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General Information
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This page is intended to provide information about what SENSOR LINE is occupied with as well as some valuable explanations in order to understand what we are talking about, what can be done with our products and why it can thus be done better rather than by using different methods. This page is also meant to serve as an "FAQ" page, but moreover answering questions which – although important – are seldom asked. If you want to be informed more thoroughly, just follow the links; we are trying to guide you to all related stuff – at least at this web site.
Fiber Optic Sensors – Why?
Fiber optic sensors have properties that make them superior to sensors with other working principles:
- They are insensitive to electromagnetic interference
- They do not cause electromagnetic interference
- They are durable and chemically inert
- They are very, very fast
- They are extremely safe, even at dangerous places
Many of the sensors in today's measuring equipment work in some electrical manner, either changing their electrical properties (e.g. Resistance, Capacitance etc.) or generating electrical quantities (voltage, current) under the influence of the physical quantity to be measured. There are several main reasons for this. First, most applications require some signal processing, this processing is most easily done with electrical methods, and so it is convenient if the quantities to be processed are already electrical ones. Second, there is often some distance between the measuring site and the place where the measuring signal is to be registered or displayed, so there is some signal transmission necessary, and this is also most conveniently done electrically. Therefore also many of the sensors with a not primarily electrical working principle are accomplished by some means to convert their non-electrical output quantity to some electrical one, and they can also be considered to be electrical sensors.
But there are some disadvantages of electricity. It interacts with electromagnetic fields, causing them and being influenced by them. So electric devices can disturb each other, and they do whenever they are given a chance. Electricity can cause heat and sparks. Both are very undesirable at places where e.g. fuel or even dynamics are present. Furthermore, electricity always requires metal. Metal corrodes, the cheaper it is, the faster. Its use is also generally difficult at places where there is much electricity. And it tends to attract one of the less pleasant electrical phenomena – lightning.
For measuring purposes the main advantages of optical fibers arise from the absence of two things:
- There is no electricity!
- There is no metal!
Thus, with optical fibers all the above mentioned disadvantages of electricity are avoided. There is absolutely no interaction with electromagnetic fields, and there is nothing comparable instead. Optical fibers can be used together with any kind of electrical and also with any kind of fiber optic equipment. The energy needed to carry signals along an optical fiber is much too small to be able to cause any danger – regardless of what kind. Optical fibers are made of glass or plastic – materials that are very durable and chemically inert. Those materials are also good isolators, so no problems arise in the presence of high voltages and/or currents. And there is no way for lightning to distinguish an optical fiber from the rest of the universe.
Optical fibers still have a third main advantage which is sometimes also important for measuring purposes:
The concept "speed" in conjunction with a signal transmission link has two aspects: First, how long it takes for a signal to be transmitted from the input to the output, second, how quickly the output signal can change its level when the input signal does. From both points of view optical fibers are exceptionally fast. The speed of a signal travelling along an optical fiber is approximately 2/3 of vacuum light speed – fast enough for most purposes. But the second aspect – technically called "bandwidth" – is much more important: It determines how many bits of information can be transmitted per second. From this point of view optical fibers are completely superior to electrical wires, because due to their lack of interaction with electromagnetic fields or something comparable they also don't have anything comparable to the capacitance of electrical cables. This fact has made optical fibers the fastest and therefore in the end the cheapest data transmission medium currently available.
For measuring purposes extreme speed is seldom that important, and so fiber optic sensors can not be considered to be cheaper than electrical ones. In fact the price per meter of optical cable is still higher than that of wire. Also, signal processing can not be done optically (yet), therefore measuring systems utilizing fiber optic sensors must always comprise an optical/electrical interface which systems with electrical sensors don't need. And unfortunately optical fibers can not be soldered or connected with screw clips. They must be exactly terminated and aligned before they can be connected at all, either by splicing or by using costly fiber connectors.
Fiber optics is not (not yet?) a technology for "penny sensors", e.g. for consumer goods. It is a means to obtain mainly safe sensors compatible with almost everything: Other equipment, regardless whether sensible or disturbing, adverse environmental conditions, dangerous substances and much more. Fiber optics is also a way to set up extremely fast measuring systems, especially when the measuring site is remote from a place where extensive measures for speed are possible. For such purposes fiber optic sensors are – even in terms of price – a superior alternative to concurrent technologies. |
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