happy.

 

[gsong321]

Amazon sells a digital thermometer for about $5 and they work reasonably well. I picked up a laser thermometer at harbor freight and that has helped to calibrate all my heaters and thermometers.

 

[Kimberly4403]

I have a digital thermometer in already yeah I could try turning heaters up

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[Jsigmo]

Amazon sells a digital thermometer for about $5 and they work reasonably well. I picked up a laser thermometer at harbor freight and that has helped to calibrate all my heaters and thermometers.

Infra red non-contact thermometers are notoriously inaccurate at temperatures near or below room temp, and are especially bad when trying to measure the temperature of anything shiny (low thermal emissivity) like water or glass.

I'd stick with a good thermometer that you actually immerse into the water to make the readings.

These ones:



Are reasonably good, and can be calibrated (at one point). They're also incredibly fast-reading in water or food.

My only complaint was that they tended to consume batteries faster than I'd like. But for the money, they beat the heck out of a number of "laboratory" thermometers that cost at least twice the money in all of the testing I did.

And it now appears that they've addressed the battery issue and the new version uses a lithium cell, which promises to last a LOT longer. I may have to get a few of the new ones myself!

They're water resistant, too, which is a plus.

When I calibrated them at the ice point of water, they read dead on at all temperatures between 0 degrees C and +25 degrees C, and were likely excellent over a much wider range.

Other small digital thermometers sold as "laboratory" thermometers for around $40 were found to have striking non-linearities over this same range, being off as much as 1.2 degrees C at any given point, with no pattern or curve to the error. They were quite disappointing, and unusable for our purposes.

Non-contact infra-red thermometers, even quite expensive ones designed for lower temperatures for food-safety testing, also proved to be far too inaccurate and non-repeatable for our purposes.

 

[Kimberly4403]

Ok I have a digital thermometer and it reads between 24-25C most of the time however during 1 cold night when house was open due to paint fumes it did drop just under 24 and ive seen it as high as 26C some days.. Both my heaters are set at 28C I need my tank to sit between 25-26 for my fish.. Should I up my heaters to 30C and see were it sits then? Should I have to constantly adjust my heaters.. Or once ive found correct temp then I can leave them be

I currently have 1 heater on each end of the tank and my temp prob is in the middle between them very unsightly until my plants grow up anyways.

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[Bob Ellis]

Once the heaters are keeping your water the temperature you want you shouldn't have to mess with them. Ignore the numbers on the heater. If you are getting 24-25C and would rather have 25-26C then turn them up one degree and see what your thermometer reads after giving them some time to heat the water that extra degree.

 

[Kimberly4403]

I can only turn up in 2 degree increments so ive upped to 30 and ill see what tank sits at in a couple of hours

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[chromedome52]

A couple of hours will not be long enough, I'd give it at least 12 hours to get a proper reading. I have an electronic TDS meter with a thermometer included (temperature can influence the hardness reading). This allows me to check both parameters on a regular basis in some 40 aquaria. I tried one of the cheap digital thermometers for aquaria, they are not that accurate IME.

 

[Kimberly4403]

I'm at work today anyways so won't check till I get home

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[Kimberly4403]

So I came home to my digital thermometer reading 26.5C

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[Bob Ellis]

How is the tank circulation? You could try one heater set to 28 and one to 30 if the water moves enough to dissipate the heat.

 

[Kimberly4403]

I have tried your suggestion of 1heater set to 30C and 1 heater set to 28C.. So far after 6hrs it has come down to and staying around 25.3-25.9C ill keep checking and see if it drops below 25 after a cool night but so far seems pritty stable..

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[gsong321]

I've actually had pretty good luck with mine. I have about a dozen digital thermometers and my laser checks out as close as any of them. I have a very good quality unit and I only use it for spot checks but it saves a lot of time and guess work...it really comes in handy for my ponds.

 

[Jsigmo]

I've actually had pretty good luck with mine. I have about a dozen digital thermometers and my laser checks out as close as any of them. I have a very good quality unit and I only use it for spot checks but it saves a lot of time and guess work...it really comes in handy for my ponds.

What we found was that when "looking at" a shiny surface, infrared non-contact thermometers "see" the reflection of whatever object is at the correct angle to that shiny surface, rather than seeing the reflective surface itself.

And this is just as it should be if you consider how a non-contact IR thermometer works.

There are two thermopiles in the unit. One is set up to measure the back surface of the module containing the two. The second one is arranged to be "illuminated" by the object being "viewed" by the gun.

It's really a pretty amazing setup.

You'll note that if you have a fancy IR gun, it will have an adjustment for the thermal emissivity of the objects you'll be reading. Setting that to match the surfaces you'll be reading really does help.

Less fancy ones have a fixed setting for the thermal emissivity. They're usually fixed at 0.95.

An ideal "black body radiator" will emit IR very well. They're a good "transmitting antenna" for the wavelengths in question. Remember that IR is simply electromagnetic radiation within a certain range of wavelengths. The ideal black body radiator will have a thermal emissivity of 1.00

But as you get to more shiny surfaces, they become worse transmitting antennas at the wavelengths in question.

Not surprisingly, this follows exactly the way normal radio frequency antennas behave. That is: An antenna which is tuned for a particular frequency (wavelength) will transmit and receive equally well at that frequency.

With IR, the physics is identical, just in a range of shorter wavelengths than we're used to in RF work.

A surface that appears "black" to our visible range of wavelengths, not only absorbs well (receives well) at those frequencies, but it also emits (radiates) well at those same wavelengths. So you can predict, to a fairly good degree, what surfaces will be good emitters versus bad emitters.

Shiny surfaces don't absorb light well. And by the same token, they're also poor emitters at those same wavelengths.

What you end up with, then, is the fact that shiny surfaces not only are poor emitters, but also tend to simply reflect the IR the same way a mirror will reflect visible light. So when you aI'm your IR thermometer at the surface of water, what it sees is a reflection of whatever is at the correct angle to that surface, just as you will see, with visible light, a reflection of something that's at the correct angle between your eye and the water.

What we found, was that we could take a reading off of the surface of ice water, and get a reading, instead, of the wall behind the container, or the person standing at the proper position that their reflection was "seen" by the IR gun.

This lead to wildly erratic readings by various analysts and lab log-in personnel when reading the same samples. So we went with very fast-reading immersion type electronic thermometers such as the ones I linked to above. We also had to begin using a system of including "temperature blanks" in every container of samples so that the actual sample containers didn't need to be opened and potentially contaminated.

Even trying to take readings off of the containers themselves proved problematic because glass containers, being shiny, gave readings of the objects or people reflected from their surfaces, rather than their true surface temperatures.

I suggested that we could patent, and have made, a type of sticker or label with a known thermal emissivity that we could apply to all of the containers so they'd present a uniform surface and emissivity for all types of bottle. But even with very repeatable and uniform surfaces, the variation we found from one IR gun to another was unacceptable. Further, they were unacceptably dependent on the ambient temperature as well.

We tried many types, most quite expensive, and just found them far too inaccurate for our purposes.

If you only need to be within + or - two or three degrees C, they might be OK IF you avoid shiny surfaces, and test its accuracy (since some examples were farther off than this, maybe more like 4 or 5 degrees off). We needed better accuracy than that.

Further, most of them were not adjustable. That meant that we had to test their calibration and then apply a calibration sticker that included a formula to correct for its errors at various actual temperatures. That meant that the analyst or log-in person had to tediously calculate the correction and then record the corrected temperature on the chain of custody or in the analysis program.

The thermometers I linked to above have a single point calibration adjustment. I calibrated them when we got them in, and once per year after that. After calibration, their reading was within 0.1 degree C over our range of interest. That meant that analysts and log-in personnel could simply write down the reading directly from the thermometer. The time saved, and reduced potential for error were enormous factors for us.

If you choose to use an IR thermometer for aquarium use, just beware of them reading reflections off of glass or water surfaces.

They will work best if held so their view-angle is perpendicular to the shiny surface in question. And getting as close as possible (preferably pressing the unit against the glass) helps by blocking reflections from the surrounding area. Still, it may read a reflection of itself, so the temperature of the thermometer itself will enter into the possible error budget.

The circuit or software in the IR gun will correct for the actual temperature of the sensor. But it cannot correct for what the sensor actually sees.

They're great tools, and fun to play with. But they may not be suitable for some applications.

A fun trick is to go outside in the middle of the day and aI'm one up at the sky. Good ones will actually read the temperature of the upper atmosphere if there's no fog, smog, or clouds to get in the way. Pretty darned cold up there, isn't it?

It's not that I don't appreciate what an amazing item an IR thermometer is. It's just that you have to understand how it works and account for what it actually "sees", and also be aware of the accuracy limitations most units seem to display.