FDC1004: Reference issues in techncal documents for FDC1004

Hello,

Thanks for the post. Let me comment on your questions below.

George Sgourakes said:

1.  "TI Designs: Capacitive-Based Liquid Level Sensing Sensor Reference Design."

A. Page 6, 4.1 Level Height Calculations Figure 2. I believe the reference height as shown for RL in Fig 2 should be hL and not hR.

The reference level sensor (RL) has a height of (hR) which stands for reference height. The level sensor (LEVEL) has a height of (hL) which stands for level height. Sorry for the confusion.

George Sgourakes said:

B. Page 12 Figure 9 Please show how CH4 is configured.

CH4 is floating, there is no electrode attached.

• CIN1 – LEVEL electrode
• CIN2 – REFERENCE LIQUID electrode (RL)
• CIN3 – REFERENCE ENVIRONMENT electrode (RE)
• CIN4 – Floating, no electrode attached

George Sgourakes said:

2. "TI Capacitive sensing: Ins and outs of Active Shielding"

Page 6, Fig 8 Shows CIN2 shielded with SHLD1 and believe it should be SHLD2.

This section of the app note contains some typos. The paragraph above should match the wording in the FDC1004 datasheet which is:

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.

Figure 8 shows an unrelated example where only the following combinations are valid:

• CIN1-CIN3
• CIN1-CIN4
• CIN2-CIN3
• CIN2-CIN4

Luke

Hi George,

I had an oversight when looking at the figures. The first question about hL and hR. The term hR is the reference height and hL is the level height, therefore the drawing is indeed correct. It is confusing because the reference level sensor (RL) is linked with the reference height (hR) and the level sensor (LEVEL) is linked with the level height (hL). Additionally, if the environmental sensor (RE) is used, it is the same height as the reference level sensor (hR).

Sorry for the confusion!

Regards,

Luke