Sensor+Test 2018

••• 10••• Innovationen Real-time layer thickness measurement Compact and cost-efficient: terahertz as a key technology for non-destructive material testing A research team led by Björn Globisch, head of the terahertz research group at Fraunhofer HHI, has successfully developed a measuring device that replaces the previously used femtosecond pulse laser with compact contin- uous-wave laser technology. The fact that this continuous-wave measurement system is capa- ble of eight measurements per second is key to allow real-time measurements without the use of a pulsed laser for the first time. The principle employed by the Fraunhofer HHI to generate tera- hertz radiation is based on an op- toelectronic process. Using a spe- cial semiconductor component, the beat of two continuous-wave lasers is converted into terahertz radiation, which corresponds ex- actly to the difference frequency of the two lasers. The lack of sig- nificant success of terahertz tech- nology in the past is largely due to the properties of the semiconduc- tors used. These properties could initially only be achieved with ma- terials that required illumination at a wavelength of 800 nanom- eters. This rather exotic wave- length means both the lasers and the optical components of the terahertz system are much too expensive and not robust enough for industrial applications. Fraunhofer HHI is using lasers that can be adjusted extremely fast (Finisar WaveSource) and by modifying electronics, data cap- ture and algorithms to accom- modate the high speeds required. This combination has increased measurement speeds by a factor of 160 compared to previous sys- tems. This has made it possible for the first time to conduct material testing in real-time with continu- ous-wave terahertz systems. Inspection of paints and coatings is an important application of non-contact terahertz measure- ment technologies. Here, layer thickness measurement makes up a significant part of quality assur- ance and production monitoring. T-Sweeper is a cost-efficient and compact measurement system that conducts real-time measurements of the thickness of multi-layer systems for the first time. Photo: Fraunhofer HHI Continued from page 1 Anzeige Non-DepletingOxygenSensorTechnologyVersusElectrochemicalOxygenSensingTechnology 1. Could you please explain the basic theory of how the two Oxy- gen Sensor technologies work? The LuminOx series is based on a proprietary luminescence quench- ing technology. They employ the properties of a specific dye which changes its lu- minescence behaviour depending upon the amount of oxygen around it. A built in LED excites this dye, causing it to produce light (lumi- nescence) and the O2 in the envi- ronment “quenches” this excitation. The rate of decay of luminescence, which is inversely proportional to the oxygen level, is interpreted and linearised by the sensor’s firmware and so allows the ppO 2 to be cal- culated. The LuminOx sensor has built in temperature and barometric pres- sure compensation. A barometric pressure sensor measurement along with the ppO 2 measurement allows an oxygen concentration (O 2 %) val- ue to be calculated. LuminOx is a digital sensor with a USART out- put, meaning there is no need for signal conditioning circuitry. The sensor can serially communicate the values of O 2 %, ppO 2 , baromet- ric pressure, internal temperature and sensor status. 2. How does this differ from Electrochemical Oxygen Sen- sors? Electrochemical sensors are com- pletely different. This type of de- vice comprises a self-powered, galvanic cell that operates like a metal/air battery. The cell constantly depletes in the presence of oxygen and the lifetime can be re- stricted by components like the liquid electrolyte and a consumable lead anode. As it is a chemical reaction using an oxidisa- tion process, some of the oxygen being measured is actually consumed. Electrochemical sensors are more restricted in regards to en- vironmental sensitivities and ap- plying them can sometimes require a bit of specialist knowledge. 3. What are the advantages of a non-depleting Oxygen Sensor? The LuminOx sensor is typically positioned against electrochemical sensors. LuminOx is able to offer a number of advantages over what has been available in the oxygen sensor market. Lifetime. LuminOx is a non-deplet- ing sensor with a 5-year life. Electrochemical sensors typically start to deplete as soon as they are exposed to any O 2 , whether a measurement is being taken or not. T h i s d e - pletion is sensitive to several environmental factors such as temperature, pressure and other gases present in the atmos- phere, making total sensor lifetime difficult to predict. Minimal cross sensitivity. The for- mulation of LuminOx is highly se- lective to oxygen. Electrochemical sensors are cross- sensitive to numerous gases. This could result in significant positive or negative measurement errors. This limits the environment and ultimately the number of markets such a product can be sold into. No external signal conditioning circuitry required. LuminOx is a digital sensor that offers multi- ple output parameters. Electrochemical sensors require an amplification stage to obtain a usable signal that is then typical- ly processed by a micro- processor. LuminOx just connects to the micro via two UART pins. Every LuminOx is fac- tory calibrated across the operating temperature and oxygen pressure ranges. Electrochemical sensor typically need the user to manage tempera- ture and pressure compensation. LuminOx is REACH and RoHS compliant To this day, exemptions in the RoHS legislation allow electro- chemical sensors to contain harm- ful materials like lead (Pb). This situation cannot continue forever and these sensors will have to be outlawed eventually. LuminOx was designed to be RoHS/REACH from the start. 4. What are the reasons a cus- tomer may replace their Elec- trochemical Sensor with an SST O 2 sensor? Many of the customers approach- ing SST for LuminOx are already familiar with oxygen sensors. Of- ten the customer will have been limited to using an electrochemi- cal cell in the past. A lack of op- tions in technology has dictated their design, how the product has to be used and the markets avail- able to them. Primarily, these customers are in- terested in improving sensor life- time. Customer comments indicate a typical figure of approx. 18-24 months (if not less) before need- ing to replace an electrochemical sensor. Cross sensitivity to other gases such as helium or background car- bon dioxide has proven problematic when out in the field and has at- tracted customers to SST. Customers designing new products take advantage of its easy to use nature. LuminOx removes some of the traditional design considera- tions and correction factors needed with electrochemical sensors. Hall 1 · Booth 513