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LDC1101EVM: Inductice Sensor Range and Resolution

Sam Ref
Expert 1610 points
Part Number: LDC1101EVM
Other Parts Discussed in Thread: LDC1101, LDC1614

Hello

We intend to purchase LDC1101-EVM.

For that we would like to know the distance measurement range (in mm) and the measurement resolution (in mm) of that EVM (if we do not change anything in that EVM).

Also, we would like to know whether we can order a coil that allow us to measure a range of 25mm. An offset is allowed in our measurement. That means we can measure 25 --> 50mm or 45 -->70mm....for example. The range will remain 25mm.

Regards

Sam

  • 0
    TI__Genius 17440 points

    Hi Sam,

    The measurable distance of any inductive sensor is based on the diameter of the sensor coil and the resolution of the LDC device. The LDC1101EVM has a sensor coil with a diameter of 14mm. In LHR mode (high resolution L-sensing mode, which we would recommend using), the LDC1101 can measure up to 50% of the coil's diameter (7mm in this case). The resolution is highly dependent upon your sample rate, your noise floor, and the strength of the response from your target. This resolution app note may help.

    For general principles of inductive sensing, these app notes should help:

    LDC Sensor Design

    LDC Target Design

    For your application, I would recommend using the LDC161x instead of the LDC1101. It is our highest resolution LDc device and can detect targets up to 200% of the sensor coil's diameter. You would need to design a coil that could detect your target at the absolute maximum distance including any offset. We ahve a sample coil board available that has some large coils that should work for the upper end of the range you mentioned. You may also wish to test some of the smaller coils on the board for the closer target distances. You will likely end up needing to design a new coil that suits both ranges. We have an excel tool that can help with this design process.

    Best Regards,

  • 0 in reply to Kristin Jones93
    Expert 1610 points
    Hi Kristin
    Thanks very much for your clear answer.

    - Practically (after noise considerations.....etc) what is the resolution we would expect from LDC161x?
    - Will LDC1101 be able to realize better resolution that LDC161x?

    Regards
    Sam
  • 0 in reply to Sam Ref
    TI__Genius 17440 points

    Hi Sam,

    The LDC161x will have better resolution than the LDC1101. It's really hard to say what kind of resolution you can expect because it's so dependent on your noise floor. The LDC161x can detect sub-micron shifts in target position, but the system resolution depends on the environment's noise floor. You'll have to test this in your target environment. Generally, we recommend using the EVM and the GUI to measure the peak-to-peak noise without the target present. Multiply this peak-to-peak value by 3 to get your noise floor, and ensure that the response to target movement is 10x greater than the noise floor. This creates a robust sensing system. If you find that you are having trouble minimizing your noise floor or maximizing your target response, feel free to post a new question. We'd be happy to help.


    Best Regards,

  • 0 in reply to Kristin Jones93
    Expert 1610 points

    Kristin

    Thanks for your response. 

    1. We want a resolution of 0.1mm. Do we have a chance of achieving that?
    2. What is the best resolution achievable using LDC161x EVM if all the right things (in terms of reducing noise....etc) are done?

    I believe if you do not have clear answers to these 2 questions you should do some tests and let us know the result and the conditions of that test. A product without specs from TI does not make much sense.

    We need large number of sensors and your tests will save us time and cost.

    One more question....

    you said usually the rough rule of thumb is; the measurable range equals twice the diameter of the coil. Will the height of the coil make any difference in that measurable range?

    Regards

    Sam

  • 0 in reply to Sam Ref
    TI__Genius 17440 points

    Hi Sam,

    1. Yes, a 0.1mm resolution is definitely achievable with inductive sensing, but there are a large number of variables that will affect your resolution. I will discuss them in (2.)

    2. The resolution for the LDC161x is actually measured in Hz, not distance. This is because the LDC measures shifts in inductance by measuring the change in resonant frequency of the sensor. The digital output codes are a ratio of the sensor frequency compared to the reference frequency. For a 40MHz reference frequency (the maximum reference frequency for multi-channel operation), the LDC161x can measure shifts in sensor frequency as small as ~0.15Hz. The magnitude of this change in sensor frequency can vary hugely depending on the mechanical setup of the sensing system, including the distance between the target and the inductor, the target's material, the target's size, and the inductor's physical size. It's not possible to calculate the expected resolution in terms of target distance without knowing this information and the noise floor.

    3. Could you clarify what you mean by the height of the coil?

    This resolution app note should be able to help you further. I also recommend LDC Sensor Design and LDC Target Design to maximize your sensor's response to your target. Finally, the LDC Tools Excel Calculator is a good tool for prototyping, and it has a section specific to the LDC161x.

    Best Regards,

  • 0 in reply to Kristin Jones93
    Expert 1610 points

    Hi Kristine

    1. Thanks

    2. We design our full system...so we have total control over aspect of it.....so what we need from you is clear answer what is best resolution that can be achieved and what is the conditions that allowed you to get that resolution....we will match these conditions (in terms of target.....or whatever),,,,or at least we will know than what we are chasing.....I do not want our people to start getting into details before we know what can possibly be achieved.

    3. a coil is a hollow cylinder it has a diameter and a height...….I understand that your pcb coil is has the height of the pcb thickness....but I am asking whether it will help (in terms of measurement range or resolution) to replace that pcb coil with a another coil that is higher/longer.

    4. Our measured range is 25mm...I guess 14mm coil would be good enough to ensure measuring the targeted range. Correct or do we need larger diameter?

    5. Does the diameter or the height influence the resolution?

    Regards

    Sam

  • 0 in reply to Sam Ref
    TI__Genius 17440 points

    Hi Sam,

    It's possible to achieve submicron resolution with the LDC1614, but this resolution isn't possible in every application. If you can share more information about your application I can offer some suggestions for how to achieve a high resolution design.

    The inductor's height does not affect the resolution nor the sensing range.

    Unless your sensor is also moving from 0mm to 45mm, you would need at least a 35mm coil to measure up to 70cm.

    Best Regards,

  • 0
    Expert 1610 points

    Hi Kristine

    Thank you for the clear answers. I will contact you again once we purchase the EVM and set up our system.


    Regards

    Sam