643
3.2 Research on temperature compensation technology
For a traditional methane sensor, its operating temperature range is 0–40°C, which is suitable
for underground coal mine environments. In gas drainage monitoring applications, a wider
operating temperature range is required for outdoor use. The laser methane sensor based on
DFB requires a laser temperature control unit hence the range of temperature control is limited, generally in the range of ±20 degree. It is more difficult to further increase the operating
temperature range as more power is needed to maintain at high or low temperatures.
From equation 3, it can be seen that there is a parameter of (λ), which is a linear function
that represents the shape of the measured absorption spectral line and is function of gas
temperature, total pressure, and the mixture of each components contented in the gas. Hence,
the variation of φ(λ) due to temperature or/and pressure changes needs to be compensated in
order to obtain an accurate measurement.
An adaptive multi-band spectral absorption technology is innovated based on VCSEL
laser technology, by which a wide operational temperature range can be achieved, in addition, this technology enable an accurate gas concentration measurement with an ultra-low
power consumption.
The measurement results of the laser methane sensor in the range of –10 degree to
50 degree are shown in Table 1.
The measurement results of 20% of methane gas over the temperature range of –10C to
50C with the use of the laser methane sensor are shown in Figure 2 (the blue and red dots are
the methane concentration before and after the temperature compensation.
Table 1. Laser methane sensor temperature compensation data (under 20% methane).
No.
Temperature
(°C)
Concentration before
temperature
compensation (%)
Concentration after
temperature
compensation (%)
Deviation
1
−9.5
24.3
20.1
0.37%
2
1.1
23.0
20.2
0.78%
3
12.3
21.1
20.0
0.00%
4
21.4
20.0
20.0
–0.24%
5
31.2
18.9
19.9
–0.80%
6
40.8
17.6
19.9
–0.75%
7
50.5
16.6
19.9
–0.87%
Figure 2. Methane concentration curve before and after the temperature compensation (at 20%
methane).
Temperature compensation curve (Concentration 20%)
30
i i t
-25
~
+
*c 20
~
+
0
·.;::;
~ 15
~
~
~
+
c
~ I
Q)
u 10
t+
t
c
0
u
5
t+
0
-30
-20
-10
0
10
20
30
40
so
60
70
Temperature(°C)
.....,._ Pre-compensation concentration
-+- Post-compensation concentration
3.2 Research on temperature compensation technology
For a traditional methane sensor, its operating temperature range is 0–40°C, which is suitable
for underground coal mine environments. In gas drainage monitoring applications, a wider
operating temperature range is required for outdoor use. The laser methane sensor based on
DFB requires a laser temperature control unit hence the range of temperature control is limited, generally in the range of ±20 degree. It is more difficult to further increase the operating
temperature range as more power is needed to maintain at high or low temperatures.
From equation 3, it can be seen that there is a parameter of (λ), which is a linear function
that represents the shape of the measured absorption spectral line and is function of gas
temperature, total pressure, and the mixture of each components contented in the gas. Hence,
the variation of φ(λ) due to temperature or/and pressure changes needs to be compensated in
order to obtain an accurate measurement.
An adaptive multi-band spectral absorption technology is innovated based on VCSEL
laser technology, by which a wide operational temperature range can be achieved, in addition, this technology enable an accurate gas concentration measurement with an ultra-low
power consumption.
The measurement results of the laser methane sensor in the range of –10 degree to
50 degree are shown in Table 1.
The measurement results of 20% of methane gas over the temperature range of –10C to
50C with the use of the laser methane sensor are shown in Figure 2 (the blue and red dots are
the methane concentration before and after the temperature compensation.
Table 1. Laser methane sensor temperature compensation data (under 20% methane).
No.
Temperature
(°C)
Concentration before
temperature
compensation (%)
Concentration after
temperature
compensation (%)
Deviation
1
−9.5
24.3
20.1
0.37%
2
1.1
23.0
20.2
0.78%
3
12.3
21.1
20.0
0.00%
4
21.4
20.0
20.0
–0.24%
5
31.2
18.9
19.9
–0.80%
6
40.8
17.6
19.9
–0.75%
7
50.5
16.6
19.9
–0.87%
Figure 2. Methane concentration curve before and after the temperature compensation (at 20%
methane).
Temperature compensation curve (Concentration 20%)
30
i i t
-25
~
+
*c 20
~
+
0
·.;::;
~ 15
~
~
~
+
c
~ I
Q)
u 10
t+
t
c
0
u
5
t+
0
-30
-20
-10
0
10
20
30
40
so
60
70
Temperature(°C)
.....,._ Pre-compensation concentration
-+- Post-compensation concentration