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ADUC7061 ADC Pin

Question asked by vnn on Oct 14, 2015
Latest reply on Oct 15, 2015 by MMA

Hello, i use ADUC7061 to measure 2 Thermocouple and 1 PT100. The first Thermocouple and PT100 are connected like

CN0281. But i use voltage divider with 2 Resistor to make ~810mV to bias both Thermocouple minus Input(AIN3 and AIN9). The second Thermocouple is connected on AIN8(+) and AIN9(-). I have the correct measurement values of both Thermocouple.

We want to control the broken wire of thermocouple. When I remove the thermocouple, I saw that the positive Pins of Thermocouple(AIN3 and AIN8) went slowly down from 810mV to 270mV(AIN3) and 3mV(AIN8). It took about 7s to go down to those levels. I think maybe it will be slower, if I measure at higher temperature.

I have two questions.

- Why does it go down so slowly ?

- Why does AIN3 not go down lower? I think when the pin is opened, it must be near ground.

The ADC0CON for first thermocouple is 0x8145 and the ADC1CON for second thermocouple is 0x8183.

The ADCFLT is 0xC283, chop on and update rate ~400Hz.

Best Regards