Introduced recently to a UK audience at the MTEC (Measuring Technology) Conference and Exhibition Shape Tape is set to change the way shapes and surfaces are measured. Alan Quinn reports

Imagine an array of fibre optic sensors embedded along a flexible ribbon of tape? The result of innovative research from the Canadian Space Agency from which it is produced under licence the remarkable Shape Tape sensor has knowledge of its position in three-dimensional space. As a result it can be used for demanding measuring tasks replacing the need for a plethora of sensors and transducers.

Output signals from the tape array are used to construct a three-dimensional real-time model of the shape on a monitor for instant observation and analysis. The tape design allows six degrees of freedom measurement at any point along the ribbon which can be a metre or more in length. The sensor array knows its position relative to a fixed origin point on the tape and can measure static or dynamic shapes including curves and twists.

Developed by Measurand Inc and marketed in Europe by RDP Electronics the simple rugged yet innovative construction means that one tape can replace large numbers of discrete sensors such as load cells accelerometers pressure and displacement transducers. Experiments can be set up more quickly and a test structure can be changed in minutes.

Shape Tape is suitable for tasks in biomechanics image capture film animation 3 CAD transport crash testing virtual reality and marine design for example.

The standard bandwidth is 1.6kHz but systems up to 10kHz have been developed. Resolution of conversion is 0.01% of range limited by the A-D conversion process.

• RDP Electronics
• Tel: 01902 457512
• Fred Thorneycroft

May 1999

The relative merits of 4-wire and 2-wire signal/power transmission configurations in industrial sensors are the subject of some debate among controls and plant maintenance engineers.

In the 4-wire scheme, a pair of twisted wires is dedicated to the precise transmission of a 4-20mA current signal linearly proportional to the variable being sensed, while two additional wires are reserved for supplying power to the sensor.

The 2-wire method, on the other hand, uses the same pair of wires for transmitting the output signal and powering the sensor’s circuits.

To minimise signal noise (maximisation of S/N ratio), which is especially important in applications below 760°C, Calex has designed 4-way circuits into its infra-red thermometers. The resulting unlimited powering current allows for extremely low-noise circuit design and component selection.

Powering, noise and installation trades-off are listed. Clearly, a 4-wire sensor is the best application for all applications where process control accuracy and stability are early considerations.

In areas where a 2-wire device is being replaced by a 4-wire one, installation of the power supply at the sensor location will eliminate the need to rewire through conduits with existing 2-wire lines, and those wires may be used for signal transmission.

Table 1 Power/Noise Considerations

	4-wire	2-wire
Power Supply	12VAC	16-40VDC (must be regulated)
Circuit Powering Current	Unlimited	3.5mA maximum
Processing Electronics	Very low noise	Fair
Temperature Signal Accuracy	Not affected by power supply fluctuations	Affected by power supply fluctuations

Calex Instrumentation

Tel: 01525 853800

Fax: 01525 851319

September 1997

A new design of web tension transducer can determine the true web force as well as the resultant angle

Available in ranges from 0-5,000lb to 0-20,000lb, the HTU web tension transducer from Nobel Systems utilises a two dimensional approach to web tension force measurement. The subject of a patent application, the technique allows both the true resultant web force and the resultant angle to be accurately determined.

The HTU transducer measures web tension forces applied across a roll, using integral horizontal and vertical axis sensors. Not only does the approach permit installation and measurement at any mounting angle or roll orientation, it also forms the basis of an expert diagnostics system that produces the highest level of web tension measurement confidence.

The HTU is machined from a high strength corrosion resistant stainless steel to yield a low profile single piece construction that incorporates tubular sensing sections at each end. Two full Wheatstone Bridges are mounted internally to each sensor and provide output signals in the X and Y planes that are externally, vectorially summed to determine the magnitude and direction of the resultant force. Each bridge is temperature compensated to 250degF, and dead weight calibrated to precision accuracy. The cylindrical sensing sections are sealed to meet IP67 requirements.

Environmental sealing ensures long term reliability in humid, wet or washdown locations.

Retrofit installations are simplified thanks to the low profile height of 36.8mm, resulting in a negligible change in the line profile. The HTU can be mounted directly to the framework with an optional pillow block adapter plate or it can accept top and bottom adapter plates.

HTU transducers are calibrated and certified with matched output signals to permit on-site pushbutton system calibration, providing minimum start-up time and maintenance-free operations.

Applications for the transducer include paper, plastics, roofing, metal strip forming and rubber forming machines. It will also offer benefits on mining conveyors.

• Nobel Systems

March 2000

The testing and development is up and Renold’s remarkable strain gauge for drive chains is now looking to perform in anger. Alan Quinn explains what it’s all about.

An intelligent chain link capable of collecting load data and predicting chain life on actual applications has been jointly developed by Renold Chain and the University of Newcastle-upon-Tyne. Whilst correctional strain gauging techniques have been used for many years it has not previously been possible to capture the actual loads and calculate stress on real applications. Monitoring has only been possible in laboratory conditions where peak and shock loads unique to each individual machine cannot be measured.

Branded Renold Smartlink the new units may be fitted to various types of transmission or conveyor chain to record dynamic loadings for subsequent analysis on a PC. In critical applications Renold engineers believe that it could be possible to fit the Smartlink permanently and to use sophisticated computer links to allow engineers to receive vital chain performance data off-site. Areas expected to benefit most include the offshore and leisure industries heavy lifting applications and general conveying.

The data recorded by the Smartlink system enables engineers to identify precisely the location of both peak and shock loads measure stresses and calculate an optimum chain size for each application. The same methodology can also be used to determine the causes of premature chain failure with the obvious safety benefits and cost savings for end users.

The system consists of the Smartlink unit currently about the size of a small calculator and a hand-held remote controller with a transmitter and receiver. Depending on the data required the hand-held units are used simply to select the required programme and then transmit the instructions to Smartlink in a similar way to programming a video recorder. The collected data is then recovered by the hand-held units and stored on an easily removed chip that can be sent to Renold Chain for analysis or alternatively downloaded onto a PC and analysed on site.

• Renold Chain
• Yvonne Alexandser
• 0161 437 5221

September 1999

The sensors and systems exhibition that comes to you…

Erwin Sick’s innovative sensors and systems are heading your way! The company has fitted out an impressive roadshow vehicle which toured Ireland, Northern Ireland and Scotland in April, and returns from a tour around the continent at the end of May. Throughout June and July the 1999 Erwin Sick Roadshow will be traversing the length and breadth of England and Wales, parking at convenient locations and making it easy for you to examine and discuss the latest developments in industrial sensors, barcode reading systems, laser measurement and safety components.

With fewer and fewer engineers now able to afford complete days out wandering around trade shows, an exhibition which comes to your town – or even your company site – is proving to be a very convenient alternative.Once on board, you’ll be able to see working displays of some genuinelyinnovative products including:

The DMH Dimensional Multifunctional Height Sensor -  laser profile measurement, an economical alternative to camera vision systems.

The PLS/LSI Programmable Laser Scanner – 180deg scanning of a safety detection area with interface allowing up to eight safety zones.

The LMS Laser Mesurement System – for volume or level measurement, anti-collision applications, object classification, etc.

The CLV430 Bar Code Reader with SMART technology – revolutionary software decoding allowing the reading of misaligned, dirty or partially damaged bar codes.

There’s also a clever model of a factory production area showing a mix of Erwin Sick products in a practical environment, as well as presentations on safety risk assessment and bar code reading.

The planned route of the 1999 Erwin Sick Roadshow ison this web site. Its specific schedule is constantly being updated as engineers request new stops at their company, so to find out the time and place of the Roadshow’s nearest visit to you, callAnn WhiteorAndrea Hornbyon 01727 831121.

• Erwin Sick Ltd.
  Waldkirch House
  39 Hedley Road
  St.Albans
  Herts
  AL1 5BN

• Telephone 01727 831121

• Fax 01727 856767

May 1999

MTE Turck has introduced the R55 colour mark sensor for print verification label detection and web cutoff registration.

The Banner R55 colour mark sensor operating at extraordinary speeds of up to 10 000 operations per second is designed for printing presses and all types of labelling and sensing registration marks on packaging material. However its versatility opens up a much wider range of industrial applications.

The electronic design includes a solid-state emitter and receiver that allows the sort of colour mark resolution once only possible with incandescent systems. The R55 solid state light source can detect all colours found in contemporary print jobs even on extremely low contrast mark such as 20% yellow ink on newsprint.

The R55 has a response time of only 50us and can therefore fulfil the fastest requirements for users with high-speed production lines and web offset presses. The speed allows smaller colour marks to achieve the required throughput. In some cases colour marks can be eliminated using an “eye spot” on the package instead. It also includes a built-in 50ms delay and one-shot logic to allow an interface with slower input devices such as PLCs.

An advanced LED moving bar graph display indicates the contrast level between the colour mark and the background. It also indicates the sensor switch point making setup fast and easy. The sensitivity can be adjusted using a 15-turn knob. It works for all applications without the need to switch between multi-coloured LEDs. But when scanning difficult colour combinations new high power green LEDs are used which give a greater range of sensing contrast compared with red or blue.

The R55 has high tolerance to web flutter or other situations where there is a slight variation in the target distance. This is achieved by a focal point of 10mm and a depth of field of +/-3mm. The built-in analogue output enables the R55 to become a sensitive instrument that can measure surface brightness and texture consistency and perform colour recognition and surface mapping.

The R55 is designed to withstand impact and severe environmental conditions. It is also leak-proof and meets IP67 and NEMA6 standards. Rugged input and output circuitry prevents damage from high voltage transients or reverse polarity and provides noise interference immunity. Outputs are protected against stray pulses at switch-on as well as continuous overload at short circuits.

• MTE Turck
• George Perkins
• 01702 525186

September 1998

Audi is now well placed to record real-time corrosion effects, thanks to Weiss Technik’s all-plastic environmental testing chamber

Asked by Audi to build an all-plastic corrosion test chamber, Weiss Technik’s construction is a two-chamber facility which can record corrosion patterns of car suspensions under mechanical stress (with temperature, torsion, vibration and spray). The chamber was also required to include a dynamic road simulation system with active, moveable actuators.

The objective was to test complete vehicle suspensions under real conditions. The call for an entirely plastic chamber was been dictated by the need for a neutral system in which there is no possibility of false readings resulting from the corrosion of, or other chemical reactions with, the chamber itself.

With the completion and installation of the chamber, Audi is now well placed to record real-time corrosion effects that occur while a mechanical stress is applied. These corrosive effects were previously unknown. New designs can now be undertaken with full data detailing the results of higher corrosion levels of cars and components under test, which ultimately results in a better product for the consumer.

All chamber inner test space is constructed from a special plastic able to withstand temperatures from -30 to +130degC. All internal components, such as fans and spray devices, are made of plastics, while the conventional internal units, such as the air handling unit, are now all external.

Metal heat exchanger

One of the largest problems to be overcome was the construction of the metal heat exchanger. Of course, metal has superior thermal properties, but traditional construction elements, such as aluminium, copper and stainless steel, are the highest contributors to secondary corrosion effects. And so a pumped, indirect conditioning system was developed to remove the need for an evaporator and refrigeration system. Another departure from current practice in the new chamber is the use of real-time testing incorporating high and low temperature tests with humidity. Historically, tests have been accelerated at high temperatures, but real-time testing is required to combine correctly all effects for all parameters.

A lightning conductor is required inside the facility to cope with the high voltage discharge caused by static.

The facility comprises two chambers of 10 and 14m?, for which Weiss Technik developed special seals to allow positioning of the moveable actuators of the dynamic road simulation system.

• Weiss Technik

February 2000

ROBERT WORRALL of Encoder Technology explains tells us why the Inductcoder sensor enjoys hostile environments

Based on the principle of magnetic induction, Inductcoder from Encoder Technology is a totally original sensor which offers significant benefits. Excellent repeatability, high resolution, high accuracy and quick response are the principal characteristics of this non-contact sensor, which could prove a particularly popular choice for applications in hostile environments. it is also exceptionally compact, light and attractively priced – indeed, it is now on special offer!

The development has resulted from sponsorship and support from the Government and from major names in the engineering industry. Now available in the UK, Inductcoder offers a serious challenge to existing position sensor technology and has already been adopted by some of the world’s leading machinery and systems manufacturers.

Typically, an absolute resolution of 220 (ie 20 bit) can be achieved with an ultra-small rotary Inductcoder sensor of only 10mm diameter! Such a device is not only extremely rugged, but is also highly effective.

Inductcoder is a digital absolute system which comprises a detecting element – a combination of magnetic coil and ferromagnetic material – and a conversion element. This converts mechanical deviation to the phase difference between the input and output signals and establishes position by measuring time.

This position data output is refreshed at every scan

(10-4s) and is interpolated further up to 10-4s x 1/128 to provide an even faster response.

Thanks to the phase difference detecting system, the relationship between amplitude and cable length does not need to be considered. Accordingly, Inductcoder has good repeatability. Minimal temperature drift is assured as compensation for any fluctuation is automatic and as the sensor uses an AC magnetic circuit, there is no hysteresis.

This unique device may be specified to suit a wide range of applications, including the control of hydraulic and pneumatic systems. Automated semiconductor production is also a prime market for the new sensor. As its detecting element consists only of magnetic coils, Inductcoder is highly resistant to vibration, shock, oil, dust and extremes of temperature.

Options include rotary, linear, wire, stroke detection, linear gauge and strain gauge types. There is an analogue output (0 to 10V, 4 to 20mA) and digital output, including parallel and series – RS232C, RS422 and Canbus. An incremental and absolute encoder high resolution signal is also available. Intelligent outputs for velocity, acceleration, multi-switch and diagnostic signal may also be specified.

• Encoder Technology

November 1999

Whether it be in the fields of measurement technology, precision tools, plant machinery or control, often the most important thing is to monitor horizontal measurements or measure angles. So many engineers have a need to measure angles of inclination with absolute accuracy.

Conductive inclination sensors are based on the idea that, when electrodes are mounted in a planar position on a substrate, one of the factors influencing the measurement of the electrolytic conductivity of a fluid is the height of the surface of the liquid above the electrodes.

Electrodes are mounted parallel to the axis of the tilt of the sensor on the bottom of an electrolyte chamber, which is partially filled with an electrically conductive liquid. When an alternating voltage is passed between two electrodes, a current flows through the liquid in the form of a stray (dispersed) field.

By tilting the sensor – and thereby reducing the level of the liquid – it is possible to confine this stray fields and, given a constant specific conductivity of the electrolyte, a resistance is formed which is a function of the liquid level.

With the pairs of electrodes arranged to the left and right at the bottom of the sensor cell with respect to the axis of tilt, an angle of inclination can be derived.

The particular advantage of this recently-patented measurement technique is that, by virtue of positioning all the electrodes on a level plane, the measurement of inclination does not depend on the different degrees of wetness of the electrodes, but is a function solely of the volume. The influence of temperature can be eliminated, making it unnecessary to measure the ambient temperature.

The technique is extremely accurate and is reproducible. Modern production methods are used to manufacture the cells. Planar microstructuring techniques produce extremely precise platinum electrode geometries and this contributes to the reliability of the data. The compact, heavy-duty measuring cells are manufactured to IP65 protection. A ceramic housing for the electrolyte is hermetically sealed by a glass-solder connection, guaranteeing a seal which is proof to gas and moisture.

The system, which is manufactured by FRABA Sensorsysteme has a CAN-Bus Interface. Both CAN specifications (standard 11 bit and extended 29 bit) are supported. A 16-bit data and address bus between CAN and microcontroller provides a very fast data transfer, so that the encoder position is available for the CAN-Bus within 10aes. A flash EPROM means that software can be customised for individual applications and that the data is stored permanently in non-volatile form. The angular encoder can send or receive 15 parameters with different identifiers.

• Litton Precision Industries
• Tel: 016284 486060
• Fax: 016284 472438
• Contact: Bill Pearce

May 1996

Roy Moffatt, Managing Director of Variohm Components, explains the basics of the cable extension transducer and how the CET originally came about.

It is possible to deploy one or more methods to measure position on machines or equipment. Cable extension transducers (CETs) are just one of these. They are used to measure the movement and displacement of objects. The body of the transducer is mounted to a fixed surface and the stainless steel cable attached to the moveable object. As the object moves, the transducer produces an electrical signal proportional to the cable’s linear extension or velocity for display, recording or feedback to a controller.

Inside the Celesco industrial grade design, a stainless steel cable is wound on a precisely machined cylindrical spool of constant diameter. This turns as the cable reels and unreels. To maintain tension, a spring is coupled to the spool. The spool is coupled to the shaft of a rotational sensor (an encoder or potentiometer). As the transducer cable extends along the movable object, it causes the spool and sensor shafts to rotate. The rotating shaft creates an electrical signal proportional to the linear extension of the cable or its velocity. The signal is in pulses per unit of distance of cable displacement for an encoder and volts per unit of distance of cable displacement for a potentiometer.

Cables made of materials other than stainless steel, including synthetics, do exist, but these are not so reliable, because they are more elastic and have higher coefficients of expansion. The cable guide (or exit point from the CET) is often via a hole bored into a self-lubricating plastic unit. These are least expensive to buy, but paradoxically, seem to perform the best. They are simple to install and, with a reading accuracy of better than 0.01%, they offer better precision than any other sensor. Cable length is usually up to 2.5m, but for special applications can be increased up to six times that length.

The CET was brought about by a specific need. In the early days of aircraft engineering, before computers were powerful enough to undertake structural calculations, a method was required to measure the movement of the wings along their length when they were jacked up hydraulically to the extreme in order to pinpoint the critical positions on the airframe.

With the aircraft body held in a fixed position, a number of CETs were fixed to the hangar roof in several places along the wing length, their cables were extended downwards and secured to the top of the wings. When jacked from below, the amount of wing flexing can be measured accurately, hopefully with potential weak points spotted.

Although originally developed for the aircraft industry, they are now found in a multitude of engineering applications.

A short brochure is available free of charge to aid the designer and engineer in selecting the right cable extension transducer for the job.

• Variohm Components
• Roy Moffatt
• Tel: 01296 770341

November 1997