The interference that be eliminated as far as possible or restrains electronic circuit is the issue that circuit design and application need to solve from beginning to end.

 

Sensor circuit is used normally measure faint signal, have very tall sensitivity, if the influence of insoluble very of all kinds interference, will reach its to measure to circuit bring bigger error, because disturb signal,can flood even measure signal normally and make circuit cannot work normally.

 

Here, studied the in-house noise when sensor circuit is designed and exterior interference, reach take reasonable and significant interference rejection step, can ensure circuit works normally, raise the dependability of circuit, stability and accuracy.

 

Sensor circuit is used normally measure faint signal, have very tall sensitivity, but receive the outside or interior very easily also noise of a few ruleless or interference signal, if these noise are mixed,the size of interference can be compared with useful signal photograph.

 

So useful signal is carried to will be flooded likely in the output of sensor circuit, or differentiate hard as a result of useful signal heft and noise interference heft, be sure to hamper the measurement of pair of useful signal.

 

It is so in the design of sensor circuit, often interference rejection design is the key with sensor circuit whether successful design.

 

The in-house noise of 1 sensor circuit

 

1.1 high frequency thermal noise

 

Because the random of electron of electric system interior moves,high frequency thermal noise is of generation.

 

Temperature is higher, electronic campaign is more intense. Of conductor interior electron in its without regular athletic meeting interior forms a lot of small electric current to fluctuate, because its are the motion that do not have foreword, its average total electric current is reason 0, but serve as a component when it (or the one part that serves as circuit) be received after enlarge circuit, its in-house electric current can be magnified become noise source, be in to the job especially high frequency frequency paragraph high frequency thermal noise affects the circuit inside blame very.

 

It is normally inside labour frequency, the thermal noise of circuit and transmission bands become direct ratio, transmission bands is wider, the impact of circuit thermal noise is bigger. Inside F of transmission bands △ , the virtual value of voltage of circuit thermal noise:

 

 

It is with the resistor of a 1 KΩ exemple, if the transmission bands of circuit is 1 MHz, appear in resistor the virtual value of noise of open circuit voltage of two end sets temperature to be room temperature T=290 K) for 4μV(.

 

Look the electromotive force of noise is not large, but when receiving its a gain to be the enlarge circuit of 106 times suppose, its output noise to be able to amount to 4 V, be opposite at this moment the interference of circuit is very big.

 

1. Noise of 2 low frequency

 

Low frequency noise basically is caused.

 

Especially carbolic film resistor, its carbon pledges material interior is put in a lot of little grain, it is discontinuous between grain, outdated flows in electric current, can make the conductivity of resistor produces change to cause voltaic change, produce similar contact to shine undesirably explode electric arc.

 

Additional, the dissilient noise that transistor produces likeness possibly also and twinkle noise, its produce the discontinuous sex close of the particle in mechanism and resistor, also concern with the impure degree of transistor.

 

1. 3 semiconductor device arise medicinal powder bead noise

 

Because semiconductor PN writtens guarantee the change of voltage of area of base of two end power is caused,accumulate the charge amount change in this area, show capacitance effect thereby.

 

When adscititious when lifting to voltage, the cavity of the electron of N area and P area moves to extinct area, be equivalent to charging to capacitance. When be being reduced to voltage, it makes electron and cavity are far from extinct area again, be equivalent to capacitance discharge.

 

When adscititious and retrorse voltage, the change of extinct area is adverse. Shed zone time of classics power base when electric current, this kind of change can cause the electric current that has shed power base division to produce tiny wave motion, produce voltaic noise thereby. Its produce F of △ of width of the size of noise and temperature, frequency band to become direct ratio.

 

1. 4 circuit board the interference of the electromagnetism component that go up

 

A lot of circuit board go up to have the electromagnetism element such as relay, coil, the distributinging capacitance that sheds the inductance of its coil when passing and crust in report to all round radiation energy, its energy can generate interference to the circuit all round.

 

Like the component such as relay its work repeatedly, connect the meeting when cutting off the power to generate retrorse maximum pressure of the instant, form instantaneous surge electric current, the high pressure of this kind of instant will produce huge impact to circuit, disturb the regular job of circuit badly thereby.

 

1. The noise of 5 resistor

 

The interference of resistor comes from the thermal noise of effect of the inductance in resistor, capacitance and resistor itself.

 

Exemple the solid core resistor that is R like value of a block, but the series-parallel connection that equivalent is L of inductance of C of capacitance of resistor R, parasitism, parasitism.

 

Generally speaking, parasitism capacitance is 0. 1 ～ 0. 5 PF, parasitism inductance is 5 ～ 8 NH. When 1 MHz of frequency prep above, these parasitism inductance capacitance cannot be ignored.

 

Of all kinds resistor can produce thermal noise, the resistor that value of a block is R (or the body resistor of BJT, raceway groove resistor of FET) when receiving circuit, the thermal noise tension that produces inside B of frequency band width is:

 

 

In type: K thises for Bo Er graceful constant; T is absolutely temperature (unit: K) . Itself of thermal noise voltage is aperiodic time function of change, accordingly, its frequency limits is very broad. The influence that so broadband belt magnifies circuit suffers noise is compared narrow frequency band is big.

 

Additional, resistor still can produce osculatory noise, its contact noise voltage to be:

 

 

In type: I is the cost of voltaic mean square that has spread resistor; F is central frequency; K is the constant that concerns with the geometrical appearance of material. Because Vc is in low frequency paragraph a main effect, so it is the main noise source of circuit of low frequency sensor.

 

1. The noise of 6 transistor

 

The noise of transistor basically has thermal noise, medicinal powder bead noise, twinkle noise.

 

Because carry,thermal noise is stream child the irregular body resistor that heats up motion to carry 3 districts inside BJT and corresponding down-lead resistor from time to time arise. Among them the noise that Rbb”” place produces is main.

 

The electric current in the BJT that says normally, it is an average only. Arrive through launching knot infuse actually base of the area carry stream child amount, in each instantaneous not identical, blast off consequently extremely electric current or collector electric current have ruleless wave motion, meeting generation comes loose a noise.

 

Because semiconductor material and workmanship level make transistor surface clean,handle bad and the noise that cause is called twinkle noise.

 

It and semiconductor surface minority carry stream child compound about, expression is blast off extremely of electric current rise and fall, spectrum density of noise of its electric current and frequency become inverse ratio approximately, call 1 ／ F noise again. It basically is in low frequency (KHz is the following) the main effect since limits.

 

1. The noise of 7 integrated circuit

 

The noise interference of integrated circuit has two kinds commonly: One kind is radiation type, one kind is to conduct pattern. These noise are spinal bigger to receiving the other electron equipment on same communication electrified wire netting to be able to arise impact. Noise spectrum is patulous to 100 MHz above.

 

In the lab, can use high frequency oscilloscope (100 MHz above) observation is common odd power source of on systematic board a certain integrated circuit and ground make a machine the weaveform between the foot, can see noise spinal summit – peak value can amount to hundreds millivolt even volt class.

 

The exterior interference of 2 sensor circuit

 

2. The interference of 1 power source

 

The direct current source of most electron circuit is provided by wave of filter of classics of alternating current source of electrified wire netting, stabilized voltage hind. If power source system is purified without the course, can generate interference to testing a system.

 

In the meantime, check the facilities of large communication power near the system in sensor open stop generation frequency very high surge voltage overlay is on voltage of electrified wire netting.

 

In addition, thunder induction also can produce the tension of high frequency surge with very tall amplitude on electrified wire netting. If these disturb signal to enter interior of sensor interface circuit along line of alternating current source, will disturb its to work normally, affect test precision of the system.

 

2.The interference of 2 ground wire

 

Sensor interface each circuit often common a direct current source, or although not common a power source, but between different power source often in all a ground, accordingly, all had shed communal resistor when the electric current of each part circuit (block of ground wire conductor) when can produce voltage drop, this voltage drop becomes the noise that affects each other between each part to disturb signal.

 

In the meantime, be in remote in measuring, sensor and measuring instrument fasten ground connection in two punish, exist between ” of two “ ground then bigger ground connection voltage, the input end in appearance is easy form in all the model disturbs voltage.

 

In all the source that the model violates is equipment commonly itself of voltage of right leakage of electricity, ground, circuitry has right interference to wait. As a result of the lopsided condition of circuit, in all modular interference can change Cheng Changmo to disturb, get rid of harder.

 

2. The interference of 3 signal passageway

 

Normally sensor is set in manufacturing site, and show, the control that installation is in the measurement unit such as the record to have certain space from the spot is indoor, need very long signal transmission line so, signal is disturbed very easily in transmission process, the signal that brings about place to transmit produces distortion or lack fidelity.

 

Long term the interference that signal transmission place encounters has:

 

(Dimensional electromagnetism field is right all round 1) long term electromagnetism induction interference.

 

(String of faze between 2) line. When strong line (or the line with signal change very rapid rate) when leaning very nearly with weak line, through space distributinging capacitance and mutual inductance generate space interference.

 

(3) is long term the ground wire interference of signal. Line is longer, criterion signal ground wire is longer also, namely ground wire resistance is greater, form bigger voltage.

 

2. The interference of interference space electromagnetic wave of 4 spaces electromagnetic wave basically has:

 

(The electromagnetism radiate of the electric field change of 1) thunder, aerosphere, ionosphere change and macula;

 

(Equipment, TV, radar corresponds to wait to emit intense electromagnetic wave through aerial in 2) area space;

 

(Electromagnetic wave of 3) local space is disturbed to what circuit, equipment arises, the glow discharge that arises like the gas discharge establishment such as neon lamp, fluorescent lamp is disturbed, the interference that the electric wave that arc discharge generates forms.

 

The 3 measure that restrain sensor circuit noise

 

3. 1 basis is different working frequency is reasonable the semiconductor with choice low noise yuan parts of an apparatus

 

In low frequency paragraph, because transistor is put in power base capacitance to mix diffuse the problem such as capacitance, noise is bigger. And because canal of knot field effect is majority carries flow child electric, the electric current of area of nonexistent power base is inhomogenous problem.

 

And the retrorse electric current between grid and electric channel is very small, of generation medicinal powder bead noise is very little. Reason is in of medium, low frequency before an effect should be used to be in charge of in class circuit, not only can reduce noise to still can have taller input impedance.

 

If need,change additionally the semiconductor component such as transistor, must pass comparative alternative, although type is same semiconductor device parameter also is discriminating.

 

Same, the noise coefficient of the carbolic film resistor in circuit and metallic film resistor also is different, the noise of metallic film resistor compares carbolic film want small, especially when advanced course small signal is inputted, can consider to use the metallic film resistance with little noise.

 

3. The working frequency with 2 different basises paragraph, the enlarge circuit with parameter proper choice

 

Choose proper enlarge circuit to have immediate effect to this class circuit not only, status of the working parameter to whole circuit, job can produce main effect.

 

When if shoot configuration in all,joining, circuit has taller enlarge gain, the influence of the class after its noise is right at the same time is minor. And in all collect configuration from time to tome the taller frequency with input impedance to also have at the same time better is noisy.

 

The circuit that differs because of this basis is due to parameter diverse demand, choose good circuit, can simplify not only route structure, also can reduce the noise interference to whole circuit at the same time.

 

Below the condition that allows in circuit performance data, use the digital circuit with interference rejection better ability as far as possible.

 

3. Filter wave segment is added in 3 sensor circuit

 

In enlarge circuit, frequency band is broader, noise is bigger also, and the frequency of useful signal often is inside certain limits, reason can add filter wave segment in circuit, filter is divided or disturb signal damply as far as possible, raise letter a confusion of voices in order to achieve to compare the purpose that restrains interference.

 

Filter wave technology arrives to restraining classics lead coupling the interference of circuit is particularly effective, in receiving the filter of corresponding frequency band signal to transmit a passageway, all sorts of filter are one of significant step that restrain the interference that need a standard.

 

Commonly used in automatic testing system filter has:

 

(1)RC filter. It is thermocouple, meet an emergency when signal source piece when waiting for the sensor with signal slow change, the passive RC filter that uses minor volume, low cost will disturb the inhibition with have better to stringing together a model the effect.

 

(Filter of 2) alternating current source. Power source network absorbed noise of all sorts of tall, low frequency, filter of commonly used to this LC will restrain the noise of interfuse power source, for example the inductance of 100μH, 0. The high frequency filter that the capacitance of 1 μF comprises can absorb intermediate waves paragraph interference of high frequency noise.

 

(Filter of 3) direct current source. Direct current source often is place of a few circuit common, cause to avoid to pass power source internal resistance disturb each other between a few circuit, RC or LC should be added to retreat Ou filter on the direct current source of every circuit, use filter to divide low frequency noise.

 

3. 4 will restrain noise through losing feedback circuit

 

Negative feedback circuit can pass the sampling of feedback signal, control to stabilize circuit, the letter a confusion of voices that raises amplifier is compared, make magnify the dynamic function of circuit wins the improvement of many sided.

 

Negative feedback signal can stabilize the static work place of circuit, stabilize the multinomial parameter such as the temperature of circuit, electric current, voltage thereby. In multistage circuit, because circuit of the first class is primitive small signal, because this often is used, is shoot circuit configuration what have bigger gain in all.

 

Unless be special need, shooting configuration circuit in all often do not add negative feedback. The negative feedback circuit of the class after the noise that so circuit of the first class produces can be passed only will restrain.

 

To multistage circuit, the static job that stabilizes this level through losing feedback signal is nodded, can restrain the generation of this class circuit noise and transmission. Because this is in multistage circuit, negative feedback circuit is a when restrain noise important step.

 

3. 5 restrain and reduce input end to slant the noise of buy circuit

 

Input end slants buy circuit noise is by the input end slants commonly buy billabong resistor arises. Should have flowed to slant can make energy excess when the dc electric current of buy resistor is too big produce voltaic noise thereby.

 

If choose to slant suitably buy circuit, noise can pass bypass capacitance weak point receives the land, can restrain noise output, reduce the effect of circuit of pair of below one class. Additionally high grade signal source also is circuit interference rejection is important assure.

 

The 4 measure that reduce sensor circuit interference

 

4. 1 equitable distribution

 

Equitable circuit distribution can reduce different job frequency paragraph the mutual interference between circuit, also make become relatively simple to disturbing the filter of signal to divide at the same time.

 

4. 1. The interference rejection measure that 1 ground wire decorates

 

Set as a result of ground wire cloth to overcome this to plant unreasonable and the interference that cause, when designing printed circuit, the circuit that ought to prevent different return as far as possible sheds classics some at the same time paragraph common ground wire.

 

It is especially in high frequency circuit and loop of big electric current, should pay attention to ground wire more receive a standard. departure of ” of “ communication ground and ” of “ dc ground, it is the effective method that reduces noise to string together faze through ground wire.

 

4. 1. The interference rejection measure of wiring of 2 power source

 

When wiring, want to part part of alternating current source and part of direct current source above all, not common ground connection lead, it is departure of a ” of “ communication ground and ” of “ dc ground, reduce noise to string together faze through ground wire.

 

Additional, in loop of direct current source, laden change can cause power source noise. Configure the noise that goes because load changes,Ou capacitance can be restrained and arising.

 

Specific configuration method is termination is inputted in power source a 10 ～ of 100μF electroanalysis capacitance, if printed circuit board the position allows, those who use 100μF above electroanalysis the interference rejection effect of capacitance will be better.

 

When wiring of power supply cord, according to printed circuit board voltaic size, increase breadth of thick power supply cord as far as possible, reduce annulus road resistance.

 

In the meantime, make the takes line and data signal to deliver way of power supply cord, ground wire consistent, conduce to enhance interference rejection ability.

 

4. 1. The interference rejection measure of layout of 3 yuan of parts of an apparatus

 

(1) restrains electromagnetism interference. Mutual possibility arises yuan of parts of an apparatus or appliance of influence or interference, ought to part as far as possible or take screen step. Should try to shorten high frequency part yuan between parts of an apparatus even the line, the distributinging parameter that reduces them and mutual the electromagnetism between is disturbed (if need to use metallic screen to high frequency part,overspread, still should be in board on the area) that cover of put apart screen takes up. Suffer yuan of parts of an apparatus of interference easily to cannot leave too nearly.

 

Strong report part (220 V) and weak report part (power supply of direct current source) , input class and the component that export class ought to part as far as possible. When down-lead of direct current source is longer, want to add filter wave element, prevent 50 Hz interference.

 

The component such as appearance of loudhailer, electro-magnet, magneto can arise constant magnetic field, the meeting generation such as high frequency transformer, relay is handed in change magnetic field.

 

These magnetic field are opposite not only all round component generates interference, be opposite at the same time all round print lead to also can produce an effect.

 

This kind of interference wants to be treated according to circumstance distinction, when should notice commonly:

 

Reduce lines of force to make the cut of lead to imprinting, decide two inductance kind when the position of component, make their magnetic field direction mutual and perpendicular as far as possible, reduce each other the coupling between;

 

Have magnetism screen to violating a source, screen cover wants good ground contact;

 

When using high frequency cable to transmit signal directly, the screen layer of cable should ground connection of one aspect of the matter.

 

(2) restrains hot interference. Temperature is elevatory the interference that cause, in printed board design also should bring to sb’s attention. When composing designs printed board, should adopt measure to undertake yuan of hot segregation between parts of an apparatus.

 

For instance yuan of sensitive to temperature parts of an apparatus, like transistor, integrated circuit and other heat quick of component, high capacity electroanalysis capacitor, unfavorable be put around heat source or the upside inside equipment.

 

Long-term job causes circuit temperature is elevatory, can affect these the working status of yuan of parts of an apparatus and function.

 

4. 2 screen technology

 

Use screen technology to be able to prevent the interference of electric field or magnetic field effectively. Screen can be divided again wait for electrostatic screen, electromagnetism screen and screen of low frequency magnetism.

 

4. 2. 1 static electric screen is my

 

With the conductivity such as copper or aluminium good metal is material, make airtight metallic container, join with ground wire, the circuit park that protects need among them, make exterior interference electric field does not affect its interior circuit, conversely, the electric field that in-house circuit produces also won’t affect way of dispatches from foreign news agency.

 

For example sensor measures circuit in, in power source transformer primary and sub between insert to leave the conductor that has crack, and its ground connection, can prevent the electrostatic coupling between two winding.

 

4. 2. 2 electromagnetism screen

 

To magnetic field of high frequency interference, use principle of electric vortex flow, make field of electromagnetism of high frequency interference generates electric vortex flow inside screen metal, waste the energy that disturbs magnetic field, eddy current magnetic field is quits and high frequency disturb magnetic field, make be avoided to suffer the effect of field of high frequency electromagnetism by protective circuit thereby.

 

Be like ground connection of electromagnetism screen layer, hold the action of electrostatic screen concurrently at the same time. The output cable of sensor uses copper commonly qualitative meshy screen, already electrostatic screen has the effect of electromagnetism screen again.

 

Screen material must choose the low resistance stuff with electric good performance, wait like aluminium or copper, silver-gilt copper.

 

4. 2. Screen of magnetism of 3 low frequency

 

If interference is low frequency magnetic field, at this moment phenomenon of electric vortex flow is not quite apparent, it is not quite good to use effects of afore-mentioned methodological interference rejection only, because this must be used,use guide magnetism material makes screen layer high, so that limit line of touch of magnetism of low frequency interference in magnetoresistive very small magnetism screen layer is in-house, make be avoided to suffer the effect that coupling of low frequency magnetic field disturbs by protective circuit.

 

The iron sheet crust of sensor testing instrument has the effect of screen of low frequency magnetism. If farther its ground connection, have the effect of electrostatic screen and electromagnetism screen at the same time again.

 

Be based on above 3 kinds of commonly used screen technologies, because this is disturbing more serious place, can use compound screen cable, namely outer it is layer of screen of low frequency magnetism, lining is electromagnetism screen layer, achieve the effect of double screen.

 

For example when capacitance type sensor is being measured actually, its parasitism capacitance is the crucial problem that must solve, otherwise its transmit efficiency, sensitivity to want to become low, must have electrostatic screen to sensor, and derivative line uses its electrode technology of double deck screen, say commonly for drive cable technology. Can overcome sensor effectively with this kind of method the parasitism capacitance in use process.

 

4. Technology of 3 ground connection

 

Ground connection technology is one of effective technologies that restrain interference, be screen technology is important assure. Correct ground connection can restrain foreign interference effectively, can raise the dependability that tests a system at the same time, reduce the interference ingredient that systematic oneself produces.

 

The purpose of ground connection has two: Security and restrain interference. Because cent of this ground connection is protective ground connection, screen ground connection and signal ground connection. Protective ground connection is a purpose with safety, the housing of sensor measurement unit, batholith want ground contact.

 

Resistor of requirement ground connection is under 10 Ω ; Screen ground connection is to disturb voltage to form low block access rightly, disturb measurement unit in case. Ground connection resistor should is less than 0. 02Ω ; Signal ground connection is the common thread of the 0 signal potential of electronic device input and output, itself likelihood and earth are insulation.

 

Signal ground wire is divided again for imitate signal ground wire and digital signal ground wire, imitate signal is common weaker, friend is higher to ground wire requirement; Digital signal is common stronger, reason asks to ground wire but a few lower.

 

Different sensor detects the means of ground of conditional butt joint also has diverse demand, must choose appropriate ground connection method, method of commonly used ground connection has a bit ground connection and many bits of ground contact.

 

4. 3. 1 a bit ground connection

 

General in low frequency circuit proposal uses a bit ground contact, it has radiative type ground wire and line of bus type ground connection.

 

Radiative type ground connection is each function circuit uses lead and connection of 0 potential datum mark directly in circuit;

 

Bus type ground connection uses the high grade conductor that has definite cut area to regard ground connection as bus namely, receive 0 potential point directly, in circuit each the ground of functional piece but nearby is received go up in this generatrix.

 

At this moment if use many bits of ground contact, loop of many ground connection is formed in the meeting in circuit, when low frequency signal or pulse magnetic field pass these loop, can cause electromagnetism induction noise, because the character of loop of every ground connection is different, close in different loop the dot produces voltage, form interference. To prevent this kind of situation, had better use the method of a bit ground connection.

 

Sensor and measurement unit make a whole testing system, but both between likelihood apart is further.

 

Because industrial scene is old ground electric current is very complex, so of crust of this two parts receiving the potential between great place is not identical commonly; If be in the 0 potential of sensor and measurement unit,two punish fasten ground connection, namely at 2 o’clock ground connection, can bigger electric current has shed the signal transmission line with very small internal resistance generation pressing falls, cause the interference that string together a model. Because method of a bit ground connection also should be used below this kind of circumstance.

 

4. 3. Many bits of 2 ground connection

 

Suggest high frequency circuit uses much spot ground contact commonly. High frequency when, although a paragraph of small ground wire also will have bigger impedance to press,fall, add the effect of distributinging capacitance, realize a bit ground connection impossibly, because this can use means of planar type ground connection, receive local form at many o’clock namely, use a good electric and planar system (if use multilayer one of circuit board) receive go up to 0 potential datum mark, each ground nearby of high frequency circuit is received go up to this electric and planar body.

 

Because electric conduction is smooth the high frequency impedance of side put oneself in another’s position is very small, assured the accord of each place potential basically, add at the same time set bypass capacitance to wait decrease pressure fall. Accordingly, this kind of circumstance should use means of many bits of ground connection.

 

4. 4 segregation technology

 

In interface circuit, if appear at 2 o’clock when above ground connection, the likelihood introduces in all block coupling interference and interference of electric current of ground annulus road. The method that restrains this kind of interference is to use segregation technology. Normally electromagnetism segregation and photoelectricity keep apart two kinds.

 

4. 4. 1 electromagnetism coupling is kept apart

 

Use segregation transformer to cut off circumfluent, because ground annulus road is cut off, the ground potential that two circuit have independence is fiducial, won’t cause interference consequently, signal undertakes delivering through coupling form.

 

4. 4. 2 photoelectricity coupling is kept apart

 

Photoelectricity coupler is a kind of report – smooth – coupling parts of an apparatus of report, it encloses composition by glow diode and photoelectricity transistor, its input and output are in electric going up is insulation, accordingly, this kind of parts of an apparatus besides be used at doing photoelectricity to control, be fought by what more and more at improving a system using now in all the model disturbs ability. Although input loop,have interference so, want it to be restricted in the door only in, won’t cause an effect to output.

 

4. Technology of 5 other interference rejection

 

(Technology of 1) stabilized voltage. The regulated power supply that at present intelligent sensor and middling of instrument appearance development use has two kinds: One kind is the whole power source of series connection attune that provides by chip of compositive stabilized voltage, another kind is DC-DC regulated power supply, instrument of this fluctuant to preventing voltage of electrified wire netting interference works normally very effective.

 

(2) is restrained in all the model disturbs a technology. Use the amplifier that need branch, the input impedance that raises the amplifier that need branch or can reduce signal source internal resistance greatly in all the influence that the model disturbs.

 

(3) software compensates a technology. Outside element is like the change of temperature and humidity change that also can cause certain parameter, cause error. Can use software to undertake correction according to the change of outside element and error curve, take out interference.

 

5 epilogue

 

Interference rejection is the issue with a very complex, very strong practicality, appearance of a kind of interference may be caused by a certain number of elements.

 

Accordingly, in sensor circuit and in measuring the design that controls a system, answer to take interference rejection step beforehand not only, still answer to divide the phenomenon that separate out encounters in time in debugging a process, the processing of ground of the interference rejection ability of principle, specific to the circuit of sensor and its system wiring, screen, power source, number or imitate ground and defend the form is improved ceaselessly, in order to increase the dependability of circuit and stability.