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Coil distance from LDC1000 and cable

FaMa
Prodigy 90 points

I try again to post an old question becouse for me it's a central matter.

My applications (axial position measure) require a long cable between sensor and LDC1000 (up to 10m). In standard application like this we had used low capacitance coaxial cable but with LDC1000 I also experienced large drift touching the cable. On other side capacitance of standard 2-conductor shielded cable at this distance put the LDC1000 out of working parameter. Can anyone help me to understand if there is any possibility to use LDC1000 with 10m cable?

Thanks!

  • 0
    TI__Expert 4890 points

    Hi,

    It can be work well when LDC1000 use a 10mm cable, but we must to avoid touching the cable, because it may change the capacitance.

    Shielded cable may change the Rp of LC, you can change Rp-max and Rp-min, then it may work.

    Regards, Sunny.

  • 0
    TI__Genius 9300 points

    Could you please provide us with the coil characteristics?

    Inductance and Rs, ideally as a function of frequency?

  • 0 in reply to Evgeny Fomin
    Prodigy 90 points

    Hi,

    thanks all for help!

    In our standard application we use two different coil with the following characteristics (w/o cable):

    1) diam. 15mm, 500kHz-9.35uH-2.02Ohm / 1MHz-9.35uH-2.48Ohm / 2MHz-9.45uH-3.77Ohm / 3MHz-9.67uH-5.17Ohm / 4MHz-10.01uH-7.24Ohm / 5MHz-10.50uH-10.14Ohm

    2) diam. 28mm, 500kHz-15.97uH-2.54Ohm / 1MHz-16.13uH-3.00Ohm / 2MHz-16.81uH-4.13Ohm / 3MHz-18.09uH-7.08Ohm / 4MHz-20.22uH-15.74Ohm / 5MHz-23.87uH-27.86Ohm

    We can design a new coil for a LDC1000 application, but the problem is to verify the use of 10m cable... Now we use COAX cable with 50pF/m capacitance but with LDC1000 we experienced big reading variation just touching the cable.

    Thanks!

  • 0 in reply to FaMa
    TI__Genius 9300 points

    Hello,

    Quick evaluation shows that the second coil should work when you route to shielded cables to the sensor.

    Parasitic cap will be on the order of 1nF, do not add any other caps, and then f = 1.25MHz, Rp ~ 5kOhms.

    Can you try it?