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LDC0851: LDC0851 or LDC1101

Part Number: LDC0851
Other Parts Discussed in Thread: LDC1101, TMAG5170

Hi,

I want to use LDC0851 for event counting for paddle wheel systems.The paddle wheel have 5 teeth and rotating about 7000 rpm.

I use pvdf teeth with 316 stainless steel about 1mm diameter.

I try to design LDC0851  with  use spreadsheet ,as you see below picture.

Closest target distance approx. 1.5mm and i want to switch 2 mm~2.2mm and  spreadsheet design says Approx switch on and off difference  0.1mm.

Is it possible to sense 0.1mm difference with LDC0851? Or  i need to use LDC1101 or other LDC series.

  • Hello, 

    Sensing a 0.1mm difference is possible with the LDC0851, but the switching distance calculation is estimated based on a target that matches the size of the coil. As for your target, I have a couple clarifying questions. 

    • The picture makes it seem like the stainless steel is a rod that goes back into the gear tooth. Is that correct? 
    • Is the sensor pointed directly at the face of the stainless steel when at the closest distance or is there some angle offset? 
    • What is the size of your gear? You mention a 1mm stainless steel target but size of the gear and the distance between teeth can make an impact on the sensing. 

    Best Regards, 

    Justin Beigel

  • Hi,

    1- Yes 1mm steel rod on gear tooth.

    2- Sensor not direclty face steel rod because 0.8 mm abs plastic have between steel rod and sensor.Closest distance 1.5 mm maximum(0.8 abs plastic + 0.7 air gap )

    3- Size of  gear 13 mm radius

    Attach picture of device dimensions.Totally have 5 teeth and each teeth dimensions 2 mm so i attach max 1.5 mm steel rod on teeth

    .

  • Hello, 

    Thank you for the additional information. For the sensor coil design, you might want to consider a smaller coil to limit the impact of the gear spoke that is not directly in front of the sensor. Having something closer to a 4 or 5mm coil diameter will crease the coupling for the nearby spokes and will allow for the target to be a bigger portion of the sensor coil. See https://e2e.ti.com/blogs_/b/analogwire/posts/inductive-sensing-target-size-matters for more information on how target size impacts sensor performance. 

    Alternatively, do you have control over the stainless steel portion of the gear? If you could replace them with small bar magnets, you could use a Hall-effect sensing approach using a magnetic switch. 

    Best Regards, 

    Justin Beigel

  • Hi Justin,

    Thanks for information.Now i try to LCDCoil EVM and test distance and may change steel rod diameter  for optimum  accuracy and i will give info about project for community help other people.

    I cannot change  steel to magnet but could you offer any  magnetic sensor for this project may i test during ,when i test ldc0851 test setup.

    Best Regards,

    Ismail SAHIN

  • Hello Ismail, 

    If you are trying to use a magnetic sensor and can't replace the stainless steel, you would have to bias the sensor with a magnet behind it and let the stainless steel impact the magnetic field sensed by the IC. This would require more design work and feasibility may depend on how responsive your stainless steel is to a magnetic field. If you want to test this, you could use something like the TMAG5170 and place a magnet on the opposite side of the sensor from the stainless steel. You can then view the magnetic field change as your target rotates. 

    Best Regards, 

    Justin Beigel

  • Hi Justin,

    only for testing i can change steel and want to try magnetic sensor performance.

    So pls offer magnetic sensor for use event high speed event counting.

    Best Regards

    Ismail

  • Hello Ismail, 

    You can use something like the TMAG5123 which has plenty of bandwidth for your rotation speed. 

    Best Regards, 

    Justin Beigel