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LDCs Sample Rate

Albi Arpo
Intellectual 300 points
Other Parts Discussed in Thread: LDC1314, LDC1614, LDC1312, LDC1612, LDC1000EVM, LDC1614EVM

Hi everyone,

I have three different applications in which I need respectively at least 2kSps, 10 kSps, 30kSps. I need only L measurment and I would like to have the best possible resolution. Moreover, I would like to use multiple coil.

I know that there are many alternatives like LDC1614, LDC1314 and LDC1000 which have different sample rates. From datasheet I see that LDC1000 has a maximum 78 ksps which is very attractive for my purpose, but from this post http://e2e.ti.com/support/sensor/inductive-sensing/f/938/t/366942  I understand that there is a strong compromise with resolution due to noise. LDC1614/12 and LDC1314/12 have the advantage of multiple coil but probably the sample rate will go down if I use multiple channel.

If I would make a new PCB and use an LDC what is the best choice? The USB interface of the EVM how much decrease the effective sample rate?


Best regards

Alberto

  • 0
    TI__Genius 9300 points

    Hello Alberto,

    LDC1000 is the only one that can handle 30ksps.

    LDC1312 can handle 2 and 10ksps (single channel)

    LDC1612 has the highest resolution, and can handle 2ksps.

    When using multichannels, sampling rate will be divided by number of samples used + little overhead.

  • 0 in reply to Evgeny Fomin
    Intellectual 300 points
    Hello Evgeny,
    thank you for your reply. I see that in LDC1614EVM GUI and in LDC1000EVM GUI there is a limit in continuous logging, respectively 10ms and 0.1 ms. Why this limit? It's USB overhead or it's necessary to accumulate a certain number of sample before comunicate with GUI. Is a limitation only due to GUI that I could bypass in custom PCB implementation?

    Best regards
    Alberto
  • 0 in reply to Albi Arpo
    TI__Genius 9300 points
    Hi Alberto,

    Forwarding your question to GUI authors.
  • 0 in reply to Evgeny Fomin
    TI__Genius 13650 points
    Hi Alberto,
    the LDC1612 and LDC1614 have 4.08ksps in single channel mode. Divide this number by the number of channels that you use in your system to get your effective sample rate.
    the LDC1312 and LDC1314 have 13.3ksps in single channel mode, 4.08ksps in dual channel mode, and 2.04ksps in quad channel mode.
    If these sample rates are sufficient and you only need L-measurements, I recommend using the LDC1312, LDC1314, LDC1612, or LDC1614 instead of LDC1000. Choose the device your channel count, sample rate, and resolution requirements best.

    The LDC131x/161x GUI currently supports 0.1ksps data logging or 1ksps streaming. These limitations are due to our GUI and Firmware architecture, and are not because of any device limitations.
    - This 1ksps streaming limitation is due to the architecture of our firmware.
    - The 0.1ksps data logging limitation is a GUI file I/O limitation.
  • 0 in reply to Ben Kasemsadeh
    Intellectual 300 points
    Hi Ben, Hi Evgeny,
    thank you very much for your reply. Now it's clearer. Yes, I need only L_measurements, so my initial choice is LDC1614 because I haven't sample rate limitation for my project and the resolution is perfect for my task. However I have now an another application where I need a sample rate of among 25-30 kS/s so probably I have to use LDC1000. So, to have this sample rate, I set in LDC1000 192-384 response time values but I see poor resolution. Is it due to internal average of fewer samples (so there is more ambiental or quantisation noise)?

    So If I understand correctly, If I want to have 2.04 kS/s with LDC1614 (dual channel mode) I need to not use the GUI and then modify the firmware?

    Best regards
    Alberto
  • 0 in reply to Albi Arpo
    TI__Genius 14270 points
    Hi Alberto,

    The LDC1000 and the LDC161x have some internal differences. Yes, with a lower response time setting the LDC1000 will have a higher noise level.

    The LDC161x GUI can support the 2.04kSPS, and other methods can be used also (take a look that the FAQ and search for 'python' to see some code for using python to interface to the LDC161x).

    Regards,

    ChrisO