Inductive sensing: Five-minute sensor coil design


Did you know you can design a PCB coil for inductive sensing in five minutes with WEBENCH®? 

If you are considering using an inductance-to-digital converter, like the LDC1000, but are concerned about the time it takes to design a sensor coil, have a look at WEBENCH® Inductive Sensing Designer.

WEBENCH Inductive Sensing Designer is an online tool that designs sensor coils for many inductive sensing applications in just five minutes. The finished coil can then be manufactured and connected to an inductive sensing evaluation board for prototyping. After the prototype stage, the coil design can be copied to the main PCB artwork.

To design a coil in WEBENCH, you can follow a simple 3-step approach: input your system requirements, select an auto-generated coil and export it to your preferred PCB layout software.

1.  Input system requirements.

Suppose you want to design the smallest possible coil on a 4-layer PCB that can measure a 10cm stainless steel target with 5μm resolution at up to 2cm distance between the target and the sensor coil. You can insert these requirements into the ‘Requirements and Conceptual Diagram’ panel. You can even pre-filter the results in the filter panel if you’d like.

Remember that the maximum target distance at a given resolution varies with coil diameter. To learn more about maximum target distance, check out this blog post: Top three LDC1000 questions.

2.  Review simulated performance of the auto-generated coils and select the best match for your system.

After clicking the 'Recalculate’ button, WEBENCH shows eight solutions that meet the system requirements. The tool calculates many coil parameters automatically, including number of turns per layer, coil inductance, and simulated resolution. It also suggests a sensor capacitor value. You don’t have to use the suggested sensor capacitor value, but the simulation curves on the ‘Charts’ screen shown below are based on the suggested value

You can sort the results by coil diameter and select the smallest 4-layer PCB. In this example, WEBENCH shows that the smallest is ‘PCB inductor coil 6’: a 3cm diameter coil with 69 turns per layer and a free field inductance of 830μH.

After clicking the 'Open Design' button of the chosen coil, you can review simulation plots (Rp vs. distance, inductance vs. distance and resolution vs. distance) and operating values. For convenience, WEBENCH also shows schematics, bill of materials and a preview image of the coil.

If the chosen coil does not suit your needs, you have the option of clicking on the ‘back’ button and selecting another coil.

3.  Export the coil to your favorite PCB layout software.

If you are happy with the design, simply click on the 'CAD File Export' button. Five common PCB CAD tools output formats are available:

I exported the coil to Altium designer. This is what the PCB project looks like in Altium:

WEBENCH is a powerful online tool that generates inductive sensing coils in only five minutes. It greatly reduces prototyping and development time for most inductive sensing systems.

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