ITC308 Erratic Operation

I have an ITC308 which has been in use to control the air temperature in a green house. It has been in operation for about 3 months and on the whole it works as it should but then on quite a few occasions it seems to go crazy, sometimes it goes into AH when the temp is no where near that, or sometimes the Process value is simply unrealistic and crazy. I found by trial and error the one thing that always fixes this straight away is to simply unplug the temperature sensor and plug it back in, and everything is back to normal.
the first time I unplugged the temp sensor was to see if moisture or dirt had got into the connection sock, but each time I found the socket to be dry and clean, but merely unplugging it and plugging it back in fixes the problem,
What is causing this?

Please check if the temperature reading of ITC-308 is correct?
Please check the alarm range composed of AL~AH. Is it close to the temperature control range of ITC-308?
The AH and AL means, when the temperature (PV) reaches/ above AH, or reaches/ below AL, it will alarm.

Hi Tania,
Thank you for your suggestions. AH and AL are well clear of temperature control range.
Problem is temperature reading from the probe. When the Controller goes crazy it is because it is getting an out of range reading from the probe. However the reason I am not concluding that it is a faulty probe is that when I unplug the probe and re-plug it back straight away, it then reads exactly the correct temperature. I would think if it was a faulty probe it would continue to transmit the incorrect temperature, but it is not doing that. Somehow the system is reset, whether the problem is with the probe or the controller, the unpluging & plugging in the probe fixes the false reading

May I ask what is its temperature deviation?
What environment was the probe placed in?

Hi Tania,

Here are the settings on my controller:

Cd: 15
Hd: 12
TS: 20 …So I am expecting Cooling to start at 35 C and heating to start at 8 C

AH: 46
AL: 0
Pt: 0

The temperature probe is suspended in air in the green house and I am measuring the air temperature. I have it in an open container so direct sunlight does not hit the probe at any time.

The ITC-308 has a 1-year warranty.
If it will turn off the heater at 20C and the ambient temperature where the probe is placed won’t reach 46C, but it still triggers the AH alarm, it may be a problem with the probe.
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