Cumulus Support

I have a problem,most temperature sensors use the standard 2wire pin head thermistor which I can calibrate with a resistor for correct temp readings.But in my WH 1081 sensors they don't use them,but I see IC about 8 pins that must have a thermistor built in,Can any of you electronics buffs tell me if this is true or not.I do like to try different thermistors now and then .
I just wander if you can calibrate these ICs. Thanks John.

Hi John,

John Timson wrote:I see IC about 8 pins that must have a thermistor built in,

Not really; a "thermistor" is normally considered to be a "NTC" resistor which changes its resistance (downwards as the temperature rises) by quite large amounts. However, the change is not linear so the resistance value normally needs additional mathematical calculations to give even a moderate accuracy over the temperature range.

The temperature sensing in Integrated Circuits normally uses the (quite small) fall in the forward voltage drop of a semiconductor diode, which is almost perfectly linear with temperature increases and generally gives better overall accuracy. But the temperature generally needs to be "calibrated" either within the package at manufacture (a memory "lookup" or perhaps "laser trimming", etc.), or subsequently by the main system microcontroller.

AFAIK, the temperature sensing in the "later" FO sensors is now done within the Humidity sensor module and passed to the main microcontroller via a data bus. So the only way to calibrate it would be to intercept the (serial) data and modify it, or to "hack" the main microcontroller (probably impossible in practice).

Cheers, Alan.

Thanks for the info Alan.On the Maplins HP1000 station I could correct the sensor readings on the display unit.Thanks John.