FDC2214: Proximity Sensing

Janine Lin

Part Number: FDC2214
Other Parts Discussed in Thread: FDC1004

Dear Bala and Clancy

These are my questions.

1. In the datasheet, it said that this FDC2214 is also for proximity sensing application. The graph shown below as the sensor size increases as well as the sensing range.

This from application note under "Capacitive Proximity Sensing using FDC2214". Does it mean, if my sensor size is 2 cm (circle), its sensing range would be 5cm?

Our application is for proximity sensing using different metal and non metal as a target.

2. FDC2214 has 4 input channels. Can i use every channel on detecting every metal? Does the type of measurement is the same as FDC1004 by using either single ended measurement

or differential measurement?

3. How to determine the sensing range in GUI? For example, when the metal is close to sensor electrode(approx. 3 cm), in the GUI the statistics shows different capacitance value.

Is it the same with FDC1004, delta is 10x of the noise floor?

4. This FDC2214 has LC resonator, does changing the inductor or capacitor value would possibly achieve the long sensing range with using small size sensor electrode(approx. 2cm)?

Thank you

over 6 years ago

0 Bala Ravi over 6 years ago

TI__Expert 6625 points

Hi Janine,
Please find my answers below:

1. That's correct as the sensor size increases the sensing range increases as well. But, please note that we are talking about the area of the sensor here. For example if you have a sensor circle of radius 2cm, your "Sqare Sensor Size" (from the plot) = pi*2cm^2.

2. Yes, you can use every channel. Each channel has an INxA and INxB. You can use both if you would like to do a differential measurement, if not you can ground INxB. Note that the all the measurement are taken in a sequential manner NOT simultaneously.

3. Yes it is similar to how it was done with FDC1004.

4. The LC is used more for the sensing frequency range, where fsensor = 1/(2*pi*sqrt(L*C)). But if you would like more sensing range, you need to increase the size of the sensor, as referred to in Part 1.

Best Regards,
Bala Ravi

Please click "This resolved my issue" button if this post answers your question

0 Janine Lin over 6 years ago in reply to Bala Ravi

Expert 2190 points

Thanks Bala for your answer.

1. I want to clarify, the diameter of my sensor (circle) is 2cm. What will be its sensing range according to the plot?

2. Does the material type of the sensor electrode affects the sensing range? What kind of material is best to be used for sensor electrode?

3. Could you please explain, what does it mean if my frequency range is high or low?

Thank you

0 Bala Ravi over 6 years ago in reply to Janine Lin

TI__Expert 6625 points

Hi Janine,
Please find my answers below.

1. Area in your case = pi*radius^2 = pi*1cm^2 = 3.14cm^2. From the plot your sensing range would be close to 15cm - 20cm.

2. Yes, the material absolutely affects the sensing range. Usually copper or aluminum or any other metal that has the lowest eddy current I*R losses and the strongest opposing magnetic field.

3. I do not understand your question. The sensor frequency is dependent on the LC tank, is that what you're referring to?

Best Regards,
Bala Ravi

Please click "This resolved my issue" button if this post answers your question

0 Janine Lin over 6 years ago in reply to Bala Ravi

Expert 2190 points

Thank you Bala.

1. How to determine if the metal has the lowest eddy current and has strongest opposing magnetic field? How to design the best sensor head?

2. Yes, sensor frequency of LC tank. Is this the same with "sensor excitation frequency"?

0 Bala Ravi over 6 years ago in reply to Janine Lin

TI__Expert 6625 points

Hi Janine,

1. In simplest terms you are looking for the most conductive metal that meets your cost and other expectations. Please refer to the following sensor design app note for some useful information: www.ti.com/.../snoa930a.pdf.

2. Sensor excitation frequency is the frequency range that the device is capable of operating at. But your LC tank decides this frequency via the formula: fsensor = 1/(2*pi*sqrt(L*C)).

Best Regards,
Bala Ravi

Please click "This resolved my issue" button if this post answers your question

0 Janine Lin over 6 years ago in reply to Bala Ravi

Expert 2190 points

Hi Bala,

1. You mean, FDC2214 sensor electrode sensitivity is also depends on LC ? More coil winding the better? Does the size of the coil has an effect on sensing range?

2. Could you please explain what will happen if the frequency range is at 10 kHz or 10Mhz? What are there differences?

3. pLease help how to get the 15 cm sensing range by using this sensor electrode size(0.25 cm^. By using the Fdc2214 evm.

Thank you for the answer.

0 Bala Ravi over 6 years ago in reply to Janine Lin

TI__Expert 6625 points

Hi Janine,
Please find my answers below:

1. The application note about sensor design that I shared with you earlier was for LDC devices, so some of it does not apply to you since you're using FDC. The LC tank will control the sensor frequency. Since you're using a FDC, you're looking for changes in capacitance (as opposed to change in inductance for LDCs). Your sensor should consist of an LC tank, where your L is a surface mount (fixed value) and your C is a capacitive plate, the size of which you can vary to increase your sensing range. Please refer to the following app note: www.ti.com/.../snoa940a.pdf

2. As long as you never fall out of the range even when your target distance changes, you should be fine.

3. Can you share your sensor schematic?

Best Regards,
Bala Ravi

Please click "This resolved my issue" button if this post answers your question

0 Janine Lin over 6 years ago in reply to Bala Ravi

Expert 2190 points

Dear Bala,

Any update? I send you a private message. Please take a look. Thank u.

0 Bala Ravi over 6 years ago in reply to Janine Lin

TI__Expert 6625 points

Hi Janine,
I replied to your question that was sent as a private message. I will go ahead and close this thread.

Best Regards,
Bala Ravi

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FDC2214: Proximity Sensing