FDC1004EVM: Configure CINx in phase with SHLD1 or SHLD2

Cedrick,

Thank you for the post.
We recently posted an FDC1004 FAQ document at: e2e.ti.com/.../976381  

It provides information on using the FDC1004, including an index to our supporting app notes and technical articles,.
Five app notes are devoted your customer's application: liquid-level sensing with the FDC1004.

Please pass this on to your customer.

If they can't find the information they are looking for in the FAQs, please let me know by updating this thread.

Hi John,

Thank you for your response.

I informed the customer about the FAQs and the app notes as you have mentioned above. Specifically, they read carefully SNOA925, tidu736a, snoa927, and the datasheet for FDC1004. But still they can not find the answer to their question. Can you please help us further on this matter?

Thank you.


Regards,

Cedrick

Cedrick,

There are no internal settings to associate CINn and SHLDx other than the settings in Table 4 of the data sheet which allows you to specify up to four measurement settings using registers 0x08, 0x09, 0x0A, and 0x0B.

The table implicitly assumes the channel specified as CHA is the "positive" channel associated with SHLD1, and the channel serving as CHB is the negative channel associated with SHLD2. Note that Table 4 footnotes (1) & (2) describe some important conditions for configuring CHA and CHB.

This is also covered in an example in the data sheet section 8.3.1:
"In differential measurements, SHLD1 is assigned to CHn and SHLD2 is assigned to CHm,
where n < m. For instance in the measurement CIN1 – CIN2, where CHA = CIN1 and CHB = CIN2 (see Table 4),
SHDL1 is assigned to CIN1 and SHDL2 is assigned to CIN2."

Measuring RE will depend on your sensor configuration. Without knowing more about your system, it is difficult to suggest anything more.

There is an example that shows a sensor configuration supporting RE measurement in our app note Capacitive Sensing: Out-of-Phase Liquid Level Technique at  https://www.ti.com/lit/pdf/snoa925
 Please see section 3.2, Sensor Layout.

Please let me know if you have any questions.

Hello John,

Thanks for the kind reply, which is very helpful.

Our customer has an additional inquiry, kindly see below.

Now I use 3 channels in different mode to measure LEVEL, RL, RE sensors respectively. (I am using a self-developed liquid level sensor, similar to the one in tidu736a). I use "Sensing Solution EVM GUI" and the FDC1004 EVM. The configuration in the GUI software are:
MEAS1: CHA = CIN1, CHB = CIN2
MEAS2: CHA = CIN2, CHB = CIN2
MEAS3: CHA = CIN3, CHB = CIN2

It looks the system works now. Please look at the attached data pictures that is copy from the GUI software. Picture 1 shows the readings when the bottle is empty, picture 2 shows the readings when the bottle is full (water level over the RE sensor).
my question is the offset value of the 3 channel outputs are in large difference. You can see, MEAS1 has a offset of 0.85pF, MEAS2 has a offset of -0.78pF, MEAS3 has a offset of 7.10 pF. So, what's the reason for this offset difference? why there is a negative value? How to handle this offset in the software or in reg map?

Thank you for your support.

Regards,
Cedrick

Cedrick,

Could you attach the pictures the customer mentioned to the thread?

Hi John,


Here's the pictures that he mentioned.image.zip


Regards,

Cedrick

Cedrick,

Apologies for the delay, but my time has been taken up by a high profile customer issue.
This will continue for a few days.
I will provide an update by Monday of next week.

Hi John,

Alright. We will be waiting for your update by next week.

Thank you for your support.


Regards,

Cedrick

Cedrick,

Apologies for the delay, but the high-profile conflict continues.

I will hopefully get to it tomorrow.