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AD7193 Accuracy Issues...

   Hello,

AD7193 calibration issue is solved & now i am getting values of offset register & Full scale register as follows.

      Offset register=8389236

      Full scale register=5584950

  AD7193 Configured as follows:

Mode register=0x0C0060

Configuration register=0x040118

Gain=1, Vref1=2.5, Chop disable, FS[9:0]=96,Continuous conversion mode,unipolar configuration

0 to 2.5V dc input connected to ch1 to check linearity of  ADC.

But i am getting 3.5% error (of the reading) near 0.1V

Zero: 0v , ADC counts=0

Span: 2.5V, ADC counts = 16754713

i/p                   ADC counts          Calculated Counts        Error(%)

0.10001          644500                     670228                     3.8387

0.20001         1315798                   1340390                    1.8346

0.30001         1987091                    2010551                   1.1668

0.4001            2660577                   2681316                   0.7734 

0.5001            3331311                   3351478                   0.6017

0.6001            4002490                   4021639                   0.4761

.......

.......

2.0001            13398607                  13403902                0.0394

2.2001            14741788                  14744225                0.0165

2.4001            16083274                  16084548                0.0079

2.5001            16754713                  16754713                

 

 

Please help me how to minimize Error..

Expected error for my application should be <.25% of the reading near zero.

 

Any help will greatly appreciated...

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  • Hi, Latika.

    Can you try to switch to bipolar mode. I think you will be having a negative differential input voltage if your inputs have the same dc bias of 1.25V and a +/-13mV . Have you also performed a noise test on the AIN7 and AIN8 or AINCOM. Same with the previous set up, by shorting the two inputs and apply a bias voltage of 1.25V. I would like to see the peak to peak noise while isolating the square wave input source.

    Thanks,

    Jellenie

  • Hello mam,

    With respect to above post now i am facing another issue...

    I want to measure this 13mV differential signal proportional to velocity....

    When i apply input from simulator i get stable result but now i am going to test it with actual velocity input ADC counts stable for lowest range & starts Suddenly varying.

    for e.g:

    My input signal is 0.556813mV full scale....

    so the calculated full scale counts for 0.556813mV with gain=128, ref=2.5,bipolar mode=239149

    i/p          (%) i/p      (mV) Calc. ADC   Counts  ADC Counts (Min) ADC Counts (Max) Difference (Count Variation )
    100% 0.556813 239149.3 208114 270184 62070
    75% 0.41761 179362 178009 180715 2706
    50% 0.208805 89680.98 88332 91030 2698
    25% 0.139203 59787.32 59399 60176 777
    0% 0 0 658 1069 411

     Please refer above result at full scale range 0.556813mV in above table ADC counts Varies between 62070 Such large variation is not Acceptable...

    With the same condition if i reduce i/p to 75% 0.41761mV in above table Count Variation reduces to 2700 Counts which is Acceptable since.

    Similarly Count variation reduces with input....

    Please Suggest what can i do to Stabilize the ADC counts.. The Max  Possible signal in my case is 1.312mV....

Reply
  • Hello mam,

    With respect to above post now i am facing another issue...

    I want to measure this 13mV differential signal proportional to velocity....

    When i apply input from simulator i get stable result but now i am going to test it with actual velocity input ADC counts stable for lowest range & starts Suddenly varying.

    for e.g:

    My input signal is 0.556813mV full scale....

    so the calculated full scale counts for 0.556813mV with gain=128, ref=2.5,bipolar mode=239149

    i/p          (%) i/p      (mV) Calc. ADC   Counts  ADC Counts (Min) ADC Counts (Max) Difference (Count Variation )
    100% 0.556813 239149.3 208114 270184 62070
    75% 0.41761 179362 178009 180715 2706
    50% 0.208805 89680.98 88332 91030 2698
    25% 0.139203 59787.32 59399 60176 777
    0% 0 0 658 1069 411

     Please refer above result at full scale range 0.556813mV in above table ADC counts Varies between 62070 Such large variation is not Acceptable...

    With the same condition if i reduce i/p to 75% 0.41761mV in above table Count Variation reduces to 2700 Counts which is Acceptable since.

    Similarly Count variation reduces with input....

    Please Suggest what can i do to Stabilize the ADC counts.. The Max  Possible signal in my case is 1.312mV....

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