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ADuCM360. One ADC drives two RTDs. Settling time consideration...

Question asked by Jackey on Jul 27, 2013
Latest reply on Aug 12, 2013 by AudeR

Hi all.


I,m using 360EVM with two RTD sensors.

RTD_1 is using : AIN2 as + input, AIN3 as - input, AIN4 as IEXC,

RTD_2 is using : AIN9 as + input, AIN10 as -input, AIN6 as IEXC.


ADC_0 is multiplexing these RTDs with sequentially.

And ADC_1 is used for other sensor.


With the Digital_Filter_Response_Model.xls file, I have got Data rate 289hz, Settling time 10ms.

SF is 26, AF is 0, Ravg2 is 0, Chop is 0.


This is my operation scenario.

Set ADC_0's input pin and reference for RTD_1 -> Start continuous conversion -> Wait 10ms -> Get a sampled data for RTD_1->

Set ADC_0 for RTD_2 -> Start -> Wait 10 ms -> Get a sampled data for RTD_2.-> finite loop..........

Thus, required time to get one sample is 13.4ms. The waiting is 10ms and one conversion is 3.4ms ( 1/289 hz).


Q1. What does mean "Settling Time" in User guide?

      This is my quess :

               ADC_0's input pin voltage is +1V and this is initial condition ->

                    apply +2V to ADC_0 input pin  -> after 10ms , user can get +2V digit value.

                     in this example , Settling time is 10ms.


             Direct factors are charging time on sampling capacitor in input stage and Flip Flop latency in Digital filter.


     Do my guess is correct?



Q2. When using two sensors with one ADC, Do my scenario is correct?

      Is there better operation scenario?

       in example code from AD, One ADC is driving Thermocouple and RTD, There is not any wait routine for settling time.

       Maybe , It's conversion rate is 3.75 hz and  settling time was ignored....


Best regards,