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Sensor frequency at LDC1000

Daniel Gorochov
Prodigy 20 points


Hi Team,

I am a student and currently I am working at inductive position sensor, where electronic and sensor are separately because of wet environment and deep temperature. LDC1000 is a great tool for that reason. Ferrite as a coil core is very good material with amplitude about 30% by positioning, almost without any noise. But for my application I can’t take ferrite, then it can be used only till -40 °C, I need it till -190 °C.  

Material I am using for coil core and for an opposite target is steel with good magnetic properties. As you know Steel causes eddy currents when dive in a magnetic field, so the LC tank frequency must be lower.

Software, which was delivered with device LDC1000, offers me a function for changing a sensor frequency. In connection with different LC combinations sensor frequency have to influence my amplitude, but when I adjust values by sensor frequency, it changes nothing. Can you explain me how I can take a sensor frequency down? Is it a software error or I overseen anything by adjusting. In general, I mean software works inaccurately and unstable by adjusting all parameters.

 Thanks!

Daniel

  • 0
    TI__Expert 4890 points

    Hi,

    This sensor frequency is just determin the restart time of LDC, when it`s get stuck, so you need not pay more attention to it, just do it as the datasheet.

    If you want to change LC tank frequency, you can change the Cap of LC tank, or you can choose another coils with different inductance.

    Regards, Sunny.

  • 0 in reply to Sunny Qin
    TI__Genius 9300 points

    Let me just add that to change the oscillation amplitude, you need to change reg.04 value.

  • 0 in reply to Evgeny Fomin
    Prodigy 20 points

    Thanks for reply. The point is, I already adapted C and L. The oscillator shows about 130 kHz. I want to reach 5 – 10 kHz. I can’t change a coil, only a capacity. When I go higher with capacity I get enormous noise, so my LC tank is with these values (10nF cap and 233mH coil) saturated.  

    I thought the sensor frequency is the right part to bring the frequency down, but like you said, sunny, it isn’t. Evgeny, I tried to change reg.04 value, but it didn’t make any difference in the program as well as in the oscillator.

    Have you some another idea how I can bring my frequency down.

     Regards, Daniel    

  • 0 in reply to Daniel Gorochov
    TI__Genius 9300 points

    Sounds like the oscillation is not stable.

    Please take a look at the signal on CFB pin, and adjust CF cap value, if necessary (see instructions in DS)

    Screenshots from CFB and INA pins would be very useful for the debug.

    What is the resistance of the coil at 5kHz? What is its self-resonance frequency?