Sensor definition：
National standard GB7665-87 to under the sensor definition is: can feel the stipulation to survey and defers to the certain rule to transform with the signal component or the installment, usually is composed by the sensitive unit and the transition element .
The sensor is one kind of detector set, can feel the information which surveys, and can examine the information which feels, transforms into the electrical signal according to the certain rule or other needs the form the information output, satisfies request and so on information transmission, processing, memory, demonstration, recording and control. It is the realization automatic detection and the automatic control most important link .
Sensor basic characteristic :
sensor static characteristic
The sensor static characteristic is refers to the static input signal, between the sensor output and the input value has the reciprocity. Because by now input value and output all with time irrelevant, therefore between them the relations, namely the sensor static characteristic may use not to contain the time variable the algebraic equation, or to the input value makes the x-coordinate, the output which if corresponds does the characteristic curve which the y-coordinate draws to describe. The attribute sensor static characteristic main parameter includes: The linearity, the sensitivity, the resolving power and are sluggish and so on.
The so-called dynamic characteristic, is refers to the sensor when the input change, its output characteristic. In the practical work, the sensor dynamic responses. This is because the sensor easily obtains to the standard input signal response with the experimental technique, and it has the certain relations to the standard input signal response with it to the arbitrary input response between, often had known former can estimate latter. The most commonly used standard input signal has the step to leap the signal and the sine signal two kinds, therefore the sensor dynamic characteristic also commonly used step leap response and the frequency response expressed.
Sensor linear
In the usual situation, the sensor actual static characteristic output is the strip curve but the non- straight line. In the practical work, for enable the measuring appliance to have the even scale division the reading, the commonly used fitting straight line approximately represents the actual characteristic curve, linear (non-linear error) is a this approximate degree performance index. The fitting straight line selection has the many kinds of methods. If takes the zero input and the full measuring range output connected theory straight line the fitting straight line; Or with the characteristic curve in each deviation for the smallest theory straight line took the fitting straight line, this fitting straight line is called the least squares method fitting straight line.
The sensitivity is refers to the sensor in the stable state working condition output change y to the input value change x ratio. It is outputs an input characteristic curve the slope. If between the sensor output and the input reveals the linear relations, then sensitivity S is a constant. Otherwise, it will change along with the input value change.
The sensitivity dimension is the output, the input value ratio of dimension. For example, some position transmitter, changes 1mm when the displacement, the output voltage change is 200mV, then its sensitivity should express is 200mV/mm. When the sensor output, the input value dimension is same, the sensitivity may understand for the enlargement factor. The high sensitivity, may obtain the higher measuring accuracy. But sensitivity higher, survey scope narrower, the stability often is also worse.
Sensor resolving power
The resolving power is refers to the sensor possibly to feel the smallest change ability which surveys. In other words, if input value from some non-zero value slow diastrophism. When the input change value has not surpassed some value, the sensor output cannot change, namely the sensor input value change is regarding this cannot distinguish. Only has when the input value change surpasses the resolving power, its output only then can change. The usual sensor each resolving power is not certainly same in the full measuring range scope, therefore in the commonly used full measuring range can cause the output to have the step jumps in the input value most sweeping change value to take the weight resolving power the target. Above target if with full measuring range minute ratio expression, then is called the resolution.
The sensor is sluggish especially
The sluggish characteristic attribute sensor in (is increasing and reverse (input value to input value) reduces) the travelling schedule to output - the input characteristic curve inconsistent degree, passes between the commonly used these two curves biggest difference value MAX and the full measuring range outputs F·S the percentage to indicate, is sluggish may create by the sensor internal component existence energy absorption.
Sensor classification: At present still did not have a unified classified method to the sensor, but quite commonly used had the following three kinds:
1. according to the sensor physical quantity classification, may divide into sensor and so on displacement, strength, speed, temperature, current capacity, gas ingredient.
2 according to the sensor principle of work classification, may divide into sensor and so on resistance, electric capacity, inductance, voltage, Hall, photoelectricity, diffraction grating thermo-element.
3 according to the sensor output signal nature classification, may divide into: The output ("1" and "0" or "opens" and "pass" for the switch quantity) the switch sensor; Output for simulation sensor; Output for pulse or code numeral sensor.
Resistance type sensor definition and type:
Resistance type sensor
The resistance type sensor is surveyed, like the displacement, the deformation, the strength, the acceleration, the humidity, the temperature and so on these physical quantity transformation types become the resistance value such one kind of component. Mainly has the resistance to be supposed the variant, the pressure anti-, the thermal resistance, hot sensitive, to be mad sensitive, wet is sensitive and so on the resistance type
resistance should the variant sensor
In the sensor resistance strain gauge has the metal the strain effect, namely has the mechanical deformation under the exogenic process, thus causes the resistance value to have the corresponding change along with it. The resistance strain gauge mainly has the metal and the semiconductor two kinds, the metal strain gauge has the tinsel type, the foil type, the division. The semiconductor strain gauge has the sensitivity high (usually is silk type, foil -like several dozens times), the crosswise effect is small and so on the merit.
Presses the anti- sensor
Presses the anti- sensor is according to the semiconducting material pressure anti- effect in on the semiconducting material substrate the component which makes after the proliferation resistance. Its substrate may directly take the survey part, the proliferation resistance inscribes the electric bridge form in the substrate. When the substrate receives the exogenic process has the deformation, various resistance values change, the electric bridge can have the corresponding balanced output. Serves as presses the anti- sensor the substrate (or called diaphragm) the material mainly for the silicon chip and, the silicon chip the silicon which makes for the sensitive material presses the anti- sensor more and more to be valued people's, in particular the gauge pressure and the speed solid state presses the anti- sensor application to be most common. The thermal resistance sensor thermal resistance sensor mainly is changes this characteristic using the resistance value along with the temperature change to survey the temperature and with the temperature related parameter. In the temperature examination precision request quite high situation, this kind of sensor quite is suitable. At present the more widespread thermal resistance material for the platinum, the copper, the nickel and so on, they has the resistance temperature coefficient in a big way, the linearity good, the performance is stable, the application temperature scope width, processes and so on the characteristic easily. Uses in to survey in -200 ℃ ~ +500 ℃ scopes thetemperatures.
The sensor selects the principle base
Sensor in the principle and the structure infinite variety, how acts according to the concrete survey goal, the survey object as well as the survey environment reasonably selects the sensor, the question which is when carries on some quantity survey first must solve. After sensor determination, also was allowed to determine with it necessary measuring technique and the measurement equipment. The measurement result success or failure, is decided in the very great degree to the sensor selects whether reasonably.
1 the basis surveys the object and the survey environment determined the sensor
The type must carry on the concrete surveying work, first must consider uses what kind of principle the sensor, after this need analyzes the various factor can determine. Because, even if is the survey identical physical quantity, also has the many kinds of principles the sensor to be possible to supply to select, which one kind of principle sensor is more appropriate, below then needs according to survey the characteristic and the sensor exploitation conditions consider some concrete questions: Measuring range size; Is measured the position to the sensor volume request; The survey way for the contact type also is the non- contact type; The signal draws out the method, wired or right and wrong contact survey; The sensor origin, the domestic product or imports, whether does the price withstand, or independently develops. After consideration above question can determine selects what kind of type the sensor, then considers the sensor again the concrete performance index.
2 the sensitivity choice is usual
In the sensor linear scope, hoped the sensor keenly goes. Because only the sensitivity high time, with is surveyed the change correspondence the output signal value only then quite to be big, is advantageous to the signal processing. But must pay attention, sensor sensitivity high, with is surveyed the ambient noise which has nothing to do with to be also easy to mix in, also can enlarge by the amplifying system, affects the measuring accuracy. Therefore, requests sensor itself to be supposed to have a higher signal to noise ratio, a reduction harasses the signal from the outside introduction factory. The sensor sensitivity is in the right way tropism. When by the survey is the single vector, moreover is higher to its directive request, then should choose other direction sensitivity small sensors; If by the survey is the multi-dimensional vector, then requests the sensor alternately keenly to go past slightly is better.
3 the frequency-response characteristic
sensor frequency-response characteristic had decided frequency range which surveys, must maintain the not distorted survey condition in the permission frequency range, in fact the sensor response always has surely retards, the hope delay time shorter is better. Sensor frequency response high, observable signalling frequency scope on width, but because comes under the structure characteristic influence, mechanical system inertia bigger, because has the frequency low sensor observable signal the frequency to be lower. In the dynamic survey, should act according to the signal the characteristic (stable state, transient state, is stochastic and so on) the response characteristic, in order to avoid has the error which goes too far.
4 he linear scope
sensor linear scope is refers outputs and inputs the direct ratio the scope. To theoretically says, in this scope, sensitivity maintenance definite value. Sensor linear scope wider, then its measuring range is bigger, and can guarantee the certain measuring accuracy. When chooses the sensor, when the sensor type determined later first will have to look whether its measuring range will answer the purpose. But in fact, any sensor all cannot guarantee the absolute linearity, its linear also is relative. When requests the measuring accuracy quite is low, in the certain scope, may a non-linear erroneous smaller sensor approximately regard as linearly, this can bring enormous convenient to the survey.
5 the stable
sensor uses period of time, its performance maintains the invariable ability to be called the stability. Affects the sensor long-term stability factor besides the sensor itself structure, mainly is the sensor use environment. Therefore, must enable the sensor to have the good stability, the sensor must have to have the stronger environment adaptiveness. In chooses in front of the sensor, should carry on the investigation to its use environment, and according to the concrete use environment choice appropriate sensor, or takes the suitable measure, reduces the environment the influence. The sensor stability has the quota target, after surpasses the lifetime, should recarry on before the use demarcates, determined sensor performance whether does change. In certain requests the sensor to be able the situation which the long-term use but also cannot easily replace or demarcate, selects the sensor stability request is stricter, must be able to undergo the long time the test
6 the precision
precision is a sensor important performance index, it is relates the entire measurement system measuring accuracy an important link. The sensor essence goes past high, its price is more expensive, therefore, sensor precision so long as satisfies the entire measurement system the precision request to be allowed, does not need to elect excessively high. Like this may in satisfy the identical survey goal in many sensors to choose quite cheap and the simple sensor. If the survey goal is the qualitative analysis, selects the repetition precision high sensor then, not suitably selects the absolute size precision high; If is for the quantitative analysis, must obtain the precise observed value, must select the sensor which the precision class can answer the purpose.
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