Digiforce Provides Non-Contact Tension Measurement

Applied Measurements has developed a low-cost device to rapidly and accurately measure tension in pre-stressed wire and cable. The patented Digiforce device has been developed as a non-contact method for determining the tension in reinforcing cables and bars for pre-stressed concrete beams. The equipment used for this tensioning process must be tested on a regular basis, but current methods are time consuming and accuracy is, in part, dependent on the skill of the operator, according to the company.

Integral to the durability and structural performance of these products is the correct tensioning of the pre-stressing steel tendons. There are approximately 30 tendons in the average 1,200mm-wide hollow-core floor slab, which may be up to 160m in length. By striking the wire or cable under tension and observing its fundamental natural frequency of vibration, it is possible to develop a battery-powered handheld instrument capable of accurately determining the tensile forces applied to them. The low frequencies and complex sound spectra have prevented accurate analysis on site.

The Digiforce addresses this issue via the integral mathematical software in order to process only those frequencies of interest that contribute to the measurement. This means that the user no longer has to refer to look-up charts or return to the office to run complex calculations relevant to that piece of equipment or installation. In terms of operation, the instrument is first programmed with the length of the wire or cable whose tension is to be measured. Also inputted is its weight per unit length.

The magnetic sensor at the end of the instrument is then placed adjacent to the part to be measured. The measurement process is triggered and the part is struck lightly with the mallet supplied. After a few moments, the tension appears on the LCD display on the instrument. Tensions in stainless-steel or other non-ferromagnetic wires can be measured by attaching clips (also supplied) made of ferromagnetic materials, as long as their masses are insignificant compared to that of the cable to be measured. The vibrations being analysed are complex and the fundamental frequencies that the method uses are in the 3-70Hz range and not the metallic note heard by the ear.

The tension is determined from the formula T = 4 x length2 x Hz2 x weight per unit length. As a result of the very low frequencies, tuned circuit filter methods are not an option. Instead, the device makes an initial 20 measurements of each oscillation and discards these. The next five measurements from 10 oscillations are then used to establish a tolerance band to establish which measurements are reasonable to contribute to the calculation and which should be rejected as spurious.

Subsequent measurements are then made and those that fall within the tolerance band are used to calculate the final measurement value. The Digiforce device features an onboard data-logging facility for collecting results and an RS232 port/USB converter for later downloads to a host PC, driver software, a mallet, a rugged carrying case and full instructions. The device is supplied with a three-year warranty.

Potentiometer Provides Non-Contact Measurement

Variohm Eurosensor has announced the availability of the Magnetopot non-contacting linear potentiometer, which provides position feedback from 8mm to 1,200mm in a low profile. Manufactured by Spectra Symbol, the Magnetopot is based upon a fully sealed membrane strip and a simple magnet. It is suitable for hydraulic and pneumatic position sensing as well as other medium precision position feedback applications such as liquid-level monitoring.

A rotary version is available for compact, low-profile angle sensing. The Magnetopot is similar in concept to a traditional membrane-type potentiometer, but rather than using a contacting wiper to connect the collector to the resistive element, it relies upon the interaction of a non-contacting external magnet and an encapsulated magnetic or ferromagnetic strip to determine the electrical output and relative position.

The thin IP65 membrane has a typical membrane thickness of less than 3.5mm - allowing the position sensor to be discretely installed with either the magnet or the membrane strip attached to the moving component. The standard linear Magnetopot is available in 11 travel range versions from 12.5mm to 1,000mm, with a choice of three-pin connection options including Crimplex solder tabs, male pins and a variety of connectors. The electrical specification includes a 10kohm resistance output over each linear position range (5kohm to 500kohm on request) with a linearity of +/-5 per cent.

The positioning resolution is dependent upon the exterior magnet strength and its proximity to the Magnetopot's magnetic strip. The rotary version is currently available with a 66mm diameter and an active centre track diameter of 46mm. The IP65 rating for the active area for both types of Magnetopot allows for intense water spray. The non-contact technology is said to provide a long and maintenance-free working life.

Non-Contact Level Measurement At 150C

Burkert has expanded both the range and media types that can be measured using non-contact radar technology, with the introduction of the Type 8136, 8137 and 8138 modular radar transmitters. The addition of the new radar sensors allows level measuring in normal, aggressive and hygienic operating environments, at pressures up to 40 bar and temperatures (on hygiene transmitters) to 150C, providing the facility for CIP and SIP.

The addition of the new radar sensors to Burkert's existing ranges of ultrasonic, guided microwave and vibrating level sensors means that Burkert can now measure open-channel flow and tank levels for a broad range of solids and liquids covering 95 per cent of all level applications, with dielectric values as low as 1.7. The radar sensors offer operating benefits across a wide range of process industries, including food and beverages (especially breweries and dairies), pharmaceuticals, water treatment (pure water and sewage) and pulp and paper.

They are reliable, non-contact devices that are suitable for CIP and SIP processes and are impervious to atmospheric conditions such as temperature, pressure, dust, vapour and condensate. The base unit in the new sensor range, the Type 8136, is a modular radar transmitter designed for simple process applications - typically measuring flow in open channels or levels in open tanks - as a superior alternative to ultrasonic transmitters. The device is designed for use at pressures up to 3 bar maximum and fluid temperatures of 80C. It is supplied with threaded connections G/NPT 11/2in and is supported by optional mounting brackets.

Developed for demanding applications, the Type 8137 operates at temperatures up to 130C and pressures up to 40 bar. Using optimised antenna, the device can measure at distances up to 30m, even in aggressive environments. In common with the Type 8136, the 8137 is supplied as standard with G/NPT 1.1/2in, but with the added options of DIN and ANSI flange connections. The final unit in the new range, the Type 8138, has been developed specifically for hygienic applications in food and beverage and pharmaceutical industries. The 8138 can operate at fluid temperatures up to 150C and, depending on the flange connection employed, at pressures up to 16 bar.

These extreme operating parameters, plus the hygienic design of the 8138's flange connections, ensure that cleaning and steam sterilisation of the device can be carried out to the highest possible regulatory standards. The Type 8138 is equipped with a Triclamp 2in connection as standard, with Varivent DN25 as well as DN50 and DN100 DIN-flanges also available. All the sensors in the new range can be delivered with or without displays. They will shortly be joined by versions suitable for potentially explosive atmospheres, according to Ex ia IIC T6, for zones 1/2G and 2G. Certification for these devices is planned but not yet carried out.

Burkert is supporting the new radar sensors with intuitive Pactware - an industry-standard software platform. This provides a configuration tool with a PC using HART communication and DTMs. The software allows simple configuration of custom tank-configurations and provides easily selectable pre-programmed open-channel flow configurations and also false echo suppression, among many other features.

Liquidyn Dispensers Allow Non-Contact Application

Integrated Dispensing Systems is offering Liquidyn dispensers that enable adhesives, sealants and lubricants to be applied to components without contacting the part. Anaerobic adhesives such as Loctite 648 can now be precisely deposited without contacting the part as a result of a newly developed dispensing head. The dispensing valve applies the adhesive by projecting a small drop over a distance of up to several millimetres (jetting) between nozzle exit and work piece.

To achieve this with the adhesive mentioned above, Liquidyn selected suitable materials for the wetted valve components to ensure the adhesive did not cure in the valve. The main problem in the past, when jet dispensing anaerobic media, was the fact that when an anaerobic adhesive comes into contact with metallic valve components in the anaerobic conditions in the valve, it would lead to the rapid hardening of the adhesive in the valve.

With careful material selection for all wetted parts, Liquidyn was able to overcome the natural tendency of the adhesive in this situation to cure. Liquidyn dispensers can also dispense high-viscosity media such as epoxy resins, silicones, fluxes and greases, as well as low-viscosity media such as instant glues, solvents and so on.

Non-Contact Sensors Measure Solar Glass Panels

Schott Solar Thin Film, a manufacturer of thin-film solar-power modules, is using non-contact measurement systems from Micro-Epsilon to inspect the quality of solar glass panels. The measurement system has helped to reduce the cost of processing defective parts. Thin-film technology is the manufacturing technology used to produce thin solar cells, which are deposited directly onto a low-cost carrier material, typically glass, metal foil or plastic film.

The advantages of using thin-film technology are the material and energy savings made during the production process, good conductivity and the ability to produce large-area solar cells. Schott Solar Thin Film delivers glass panes with a conductive layer (electrode). To optimise the production yield of the thin-film solar cells, all incoming glass panes are measured and inspected on delivery. Here, one of the most important criteria is the evenness or flatness of the glass panes.

This must be accurate to just a few millimetres across the complete surface of the glass, which means they need to be measured to an accuracy/repeatability of hundredths of a millimetre. Other inspection criteria are thickness, length, width and squareness of the glass. The edge must also be inspected for cracks, shell defects or breakouts. The QA station Schott uses comprises several stages. Loading is carried out by a robot that places the glass panes onto a conveying unit. The panes are then automatically inspected for their length, width, squareness, edge damage, thickness and evenness.

These tasks are performed using a measurement system supplied by Micro-Epsilon. For these inspection tasks, Micro-Epsilon employs two different optical-measurement methods: confocal chromatic sensors and the light intersection method. The glass pane, which is lifted onto the conveyor belt by a robot, is placed on a solid block of granite in order to have a defined, flat reference surface. Six OptoNCDT 2401 confocal chromatic sensors are positioned on a traversing beam directly above the pane and measure the thickness and planarity in six planes. In this way, the glass pane can show a target thickness of 2 - 4mm.

The required flatness and thickness must be accurate to within millimetres or tenths of a millimetre, which means that the measurements must be precise, down to hundredths of a millimetre. The desired distance or thickness information for the confocal principle is obtained from polychromatic white light. A conventional LED provides the light source. The sensors have a measuring range of 10mm and only measure the thickness from one side. During the traversing process, a Micro-Epsilon Scancontrol laser scanner circumnavigates the glass pane. Therefore, the edge of the pane is simultaneously inspected for damage and its geometric values (length, width and squareness) are measured.

A maximum deviation of +/- 1mm is permitted for a length of 1,300mm and a width of 1,100mm. For this, a laser line is projected onto the pane and the diffuse reflected light is received by a CMOS matrix. In this way, the surface profile of the edge of the pane can be accurately reproduced. Next, the film resistance and the transmission of the pane are measured. If the pane is defect-free, it is then channelled into the production process by another robot. Another QA station is located at goods despatch for edge inspection of the flat glass panes refined by the production process.

Here, damage to the edge of the pane is inspected. The test rig is an identical design to the system in goods inwards. An optical laser scanner on a traversing beam carries out the quality inspection by circumnavigating the glass pane. Micro-Epsilon's measuring system enables rapid, 100 per cent inspection at goods inwards and despatch. The system, which was specially developed for these inspection tasks, reduces the cost of processing defective parts.