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LDC1101: non metal sensing

Mabel
Prodigy 70 points
Part Number: LDC1101
Other Parts Discussed in Thread: FDC2214

LDC1101 can be used to detect nearby metal. Because of the eddy current, as a metal is approaching an inductive sensor, the measured inductance should be lower.

our sensor consists of two semicircles for capacitive sensing and coils for inductive sensing and uses LDC 1101 for inductive sensing. When metal is approaching the sensor, the inductance gets lower. However, when my hand is approaching the sensor, unlike the metal case, the inductance gets higher.. Do you by any chance know why this happens?

  • 0
    TI__Expert 7599 points

    Hello User,

    LDC1101 device is capable of measuring metal approaching the sensor. As you have pointed out the operation of the LDC1101 uses the eddy current principle to detect the change in the resonance of the LC tank. The change in the frequency determines if the metal is closer to the sensor coil. LDC1101 is meant for metal sensing applications only. 

    Since you have a capacitive sensor along side with LDC1101 I am unsure if you have mechanical isolation and separation between the 2 sensors. Most likely that could be the cause as the capacitive sensor could be triggering the LDC1101 sensor. 

    If you have more questions regarding inductive sensing technology please look at our FAQ The FAQ does have detailed explanation on the principles and also design guidelines for the Inductive sensing technology. For more information regarding the product please refer to the product page http://www.ti.com/product/LDC1101/technicaldocuments 

    Thanks. 

  • 0 in reply to Arjun_Prakash
    Prodigy 70 points

    To be specific, we use FDC2214 for capacitive sensing and LDC 1101 for inductive sensing. And the capacitive sensor is connected to only FDC2214 and the inductive sensor is only connected to LDC 1101. Both FDC2214 and LDC1101 exists on the same PCB. The capacitive sensor is surrounded by the inductive coil shape sensor.  Although each sensor (capacitive sensor and inductive sensor) is connected to the different chip, is it possible for the capacitive sensor to have an influence on the inductive sensor's inductive sensing when a hand is approaching? 

    And I wonder how capacivie sensor could be triggering the LDC1101 sensor although capacivie sensor is not connected to LDC1101.

  • 0 in reply to Mabel
    TI__Expert 7599 points

    Hello,

    As the FDC2214 and LDC1101 are far apart but it does sound like the coil for the FDC2214 and LDC1101 are closer to each other. When you move your hand across the capacitive sensor if there is a possibility that the eddy currents from the LDC1101 coil could be coupling into the FDC2214 coil and it could lead to false detection. 

    On the LDC1101 in the datasheet as per section 9.1.11, have you checked the sensor drive settings to ensure the sensitivity of the external influence on the coil design ? Also, section 9.2.2.2 should provide some guidance on the settings if LDC1101 is configured in L measurement only.