Unstable ADC reading


We use this board for ESS Testing our product. We use one of the analog inputs to read the voltage from a temperature sensing circuit inside a temperature chamber. The software shows the temperature reading is not stable. I used the NCD Base software to read the analog input in loop mode. The numbers coming back are ranging as much as 21 numbers while the temperature is stable. A voltmeter on the input to the board shows the voltage is stable, much more stable than the readings from the software would indicate. For instance, at one point, I was reading 10-bit values between 205 to 223, which corresponds to a voltage between 1.0019V and 1.1045V - while the voltmeter was reading 1.053V ±3mv. The values read back correspond to about 60°C to 70°C - while the actual temperature was 65°C.

Is this expected behavior for this board? Or should it be replaced?

Do you have the on board pull UP/DWN jumper in the DWN position? If not you need to move it to the DWN position. This should help stabilize the readings.

How long is the wire that connects the sensor to the input? If it is long then you need to make sure you are using a twisted pair cable such as a CAT5 or CAT6.