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PSoC 4 MCU

YuMa_1534086
Contributor

Hello.

Below is description of CapSense application note(AN64846) about proximity sensor.

=============================================

Wire:

A single length of wire works well as a proximity sensor.

The proximity distance achieved with a wire loop sensor is higher compared to a PCB trace.

But using a wire sensor is not an optimal solution for mass production because of manufacturing cost and complexity.

=============================================

Why is the proximity distance of wire method higher than PCB trace method?

Does not wire method’s noise become larger than PCB trace?

Because wire method can not have both GND/Shield mesh pattern and GND loop around proximity sensor.

Best Regards.

Yutaka Matsubara

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1 Solution
BragadeeshV
Moderator
Moderator

Hi YuMa_1534086​,

The proximity distance achieved using a wire loop is more or less the same as achieved using a 1.5 mm PCB trace width loop of the same diameter.

Wire loops are more susceptible to noise since we can not have a ground loop near it. Also, it is not possible to restrict the field lines as much as we can control in a PCB trace. One more issue is that since wire is a mechanical part, there are chances of it getting broken or displaced. These could cause measurement errors.

In terms of noise immunity, it is better to choose a proximity trace with a ground loop around it.

Hope this answers your question.

Regards,

Bragadeesh

Regards,
Bragadeesh

View solution in original post

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7 Replies
YuMa_1534086
Contributor

Hello.

I think that wire method’s noise may become larger than PCB trace.

Because wire method can not have both GND/Shield mesh pattern and GND loop around proximity sensor.

So I could not understand why the proximity distance of wire method becomes higher than PCB trace method.

Could you please let us know this reason?

Or is my understanding wrong?

Best Regards.

Yutaka Matsubara

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BragadeeshV
Moderator
Moderator

Hi YuMa_1534086​,

The proximity distance achieved using a wire loop is more or less the same as achieved using a 1.5 mm PCB trace width loop of the same diameter.

Wire loops are more susceptible to noise since we can not have a ground loop near it. Also, it is not possible to restrict the field lines as much as we can control in a PCB trace. One more issue is that since wire is a mechanical part, there are chances of it getting broken or displaced. These could cause measurement errors.

In terms of noise immunity, it is better to choose a proximity trace with a ground loop around it.

Hope this answers your question.

Regards,

Bragadeesh

Regards,
Bragadeesh

View solution in original post

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YuMa_1534086
Contributor

Bragadeesh-san.

Thank you for your response.

>>> The proximity distance achieved using a wire loop is more or less the same as achieved using a 1.5 mm PCB trace width loop of the same diameter.

However, the description that wire proximity distance is higher than PCB trace is clearly described in design guide.

(“The proximity distance achieved with a wire loop sensor is higher compared to a PCB trace.”)

What is the intention of this description?

Many users think that wire proximity performance(excludes ease of manufacture or maintenance) is better than PCB trace.

Best Regards.

Yutaka Matsubara

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BragadeeshV
Moderator
Moderator

Hi YuMa_1534086​,

It is true that proximity wire sensors are more sensitive than Copper traces. The reason is that the prox wire sensors are usually far from the board and is not near any ground plane in the PCB unlike PCB copper traces. This is the reason we recommend to use shield electrode when using prox copper trace so that it is shielded from the near by ground plane.

Regards,

Bragadeesh

Regards,
Bragadeesh
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YuMa_1534086
Contributor

Dear Bragadeesh-san.

>>> It is true that proximity wire sensors are more sensitive than Copper traces.

I think that higher sensitivity means higher noise.

Because there is no GND near proximity wire.

So SNR may be same or lower than copper traces even if proximity wire is used.

CapSense design validity should be considered by SNR(contains noise), not only sensitivity.

So I think that it should be annotated in design guide or following description should be deleted.

Many users consider that the meaning of “high sensitivity” and “high SNR” is same.

Please advise it.

==============================================

The proximity distance achieved with a wire loop sensor is higher compared to a PCB trace.

==============================================

Best Regards.

Yutaka Matsubara

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BragadeeshV
Moderator
Moderator

Hi YuMa_1534086​,

You are right. I've mentioned this in the post 3 of this discussion. We will work on updating this information in the design guide. Thank you for your continued interest with Cypress products.


Regards,

Bragadeesh

Regards,
Bragadeesh
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YuMa_1534086
Contributor

Bragadeesh-san.

Thank you for your support.

I understand.

Best Regards.

Yutaka Matsubara

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