TIDA-00317: Water level sensing solutions

Ryan Thompson

Part Number: TIDA-00317

Hi,

I have an application for sensing water level in a small reservoir (about a quart of volume). Ideally, the electronics would be located a foot or two from the sensing electrodes that are submerged in the water, so the connections are made via cable. Also, the electrodes need to be stainless steel, and submerging a printed circuit board is not acceptable. I will design the stainless steel electrodes.

I saw this on your website.

www.ti.com/.../tida-00317 level sensor&tisearch=Search-EN-Everything

Is this the best solution for my application?

Thanks,

Ryan Thompson

Expert 7980 points

Yibo Yu
- May 11, 2017 12:00 AM
Hi Ryan,

The reference design provides a good approach for sensing liquid level. In particular, it is immune to hand or other interference. However, in order for the out-of-phase approach to work well, the shielding electrodes and sensing electrodes have to be well balanced, which can be easily achieved on a PCB.

Regards,
Yibo
- Reply
- Cancel
- Cancel
- Reply Suggest as Answer Use rich formatting
Prodigy 110 points

Ryan Thompson
- May 11, 2017 1:49 PM
In reply to Yibo Yu:
Hi Yibo,

Thanks for the information. We are looking at the gerbers for the liquid level sensor board, and the stackup is for a 4 layer board, with the 2 outside layers not having any copper. What is the intent of this? Is a 2 layer board with soldermask not sufficient? Note that we want to use a rigid/FR4 2 layer board to do some initial testing, but we can go to 4 layers is the outside blank layers are needed.

Ryan
- Reply
- Cancel
- Cancel
- Reply Suggest as Answer Use rich formatting
Prodigy 110 points

Ryan Thompson
- May 11, 2017 3:23 PM
In reply to Ryan Thompson:
After talking to our PCB designers, I now believe the extra layers are to providing stiffening in the sensor area yet still allow the tail to be flexible. Please confirm. With that understanding, we may just build an 0.062" 2 later rigid board and live with the tail section being rigid.

Ryan
- Reply
- Cancel
- Cancel
- Reply Suggest as Answer Use rich formatting
Expert 7980 points

Yibo Yu
- May 11, 2017 11:06 PM
In reply to Ryan Thompson:
Hi Ryan,

The sensor board is a rigid-flex PCB. The rigid portion is for the connector only which is located at the end of the tail. It can be used for connecting to the FDC1004 EVM.

The sensor portion was meant to be flexible in this design (though it does not have to be), so that it can be attached easily to containers of various shapes. The flexible sensor portion uses 2 layers only. The TIDA-00317 document has more information on how the inputs and shields are connected.

Regards,
Yibo
- Reply
- Cancel
- Cancel
- Reply Suggest as Answer Use rich formatting
Prodigy 110 points

Ryan Thompson
- May 23, 2017 6:49 PM
In reply to Yibo Yu:

Hi Yibo,

We have started testing using the TI reference design for the liquid level sensing PCB. Overall the testing is going well, but there appears to be some strange behavior either with the FDC1004EVM or the GUI software. Measurement 3 is the CIN3 differential with CIN4 per the PCB layout and documentation (reference enviromental sensor), but it periodically shows a capacitance value that is way off (~10pF). See screenshot below. Any idea what is going on here? Is there a known bug in the EVM firmware or the GUI?
- Reply
- Cancel
- Cancel
- Reply Suggest as Answer Use rich formatting
Expert 7980 points

Yibo Yu
- May 25, 2017 1:14 AM
In reply to Ryan Thompson:
Hi Ryan,

It seems that the screenshot did not get attached. Could you attach the screenshot again?

Regards,
Yibo
- Reply
- Cancel
- Cancel
- Reply Suggest as Answer Use rich formatting
Prodigy 110 points

Ryan Thompson
- May 25, 2017 1:53 PM
In reply to Yibo Yu:

Hi Yibo,

I'll try again, this time as a .pdf. Please see attachment.

RyanLiquid_Level_Sensing_screenshot.pdf
- Reply
- Cancel
- Cancel
- Reply Suggest as Answer Use rich formatting

TI E2E™ Community

TI E2E™ Community Groups

Other Communities

Other Technical & Support Resources

All content and materials on this site are provided "as is". TI and its respective suppliers and providers of content make no representations about the suitability of these materials for any purpose and disclaim all warranties and conditions with regard to these materials, including but not limited to all implied warranties and conditions of merchantability, fitness for a particular purpose, title and non-infringement of any third party intellectual property right. TI and its respective suppliers and providers of content make no representations about the suitability of these materials for any purpose and disclaim all warranties and conditions with respect to these materials. No license, either express or implied, by estoppel or otherwise, is granted by TI. Use of the information on this site may require a license from a third party, or a license from TI.

Content on this site may contain or be subject to specific guidelines or limitations on use. All postings and use of the content on this site are subject to the Terms of Use of the site; third parties using this content agree to abide by any limitations or guidelines and to comply with the Terms of Use of this site. TI, its suppliers and providers of content reserve the right to make corrections, deletions, modifications, enhancements, improvements and other changes to the content and materials, its products, programs and services at any time or to move or discontinue any content, products, programs, or services without notice.

m.ti.com (Mobile Version)

TI is a global semiconductor design and manufacturing company. Innovate with 100,000+ analog ICs and
embedded processors, along with software, tools and the industry’s largest sales/support staff.

TI E2E Community

Capacitive Sensing

Capacitive Sensing Forum

TIDA-00317: Water level sensing solutions