Backyard Aquaponics
A place to discuss aquaponics

Ever wondered how accurate cheap "K" type thermo couple thermometers are?
I did...
So I borrowed a certified reference thermometer form work.
Did some un-scientific spot checks on the various thermometers I have around the place.

Observed results go something like this

P650-PT Platinum wire certified RTD + or - 0.03 degrees (Reference)
EHIM Aquarium thermocontroler. within 0.1 degrees Get what ya pay for !
TEMP ALERT - Indoor/ outdoor + or - 0.5 degrees Got lucky with this one.
THERMO CLOCK - Indoor / outdoor + or - 1.5 degrees Nice big display
Aquaone aquarium themometer + or - 1.5 degrees Varying results.

I'm thinking it is just a matter of luck how accurate the cheapo thermometers are, but for the price and our application they appear to do fine.

lol, I reckon they're all about 10°C more accurate than the thermostat on the aircon in my office

would be great to see this test against a cheapo alcamohol thermometer too...

And at different temps they can fluxuate.

Get an accurate mV dial gauge, or digital if it's any good, and some LM35 from National Semiconductors... Very simple very accurate readings... 0.5 degrees or better if I recall... I'm sure there's a datasheet here somewhere. And what's better is last time I looked you could order them as free samples!

Interesting...
I want to hook up something so that my outdoor waterbed (no gravel) only circulates when the temperature water is above say 24°C (ideally whenever it is warmer than the fishtank)...

should I just do what Ron suggests?
viewtopic.php?p=159739#p159739
Fridgemate (single temp probe as far as I can see) sells for about $50 - can I do better than this?

You probably wont be able to do anything easier

They come with more temp probes, you just need to buy them.

The one has an optional SS probe

http://mashmaster.com.au/p/365439/fridgemate-mkii-digital-temperature-controller-kit.html

Hi Steem,

I have one running on my brew fridge and it can be set with a hysteresis (sp) of +- 1C, the following two places stock them here in SA.

http://www.beerbelly.com.au/ talk to Wayne (also does stainless fittings)
http://www.stillbrewing.com.au/ talk to either Brad or Phill

Himzo.

Check out
http://martybugs.net/electronics/tempsensor/

Requires a bit of electronics knowledge to get to work.

They are pretty easy to hook up to a PC via the serial port - but you might need a bit of work to get them to actually turn on/off a pump etc.

I have some hooked up to a PC at the moment, and added some software + hardware to turn on lights/refrigeration/pumps/feeders etc based on time and temp. Involved some programming and a bit of electronics work - but not impossible if you want to have a go...

(You can get free samples from Maxim too-if you don't want to buy them)

thanks all, I'm looking into getting one.
Of course the lowest tech, lowest cost solution is a pump on a timer, set it for roughly when temps are high enough. The feeble brain and feebler wallet might make the decision for me...

The tempmate looks like an easy option. All the fiddly electronics is already done for you.
Let me know if you want a hand to wire it up.
I'd offer to make a purpose built differential thermostat, but summer might be over before I finished it...