The title of this blog sounds like an excerpt from a science fiction movie, but in reality, integrating multiple sensor analog front-ends (AFEs) into a single device is nothing new. Suppliers have been releasing duals and quads of just about every building block, analog-to-digital converter (ADC) or digital-to-analog converter (DAC) since the integrated circuit became a mainstream product.
But what about industrial applications such as inductive sensing? (For those of you not familiar with inductive sensing, check out my article in Electronic Design, “Redefining Inductive Sensing.”) It turns out that inductive sensing has been around since the late 1950s, but the idea of integrating the entire AFE into a single device was a Texas Instruments first.
If one channel is good, then adding more channels and increasing the resolution is even better. Many applications such as multiaxis position sensing or copier-paper-path-jam detection require more than one channel. A great automotive application is measuring brake pads. For cars, this is currently limited to high-end luxury vehicles; but for commercial trucks, it’s a necessity, often monitored by onboard computers to alert both the driver and service personnel that there may be a problem. If the brake pad gets excessively worn, the truck’s brakes can fail in a panic stop.
At minimum, you’d need four channels per axle. This is done by placing a sensing coil in the middle of the brake piston, spaced from the disk (see Figure 1). Pads can be engineered to either be transparent to the alternating current (AC) field or have a strategic hole cut for the sensing coil to “see” through. As the pads wear, the coil moves closer to the disk, and this determines how much of the pad remains.
Figure 1: Example of using multiple channels of inductive sensing to measure brake-pad wear
Another application exists in low-cost 3D printers. In many robotic and heavy-duty applications, linear variable differential transformers (LVDTs) are used to sense linear position, but for low-cost 3D printers, this can be too expensive. Another way to sense linear position is with an asymmetrical (or stretched) coil etched directly onto a printed circuit board (PCB) and a simple rectangular target. This method shapes the AC magnetic field along the length of the coil, allowing the inductive sensing AFE to detect position extremely accurately – and very inexpensively. (For more information on this method, see this application note.)
Using an LDC1614 multichannel inductance-to-digital converter (LDC) with this method can provide four degrees of freedom – plenty for a low-cost appliance such as a desktop 3D printer.
So when you need to sense distance or position very accurately for either multiple dimensions or simply multiple channels, take a look at the newest series of LDCs from TI. The applications are endless and limited only by your imagination.
Additional resources
- Learn more about inductive sensing.
- Read other blog posts about designing with LDCs.
- Start a multichannel LDC design with WEBENCH® Inductive Sensing Designer.
- See how LDCs work in the Touch on Metal Buttons with Integrated Haptic Feedback Reference Design.