Of course, the term comes from Latin, but you may already know it. Fully complements the possible original meaning of 'perception'. It is more about the 'senses' of a control system than that their results always have a 'sense'. At best, they simply do what they were designed for.

One should beware of a mystification of technology. Technical parts are no disobedient childs with a soul. Although relieving, but plenty out of place. The Brockhaus simply describes the sensor as a 'reading recorder and refers first of all to its small size which is favorable for practical use and low price thanks to mass production. At times, other branches of industry with far fewer large quantities of money are doing their bit.

There are large numbers of them, which makes it difficult to assign them to certain fields of activity. Often there are listed the not very strongly limited activities of the sensor, but the various functions of the overall system. The range of action of a sensor is actually clearly defined, irregular action in turn extremely undesirable. The implementation of physical, chemical or electrical signals should always lead to the same results in terms of its lifetime.

This is called reproducibility, a term that otherwise refers to scientific work. Something explored should possibly be reproducable by others without great preconditions. For the sensor it is much easier. For example, it should turn a certain temperature into the same voltage signal over years, whether new or shortly before its end, whether installed in the vehicle or in a water bath.

Of course, there are prerequisites for this, for example, that of an always equal voltage supply, defined as a voltage difference between plus and minus, producing a value that is not always reliable relative to the mass of the bodywork. Therefore, more recently, the additional ground cable for generating a so-called 'reference voltage'. But what is it really?

It would have to be understandable that for measuring sensors need a secure base, right? For the length measurement, the original meter in Paris was replaced by the wavelength at the cesium atom, although this was already made of very durable platinum. A reference in everyday life is a kind of more objective source of judgment. Ask the person you trust.

It is therefore based on a voltage and usually has only the 5 volts. Now divide the realistic range of 4.8 V by the 160°C between -40°C and +120°C, then the fluctuation of the output voltage of only 0.3 V means that the temperature difference is already 10°C. Do you now realize how important a constantly stable basic voltage, which is largely independent of external influences and resulting currents, in short term a 'reference voltage'?

Very stable reference voltages are made by semiconductor elements and thereby not too high currents are assumed. At the same time, independence from temperature is very important. One way to do this: couple components with, for example, NTC and PTC properties. Semiconductor elements are now also integrated in the sensors.

Sometimes is differentiated not always in an understandable manner between passive and active components, the latter are often referred to because of their additional power supply. This definition is not used extensively, but we want to stick to it for the rest of this book. We will use the terms sparingly anyway, as well as the 'intelligent' sensor. We simply for example discribe its ability to be able to communicate with the control unit.

Sensors are to be found mostly not very easy and they are not always unique. Combinations are possible, for example, with those that perform other measurements. In the past, two could work equally well in one housing. But this has stopped since the signals are either even given by the sensors themselves or by their control units on a bus system, such as CAN or LIN.

Previously, there was a fixed substitute value when a signal failed. But how should that eg go with the engine temperature? If the temperature represented by this value is too high, the cold engine may not start, and if it is too low, it will never enter the by lambda controlled area. Therefore, the control unit accesses the outputs of other sensors, here eg the temperature of the intake air manifold and perhaps calculates an approximately matching of the coolant over the time of the engine run.