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tidud25a problem regarding LC sensor

Other Parts Discussed in Thread: CC1310, CSD

HI sir,

i am working on the tidud25a.pdf , the previous work of mine are :

i am tuning the value of  C and L in scs,

i have a problem that at the very beginning of running the SCP in scs, the ticks show value of 2000(for example), after 30minute , it drops to 1995 , and after 30 minute, it drop to 1990..............

all the pasts i use already follow the BOM, do any solution can be suggest?

thanks

Jeff

  • HI milen,

    i test more today , and same things happen ,  after some time the ticks value will vary(decrease),

    so my boss is asking is there a way to calibrate it in CCS or you have other solution for it?

    thanks

    Jeff

  • Jeff,

    This variation is most likely related to changes of the temperature inside the CC1310 device when it runs continuously. Note that each tick is 10.667ns, so 5 ticks delta are around 53ns. The clock for the Sensor Controller will have some jitter and the Comparator used for the ticks counting may also vary slightly due to temperature change.

    I think it is relevant to know if such variation of 53ns is small enough compared to the value you measure, e.g. one full oscillation cycle of 1500ns.

    I haven't implemented any calibration for such variation - i think you need to measure your design at worst case ambient temperature (e.g. -10C to  +85C) to see how the ticks change over the full temp. range of your application.

    You could also try to use one oscillation cycle less for your rotation detection (e.g. reduce from 20 cycles down to 19 cycles) based on the results of the worst case temp. testing. That can help accommodate for all variations of the number of ticks across the temperature.

    Another easy test is to use a cooling spray at CC1310 and see if lower device temperature delivers higher tick count.

    Regards,

  • HI milen,

    thanks for your reply.

    we do suspect the draft is either from CC1310 or from the LC  part. As the LC and the mosfet will open to start the pulse.

    "I haven't implemented any calibration for such variation - i think you need to measure your design at worst case ambient temperature (e.g. -10C to  +85C) to see how the ticks change over the full temp. range of your application."

    So in scs case, as my scs is open and running all the way, so i can change that accordingly ? as the ticks valus is assigned in constant, and also the change is ticks value is too significant compare to that.
    We would like to ask do it happen to you also the change of tick value in scs?

    thanks

    Jeff

  • HI milen,

    i attached one of the waveform i capture , acccording to the tutorial, there should not exist any interference of the waveform,

    the top and bottom are the waveform of the LC , seems the interference still exist

  • Jeff,

    i used a fixed value for the ticks in my SCS project (also easier for testing) but you can modify that to a variable, which gets an updated value from the Application side during runtime.

    Are you sure that you are setting the output of the unused LC-sensor to GND while you are "kicking" oscillation on the other one?
    From the waveform attached it looks like that is not the case.
    You already had a nice looking waveform, what did you change since then?

    Regards,
    Milen
  • HI Milen,

    I just tune the value of capacitor only as the "TURN KEY" inductor was not easy to acquire . what is the max. distance between the disc and the inductor you can achieve?
    Thanks

    Jeff
  • Jeff,

    see front page of UG:
    Features
    • Meets Measurement Accuracy ....
    • Accurate Measurement at a Distance of 4.2 mm to a Wheel (11-mm Diameter)
    the 4.2mm were measured with the CSD FET with the smaller pin pitch.

    Which FET do you have now on your PCB?
    Can you go back to the state where you had the "good" waveform?

    Also note that putting the two inductors very close to each other will increase the coupling - i think that is what you see here.
    That's why the UG says it is best to have a mechanical fixture, which keeps the inductors at a fixed distance apart (e.g. 1-2mm).

    If you tune the capacitor because you have another inductor, you may also want to adjust the "kick" pulse duration that starts the oscillation.
    Try a few settings to see if that helps with the waveform and also increase the distance of the inductors and check the effect on the waveform.

    Regards,
    Milen

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