is very small, so that the influence of the ambient temperature on the pressure can be neglected;

Step 102, sequentially introducing H₂S gas with different preset concentrations into the ultraviolet difference spectrum gas sensor 2 from the inlet for gas to be detected 9 of the closed box 1 (in this embodiment, the range of the H₂S gas sensor is 1000 ppm, so that preset gas concentration values C₀of the introduced H₂S gas are 0 ppm, 250 ppm, 375 ppm, 500 ppm, 625 ppm, 750 ppm and 1000 ppm, respectively), and discharging the gas from the outlet for gas to be detected 10 after the gas is detected by the ultraviolet difference spectrum gas sensor 2, wherein every time the gas is introduced, when the gas concentration value measured by the ultraviolet difference spectrum gas sensor 2 reaches a stable value, the gas is continuously input, the internal pressure of the working air chamber 8 is changed to simulate the change of the ambient pressure, and when the internal pressure of the working air chamber 8 reaches a preset pressure value, the gas concentration measured by the ultraviolet difference spectrum gas sensor 2 reaches a stable value, and is transmitted to the industrial control computer 5 for output, and finally gas concentration values C_bof gas with different concentrations at different pressures p_hbefore pressure compensation are obtained, as shown in Table 1; the specific method of changing the internal pressure of the working air chamber 8 in step 102 is as follows:

the industrial control computer 5 is used to control the driving motor 73 to drive the regulating rod 72 so as to drive the piston 71 to move inside the closed box 1, thereby changing internal volumes of the pressure regulating air chamber 6 and the working air chamber 8, so that the pressure inside the working air chamber 8 can obtain a predetermined pressure value, and the pressure of the external environment can be simulated; when the volume of the pressure regulating air chamber 6 becomes smaller, the volume of the working air chamber 8 becomes larger, so that the internal pressure of the working air chamber 8 decreases; when the volume of the pressure regulating air chamber 6 becomes larger, the volume of the working air chamber 8 becomes smaller, so that the internal pressure of the working air chamber 8 increases; the internal pressure of the working air chamber 8 is displayed in real time by the digital pressure sensor 3, and is fed back to the system program of the industrial control computer 5;

TABLE 1

Gas concentration values C_bmeasured by H₂S gas sensor,

into which H₂S gas with preset gas concentration values

C₀is introduced, at different pressures P_h

C₀/ppm

0
250
375
500
625
750
1000

p_h/kPa
C_b/ppm

80
5.45
320.76
484.61
640.53
813.29
961.78
1299.87

85
4.08
312.91
472.18
620.73
787.14
946.41
1274.13

90
3.27
264.63
403.25
535.32
673.47
799.95
1067.37

95
2.18
231.74
350.22
465.66
585.88
694.78
930.88

100
1.63
278.24
409.46
550.49
676.81
787.89
1084.10

105
2.72
289.67
437.78
582.07
732.35
868.48
1163.60

110
3.81
308.73
470.45
624.54
785.71
933.27
1245.27

115
4.36
333.78
503.66
662.11
839.62
1009.50
1359.07

120
5.99
352.84
533.07
704.58
894.61
1057.96
1429.86

- Step 2, establishing a formula model of the relationship between ratios k and detection ambient air pressure difference parameters Δp based on the ratios k of the gas concentration values of gas with different concentrations at different pressures p_hbefore pressure compensation obtained in step 1 to a reference standard concentration value, determining relevant parameters of the formula model by a linear fitting method so as to obtain an accurate mathematical relationship between the ratios k and the air pressure difference parameters Δp, and applying the mathematical relationship to the post-processing of actually measured data of the gas concentrations to reduce non-linear errors caused by the fluctuation of the detection ambient air pressure in the actual detection of the gas sensor, specifically comprising the following steps:
- Step 201, defining an air pressure difference parameter Δp, the expression of which is:
  
  Δp=p_h−p₀ (1)
- wherein in the formula, p_his the air pressure value at different pressures, kPa; p₀is the ambient pressure value when the ultraviolet difference spectrum gas sensor is calibrated, kPa, and in this embodiment, p₀=100 kPa;
- Step 202, selecting a preset introduced-gas concentration value C₀which is 50% of the full range of the ultraviolet difference spectrum gas sensor as a reference standard concentration value, calculating ratios k of the gas concentration values C_bmeasured by the ultraviolet difference spectrum gas sensor 2 under air pressure difference parameters Δp at different pressures p_hto the reference standard concentration value at the reference standard concentration value, and then fitting a change relationship between the ratios k and the air pressure difference parameters Δp using a fifth-order polynomial; wherein
- in this embodiment, C₀=500 ppm is selected as the reference standard concentration value, and the ratios k of gas concentration values C_bmeasured by the ultraviolet difference spectrum gas sensor 2 under air pressure difference parameters Δp at different pressures p_hto the reference standard concentration value C₀=500 ppm at the reference standard concentration value are calculated, and the air pressure difference parameters Δp and the ratio k are shown in Table 2;

TABLE 2

Air pressure difference parameters Δp

and ratios k when C₀= 500 ppm

Δp/kPa
−20
−15
−10
−5
0
5
10
15
20

k
1.28
1.24
1.07
0.93
1.1
1.16
1.25
1.32
1.41

- compared with the lower-order polynomial fitting, a fifth-order polynomial has a higher degree of linear fitting, and compared with the higher-order linear fitting, although the fitting degree can be further improved, the improvement is not obvious, and more parameters will be introduced, so the fifth-order polynomial fitting is selected. This polynomial is denoted by the letter K. The data in Table 2 are subjected to polynomial fitting, and after repeated tests, the fifth-order polynomial with the highest fitting degree is selected, and the fitting degree is as high as 0.89537. The fitting formula is:
  
  K=a+b*x+c*x²+d*x³+e*x⁴+f*x⁵ (2)
- wherein in the formula, K is an air pressure compensation coefficient; a, b, c, d, e and f are fitting parameters respectively, x is the air pressure difference parameter Δp, kPa; refer to FIG. 2 for a fitting curve in this embodiment, wherein a=1.04614, b=0.02316, c=0.00132, d=−0.000148645; e=−0.00000142494, f=0.000000247309;
- Step 203, substituting each Δp obtained in formula (1) as x into formula (2), to obtain an air pressure compensation coefficient k′ corresponding to each air pressure difference parameter Δp after fitting, as shown in Table 3;

TABLE 3

Air pressure compensation coefficient values k′ corresponding

to air pressure difference parameters Δp after fitting

Δp/kPa
−20
−15
−10
−5
0
5
10
15
20

k′
1.281
1.237
1.056
0.98
1.046
1.176
1.272
1.305
1.412

- Step 3, calculating gas concentration values C_aafter air pressure compensation at different pressures p_hby formula (3), as shown in Table 4;
  
  C_a=C_b/k′ (3)
- wherein C_bis the gas concentration value of gas with different concentrations at different pressures p_hbefore pressure compensation in Table 1, ppm; k′ is the air pressure compensation coefficient value corresponding to each air pressure difference parameter Δp after fitting;

TABLE 4

Gas concentration values C_aafter air pressure

compensation at different pressures p_h

C₀/ppm

0
250
375
500
625
750
1000

p_h/kPa
C_a/ppm

80
4.25
250.46
378.38
500.13
635.02
750.97
1014.95

85
3.30
252.86
381.57
501.61
636.08
764.79
1029.62

90
3.09
250.55
381.79
506.83
637.63
757.38
1010.57

95
2.22
236.41
357.28
475.03
597.68
708.78
949.63

100
1.56
265.97
391.40
526.21
646.96
753.14
1036.29

105
2.31
246.27
372.18
494.86
622.62
738.35
989.25

110
3.00
242.79
369.97
491.16
617.91
733.95
979.31

115
3.34
255.86
386.09
507.55
643.62
773.85
1041.81

120
4.24
249.96
377.64
499.15
633.77
749.49
1012.95

- Step 4, establishing a model of a measured gas concentration error ΔV caused by change in ambient pressure as follows:
  
  ΔV=C_a−C₀ (4)
- wherein in formula (4), ΔV is the gas concentration error value, ppm; C₀is the preset introduced-gas concentration value, ppm;
- Step 5, comparing the gas concentration error value with the maximum permissible error W of the gas concentration, if ΔV≤W, completing the iteration; if ΔV>W, calculating C′_aby formula (5),
  
  C′_a=C_a/K (5)
- calculating ΔV′ by formula (6),
  
  ΔV′=C′_a−C₀ (6)
- re-judging the magnitude relationship between ΔV′ and W, and completing the iteration until ΔV′≤W, otherwise repeating calculations by formulas (5) and (6).

Since the ambient pressure has positive deviation and negative deviation, ΔV has a positive value and a negative value, if it is found that the deviation becomes large during the iterative calculation process, it is necessary to terminate the iteration, fine-tune the calibration benchmark and perform compensation again until the basic requirement is met.

Embodiment 4

An ambient pressure compensation method for an ultraviolet difference spectrum gas sensor is implemented by the ambient pressure compensation structure for an ultraviolet difference spectrum gas sensor in Embodiment 2, and comprises the following steps:

- Step 1, adopting the above ambient pressure compensation structure for an ultraviolet difference spectrum gas sensor, introducing NH₃gas with different concentrations into the ultraviolet difference spectrum gas sensor 2 inside the closed box 1, and measuring gas concentrations at different pressures p_h(pressures p_hbeing 80 kPa, 85 kPa, 90 kPa, 95 kPa, 100 kPa, 105 kPa, 110 kPa, 115 kPa and 120 kPa, respectively):
- Step 101, controlling, by the industrial control computer 5, the thermostatic controller 4 to work so that the internal temperature of the closed box 1 reaches the ambient temperature t and is kept constant, wherein the temperature t is set at 25° C., and the thermostatic controller 4 guarantees that the change in the ambient temperature of the closed box 1 is very small, so that the influence of the ambient temperature on the pressure can be neglected;
- Step 102, sequentially introducing NH₃gas with different preset concentrations into the ultraviolet difference spectrum gas sensor 2 from the inlet for gas to be detected 9 of the closed box 1 (in this embodiment, the range of the NH₃gas sensor is 50 ppm, so that preset gas concentration values C₀of the introduced NH₃gas are 0 ppm, 12.5 ppm, 18.75 ppm, 25 ppm, 31.25 ppm, 37.5 ppm and 50 ppm, respectively), and discharging the gas from the outlet for gas to be detected 10 after the gas is detected by the ultraviolet difference spectrum gas sensor 2, wherein every time the gas is introduced, when the gas concentration value measured by the ultraviolet difference spectrum gas sensor 2 reaches a stable value, the gas is continuously input, the internal pressure of the working air chamber 8 is changed to simulate the change of the ambient pressure, and when the internal pressure of the working air chamber 8 reaches a preset pressure value, the gas concentration measured by the ultraviolet difference spectrum gas sensor 2 reaches a stable value, and is transmitted to the industrial control computer 5 for output, and finally gas concentration values C_bof gas with different concentrations at different pressures p_hbefore pressure compensation are obtained, as shown in Table 5; the specific method of changing the internal pressure of the working air chamber 8 in step 102 is:
- the industrial control computer 5 is used to control the driving motor 73 to drive the regulating rod 72 so as to drive the piston 71 to move inside the closed box 1, thereby changing internal volumes of the pressure regulating air chamber 6 and the working air chamber 8, so that the pressure inside the working air chamber 8 can obtain a predetermined pressure value, and the pressure of the external environment can be simulated; when the volume of the pressure regulating air chamber 6 becomes smaller, the volume of the working air chamber 8 becomes larger, so that the internal pressure of the working air chamber 8 decreases; when the volume of the pressure regulating air chamber 6 becomes larger, the volume of the working air chamber 8 becomes smaller, so that the internal pressure of the working air chamber 8 increases; the internal pressure of the working air chamber 8 is displayed in real time by the digital pressure sensor 3, and is fed back to the system program of the industrial control computer 5.

TABLE 5

Gas concentration values C_bmeasured by NH₃gas sensor,

into which NH₃gas with preset gas concentration values

C₀is introduced, at different pressures P_h

C₀/ppm

0
12.5
18.75
25
31.25
37.5
50

p_h/kPa
C_b/ppm

80
0.24
13.89
20.98
27.73
35.21
41.64
56.27

85
0.18
13.55
20.44
26.87
34.08
40.97
55.16

90
0.14
11.46
17.46
23.17
29.15
34.63
46.21

95
0.09
10.03
15.16
20.16
25.36
30.08
40.30

100
0.07
12.05
17.73
23.83
29.30
34.11
46.93

105
0.12
12.54
18.95
25.20
31.70
37.60
50.37

110
0.17
13.37
20.37
27.04
34.01
40.40
53.91

115
0.19
14.45
21.80
28.66
36.35
43.70
58.83

120
0.26
15.27
23.08
30.50
38.73
45.80
61.90

- Step 2, establishing a formula model of the relationship between ratios k of gas concentration values C_bmeasured at different pressures p_hto a reference standard concentration value and detection ambient air pressure difference parameters Δp based on the gas concentration values of gas with different concentrations at different pressures p_hbefore pressure compensation obtained in step 1, determining relevant parameters of the formula model by a linear fitting method so as to obtain an accurate mathematical relationship between the ratios k and the air pressure difference parameters Δp, and applying the mathematical relationship to the post-processing of actually measured data of the gas concentrations to reduce non-linear errors caused by the fluctuation of the detection ambient air pressure in the actual detection of the gas sensor, specifically comprising the following steps:
- Step 201, defining an air pressure difference parameter Δp, the expression of which is:
  
  Δp=p_h−p₀ (1)
- wherein in the formula, p_his the air pressure value at different pressures, kPa; p₀is the ambient pressure value when the ultraviolet difference spectrum gas sensor is calibrated, kPa, and in this embodiment, p₀=100 kPa;
- Step 202, selecting a preset introduced-gas concentration value C₀which is 50% of the full range of the ultraviolet difference spectrum gas sensor 2 as a reference standard concentration value, calculating ratios k of the gas concentration values C_bmeasured by the ultraviolet difference spectrum gas sensor 2 under air pressure difference parameters Δp at different pressures p_hto the reference standard concentration value at the reference standard concentration value, and then fitting a change relationship between the ratios k and the air pressure difference parameters Δp using a fifth-order polynomial; wherein