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ADS8328 READINGS FLUCTUATING

RAM LODH
Prodigy 140 points

Other Parts Discussed in Thread: ADS8328, TL431

I HAVE CONFIGURED ADS8328 IN  

1)MANUAL CHANNEL SELECTION . 2) TRIGGER SELECT - MANUAL. 

I HAVE SELECTED ONLY CH0.

VREF TO ADC8328. IS 2.5V.

I AM GIVING ANALOG INPUT (0V TO 2.5V) THROUGH AGILENT MULTIFUNCTION METER.

AND OBSERVED THE FOLLOWING READINGS.

SR NO

INPUT (V)

ADC COUNT

 

1

1.000 to 1.005

27651

steady

2

1.006

 27651  ,  28163

fluctuat

3

1.007

 27651 , 28163  , 28419

fluctuat

4

1.009

28419,  28163 , 28546

fluctuat

5

1.1 to 1.119

30723

steady

6

1.120

3072  , 331491

fluctuat

7

1.138 to1.157

31747

steady

8

1.158

31747 , 32515

fluctuat

9

1.5 to 1.509

40963

steady

10

1.510

40963 , 41987

fluctuat

11

2.4  to 2.404

64515

steady

12

2.405

64515 , 65535

fluctuat

13

2.410

65535

steady

 

It is observed that adc value is not changing for all  analog input s it remain constant for some range as in reading numbers -   1 ,5 ,7 ,9 ,11. i.e. adc count is not changing for every step change in analog input.

frquently  It is observed  that when  fluctuating  difference between adc count is 64, 256, 512 like this . for  same analog input .

please help me for get rid of fluctuations and above step response.

  • TI__Guru**** 182881 points

    Hi again Ram,

    if you convert the decimal numbers you provided as the conversion results for the ADS8328 to HEX, you'll see values like 0x6C03, 0x6E03, 0x6F03...0xFC03.  Bits 0-3 are 0010 or 0011 and bits 4-7 are always '0'.  Something is wrong in your communications with the device.  Please send new screen captures of your serial interface.

  • in reply to Tom Hendrick
    Prodigy 140 points

    new screen captures of your serial interface.

  • Prodigy 10 points

    Hi Tom ,

    This is Ram ,I have changed VREF ic  from TL431 to  REF3325 , now VREF=2.4V

    I have taken some readings. i have attached screen shot in previous post asked by you.

    also sanjay pithadia has some query to you.

    date

    23/05/2012

     

     

     

     

    VREF=2.4V

     

     

     

    sr. no

    input (v)

    adc count hex

     adc count decimal

     

    1

    1.000  t0 1.005

    0x6c03

    27651

    Constant

    2

    1.009

    0x6f03

    28419

    Constant

    3

    1.011

    0x6f83,0x6f03

    28547, 28419

    Fluctuate

    4

    1.013

    0x6f83,0x6fc0-c2,c3

    28547 , 28608-9

    Fluctuate

    5

    1.015

    0x6fec to 6fc3

    28652 to 28611

    Fluctuate

    6

    1.026 to 1.043

    0x7003

    28675

    Constant

    7

    1.924 to1.929

    0xd003 , 0xcc03

    53251 , 52227

    Fluctute

    8

    1.931

    0xd003

    53251

    Constant

    9

    2.298 to2.309

    0xf403

    62467

    Constant

    10

    2.39

    0xfc03

    64515

    Constant

    11

    2.4

    0xffff

    65535

    Constant

     

     

     

     

     
  • in reply to RAMBABU LODH
    TI__Guru**** 182881 points

    Hi Rambabu,

    Sanjay sent me your schematic and I'll look over it.  What is causing the various delays in your SCLK?  How much ringing is there in that signal?