644
The current design of the sensor can be operated at the temperature range of –15°C∼55°C
for coal mine applications. It is possible to extend the operational temperature range of
–30°∼70°C for other application requirements.
3.3 Research on pressure compensation technology
The conventional methane sensor is used at pressures range of 50 to 150 kPa in gas drainage applications. In the some applications, a wider pressure range is required. In this case, it
is necessary to adopt a pressure compensation scheme to eliminate the measurement error
induced by the pressure variations. To this end, a pressure high-precision compensation technology is innovated and developed based on using VCSEL laser technology, with the use
this pressure compensation scheme, an accurate measurement within the pressure range of
30–200 kpa was achieved.
Figure  3. Compression of the measured methane concentration data before and after the pressure
compensation (at 20% of methane concentration).
Table 2. The measured methane data with the use the pressure compensation scheme (at 20% of methane concentration).
No.
Pressure (Kpa)
Pre-compensation
concentration (%)
Post-compensation
concentration (%)
Deviation
1
202.9
20.4
19.9
–0.09%
2
181.5
20.3
19.9
–0.07%
3
159.0
20.3
19.9
–0.06%
4
140.4
20.2
19.9
–0.07%
5
119.1
20.1
19.9
0.09%
6
100.4
19.9
20.0
0.18%
7
90.3
19.8
20.0
0.17%
8
80.3
19.6
19.9
0.09%
9
70.8
19.4
19.9
0.04%
10
59.6
18.9
19.9
–0.09%
11
51.2
18.5
19.9
–0.18%
12
39.4
17.4
19.9
–0.25%
13
31.3
16.2
20.0
0.17%
Pressure compensation curve
( Concentration 20%)
25
r
r
-20
7 '· ••• • • ••
t
*c
0 15
. .,
t
~
~
c 10
t
(l)
u
c
0
u 5
t
0
0
50
100
150
200
250
300
Pressure(kPa)
-e- Pre-compensation concentration -e- Post-compensati on concentration