The Sensor + Test Exhibition at Nurnberg, 2008

The Sensor + Test Exhibition in Nurnberg featured many of the normal industrial sensors seen in UK exhibitions, so this report concentrates on some of the developments seen with optical sensors.

Many of these were directed at gas analysers, as have been reported before.


PAS-Tech Gmbh from Hamburg featured their Photo-Acoustic Spectroscopy (PAS) systems , which uses a diode laser to excite the molecules of low concentrations of contaminant gases (dipoles).

The difference between the PAS system and conventional spectroscopy techniques is that PAS-Tech use the acoustic or pressure waves produced by that vibration to detect the small concentration of the contaminant.

Basically the system uses a microphone to pick these signals out.

PAS-Tech was founded only in 2002, but has an impressive array of medicinal and industrial applications, offering gas sensitivity down to 0.001ppm: see

* MKS.

MKS is a US origin company well known for mass flow controllers and systems, although they are not yet sending information to Processingtalk.

However they also offer a more conventional FTIR based gas analyzer range: the MultiGas 2030-HS is a high resolution gas analyzer designed to monitor automobile, diesel and catalyst combustion exhaust at 5 Hz sampling frequencies.

This can monitor 20 gases or more, simultaneously, at this sampling rate.

MKS produce several residual gas analysers for monitoring anything left over from CVD processes, etching or ion implantation systems.

See MKS on

* HBM.

HBM are one of the major strain gauge manufacturers in the world, producing over 5Million gauges a year, and a lot of associated equipment.

At Sensor + Test 2008 they showed their recent fibre-optic developments in strain gauge sensors.

Basically the optical fibre is treated to create a Bragg grating in the section of the fibre that is to be strained.

This section is provided with a carrier that enables the sensor to be bonded to the substrate or test piece in exactly the same way as a conventional strain gauge.

When the fibre is then strained, or stretched, the spacing in the Bragg grating is also stretched.

Laser light transmitted down the fibre is reflected by the Bragg grating at a specific frequency where the wavelength is equivalent to the grating spacing: by tuning the laser frequency, for example over the range 1510-1590 nanometres, the position of the peak of the reflected power gives a measure of the grating width.

The typical width of the peak to be measured might be 0.2nm, so several, say up to 10 peaks, can be monitored by one swept frequency source.

This means that a single optical fibre can carry 10 separate Bragg gratings, making one fibre monitor 10 strain points: See

HBM have developed the electronic units to monitor these different peaks, and can even offer combined optical/electrical strain gauge monitoring systems.

They are building operational sensors for commercial use: tests have shown the fibre-optic cable to easily monitor large strains, such as 7500 um/m, without any hysteresis or ageing, over 2500 cycles (when a conventional strain gauge lasted 100 cycles only): the operational life is expected to exceed 10Million cycles.

This makes the technique useful for monitoring composite materials, plastics or carbon fibre constructions, for example in aircraft components.

The optical strain sensors have also been used on bridge structures, such as stone bridges, and metal bridges: the fast response time allows such sensors to monitor the flexing of the bridges when trains pass over them at different speeds, accelerations etc, turning the sensors into low frequency vibration or flex sensors.

In such outdoor situations there is a possible need for temperature compensation of the optical fibre expansion, or alternatively a second optical sensor, not subjected to a strain, is positioned next to the strained sensor, to provide the zero reference.

But if the flexing amplitude is the only measurement of interest the zero line is irrelevant.


Not quite optical, Sonotec, from Halle near Leipzig, presented their multiple ultrasonic products for through the pipe wall monitoring of liquid level, whether chemical, pharmaceutical or liquefied gases, leakage detection, pipe-cleaning Pig position monitoring, pump protection, bubble detection in liquids and so on.

For the applications you cannot do with optics, Sonotec maybe can do them with ultrasonics:


At EasyFairs Solids this year, Minsterport in the UK showed the Rembe particulates flowmeter, able to monitor powder flows to 0.25% accuracy: Rembe was again at Sensor + Test, showing off the same C-Lever flowmeter, which has successfully been applied to chalk, titanium dioxide, cereals, pigments, sunflower seeds and dried sludge – monitoring flows between 50 and 2000kg/h, on particle sizes up to 10mm.

OK its not quite optical, but you can see how it works, and it provides an electronic measurement of the flow.