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RE: What ADC should I use for a moisture analyzer

sandeep malladi
Prodigy 205 points
Other Parts Discussed in Thread: ADS1262, REF5050, ADS124S08, ADS1234Hello Bob, Thanks for the quick responses you had provided me. I would like to design a moisture analyzer with the given specification below Maximum 600 g, Resolution = 0.01 g (if Possible 0.001 g),Accuracy = 0.03 g(if possible 0.003 g ),Data rate 10 Hz,4 load cell interfacing with A to convertor. As the moisture analyzer is a device which provides heating technique to remove moisture from the material. As it may go as high as 160 degrees. So the question I would like to know as stated below. 1. I would like to select the ADC with the requirements as stated above. As per in my mind I have is ADS1262/63 which has low noise performance and compared with other devices its really make it to the requirements. I would like to know are there any A to D converters which are advanced and better than ADS1262 which are most recently released. As this takes some time to come in to market and I need to be up to date with market and technology. 2. Every A to D convertor has its drift towards the temperature when the temperature goes high is there an option where I can compensate the temperature drift. If there is any how does this technique works by giving me some pointers or application notes.
  • 0
    TI__Guru** 113725 points

    Hi Sandeep,

    I split the post from the previous thread as you now have changed topic.  It is not entirely clear as to what the maximum temperature of the ADC will be in your system?  You stated 160 deg C, but that is beyond the maximum operating temperature of most devices. 

    Also, you mentioned 10sps data rate, so what is the actual throughput required of the system with using 4 load cells?  Many ADCs will have a sinc filter requiring a number of conversions before the data is valid when switching the ADC mux.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 205 points

    Hello Bob,

    Thank you for the reply.

    Q : It is not entirely clear as to what the maximum temperature of the ADC will be in your system?  You stated 160 deg C, but that is beyond the maximum operating temperature of most devices.

    Answer :

    I am sorry that I had missed a point to explain. Generally speaking the heat used for material drying would be 160°C or more. Let me be more precise, so now I would like to split the moisture analyzer in to 2 parts first one is heating mechanism for drying the material and second part is that to weigh material and tell the user the percentage of moisture content. between these two sections we have an insulating material which does not allow direct 160°C to fall on the ADC or other electronics components but there would be at least 30-50°C temperature  which may transfer though housing material or any other means at the worst case let's assume.  Will this temperature effect the ADC measurements.

    Q: Also, you mentioned 10sps data rate, so what is the actual throughput required of the system with using 4 load cells?  Many ADCs will have a sinc filter requiring a number of conversions before the data is valid when switching the ADC mux.

    Answer :   The throughput that I require is every measurement gets updated between 3 - 6 seconds  or may 6 seconds worst case.

    Q : Another Question regarding the best selectable Reference voltage I had seen REF5050 but the accuracy 0.05% fs. 5v + or - 0.26v is there selectable Reference voltage of 5v with 0.005%, as i require 5v to be very stable?

  • 0 in reply to sandeep malladi
    TI__Guru** 113725 points

    Hi Sandeep,

    Sorry for the delayed response.  There will be some gain and offset drift associated with any temperatures changes.  This will include references, supplies, ADCs, resistors, capacitors, PCB layout, etc..  With many of our ADCs you can issue periodic offset calibrations to reduce the affects of offset drift.

    Based on your timing some ADC possibilities are the ADS1234, ADS124S08, and the ADS1262.  You can compare the various drift parameters by the specifications in their respective datasheets.

    I doubt that the REF5050 is going to be a good choice.  The output is limited to 10mA, which is fine for using it simply as a reference to the ADC, but with respect to canceling some of the drift affects you want to make your measurements ratiometrically by using the same voltage source for the reference as you do for the excitation of the load cells.  The reference drift and much of the noise will cancel using this measurement method.  Using a quality 5V LDO regulator will have more drive capacity than the REF5050 and should be sufficient for your system.

    Best regards,

    Bob B