Lasers can be used in non-contact distance sensors. In industrial machinery or for plant-floor applications, triangulation-based laser displacement sensors are used most often. Laser-based triangulation displacement sensors combine high resolution and comparatively long ranges.

Sensor manufacturers generally offer versions with <10 µm resolution and ranges to 1 m. Highest-resolution specifications usually are possible over relatively small windows and at shorter ranges. Therefore, 1 µm resolution and a 1 m sensing distance will not happen simultaneously.

Triangulation technology (see diagram) uses a laser light source to project a well-collimated beam onto the target. Light reflected by the object passes through a lens that focuses the reflected beam onto a receiver. Changing the distance between sensor and target changes the angle of the returning light and the position of the beam on the receiving array, typically a charge-coupled device (CCD) line. The CCD signal feeds a microcontroller, which provides measured values as output using analog signals.

To limit signal noise, laser measurement sensors perform internal sampling, sometimes called integration or averaging. During sampling, the device averages multiple readings for smoother, more accurate output. Integrating more samples creates higher resolution, but increases the measurement time.

Faster decisions, response

Advanced sensing arrays and fast microprocessors can allow response times to be as fast as 250 µs without a decrease in resolution.

Some sensors project a laser line, rather than a laser point, bringing in more data to smooth over and tune out irregularities.

Stephen Petronio is photoelectric product manager with Baumer Electric.

www.baumerelectric.com/usa