Confocal displacement sensors are just 4mm diameter

As well as axial measurement, the new range of sensors also includes a 90-degree version that enables users to measure (radially) the inner surfaces of small components. The sensor head can be rotated inside the bore to measure surface defects inside and to check the concentricity (roundness).

As well as inspecting drilled holes and recesses, other potential applications include: checking liquid fill levels in medical test tube racks and trays; measuring grooves inside pipes; measuring the thickness of any transparent material, including glass and film; measuring mirrored or highly reflective surfaces (which are difficult to measure with laser sensors).

Versatile

The sensor is suitable for use in a range of industry sectors, including medical, biotechnology, pharmaceuticals, aerospace component inspection, electronics component and PCB measurement, machine gauging/inspection and general engineering.

Developed and manufactured by Micro-Epsilon, the new optoNCDT 2402 confocal miniature displacement sensors are based on the company's patented lens design. Manufactured using Micro-Epsilon's own special optical production technology, the sensor is claimed to be the smallest-diameter confocal displacement sensor available on the market.

At a measuring range of 1.5mm, the sensor has a resolution of 0.06um at 0.004 per cent FSO (full scale output). Measuring rate is from 30Hz up to 30kHz and operating temperature is from 10-50degC.

Thanks to a titanium housing, the optoNCDT 2402 sensor weighs just 50g and is therefore suitable for machine builders and design engineers that require a lightweight, miniature displacement sensor. The sensor head comprises precision optical parts without any electrical components, which is said to enable a higher level of stability to be achieved than is possible with other laser optical devices.

System architecture

Micro-Epsilon's complete measurement system consists of a sensor, an optical cable and a controller. Up to six different sensors can be factory-calibrated for one corresponding controller.

The optoNCDT2402 sensor is the latest product in Micro-Epsilon's optoNCDT 2400 range of confocal displacement sensors. All sensors in the range have no moving parts and can therefore be considered wear-free. The sensors work on the confocal measurement principle.

About the confocal measurement principle

Polychromatic white light is focused onto the target surface by a multi-lens optical system. The lenses are arranged such that the white light is dispersed into a monochromatic light by controlled chromatic aberration. A specific distance is assigned to each wavelength by factory calibration. Only the wavelength that is exactly focused on the target is used for the measurement. This light reflected from the target surface is passed through a confocal aperture onto a spectrometer that detects and processes the spectral changes.

The spot size of the device is very small - in the region of 7-10 microns, depending upon measurement range - and is always constant in diameter. This measuring principle enables displacements and distances to be measured with high precision and exact spatial resolution. Both diffuse and specular surfaces can be measured. With transparent materials such as glass, a one-sided thickness measurement can be achieved, along with the distance measurement. Shadowing is also avoided because the emitter and receiver are arranged in one axis.

A further advantage of the white light technology is that it also gives greater stability than laser-based technologies against shiny, transparent and mirrored surfaces.

More information and datasheets are available at www.micro-epsilon.co.uk/uk-en/Sensors/Optical---Laser/.