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LDC161x Inductance dropping with time

Jade Vanbuis
Prodigy 20 points
Other Parts Discussed in Thread: LDC1614EVM

Hello,

I am measuring an inductance and I chose to use a 1MHz frequency sensor to have the better resolution possible. I use the 40MHz clock available in the LDC1614EVM with RCOUNT putted at its maximum.

But when I observe the value of the inductance I can see that it falls with time, with no apparent reason (no movement around, etc.).

I was wondering which parameter could be reponsible for this behaviour.

Here is a picture of the inductance dropping. As you can imagine, the sensor frequency is increasing the same way.

The inductance value is not the same as the one read before with a inductance meter in the same conditions and so the sensor frequency is higher than the one expected. I do not know is this information is relevant but...

Thank you for your help,

Jade V.

  • 0
    TI__Genius 13650 points

    Hi Jade,

    the drift that you are seeing is dominated by the temperature coefficient of your sensor capacitor. Please ensure you are using a C0G/NP0 type sensor capacitor. However, even with this capacitor, a change in capacitance of up to 30ppm/degree C is possible. 

    Please compare the drift (in codes) to the signal that the target produces. For all except for the highest accuracy applications, the drift is usually very small compared to the signal, so that it is not necessary to do something about it. 

    In very high precision applications, you may need to use an additional reference channel or an external temperature sensor to compensate for the drift. 

  • 0 in reply to Ben Kasemsadeh
    Prodigy 20 points

    Hi Ben,

    Thank you for your fast answer. As you suggested the drift is very small compared to the signal so I need to decide if I really need a such precision.

    Thank you again,

    Jade

  • 0 in reply to Jade Vanbuis
    TI__Genius 13650 points
    Hi Jade,
    please note that the GUI also has a 'show statistics' button which allows you to monitor the noise floor which should help to determine the system SNR.