issues with erratic temp readings on controllers

[barkar]

Anyone have any issues with erratic temp probes in wiihi or stc s ? I have one which has suddenly shot up 20c and another which wad working fine but now operating at a healthy 89 c at room temperatures ? The actual temp is about 10 c in the shed .its odd cause they worked fine up till now

[DEMPSEY]

Probe on my 800+ went wonky like that and began reading 48C when it was'nt 48C. Bought a few replacement probes and replaced the probe,problem solved.

[barkar]

Sorry , yeah haven't checked the innards of the control box yet but I presume one of the wires pulled loose, ill try adjusting the coefficient to reflect the right temp, so yers just needed a new probe , are those probes k thermocouples do Ye know

[Will_D]

Yep, cheapo k type.

No they are not! They are thermistors!

[barkar]

Hmm dont know if i want to ask but whats the difference ? i seen loads of ntc 10ohm ones with 3 wires pins , woudl that work?

[Will_D]

A Thermocouple is formed when two disimilar metals are fused together. The circuitry detects the very small (milliVolts) voltage produced by this. It is amplified and converted to a temperature. Typical temp range for a K-type is -50 to 800C. The two leads have a plus and minus polarity - that is why the plugs are polarised. They are considered very accurate.


The Atc/Stc controllers use a thermistor. This is a resistor who's value changes with temperature so you convert the resistance to a voltage and then to a temp. It can be wired either way round. Not as accurate as the other 2.


If you see 3 wires then what you have is probably a DS1820 digital sensor. This runs what is called the "one-wire" interface (actually needs a minimum of two for short distances as its powered from the data line. For long runs the 3rd wire is 5V).

These produce a packet of data with it's address and temperature. You need an Arduino or the like to read these. They are very acurate and because of the "addressability" they can be wired in parrallel to you single input pin.

[barkar]

so just look for a ntc then is it ?or a k type if no cheaper alternative