Laser sensors offer high accuracy at long stand-off distances

With most laser sensors, the accuracy of the sensor reduces as the measuring range (or base distance to the target) increases. The smaller the distance between sensor and the target being measured, the smaller the measurement error will be. However, for some measurement tasks, it simply is not possible to mount the sensor close enough to the target, either due to physical obstacles, high shock loads, vibrations or high process temperatures.

In the rail industry, for example, it is common to measure the movement of the carriage with respect to the rail. However, due to the high shock loads and vibrations levels, it is not possible to mount laser sensors on the bogies of the carriage near to the rails. Therefore laser sensors with longer measuring ranges are required, which enable the sensor to be mounted further away on the carriage. Similarly, in the steel industry, due to the physical size of the steel strip and process temperatures, it is not possible to mount laser sensors close to the strip steel during production. Again, laser sensors with longer measuring ranges are required.

Compared to conventional non-contact, laser displacement sensors, Micro-Epsilon's new optoNCDT 1810-50 and optoNCDT 2210 measure targets at a large stand-off distance, whilst still maintaining excellent accuracy and resolution. The 1810-50, for example, offers a measuring range of 50mm (from 550mm up to 600mm) and a resolution of 5um at a measuring rate of 2.5kHz. The 2210-10 offers a 10mm measuring range (from 95mm up to 105mm) with a resolution of 0.5um at a measuring rate of 10kHz. The 2210-20 offers a 20mm measuring range (from 90mm up to 110mm) with a resolution of 1um at a measuring rate of 10kHz.

Standard and custom models

Chris Jones, Managing Director at Micro-Epsilon UK, comments: "In addition to the three standard sensors, we can offer OEM customers special versions of the sensor with customised stand-off and resolutions to suit their application. None of our competitors is able to offer this type of service."

The optoNCDT 1810-50 and 2210 operate using the laser triangulation principle. A laser diode projects a visible point of light onto the surface of the target object. The light reflected from this point is then projected onto a CCD array. If the target changes position with respect to the sensor, the movement of the reflected light is projected on the CCD array and analysed to output the exact position of the target. The measurements are processed digitally in the integral controller. The data is output via analogue signals (current/voltage) and digital interfaces (RS422 or USB).

Micro-Epsilon says that what differentiates the optoNCDT 1810-50 and 2210 sensors from current competing laser sensors is the ability to compensate automatically in real time for difficult-to-measure surfaces. The patented real-time surface compensation (RTSC) feature and high-speed software algorithms dramatically reduce signal noise. When customers need to measure against a shiny surface, ideally they want a sensor that is able to adjust the laser pulse duration (or 'laser on' time) automatically to give them the optimum exposure time on the CCD for that particular surface. This, in turn, provides higher accuracy due to lower noise level on the output signal.

For more information on Micro-Epsilon's non-contact laser displacement sensors and systems, visit www.micro-epsilon.co.uk/uk-en/Sensors/Optical---Laser/.