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Original question:

ADS1232

ADS1232: ADS1232 - EXTERNAL CRYSTAL CLOCK SOURCE

Erisson Siqueira
Prodigy 80 points
Part Number: ADS1232

Hi,

I'm doing an average read value of ADS1232 and I think it's possible to get a good mean after a long period of time, in my case it was about 3 seconds. So I would like to know if increasing the frequency of the external crystal I can get the average in a shorter period of time. What would be the maximum and minimum crystal frequency I can use? Is this information in the datasheet?

See the image below:

  • 0
    TI__Guru** 113765 points
    Hi Errisson,

    The specification in the ADS1232 datasheet on page 4 is listed as "External Clock Input Frequency". This ranges from as low as 200kHz up to a maximum of 8MHz. All timing in the datasheet are with respect to a 4.9152MHz crystal frequency. Other input frequencies would scale in proportion to 4.9152MHz.

    Crystals are cut at variety of values and 8MHz is a standard value. There are also crystal oscillators or microprocessor timers/clocks that could be used as an external source. However, a faster clock will also increase noise.

    Averaging is most successful if the noise is Gaussian and there will be a practical limit due to the effects of drift. For the ADS1232 I have had pretty good success up to averaging 100 samples.

    Prior to any averaging it is best to reduce noise from all external sources as much as possible. Noise sources can be EMI/RFI that can alias back into the pass band of the device, but can also come from low frequency sources created from air currents/temperature as well as vibration. There can also be sensor element self-heating that can take place. So there are a variety of events or external forces that can affect the result and averaging may or may not help in all cases.

    Other often overlooked areas in the measurement are reference settling and phase differences in the ratiometric measurement. So there may be time required for analog settling apart from just averaging at device power up.

    In the graph you show in the post it is not clear what the data rate is , but there does appear some periodicity to the waveform. An example of how this can happen is when 80sps is used where power line-cycle noise is within the pass band.

    From the graph, the result appears to have noise of approximately 275 codes p2p before averaging. This is about 2 bits more noise than I would expect if the data rate is 10sps.

    Best regards,
    Bob B