Edge, gap and diameter measuring sensors from Eltrotec

Measuring sensors are essential for edge tracking in the paper industry, in steel working and in press-fit systems on automatic presses, but also just as necessary for measuring wire coils and other wound items. In this field, Eltrotec offers a range of specialized sensors with varying degrees of complexity. Tracking edges and monitoring and measuring distances, diameters and clearances is an essential part of all automated production.

Laser beam sensors and laser micrometers are composed of a transmitter and receiver, which are sometimes situated at a large distance from one another. Edges and gap widths are measured by means of a parallel laser line, which is generated using telecentric lenses and slit diaphragms. The shadow of an edge or gap produces a proportional, linear, analog output signal in the receiver. The values are the same at each point even at distances of up to 8 meters, so enabling reliable edge tracking. For these tasks, Eltrotec provides the series LBS-MA-34, LZS, LBM and CLS-K, with various measuring orifices or gap widths with fiber optic cross-sectional converters. In cases where there is insufficient space for a laser distance sensor or the ambient temperature is too high due to the sensor’s proximity, thickness measurements in shadow mode between the transmitter and receiver can be measured against a solid background. The CLS-K fiber optic amplifier series is suitable for scanning distances of up to 200 mm and ranges of up to 2000 mm. It is employed for position detection, position and presence monitoring and for checking lengths and diameters. The measuring frequency is up to 8 kHz, and signals from 0.1 to 5 VDC or 4-20 mA are generated at the analog output. Here, resolutions from 0.1 mm are achieved for small measuring ranges. For glass detection or coating monitoring of sheets, a version with UV light source is also available as an option.

Fiber optic amplifiers for measuring web breaks and edges are used in the paper industry, for example in cases where ambient conditions – temperatures of approx. 100 °C and humidity of up to 98 % – are too extreme for any electronic equipment. For other applications, which require greater accuracy and/or traversing speed, laser beam sensors are the right choice. Some applications do not require the light quantity to be measured, but individual points of light instead. Angles and resolutions can also be varied. The LZS and LBM series offer versions with a CCD sensor, which delivers resolutions in the micrometer range, from 0.25 m. In order to position large panes of glass up to eight meters wide together with an accuracy of 0.1 mm in window production, a beam sensor with CCD is used, which scans and automatically adjusts up to 50 switching thresholds from different types of glass. The high-resolution CCD sensors are also capable of measuring diameters, clearances, edges and segments. Laser micrometers also enable measurement of the gap between running shafts without problem. The visible laser beam makes sensor adjustment especially easy. A glass lens with interference and polarizing filter is available for very dirty environments and difficult surfaces. The LZS series is suitable for straight measurements, and a 90° version offers measuring ranges up to 100 mm. It measures with a frequency of up to 25 kHz. The LBM40 series has no rotating mirrors, and is therefore completely non-wearing. It is equipped with an LED light source, which has a resolution and accuracy three times greater than that of laser versions. Consequently, this version is especially suited to measuring edges, diameters and segments in the micrometer range. The 40-mm measuring range boasts a resolution of 0.25 micrometers and a maximum range of 400 mm, with fixed mounting rail.

When tracking on running conveyors for the purpose of guiding webs precisely for cutting or folding processes, special conditions may predominate. Line sensors with red, IR or UV light achieve the best possible contrast for tracking, even if measurement is only possible with lighting from one side using coaxial illumination. The measured values obtained can be displayed online, using software that also permits gap and edge values to be monitored. Output to the machine control system is analog, digital or via serial interface. When the electronic components are arranged separately, fiber optic sensors are also suitable for potentially explosive environments. The fiber optics contain cladding with a low refractive index and a highly transparent core with a high refractive index. This core is made up of transparent plastic or glass. High temperatures, large distances or specific transmission wavelengths require glass fibers; simpler applications can be handled using plastic fibers. The transmitted light signal comprises visible, infrared or ultraviolet light, which is transmitted using the principle of total internal reflection. Temperature ranges of up to 400° can therefore be handled safely. The fiber optics are resistant to weak acids, alkalis and aggressive cleaning agents.

Thanks to Eltrotec’s modular system, the mechanical design of the transmitter and receiver components can be adapted. The size of the housing must also be considered. If an existing machine frame is to be retrofitted with sensors for measuring the gap between two incoming steel sheets, a compact, customized housing is preferable, and can be provided by Eltrotec even for small series. If gap sizes of less than 0.2 mm are to be measured and controlled, the wavelength of the transmitter, the diaphragms and the electronics can all be adapted specifically for this application.