热电偶及补偿方法

Thermocouple

A

thermocouple

is

a

temperature-measuring

device

consisting

of

two

dissimilar

conductors

that

contact

each

other

at

one

or

more

spots,

where

a

temperature

differential

is

experienced

by

the

different

conductors

(or

semiconductors). It produces a

voltage

when the temperature of one of the spots

differs from the reference temperature at other parts of the circuit. Thermocouples

are a widely used type of

temperature sensor

for measurement and control,

[1]

and

can also convert a

temperature

gradient

into contrast to most other

methods

of

temperature

measurement,

thermocouples

are

self

powered

and

require no external form of excitation

. The main limitation with thermocouples is

accuracy;

system

errors

of

less

than

one

degree

Celsius

(

°

C)

can

be

difficult

to

achieve.

Any junction of dissimilar metals will produce an

electric potential

related to

temperature.

Thermocouples

for

practical

measurement

of

temperature

are

junctions of

specific

alloys

which have a

predictable

and

repeatable

relationship

between

temperature

and

voltage.

Different

alloys

are

used

for

different

temperature

couples

are

usually

standardized

against

a

reference

temperature of 0 degrees Celsius; practical instruments use

electronic methods

of

cold-junction compensation

to adjust for varying temperature at the instrument

terminals.

Electronic

instruments

can

also

compensate

for

the

varying

characteristics of the thermocouple, and so

improve the precision and accuracy

of measurements.

补偿导线的作用：

1

）

、利于热电偶参考端温度的修正和集中控制。

测量仪表一般安装在远离热源和环境温度较稳定的地方，而普通热电偶的接线盒（参考端安装 的地方）距

被测对象很近。必须用导线把热电偶参考端与仪表连接。若用普通铜导线连接 则热电偶参考端温度较高而

且不稳定，给测量带来误差。若将热电偶延长使热电偶参考端 远离热源，理论上是可以的，但会造成热电

极材料的浪费。补偿导线就是为解决这个矛盾 而产生的。它的特点是在参考端温度可能的变化范围内

（

0-< /p>

100℃或

0-

150℃）由补偿导线两 极组成的热电偶其热电特性与所配热电偶的热电特性相同，即：

Ea'b'

（

tn

，

0

）

=Eab

（

tn

，

0

）

根据中间温度定律可知，热电偶回路中加入补偿导线后，其热电势仅与测量端 温度

t

和补偿导线与仪表连

接处

t0

有关，而与参考端温度

tn

的变化无关，就象把热电极延长到仪表处，

所以补偿导线的作用只是延

长了热电偶，它并不能消除参考端温度不为0℃时的影响。

因此还必须 利用诸如0℃恒温器法、计算法、仪

表自动补偿法等方法将热电偶参考端温度修正到0℃ 。

Thermopile

A

thermopile

is an electronic device that converts

thermal energy

into

electrical energy

.

It

is

composed

of

several

thermocouples

connected

usually

in

series

or,

less

commonly,

in

parallel

.

Thermopiles do not respond to absolute

temperature

, but generate an output

voltage

proportional to a

local temperature difference

or

temperature gradient

.

Thermopiles

are

used

to

provide

an

output

in

response

to

temperature

as

part

of

a

temperature

measuring

device,

such

as

the

infrared

thermometers

widely

used

by

medical

professionals to measure body temperature. They are also used widely in

heat flux sensors

(such

as

the

Moll

thermopile

and

Eppley

pyrheliometer

< br>)

[1][2][3]

and

gas

burner

safety

controls.

The

output

of

a

thermopile

is

usually

in

the

range

of

tens

or

hundreds

of

millivolts.

[4]

As

well

as

increasing the signal level, the device may be used to provide spatial temperature averaging.