FDC2114 datasheet(40/61 Pages) TI1

40 / 61 page

(0)

Lev

ref

Level

FDC2212, FDC2214, FDC2112, FDC2114

SNOSCZ5A – JUNE 2015 – REVISED JUNE 2015

www.ti.com

Application Information (continued)

distance between the sensing plate and the shield should be adjusted to achieve the required sensitivity

10.2 Typical Application

The FDC can be used to measure liquid level in non-conductive containers. Due to its very high excitation rate

capability, it is able to measure soapy water, ink, soap, and other conductive liquids. Capacitive sensors can be

attached to the outside of the container or be located remotely from the container, allowing for contactless

measurements.

The working principle is based on a ratiometric measurement; Figure 56 shows a possible system

implementation which uses three electrodes. The Level electrode provides a capacitance value proportional to

the liquid level. The Reference Environmental electrode and the Reference Liquid electrode are used as

references. The Reference Liquid electrode accounts for the liquid dielectric constant and its variation, while the

Reference Environmental electrode is used to compensate for any other environmental variations that are not

due to the liquid itself. Note that the Reference Environmental electrode and the Reference Liquid electrode are

the same physical size (hREF).

For this application, single-ended measurements on the active channels are appropriate, as the tank is

grounded. Use to determine the liquid level from the measured capacitances:

where

•

CRE is the capacitance of the Reference Environmental electrode,

•

CRL is the capacitance of the Reference Liquid electrode,

•

CLev is the current value of the capacitance measured at the Level electrode sensor,

•

CLev(0) is the capacitance of the Level electrode when the container is empty, and

•

hREF is the height in the desired units of the Container or Liquid Reference electrodes.

The ratio between the capacitance of the level and the reference electrodes allows simple calculation of the liquid

level inside the container itself. Very high sensitivity values (that is, many LSB/mm) can be obtained due to the

high resolution of the FDC2x1x, even when the sensors are located remotely from the container. Note that this

approach assumes that the container has a uniform cross section from top to bottom, so that each incremental

increase or decrease in the liquid represents a change in volume that is directly related to the height of the liquid.

Submit Documentation Feedback

Product Folder Links: FDC2212 FDC2214 FDC2112 FDC2114

FDC2114 Datasheet(PDF) 40 Page - Texas Instruments