Temperature Controller - Poor temp Readings

[Deeko99]

Hi

I recently bought one of these:

http://www.ebay.co.uk/itm/10A-12V-Digit ... =undefined

With the idea of using it to control the temp of my HLT. I ahve plugged a Burco into the unit with its own thermostat set to 'High' and dipped the supplied probe (?NTC) into the water. On my first test run today I attempted to get it up to 77C. When i got there I though i'd check with my trusty hand held thermometer and a spirit one. Turns out the water was 86C!- quite a margin of error!

I then attempted the ice cold water calibration test - the temperature controller was only 1 degree out. I've tried calibrating against the other thermometers at various temperatures -It seems to get more inaccurate the warmer the water temp - Has anyone else had similar issues? Do i need a new probe? i have tried to do a bit of my own research but seem to have opened a can of worms - I didn't realise how bloody complex temp control could be!

Picture of setup:

http://imgur.com/lUmEEI5

Any advice appreciated - Thanks.

[GrowlingDogBeer]

Have you got the sensor in the liquid.

[AnthonyUK]

With these types of simple controllers you really need to recirculate the water. You may have found that the sensor was reading more or less correct at the point it was measuring but by the time it switched off the water wasn't the same temp all over.

IMO a PID is usually a better option for this application.

[Deeko99]

Sensor is in the liquid and I periodically gave it a good stir. I knew that this approach wasnt the most accurate but didnt expect such a variance in temp!

[Hairybiker]

You can usually do a calibration set on them. Have a look in the manual if there is one.
Get the liquor to the temp you want/a glass or why. Then check using the good thermometer, and set the adjustment on the stc so it reads the same.
Mine was 4 deg out.