Because sensor application is very wide, the type is varied, there is application in all trades and professions. Accordingly, basically introduce the type selecting of the oscillatory sensor that is used at oscillatory test here. By measure oscillatory parameter classification to be able to divide it is 3 kinds big: Displacement sensor, speed sensor and acceleration sensor (also call accelerometer) . Generally speaking, displacement sensor applies to low frequency to measure, speed sensor applies to intermediate frequency to measure, acceleration sensor is applied to in high frequency measure. Because acceleration sensor has noisy range of manufacturing technology maturity, frequency wide, dynamic limits big, installation is convenient wait for a characteristic, apply in oscillatory test consequently the widest. Accordingly, basically introduce the type selecting of acceleration sensor here.

 

Main content includes the article:

 

1.Sensor classification;

 

2.Common accelerometer type;

 

3.Type selecting index;

 

4.Type selecting principle.

 

1.Sensor classification

 

Basically introduce two kinds of classification in this, one kind is active and passive, another kind is segregation and blame segregation.

 

Active sensor is to point to measure sensor translate into electric energy to measure output blame electric energy, change energy itself only, do not change the sensor of energy signal, also call energy to change sexual sensor or transducer. Consequently, drive of exterior energy source needs when this kind of sensor works, be like incentive voltage, ability works normally. Because need to undertake energy is changed, consequently, sensor interior enclosed an electron yuan parts of an apparatus, the meeting in measuring a process brings noise. This kind of sensor if ICP (also call IEPE model) acceleration spends sensor, sensor of 0 frequency acceleration.

 

Passive sensor is the sensor that points to to power source is received to be able to work normally outside needing to use, and can pass exterior get absoluteness the sources of energy. This kind of sensor does not have noise influence to surveying a system, perhaps affect very small, be like meet an emergency piece (flower) , sensor of the type that suppress report.

 

Keeping apart sensor is to point to sensor and wait for measure be apart leaves between the structure, electric current cannot be between both current. Segregation sensor departs from electric angle and photograph of the structure that be measured, like meet an emergency piece (flower) normally with be measured the structure is photograph segregation. The usual practice that sensor implementation keeps apart is in sensor bottom installed segregation parts of an apparatus, make electric current cannot current, if the graph shows gules parts of an apparatus 1 times,be segregation parts of an apparatus namely.

 

Graph sketch map of 1 segregation sensor
 

Blame segregation sensor is to point to sensor and segregation is not had between the structure that be measured, electric current can undertake between both current. This kind of sensor resembles thermocouple, certain acceleration sensor. This kind of sensor that is not segregation asks to use float land normally or keep apart ground wire, circulate in order to avoid ground contact, circulate about ground connection, read please ” the error that exists in sampling process, you affirm not all-knowing principle! ” . If sensor oneself is not kept apart, the user can use electric segregation parts of an apparatus to realize segregation by oneself, this kind of parts of an apparatus is like mica sheet, glass piece wait with epoxy resin. When measuring a structure to undertake metrical to be in what working status falls to wait for, recommend use “ to keep apart ” sensor.

 

 

Vibration measures general use accelerometer, because accelerometer has the following advantage,be: Manufacturing technology maturity, dynamic limits limits of big, frequency wide, degree of linearity good, stability tall, installation is convenient wait for a characteristic. Commonly used at in diagnostic experiment of malfunction of instrument of the mode experiment of brief summary compose, car experiment, a favourable turn coming back and oscillatory control experiment. Basically introduce the acceleration sensor of two kinds of types in this: Press sensor of electric type and ICP acceleration.

 

Press sensor of electric type acceleration: It is a kind of passive sensor, belong to inertial type sensor. Use piezocrystal, be like quartz the ” of crystal, “ piezoelectric effect that presses electric pottery and porcelain to wait: When accelerometer experiences vibration, the force that pledges gauge block is added on the component that suppress report also changes subsequently. After piezocrystal suffers force to be out of shape, its interior can produce polarization phenomenon, generate the charge with contrary symbol in two its surfaces at the same time, should be measured oscillatory frequency is far the natural frequency under accelerometer (syntonic frequency) when, criterion the change of force becomes direct ratio with the acceleration that be measured. After outside force purify, regain not electrified position afresh again, this kind of phenomenon calls ” of “ piezoelectric effect, the crystal that has ” of “ piezoelectric effect calls piezocrystal.

 

Output of the accelerometer that suppress report is charge type, reason need and charge amplifier cooperate to use, next signal is transmitted again collect appearance or with inside the collection that buy charge recuperates appearance joins directly. Charge amplifier makes negative feedback with capacitance, the does not suffer cable electric capacity basically effect in using, but can get the influence of electrostatic field. In charge amplifier, use yuan of parts of an apparatus of high quality normally, input impedance is tall, the price is consequently more expensive also, the comparison that uses commonly is little.

 

ICP acceleration sensor: Because press the output of electric type sensor,telegraphic date is faint charge, and sensor itself has very great internal resistance, reason output energy is very small, circuit is received to bring certain difficulty after this gives. For this, be defeated by sensor signal to the preamplifier of tall input impedance first normally. After alternating through impedance, charge volume is changed into voltage, next the record instrument that reexport gives sequel. Current, manufactory home already had a sensor of acceleration of the type that suppress report and preamplifier compositive the acceleration sensor that be together, namely: ICP acceleration sensor, also call IEPE acceleration sensor, went to the lavatory to use not only, and also reduced cost greatly.

 

ICP acceleration sensor because inside buy special compositive recuperation circuit, accordingly, belong to active sensor. And this circuit wants regular job to need power supply of constant current source. Current and general 24 when use collect appearance to take constant current function oneself commonly, can use with ICP sensor join directly consequently.

 

Inside buy the ICP of integrated circuit advantage is low price, interference rejection is good, but long lead is used, but the sensor of the acceleration that suppress report that its high temperature resistant, dependability outputs as charge, and dynamic limits also is restricted because of outputting the influence of voltage and bias voltage. The noise of low frequency frequency of ICP sensor basically suffers the discharge time constant of sensor to affect, because signal of this great majority is comfortable,move implement use communication coupling. About communication and dc coupling, read please ” the distinction of signal AC and DC ” one article.

 

 

The acceleration sensor of model of avery kind of has particularly appropriate application setting, accordingly, the requirement must be used according to the test when the test, choose the most appropriate acceleration sensor. When choosing accelerometer, basically mix from element of sensor function, environment, electric character 4 respects go to physical character consideration.

 

Function includes sensitivity, span, frequency the index such as noisy character, syntonic frequency, transverse effect and degree of linearity. Environmental element includes the job to temperature, temperature is answered and pound the limit to wait. Electric character includes incentive voltage and electric current, stabilization period to wait. Physical feature includes sensitive material, structural design, dimension, weight and means giving a clue.

 

Function index:

 

Span / sensitivity: Every sensor has measure range, measure the sensor with big Cheng normally, sensitivity is low, the sensor with small span, sensitivity is tall. Normally sensor outputs the upper limit of voltage to be 5V, accordingly, sensor sensitivity is the quantity of sensor to output voltage 5V greatly by what get with span. If the sensitivity of some model sensor is 50mV/g, criterion the span of this sensor is 100g. Normally ICP acceleration sensor satisfies this rule, and other type, be like sensor of 0 frequency acceleration, do not satisfy this rule. On the other hand, sensor sensitivity is taller, criterion the quality of sensor is greater, sensor output voltage is bigger, letter a confusion of voices is taller than jumping over, resolution is stronger. To checking differring structure, should choose the sensor span that matchs, normally, building bridge and exceed vibration of acceleration of structure of instrument of large scale computer to measure class to be controlled in 0.1g ～ 10g, the vibration of mechanical equipment is controlled in 10g ～ 100g.

 

Syntonic frequency: Sensor itself also is a structure, consequently, also put in natural frequency, normally, the first-order natural frequency sensor calls syntonic frequency. Sensor size is smaller, syntonic frequency is taller. The frequency of use upper limit of accelerometer depends on a syntonic frequency in frequency curve. The 1/3 that the working frequency limits of general sensor is frequency of its oneself resonance is the following.

 

Frequency noise is characteristic: The working frequency upper limit of general acceleration sensor is the 1/3 left and right sides of oneself resonance frequency. On the other hand, character of acceleration sensor low frequency is normally wronger, signal attenuation is serious, and be in high frequency paragraph of degree of linearity is poor, nonlinear the effect is serious. If pursue,the 2 frequency that are some model accelerometer ring curve, can see from inside graph, it is under 2Hz signal attenuation is serious, frequency noisy performance is poor, differ in 12KHz above degree of linearity, its resonance frequency is 38KHz about. Accordingly, the working frequency of this sensor is 12KHz the following. When choosing accelerometer, the frequency upper limit of accelerometer is tallish at be being measured oscillatory frequency of the structure can. General, the frequency limits of civil engineering structure is controlled in 0.2~1KHz, mechanical equipment is intermediate frequency paragraph, frequency limits is controlled in 0.5~5KHz. Additional, the frequency range that the installation stiffness of sensor can measure to sensor is influential also, about this, consult please ” how does sensor install ability to satisfy a test to ask, is the error the smallest? ” .

 

Graph the frequency noisy curve of 2 some accelerometer
 

Degree of linearity: Onefold sensitivity can be inputted only when be being measured as a result of sensor, accordingly, use at the description to be inside certain frequency noise limits, whether does the sensitivity of sensor satisfy the index of actual sensitivity, it is degree of linearity namely. Relative to character, in low frequency paragraph (if 5Hz is the following) , the sensitivity of sensor will be little at actual sensitivity, and be in high frequency paragraph (if be more than working frequency upper limit) , criterion sensitivity can be more than actual sensitivity. Have inter frequency only paragraph, sensitivity satisfies linear concern, if pursue,2 are shown. If sensor does not undertake metrical in linear interval, measure gotten amplitude error bigger, general requirement sensor is nonlinear

 

Transverse effect: When the vibration that measures a certain way, signal output should feel way for vibration completely, but there also is signal output in as perpendicular as this direction direction actually, this kind of effect calls transverse effect. Transverse effect sensitivity is lower, performance is better, but relative to character, sensor is put in certain transverse effect, normally nominal and transverse effect

 

Environmental element:

 

Use environment: The effect of the environmental element such as temperature, humidity, dust suffers when sensor is used. A kind of any sensor have the working temperature range of oneself, because this needs fibrous root occupies the temperature that measures bit of place actually, and environmental temperature will choose appropriate sensor. Additional, damp to checking an environment to exist, corrode and when the influencing factor such as electromagnetism field, choice sensor also should consider these factors.

 

Temperature answers: The sensitivity of sensor can get the influence of temperature, produced a change when temperature, if we return the sensitivity below use normal temperature, can give measure bring an error. If pursue,the 3 temperature that are some sensor answer a curve, can see from inside the graph, when room temperature, the sensitivity of sensor does not have deviation, but when temperature is far from room temperature, sensitivity error is bigger and bigger. Accordingly, the working temperature of sensor should answer the sensitivity in the curve to agree without the temperature of deviation with temperature.

 

Graph the temperature of 3 some accelerometer answers a curve
 

Pound the limit: The instantaneous that states sensor can be endured pounds limitation, express with peak value normally, if the concussion limit of some sensor is ±7000g Pk.

 

 

Incentive voltage / electric current: Active sensor needs to offer incentive voltage / voltaic ability works normally, like ICP sensor need offers the constant current drive of 20-30VDC incentive voltage and 2-20mA. Current data collects appearance general inside buy such power supply device, accordingly, can give ICP sensor power supply directly. But the acceleration sensor that still has a lot of other kinds, be like MEMS acceleration sensor, sensor of equilibrium type acceleration, if collect appearance to cannot offer corresponding incentive voltage / electric current, need to choose way of exterior power supply.

 

Stabilization period: To ICP sensor, because be put in discharge constant, when giving sensor power supply, the signal that sensor outputs can stabilize base line slowly from boundless far around, this time calls stabilization period. And when we are undertaking metrical, the signal that should need sensor to output undertakes metrical again after stability. Normally this time needs a few seconds only.

 

 

Sensitive data: To pressing most of electric type and ICP sensor to use quartz crystal is mixed the pottery and porcelain that suppress report serves as sensitive data. Quartz the interpose report of crystal and the temperature stability of the constant that suppress report are good, comfortable make the sensor with very wide temperature at charge for the making of sth. . The pottery and porcelain suppressing report that has piezoelectric effect is artificial complex, the primitive pottery and porcelain that suppress report does not have piezoelectric effect. Because press electric pottery and porcelain to make technology more convenient, be able to bear or endure wet, high temperature resistant wait for an advantage, most of current the sensor that suppress report uses the pottery and porcelain that suppress report to serve as sensitive data.

 

Dimension and quality: Acceleration sensor appearance is mixed with cylinder hexahedral be in the majority, and cylindroid accelerometer divides coping to give line and flank to give a clue again two kinds of means. When the over all dimension that chooses accelerometer, basically suffer the effect that installs positional space, to installing the position the space measures a place finitely, must choose appropriate sensor over all dimension. On the other hand, when selecting sensor kind, return the influence of the add quality that the weight that must consider sensor itself brings, when checking light simple structure especially, effect of sensor itself weight is distinct. The likelihood is treated measure structural total mass for, the total mass of sensor is very few, but, those who participate in vibration is not overall quality of the structure, share oscillatory that part quality however, call effective quality, right now, the total mass of sensor may be opposite the effective quality at the structure will be very great, right now the influence of add quality meets sensor apparently. Additional, when sensor is installed, the likelihood still can use tool, right now the quality of tool can exist to structural vibration amplitude influence. Oscillatory to a few cabinet and light-duty structures or when oscillatory parameter is measured on thin plate, sensor and the load of “ additional ” that secure a quality to cause may change primitive vibration of the structure, make be measured the result is invalidly thereby. Accordingly, small and light sensor should be used below this kind of circumstance, the influence of load of — of estimation accelerometer quality.

 

Ar =as*ms/(ms+ma)

 

In type, ar—— contains the structural acceleration of accelerometer to answer;

 

As—— does not contain the structural acceleration of accelerometer to answer;

 

Ms—— waits for the equivalent quality of the ” of structural “ component that installs accelerometer;

 

The quality of Ma—— accelerometer.

 

Accordingly, should notice to change the amplitude of structural vibration and frequency because of add quality, this is in large engineering construction test, not outstanding, and impact of mechanical to diminutive component is bigger, the consideration wants in checking an analysis. Does the effect that measures frequency about be opposite consult please ” how does add quality check evaluation sensor the influence of mode frequency? ” one article.

 

 

 

1.Of basis and follow-up equipment match a gender to select sensor kind, if appropriate of ICP recuperation equipment uses ICP sensor, charge recuperates equipment appropriate to choose sensor of the type that suppress report.

 

2.When measuring a structure to undertake metrical to be in what working status falls to wait for, appropriate uses “ to keep apart ” sensor. If sensor oneself is not kept apart, insulating material can be added to regard segregation as parts of an apparatus in sensor bottom.

 

3.The appropriate of oscillatory volume level of the position that measure a place is the 60-80% of the sensor span of the choice, can assure to believe a confusion of voices to compare so tall, won’t overload.

 

4.The bandwidth that summary prep above measures the working frequency range of the sensor of the choice actually can.

 

5.Choose appropriate sensor because of always according to the environment, if measure the temperature of place, humidity to should make sure chosen sensor works normally, and measure amplitude insusceptible.

 

6.According to measuring positional space to choose sensor dimension is mixed means giving a clue.

 

7.Must consider sensor weight to be affected to what measure to light simple structure.

 

8.Choose sensor according to industry application, if mechanical industry appropriate chooses oscillatory quantity step is big, the sensor with frequency wide frequency, and construction industry appropriate chooses span small, sensitivity is tall, the sensor with low frequency good performance.

 

Accordingly, when choosing sensor, must mature above element, choose the most appropriate sensor to undertake metrical, because sensor itself gives calibration tape the effect that come,decrease as far as possible.