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LDC3114: Using for sensing motor position

Mechtex
Prodigy 110 points
Part Number: LDC3114
Other Parts Discussed in Thread: LDC0851, LDC1314

Hi,

Can we use LDC3114 sensor to sense motor position? I have a bldc motor and on the rotor side I have mounted a metal plate with slots.

1. Can I use this device to sense motor position and give output in the for of a A B incremental encoder signal?

2. Will it work at 15,000 RMP?

3. How do I go about designing the sense coils for this application?

Thanks in advance.

  • 0
    TI__Mastermind 39385 points

    Aadit,

    Thank you for your inquiry and your interest in TI products.

    We don't have any info on using the LDC3114 for the application you describe.
    That's not to say it won't work; we just haven't developed any guidance for it.

    If you are committed to using a slotted metal rotor as you have described, then please take a look at some related information for a different part, the LDC0851.
    Please scroll toward the bottom of the LDC0851 product folder until you see the reference designs.
    They may not address the specific rotor and sensor design you have proposed, but they may serve as a starting point for the larger sensing system.
    We have a coil design tool that supports that part available here. 

    If you can change from the metal rotor to a ring magnet on the motor shaft, you could consider using a Hall-based sensor/latch like the TMAG5111.
    That page has some app notes and tools if you are not familiar with those kinds of parts.

    This may be a lot to consider - and its not clear if it directly addresses your problem - so if you need some help, we can go through it a step ant a time.

    Please let me know if you have any questions.

    Regards,
    John

  • 0 in reply to John Miller - Sensing
    Prodigy 110 points

    Hi John,

    I did look into LDC0851, but it is out of stock and we need to complete the development as soon as possible. Hence I was trying to piece together a solution with parts that are in stock.

    I have also explored the magnetic sensor part. However, we need to fit the disk near the rotor magnets that are rather strong and will mess up the position readings if I use a separate magnet. The rotor magnet strip is a multiple pole pair magnet and hence it will be a nightmare to calibrate in production. I am open to using the magnetic sensor if we can find a way around these issues.

    Coming to the inductive sensor part, I guess I'll simplify my question, will the sensor be able to detect the gaps (i.e change in the distance on the disk) at 25kHz (i.e gaps moving that fast)? I can use one coil as a reference and the second to detect the gaps. Two sets of these four coils 90 degrees apart should give me quadrature data.

    I can also use the wrapped around diamond design on the metal plate (as shown in the LDC1314 1-degree dial design guide) and then extrapolate the angle from the raw data and give quadrature output accordingly using an MCU.

    Let me know if you think any of this is feasible.

  • 0 in reply to Mechtex
    TI__Mastermind 39385 points

    Aadit,

    Both ideas sound plausible.
    Unfortunately we don't have any detailed guidance we can offer on the approach using air gaps. 
    It should work, but particular attention will need to be paid to the size of the gap versus the width of the coil sensors.
    There is a blog that may help available here, that looks at the relative sizing between the target and coil. 
    In your case, instead of the target, it is an air gap, but perhaps the info will be helpful.

    The approach used in the 1-degree dial design should work as well. 

    Regards,
    John