ADC Drifting
- Thread starter gdenehy
- Start date
BeanieBots
Moderator
The ADC itself will not drift but other factors might.
That can include the thermister. Moisture ingress for example.
The PICAXE uses it's power supply for the ADC reference.
If the thermister forms part of a potential divider, then it should be reasonably immune to variations in power supply voltage but not completely. At higher voltages, the self heating effect of the current in the thermister will make measuring tempertatures of low heat conduction materials (such as air) seem higher than they really are.
Bad wiring, long leads, wrong material connectors, electrical noise and many other factors can play a part.
Please post your full circuit diagram so that we can advise more specifically.
That can include the thermister. Moisture ingress for example.
The PICAXE uses it's power supply for the ADC reference.
If the thermister forms part of a potential divider, then it should be reasonably immune to variations in power supply voltage but not completely. At higher voltages, the self heating effect of the current in the thermister will make measuring tempertatures of low heat conduction materials (such as air) seem higher than they really are.
Bad wiring, long leads, wrong material connectors, electrical noise and many other factors can play a part.
Please post your full circuit diagram so that we can advise more specifically.
It is all on a breadboard - no solder connections.
The wires are laying all coiled up and all wrapped around other cables all over the place.
The wires are about 2m of cheap speaker cable.
i think I might need to address these issues before worrying to much about anything else then
The wires are laying all coiled up and all wrapped around other cables all over the place.
The wires are about 2m of cheap speaker cable.
i think I might need to address these issues before worrying to much about anything else then
BeanieBots
Moderator
It is all on a breadboard - no solder connections.
The wires are laying all coiled up and all wrapped around other cables all over the place.
The wires are about 2m of cheap speaker cable.
i think I might need to address these issues before worrying to much about anything else then
Doesn't need to be soldered to introduce thermocouple effects.
Corroded contacts can act like a battery. I've seen > 0.5v just with oxidised copper.
Coiled up = transformer that can pickup mains and any other RF around.
Wrapped around other cables is the same as a capacitor connected to them.
Cheap speaker cable is VERY bad for use with sensors. Use quality co-ax.
Better still, put all amplification etc close up to the sensor as described in the other thread.
inglewoodpete
Senior Member
Two great unknowns with ADC are noise on the supply rail and noise on the ADC in wire. However, these will introduce a randomness to readings rather than drift.
BeanieBots
Moderator
Thermisters drift!