Inductive sensing provides contact-less sensing of conductive objects using only an AC magnetic field. This approach has many compelling features, including low cost, high reliability, low power consumption, and robust operation even in challenging environments experiencing high temperatures or in the presence of moisture, dirt, or oil. In addition, TI’s LDC devices do not require permanent magnets, and are not affected by permanent magnets. LDC technology can measure a wide range of target movement configurations, as shown in Figure 1-1.

Figure 1-1 LDC Sensing Configurations

An axial sensing configuration is where the conductive target moves along an axis that is perpendicular to the plane of the coil, as shown in the upper section of Figure 1-1. The LDC sensor measures the change of inductance caused by the movement of the target. The target is constrained so that it only moves in one axis. As the target distance from the sensor varies, the LDC output will correspond to the target distance.

This common configuration can be used for a wide variety of systems, from measuring extruded material to sensing whether a door is open or closed.

The axial sensing configuration can be used for human-machine interface (HMI) applications such as buttons or keypads using continuous metal surfaces. By attaching a metal film as thin as 10 µm to the inside surface, Inductive touch buttons can be constructed with non-conductive materials such as glass, plastic, and even wood. This type of implementation can be used for rugged, waterproof, long-life interfaces which can work in harsh environments where other technologies fall short. Details on one implementation of this capability can be found at Touch on Metal Buttons Reference Design, which uses the LDC1614.

Some LDC devices, such as the LDC2114, include algorithms and output features that make them drop-in replacements for currently existing mechanical implementations and simplify software design. For more information on these algorithms, see the LDC2112 and LDC2114 Internal Algorithm Functionality application report.

Another example which uses LDC sensing to create more reliable snap-dome switches can be found at 16-Button Inductive Keypad.