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Gap, roller gap, roller convexity

If two object edges are joined together, a gap always remains. If the gap has to satisfy technical or visual requirements, the course with respect to the size must be checked. If the gap should be measured completely, laser scanners in the scanCONTROL series are ideally suitable for this. Point laser sensors in the optoNCDT group are also used for precise gap measurement over a track.

Special roll gap measurement on calender press

For continuous, uniform material processing in the field of sealing technology, the gap between the rolls must be set with the hydraulic adjustment device and maintained constant. For this reason the top and bottom rolls are provided with a shoulder and an aluminium ring as measurement objects to the left and right. Using the aluminium ring, errors due to the roll material can be avoided. Two eddy current sensors mounted opposite one another measure the distance to the aluminium ring from a fixed reference point. The roll gap can be found from the sum of the two distances.



Combustion engines must withstand maximum loads during a long service life. In order to deal with this requirement, eddy current sensors from the eddyNCDT series are installed in the engine for many different measurements. As the smallest eddy current sensors in the world, these sensors can be used in the fuelled condition. Examples of measurement already being carried out are: valve lift, needle lift, breathing of the cylinder head, lubrication gap on the cylinder, oil film thickness, crankshaft concentricity, crankshaft axial movement and piston secondary movement


Piston – Top Dead Centre

The Top Dead Centre of the cylinder movement is measured for adjustment of the precise ignition point in engine development. In doing so, a miniature eddy current sensor is integrated in the cylinder head cover. From this position, it precisely measures when the piston is at the smallest distance from the sensor. The ignition is optimum at precisely this time. Earlier or later ignition would reduce the efficiency of the engine. This measurement is only possible in towing operation.


Piston Secondary Movement and Piston Ring Position

To improve the construction of internal combustion engines and damage analyses, it is neccessary to measure the thermal and mechanical loads in the engine. Two important variables here are the transverse movement of the piston (secondary movement) and the position and deformation of the piston rings during the individual operating strokes. The measurements must be made under operating conditions in order to provide reliable results. To do this, the engine is run on the bench either in test mode or normal operating mode.


Piston secondary movement

Among other things, the lateral movement of the piston in the cylinder is crucial for the service life of engines. Miniature eddy current sensors for this are integrated in the piston which measure onto the cylinder wall. If the distance is too large or too small, the piston has too much play or continuous lubrication cannot be ensured. The sensor cables are routed out of the engine along the connecting rod over a rocker in the gearbox.


Sorting crabs

Crabs are sorted by size in a sorting system. Thereby, the crabs are transported using a vibrating unit on a roller which has a clearance between 20 mm and 40 mm. For checking the clearance, an induSENSOR series LVP is used which measures the changing clearance and shows it on a digital display. The sensor is designed in stainless steel for the food industry.


Exact crusher gap adjustment in rotary crushers

Rotary crushers for quarries or ore mines can grind up to 3500 t of material to the desired grain size in one hour. For this purpose an eccentric bearing bush generates a rotary-oscillating movement of the crusher axle, thereby constantly changing the gap

between the crusher jaws and the crushing cone. For grinding the set gap continuously moves along the inside perimeter of the crushing room. With a longdistance sensor in the hydraulic cylinder the crushing gap can be exactly adjusted by raising and lowering the axle.


Measuring the bearing gap in wind turbines

To date, bearing gaps were measured during standstill based on a tactile principle. Therefore, long inspection intervals were required, which in turn, may increase the risk of a complete plant failure. Moreover, these deliberate stoppages intended for measuring and inspection purposes cause considerable additional costs. Micro-Epsilon acquires the measurement values during plant operation, thereby enabling reliable, cost-saving real-time analysis.

This measurement task is performed with the inductive eddyNCDT 3005 measuring system based on eddy currents. It includes a sensor with a measuring range up to 6 mm, which is permanently connected to the controller via a 1 m long cable. As the system is oil-tight both on the front and rear side, it is ideally suited to this application even when typical oil pressures reach 1 to 2 bar in the bearing. The eddyNCDT 3005 inductive system is already being used in wind turbines to analyse and optimize the maintenance intervals of wind turbines. In addition, the data acquired in the test bench throughout the design period can be taken into account and used for dimensioning purposes of new components. The sensors can be used in the test bench and in high volume applications for Condition Monitoring. Serial use offers major advantages as the sensor technology can already be aligned and precisely adjusted during installation and initial operation.


Air gap measurement in large electric motors

With very large electric motors (diameter larger than 10m) it is important for reasons of cost effectiveness and energy efficiency, to know the radial run out of the rotor from the stator inside the motor. These electric motors are intended for use in rock grinding mills for cement production or mining. Due to imbalances during operation, the rotor may touch the stator, which would cause much damage. This is why sensors are used to measure the distance between the stator and rotor and to monitor the so-called rotor gap whilst the motor is in operation. For this application, capacitive sensors with a measuring range of approx. 30mm are used.


Inspecting gaps in car trims

In high quality vehicles, the trim typically consists not only of a single material (e.g. plastics) but many different bonded materials. This offers various design options but also many additional functions e.g. illumination using semi-transparent parts. Bonding or welding these elements requires precise handling, as parts that are only slightly misaligned can cause large deviations in the corresponding gap size. In order to meet the high requirements demanded by automotive manufacturers, it is necessary to inspect all trim prior to delivery and to rework any defective parts. And this is where the scanCONTROL 2910-25 laser scanner comes in.


Detection of turbocharger rotor dynamics

In order to inspect the behaviour of turbochargers during different stress states, eddy current displacement sensors are applied in turbocharger test benches. The miniature design of the sensors and their resistance to oil and high temperatures enable the precise detection of the lubricating gap of hydrodynamically stored rotor shafts.


Lubrication gap

Sliding bearings are used for crankshaft bearings in the engine. A specific minimum distance is required so that the bearing operates as wear-free as possible. Miniature eddy current sensors are integrated in the bearing for this. They measure the distance through the bearing half-shell on the crankshaft. It can thus be established whether sufficient oil is lubricating the shaft in the bearing. If the film of oil breaks down, the distance to the shaft must be almost zero. This is because a certain minimum clearance from the bearing to the shaft is required due to the viscosity of the oil.


Measuring the lubricating gap in plain bearings

The lubricating gap of a plain bearing is influenced by several factors such as temperature, speed, angle, load etc. This influence can only be measured under operating conditions.

Therefore, a measurement system which detects the gap size or the shaft displacement is subject to strict requirements: temperature stability, resistance to pressure, oil resistance, small size.

eddyNCDT systems with the miniature sensors U 05 and S 05 have been used successfully for displacement measurements in the crankshaft bearing of internal combustion engines. The special design of these minia-ture sensors enables them to be inserted in even the smallest of bearings where they deliver reliable, accurate measuring results and high resolution of the values.


Gap analysis in axial piston pumps

So far, gap measurements inside the pumps were not possible because of the extreme requirements. The sensors must be resistant to high speeds, high pressures up to 1,000 bar and temperatures above 100 °C. Furthermore, the pumps are extremely compact, which significantly limits the space available for integration of sensors. Thanks to the extremely small sensor designs and their high pressure and temperature stability, the eddyNCDT inductive miniature sensors are ideal for this application. The eddyNCDT 3300 eddy current measuring system, which is one of the most powerful systems in the world, is therefore used on the test rig for evaluating the pumps.


Gap detection on glass

Glass substrates are required for certain medical tests. During manufacture of silicon chips, the substrate is milled in a defined grid with a depth of 800µm. For separation, the substrate is broken at pre-defined breaking points in a breaker station. For this, the glass pane must be positioned precisely. An optoNCDT 1700 sensor is used here for gap measurement.


Closed-loop gap control in magnetic bearings

A shaft weighing about 40kg is supported in magnetic bearings. A ferromagnetic shaft journal is suspended in a magnetic field which is excited by surrounding excitation coils. To regulate the gap two sensors at each end measure in the radial direction, mutually offset by 90°, and one sensor measures axially against the shaft. Non-contacting and wear-free magnetic bearings are used in ultra-clean atmospheres and in extreme ambient conditions.


Gap measurement of tripping pins

When triggering a switching operation in test equipment for camshafts, a tripping pin is moved at high speed. A gap measurement detects whether the tripping pin has been completely extended and if it has been triggered with the required speed. Evaluation of the displacement-time-signal determines all parameters reliably. The optoCONTROL 1200/90 optical micrometer carries out these measurements.


Eddy current sensors in tribology testers

Eddy current sensors from Micro-Epsilon are used for various measurement tasks in tribology testers of the ITR in Clausthal. They withstand the harshest ambient conditions there as they measure directly on the shaft in the tester. A tester with water lubrication and a tester which examines plain bearings for the automotive industry have already been realised. The position of the test bearing case and the relative movement between the rotor and the test bearing is detected in the tester using eddy current sensors.


Monitoring oil gaps in hydrostatic bearings

Hydrostatic bearings are used in large plant and machinery such as stone mills, telescopic installations etc. Monitoring the gap size is a critical factor, as any disturbances in the hydraulics can cause pressure drops, which in extreme cases, can cause the gap to close, resulting in damage to the bearings and ultimately system failure. Here, it is important to have a system that is easy to install as also ageing plants have to be retrofitted. Due to the long service life and the worldwide use of this plant, the sensor should be easy to replace. For this reason, non-contact eddy current displacement sensors of the eddyNCDT 3001 series are used.


Oil film thickness measurement in an internal combustion engine

Included in the objectives of current engine development are minimization of pollutants and the reduction of oil consumption. In order to be able to take measures in achieving these objectives, then along with a number of other factors, it is very important to obtain knowledge of the behaviour and the thickness of the oil film between the cylinder wall

and piston or piston rings In this respect the upper third of the cylinder bore is of particular interest.


Measuring glass cups

In the production of drinking glasses, the stem and cup are connected using a gas burner. In order to enable the precise connection of the glass stem and cup, the distance between stem and cup needs to be measured. Monitoring this gap size allows for feed rate control during production. An optoCONTROL optical micrometer measures this gap.


Roller clearance

The distance of both rollers from each other or from the roller to the support surface is the crucial dimension for rolling processes for metals, plastics or other materials. In the case of sensitive processes and high material accuracies, the clearance must be checked constantly so that imminent rejection is avoided. The contacting inductive and the non-contact methods are suitable for this. In the case of contacting methods, the sensor is mounted on the outside on the roller guide. The change in clearance is transmitted to a plunger whose position change is measured by the inductive sensor.

In the case of the non-contact method, the roller is between the transmitter and receiver of an optical micrometer. The emitted light curtain is partially covered by the roller. The remainder reaches the receiver through the gap. The gap can be calculated based on the light quantity measurement.


Monitoring mold deformations in aluminium die-casting

Monitoring tool deformation using inductive sensors based on eddy current enables high product quality combined with improved tool life and reduced rework. Usually, three to four eddyNCDT 3005 eddy current systems are used to ensure consistent gap monitoring.

A system consists of a compact and robust controller, which together with the cable and sensor form a solid unit. The integrated system design increases robustness and resistance to external factors, making the system insensitive to harsh industrial environments with high temperatures, dust, dirt or pressure, and delivers accurate results regardless of the environment. Due to the compactness of the eddyNCDT 3005 system, subsequent integration into an existing machine is possible at any time.


Windscreen gap

The final appearance of a product plays a crucial role everywhere that panes are positioned automatically. Apart from the shape, stability, colour etc., the final appearance is also dependent on the position of the glass in the frame. The pane must be inserted in as centred a position as possible. A laser scanner also detects automatically for the insertion of the glass whether the gap is the same on all sides or not. If differences occur, the pane can still be moved somewhat. The extremely difficult conditions of the different reflection factors of glass and frame (metal, wood, plastic) do not affect the quality of the measured data.


Cylinder breathing of the cylinder head gasket

Specially shaped eddy current sensors are integrated directly in the crankcase where they measure, for example, the expansion of the cylinder head gasket during the stroke. Pressures of up to 50 bar are produced for every ignition of a cylinder, which slightly raise a tightly bolted cylinder head. This movement is compensated for by the cylinder head gasket, which is why it is referred to as “cylinder head gasket breathing”. How far the cylinder head moves is measured by eddy current sensors. This data provides information about the durability of the gasket and save customers from fatal engine damage.