Temperature sensor is defined

 

Temperature sensor is to point to the sensor that can experience temperature and is changed into usable output signal. Temperature sensor is the core part that temperature measuring instrument expresses, breed is various. Temperature sensor is very accurate to the measurement of environmental temperature, apply extensively at the domain such as agriculture, industry, workshop, storeroom.

 

Temperature sensor develops the history

 

The Christian era 1600, galilean development goes aeriform thermometer. Centenary hind, development is become after all thermometer and mercuric thermometer. As the need that modern technology admits, develop sensor of temperature of component of electromotive force of a tinsel resistor, difference in temperature, bimetallic type in succession. After 1950, in succession research and development makes semiconductor thermistor. Recently, the flying development as raw material, processing technique, temperature sensor that develops an all sorts of types in succession again.

 

Temperature sensor is classified

 

By measure means to be able to be divided for contact and blame contact two kinds big.

 

1, contact

Of contact temperature sensor detect the part has good contact with the object that be measured, weigh a thermometer again.

 

The thermometer is passed conduct or convection achieves hot balance, make thermometric indication can show the temperature of the object that be measured directly thereby.

 

Measure precision commonly taller. Measuring lukewarm range certainly inside, the thermometer is measurable also the temperature of object interior distributings. But very young to athletic body, little cause or thermal capacity boy or girl friend can produce bigger measurement error, commonly used thermometer has bimetallic thermometer, vitreous liquid thermometer, pressure type thermometer, resistor thermometer, thermal resistor and couple of difference in temperature to wait. They apply extensively at the branch such as industry, agriculture, commerce. In daily life people often also uses these thermometers.

 

2, blame contact

Its sensing element and each other of the object that be measured are not contacted, say to be not contact to measure lukewarm meter again. This kind of appearance is usable will gauge mobile, little cause and thermal capacity small or temperature change is rapid (twinkling changes) the exterior temperature of the object, the temperature that also can be used at measuring temperature field distributings.

 

The most commonly used blame contact measures lukewarm appearance to be based on boldface radiant basic law, call radiation to measure lukewarm meter. The luminosity temperature that of all kinds radiate measures lukewarm method to be able to measure a correspondence only, radiation temperature or colorimetric temperature. Have pair of boldface only (absorb all radiation not the object of reflex) what measuring temperature just is actual temperature. If be about to determine the actual temperature of the object, must undertake material surface launchs the correction of rate. And material surface emissive rate depends on not only temperature and wavelengh, and still wait with exterior condition, film and microcosmic organization about, measure accurately very hard accordingly.

 

The advantage that is not contact temperature sensor is to measure upper limit not to suffer feeling lukewarm component to be able to bear or endure the limitation of lukewarm degree, be opposite consequently highest can measure temperature in principle to was not restricted.

 

 

According to sensor material and electronic component character cent is thermal resistance and thermocouple two kinds.

 

1, thermal resistance

Thermal resistor is to use semiconductor data, it is negative temperature coefficient mostly, block value increases along with temperature and reduce namely.

 

Temperature change can cause large block to be worth a change, accordingly it is the most acute temperature sensor. But the extreme difference of degree of linearity of thermal resistor, and with production craft has very big concern.

 

Thermal resistor returns those who have its oneself to measure skill. Thermal resistor volume is minor it is an advantage, it can be stabilized very quickly, won’t cause hot load. Nevertheless also accordingly very not strong, big electric current can be caused from heat. Because thermal resistor is parts of an apparatus of sex of a kind of resistor, any current source can be on its cause because of power calorific. Power is equal to voltaic square and resistor indigestion. Because this should use small current source. If thermal resistor is exposed,be in high fever, will cause permanent damage.

 

2, thermocouple

Thermocouple is temperature the most commonly used temperature sensor in measuring. Its are main advantage is wide temperature limits and get used to all sorts of atmosphere environments, and strong, price is low, need not power supply, also be the cheapest. Couple is the simplest with the most general temperature sensor, but thermocouple does not suit high accuracy measure and apply.

 

Output the mode of signal according to temperature sensor, can differentiate roughly it is 3 kinds big: Sensor of sensor of sensor of digital type temperature, logistic output temperature, imitate type temperature.

 

 

1, sensor of digital type temperature

It uses the sensor of digital type temperature that silicon craft produces, its use PTAT structure, structure of this kind of semiconductor is had accurate, the good output related to temperature is characteristic.

 

2, sensor of logistic output temperature

In a lot of application, we do not need to measure temperature value strictly, cared temperature to whether exceed range of a set only, once temperature exceeds the range of a regulation, issue alarm signal, start or close fan, air conditioning, heater or other control facility, can choose logic to output type temperature sensor right now

 

3, sensor of imitate type temperature

Imitate temperature sensor, be opposite like thermocouple, thermal resistor and RTDS the monitoring of temperature, linear inside limits of a few temperature bad, need undertakes Leng Duan compensate or down-lead is compensated; Heat is inertial big, answer time slow. Sensor of compositive imitate temperature is compared to it, have sensitivity tall, degree of linearity is good, answer speed to wait for an advantage quickly, and it still processes drive circuit, signal circuit and necessary logistic control circuit compositive in sheet piece on IC, have real measure small, use convenient wait for an advantage. Common imitate temperature sensor has voltage of LM3911, LM335, LM45, AD22103 output, output of AD590 electric current.

 

 

Principle of temperature sensor job

 

1, thermocouple sensor oh working principle

 

Should two kinds of different conductor and semiconductor A and B form a loop, its when two end join each other, the temperature that wants two node part only is different, temperature of one aspect of the matter is T, call working end or hot end, temperature of other one aspect of the matter is TO, call free end or Leng Duan, there is electric current to arise in loop, the electromotive force that exists in loop namely calls hot electromotive force. Because temperature is different,this is planted and the phenomenon of generation electromotive force calls Sebeck effect. The effect that concerns with Sebeck has two: One of, when the joint that electric current has shed two different conductor, be absorbed here or emit quantity of heat (depend on directional) of electric current, call Peltier effect; Secondly, when the conductor that should electric current has shed existence temperature gradient, conductor is absorbed or emit quantity of heat (depend on electric current is opposite the directional) at temperature gradient, call Thomson effect. The combination of two kinds of different conductor or semiconductor calls thermocouple.

 

2, principle of resistor sensor job

 

The resistance of conductor changes along with temperature and change, through measuring its block value pushs cipher out to be measured the temperature of the object, using the sensor that this principle makes is resistor temperature sensor, this kind of sensor basically is used at – the temperature inside limits of 200—500 ℃ temperature is measured. Pure metal is the main production material of thermal resistance, the material of thermal resistance should have the following character:

 

(Temperature coefficient of 1) , resistor wants big and stable, good line sexual relationship should be had between resistance and temperature.

(Rate of 2) , resistor is high, thermal capacity is small, response rate is rapid.

(The reproduction sex of 3) , material and craft sex are good, the price is low.

(4) , measuring character of physics of the chemistry inside lukewarm limits to stabilize.

 

Current, the widest platinum and copper apply in industry, already made a standard measure tepid resistance.

 

3, infra-red temperature sensor

In nature, the temperature prep above when the object is absolutely when zero, as a result of it interior heats up athletic existence, meet ceaselessly to all around radiation electromagnetic wave, included wave band to be located in 0.75 ～ among them the infrared ray of 100μm, infra-red temperature sensor uses what this one principle is made and become namely.

 

 

4, sensor of digital type temperature

It uses the sensor of digital type temperature that silicon craft produces, its use PTAT structure, structure of this kind of semiconductor is had accurate, the good output related to temperature is characteristic. The output of PTAT becomes digital signal through occupying modulation of sky comparing comparator, the concern that takes sky comparing and temperature is as follows type: DC=0.32 0.0047*t, t is Celsius. Reason of output number signal and microprocessor MCU are compatible, the high frequency sampling that passes processor but of signal of square wave of voltage of cipher out output occupy sky comparing, can get temperature. This temperature sensor because its are special craft, resolution excel 0.005K.

 

5, sensor of logistic output temperature

Set limits of a temperature, once temperature exceeds the range of a regulation, issue alarm signal, start or close fan, air conditioning, heater or other control facility, can choose logic to output type temperature sensor right now. LM56, MAX6501-MAX6504, MAX6509/6510 is its model delegate.

 

6, imitate temperature sensor

Common imitate temperature sensor has voltage of LM3911, LM335, LM45, AD22103 output, output of AD590 electric current.

 

AD590 is sensor of the voltaic output of company of American imitate parts of an apparatus temperature, limits of power supply voltage is 3~30V, 223μA of output electric current (- 50 ℃ ) ~423μA (150 ℃ ) , sensitivity is 1μA/ ℃ . Should string together in circuit when receiving sampling resistor R, the voltage of two end of R can regard output as voltage. The block cost that notes R cannot be obtained too big, in order to assure AD590 two upright voltage not under 3V. AD590 outputs voltaic signal to transmit a distance to be able to achieve 1km above. Regard a kind of tall block as current source, highest can amount to 20MΩ , so it need not consider the error that select switch or the ballast resistor that CMOS multichannel converter introduces cause. Apply to much dot temperature is measured and remote the control that temperature measures.

 

 

Single temperature sensor note

 

1, whether does lukewarm to measuring component have the ambient conditions of the object that be measured damage.

2, whether does the temperature of the object that be measured want a record, call the police and automata, whether to need remote measure and convey. 3800 100

3, the circumstance that changes along with time in temperature of the object that be measured, the lag that measures lukewarm component whether suit measure lukewarm demand.

4, the volume that measures lukewarm range and precision requirement.

5, measure lukewarm component volume proper.

6, if the price is protected, use convenient.

 

How to avoid an error

 

When temperature sensor is being installed and be being used, ought to avoid the occurrence of the following error, assure optimal measure the effect.

 

1, installation is improper the error that introduce

The position that installs like thermocouple and the actual temperature that insert deepness to cannot mirror the chamber of a stove or furnace, in other words, thermocouple should be not installed in too stand by the door and heating place, the 8 ～ that insertion deepness should be in charge of a diameter for protection at least 10 times.

 

 

2, thermal resistance error

When high temperature, if there is a coal ash on protective canal, dust is added above, criterion thermal resistance increases, the conduction with hot block up, at this moment the true value that temperature indication compares the temperature that be measured is low. Accordingly, should maintain thermocouple to protect a canal external clean, in order to reduce an error.

 

3, the error that insulation becomes poor and introduces

If thermocouple was isolated from, protection is in charge of and haul line board dirt or saline broken bits causes thermocouple too much extremely as undesirable as the insulation between furnace wall, more serious below high temperature, the loss that this can cause pyroelectricity situation not only and still can introduce interference, the error that causes from this can amount to about a hundred degrees sometimes.

 

4, the error that hot laziness introduces

Because the hot laziness of thermocouple makes the indicated value of appearance lags behind at be being measured the change of temperature, undertaking this kind of influence when be being measured quickly is highlighted particularly. Should use hot electrode as far as possible so the thermocouple with lesser diameter of canal of fine, protection. When measuring lukewarm environment to permit, can take protective valve even. Because existence measures lag, detect with thermocouple the amplitude with the fluctuant temperature that go out relatively the amplitude with fluctuant furnace temperature is small. Measure lag bigger, the amplitude with fluctuant thermocouple is smaller, the difference with actual furnace temperature is bigger also.