CN105509918A - Temperature-potential conversion method for K-type thermocouple - Google Patents

Abstract

The invention discloses a temperature-potential conversion method for a K-type thermocouple, and the method comprises the steps: building a conversion relation expression between the potential value and temperature of the thermocouple; obtaining the corresponding thermocouple potential value through looking up a thermocouple reference table according to the temperature Tj; substituting the thermocouple potential value into the conversion relation expression; obtaining all coefficient values through employing a polynomial fitting algorithm; enabling the determined coefficient values to be substituted into the conversion relation expression, and obtaining the corresponding temperature value according to the potential value actually measured according to the thermocouple. The method can obtain the corresponding more accurate temperature value under the low-temperature condition according to the potential value outputted by a thermocouple sensor, also can detect the error and precision of the thermocouple, and achieves the automatic verification and automatic testing of temperature.

Description

A kind of temperature-electromotive force conversion method of K type thermopair

Technical field

The invention belongs to field of temperature measurement, be specifically related to a kind of thermometry of K type thermopair.

Background technology

In thermocouple auto-verification and thermocouple automatic thermometric system, usually relate to cold junction compensation problem.Currently used temperature-electromotive force change type is the temperature-electromotive force conversion polynomial expression being provided K type 0 ~ 1372 DEG C of warm area by institute in " GB/T16839.1-1997 thermocouple indexing table ":

$E=\underset{i=0}{\overset{n}{\mathrm{\Σ}}}{C}_i{\left(t_{90}\right)}^i+{\mathrm{\α}}_0{e}^{a_1{\left(t_{90}-126.9686\right)}^2}$

Its multinomial coefficient Ci value is as follows:

C ₀＝-1.7600413686×10 ^-2

C ₁＝3.8921204975×10 ^-2

C ₂＝1.8558770032×10 ^-5

C ₃＝-9.9457592874×10 ^-8

C ₆＝5.6075059059×10 ^-16

C ₇＝-3.2020720003×10 ^-19

C ₈＝9.7151147152×10 ^-23

C ₉＝-1.2104721275×10 ^-26

Exponential term coefficient is:

α＝-1.185976×10 ^-1

β＝-1.183432×10 ^-4

Carry out temperature-electric Potential value conversion according to above-mentioned polynomial expression and show that " former scaled value " is in following table, and also list institute's K type that provides " scale division value " in " GB/T16839.1-1997 thermocouple indexing table " in following table, under same temperature, difference (being scaled temperature value) " error " of two electricity Potential also sees the following form 1: 150 DEG C time, reach 5.41 DEG C, thus above-mentioned standard-phasing meter institute to provide the temperature of K type 0 ~ 300 DEG C of warm area-electromotive force to change polynomial error large.

The former scaled value of table 10 ~ 300 DEG C warm area and the corresponding scale division value table of comparisons

Sequence number	Temperature value DEG C	Former scaled value mV	Scale division value mV	Error DEG C
					1	0	0	0	0
2	10	0.350	0.397	-1.18
					3	20	0.737	0.798	-1.53
4	50	1.905	2.023	-2.88
					5	100	3.870	4.096	-5.38
6	150	5.916	6.138	-5.41
					7	200	8.012	8.138	-3.15
8	250	10.114	10.153	-0.95
					9	300	12.202	12.209	-0.17

As can be seen here, existing temperature detection mode at low temperatures error is large, and mostly adopts look-up table, or compensating wire penalty method, like this can be very inconvenient when thermocouple calibration or thermometric instrument calibrating.

Summary of the invention

The object of this invention is to provide a kind of temperature-electromotive force conversion method of K type thermopair, can thermopair accurate temperature measurements value be passed through, and convenient and simple.

Technical scheme of the present invention is: a kind of temperature-electromotive force conversion method of K type thermopair, is characterized in that: specifically comprise the following steps:

First, the potential value of thermopair and the conversion relational expression of temperature is set up:

$E_j=\underset{i=0}{\overset{n}{\Σ}}{C}_i{\left(T_j\right)}^{i/2}$

Wherein, i=0,1,2 ... n, n be more than or equal to 9 integer; T _jfor the temperature value of random selecting between 0-300 degree, j=0,1,2 ... n;

Secondly, according to temperature T _jlook into the thermopair potential value that thermocouple indexing table obtains its correspondence, substitute in above-mentioned conversion relational expression, adopt fitting of a polynomial algorithm to obtain each coefficient C _ivalue;

Then, the C will determined _ivalue substitutes in above-mentioned conversion relational expression again, can obtain corresponding temperature value according to the actual potential value recorded of thermopair.

Beneficial effect: the potential value that the present invention can export according to thermocouple sensor at low temperatures obtains corresponding temperature value more accurately, can also detect thermopair error, precision, the present invention does not need to adopt look-up table, or compensating wire penalty method, temperature automatic Verification can be realized and temperature is tested automatically.

Embodiment

For making object of the present invention, content and advantage clearly, the specific embodiment of the present invention is described in further detail.

The invention provides the temperature-electromotive force conversion method of a kind of 0 ~ 300 DEG C of warm area K type thermopair accurately, specifically comprise the following steps:

First, the potential value of thermopair and the conversion relational expression of temperature is set up:

$E_j=\underset{i=0}{\overset{n}{\Σ}}{C}_i{\left(T_j\right)}^{i/2}$

Wherein, i=0,1,2 ... n, n be more than or equal to 9 integer; T _jfor the temperature value of random selecting between 0-300 degree, j=0,1,2 ... n;

Secondly, according to temperature T _jlook into K type scale division value and thermopair potential value that " GB/T16839.1-1997 thermocouple indexing table " obtains its correspondence, substitute in above-mentioned conversion relational expression, adopt fitting of a polynomial algorithm to obtain each coefficient C _ivalue;

Then, the C will determined _ivalue substitutes in above-mentioned conversion relational expression again, can obtain corresponding temperature value according to the actual potential value recorded of thermopair.

When examining and determine the precision of thermopair, actual temperature being substituted in described conversion relational expression, obtaining the standard electrode potential value of thermopair, the potential value of this standard electrode potential value and thermopair actual measurement is contrasted whether can obtain this thermopair qualified.

During i=9, coefficient C _ibe worth as follows:

C ₀＝0

C ₁＝-1.2323845815×10 ^-3

C ₂＝4.0590956192×10 ^-2

C ₃＝-5.3889186283×10 ^-4

C ₄＝2.2654027713×10 ^-4

C ₅＝-5.4040527108×10 ^-5

C ₆＝8.5452646225×10 ^-6

C ₇＝-7.5731440717×10 ^-7

C ₈＝3.3108817261×10 ^-8

C ₉＝-5.5622322472×10 ^-10。

Respectively coefficient is substituted in conversion relational expression of the present invention, and by each temperature value substitution formula, calculate corresponding potential value as shown in table 2.The value (claiming new scaled value) calculated at synthermal its new conversion formula lower of 0 ~ 300 DEG C of warm area with in " GB/T16839.1-1997 thermocouple indexing table " provide both K types " scale division value " maximum differ 0.001 millivolt (0.024 DEG C) completely can as the temperature of this warm area/potential value change type.

The new scaled value of table 20 ~ 300 DEG C warm area and the corresponding scale division value table of comparisons

Sequence number	Temperature value DEG C	New scaled value mV	Scale division value mV	Error DEG C
					1	0	0	0	0
2	10	0.397	0.397	0
					3	20	0.798	0.798	0
4	50	2.023	2.023	0
					5	100	4.096	4.096	0
6	150	6.138	6.138	0
					7	200	8.138	8.138	0
8	250	10.154	10.153	0.024
					9	300	12.210	12.209	0.024

The above is only the preferred embodiment of the present invention; it should be pointed out that for those skilled in the art, under the prerequisite not departing from the technology of the present invention principle; can also make some improvement and distortion, these improve and distortion also should be considered as protection scope of the present invention.

Claims (3)

1. temperature-electromotive force conversion method of K type thermopair, is characterized in that: specifically comprise the following steps:

First, the potential value of thermopair and the conversion relational expression of temperature is set up:

$E_j=\underset{i=0}{\overset{n}{\Σ}}{C}_i{\left(T_j\right)}^{i/2}$

Wherein, i=0,1,2 ... n, n be more than or equal to 9 integer; T _jfor the temperature value of random selecting between 0-300 degree, j=0,1,2 ... n;

Secondly, according to temperature T _jlook into the thermopair potential value that thermocouple indexing table obtains its correspondence, substitute in above-mentioned conversion relational expression, adopt fitting of a polynomial algorithm to obtain each coefficient C _ivalue;

Then, the C will determined _ivalue substitutes in above-mentioned conversion relational expression again, can obtain corresponding temperature value according to the actual potential value recorded of thermopair.

2. temperature-electromotive force the conversion method of a kind of K type thermopair according to claim 1, it is characterized in that: when examining and determine the precision of thermopair, actual temperature is substituted in described conversion relational expression, obtain the standard electrode potential value of thermopair, the potential value of this standard electrode potential value and thermopair actual measurement is contrasted whether can obtain this thermopair qualified.

3. temperature-electromotive force the conversion method of a kind of K type thermopair according to claim 1 and 2, is characterized in that: during i=9, coefficient C _ibe worth as follows:

C ₀＝0

C ₁＝-1.2323845815×10 ^-3

C ₂＝4.0590956192×10 ^-2

C ₃＝-5.3889186283×10 ^-4

C ₄＝2.2654027713×10 ^-4

C ₅＝-5.4040527108×10 ^-5

C ₆＝8.5452646225×10 ^-6

C ₇＝-7.5731440717×10 ^-7

C ₈＝3.3108817261×10 ^-8

C ₉＝-5.5622322472×10 ^-10。