2 degree thermometer discrepancy

[mattttam]

My cheap digital thermometer is pretty accurate - my more expensive (still relatively cheap) one has been climbing temperatures over the past 24 hours.

At first I thought the thermostat in the heater had gone. But checking the stick on and the other digital shows that it's just wrong.

Any possible causes of this? Is it just broken or is there something I can try?

Thanks!

 

[rebel]

How do you know which thermometer is accurate? do you have a way of calibrating them?

 

[parotet]

Hi all

Regarding the thermometer reading... I don't keep fancy shrimps or fish, so reading accurate temperatures is not really a concern for me. I even assume that my thermometers won't be giving the same readings, as they are also cheap ones: I have what I paid for... so not scientific instruments.
You can try all the thermometers you have at home in the same time and note the differences.

For checking the heaters (especially after the summer break) I use them in a small container with cold tap water: in a small volume you should notice a faster change in the temperature (sometimes touching the heater is enough to see if it is working).

Jordi

 

[zozo]

I'm also using several thermometers.. 🙂 A hang on old fashion glass one probably filled with alcohol.. And a few digital ones, also my heating is regulated with an electrinoc thermostat measuring temp with a probe.

My glass thermo says 23,2 c, the digital one says 24.8. The one which regulates the heating has a calibration function. I calibrated this one with the digital in the tank, so both say the same. 🙂 Now the fun part starts, in the summer when the room temp heated up till 29 c, the discrepatie became also greater. The heaters thermostat said 30 c and the one in the tank sayd 28c. So it needs recalibration if the desired temp treshold changes.. But when it goes down again both settle again at 24.8 again. 🙄 Oh and i also have a pocket EC / pH meter with temp probe again saying something else..

Both factory specs of the electronic versions state they both use a 1000K Ohm Heat sensitive Resistor as temp probe. One has a toleration 1% accuraty the other 0.5% accuraty. There you have you discrepanties, the 1000K Ohm probe. This probe passes the electrical current from and to the meter.. Warmer or colder this current changes, these changes are again electronicale recalculated to a number on a display. Those 1000K Ohm probes are a bit wonky, lets call it 50 cents accuraty. 😉

Anyway it's not such a big deal, it al is an estimation of being near the right temperatur, a few degrees difference isn't a problem..

 

[mattttam]

Thanks all.

No they aren't calibrated, but the glass one, the stick on, and the cheapest digital one are all more or less the same.

The one that climbs and drops sporadically just had me worrying the heater thermostat had gone caput and my fish where about to slow cook; obviously checking the others helped me relax. I'm not worried about perfect accuracy - it was just the fast climbing temperature readings that had me concerned.

Thanks 🙂