COL 10(4), 042802(2012) CHINESE OPTICS LETTERS April 10, 2012
Study on long distance transmission technique of weak
photocurrent signal in laser gas sensor
Liming Wang (ááá²²²)
1
, Yujun Zhang (ÜÜÜ)
1∗
, Hongbin Li (ooo÷÷÷RRR)
2
, Yi Zhou (±±± ÀÀÀ)
1
,
Kun You (ccc %%%)
1
, Ying He (ÛÛÛ CCC)
1
, and Wenqing Liu (444©©©)
1
1
Key Laboratory of Environmental Optics and Technology, Anhui Institute of Optics and Fine Mechanics,
Chinese Academy of Sciences, Hefei 230031, China
2
Key Laboratory of Pulsed Power Laser Technology, Institute of Electronic Engineering, Hefei 230037, China
∗
Corresp onding author: yjzhang@aiofm.ac.cn
Received September 13, 2011; accepted October 13, 2011; posted online December 28, 2011
The continuous monitoring of H
2
S gas concentration is a common problem in natural gas desulfurization
pro cess technology. Tunable diode laser absorption spectroscopy (TDLAS) is a preferred technology for
continuous monitoring of gas in industrial sites, because of its high selectivity, high sensitivity, and fast
resp onse. We discuss the technical solutions of on-line monitoring of H
2
S in natural gas desulfurization
pro cess technology based on TDLAS, and study the security design of monitoring system in inflammable
and explosive areas. We also design a weak photocurrent signal converting circuit and perform experiments
on transmission characteristics of different distances. The signal-to-noise ratio (SNR) of laser absorption
sp ectrum does not decrease after the 1 500-m transmission. The detection limit is 300 ppb. The system
can b e operated stably and reliably, and satisfies the need for continuous monitoring of the H
2
S in natural
gas desulfurization process.
OCIS codes: 280.0280, 300.6260, 280.3420.
doi: 10.3788/COL201210.042802.
The continuous monitoring of H
2
S gas concentration is
necessary in desulfurization instruments. An intrinsically
safe design solution can ensure the long-running reliabil-
ity of the monitoring system, because natural gas is in-
flammable and explosive
[1]
.
Tunable diode laser absorption spectroscopy (TDLAS)
has characteristics of high selectivity, high sensitivity,
fast response, and optical fiber transmission. Therefore,
we used single-mode fiber (SMF) to transmit the tuning
laser signal to the measurement site for the H
2
S mon-
itoring system in natural gas desulfurization process
[2]
.
After being absorbed by gas, the laser signal is converted
to current signal at µA-level by a photoelectric detector
and transmitted to control room using a long-distance
twisted-pair cable
[3]
. Thus, the intrinsic safety of the on-
site sensing part has been ensured. Unfortunately, the
experimental results show that the signal-to-noise ratio
(SNR) dropped dramatically, thereby greatly affecting
the data retrieval of laser absorption spectra when the
transmission distance is longer than 50 m. In this let-
ter, we designed a weak photocurrent signal converting
circuit and performed experiments on transmission char-
acteristics of different distances. The signal waveform of
laser absorption spectrum maintained the original state
parameters after the 1 500-m transmission. The detec-
tion limit is 300 ppb. The system can be operated stably
and reliably, and satisfies the need for continuous moni-
toring of H
2
S in natural gas desulfurization process.
Laser gas sensor is a gas detection apparatus for high-
resolution absorption spectrum when laser is used as light
source. Based on the Beer-Lambert law, the transmission
of laser through gas can be written as
[3]
T = I
ν
/I
0
= exp
£
− S(T )g(ν − ν
0
)NL
¤
, (1)
where I
ν
is the intensity of measured gas after an ab-
sorption whose optical path length is L, I
0
is the initial
intensity, S(T ) is the absorption line strength at central
frequency ν
0
, g(ν − ν
0
) is the line shape function, and
N is the concentration of absorbing gas molecules. Peak
absorption coefficient α(ν
0
, T ) is defined as
α(ν
0
, T ) = S(T )g(ν − ν
0
)N. (2)
The line shape function g(ν − ν
0
) is 1, so the integral
absorption coefficient is given by
α(T ) = S(T )N. (3)
The concentration of measured gas is given by
N =
−
R
ln
h
I(ν)
I
0
(ν)
i
dν
S(T )L
, (4)
where dν is the wavelength point of scanning absorption
spectrum.
The minimum of measured gas concentration depends
on the gas absorption line strength S(T ), the optical path
length of absorption, and the resolution of transmission
detection generated through Eq. (4). The transmission
detection resolution depends on the SNR of absorption
spectroscopy and the precision of analog-to-digital (A/D)
conversion.
The composition principle of laser gas sensor is shown
in Fig. 1. We used a distributed-feedback (DFB) laser
as light source and measured the single absorption line of
H
2
S at 1.576 µm. We tuned the laser output wavelength
at 1.576 µm using the temperature controller of laser.
The laser central current was generated by the current
controller, and the wavelength scan current limited the
wavelength of the laser output in the range from 1.576 to
1.577 µm. After being split by a 1 : 9 beam splitter, the
1671-7694/2012/042802(4) 042802-1
c
° 2012 Chinese Optics Letters
下载后可阅读完整内容，剩余3页未读，立即下载
weixin_38600460
- 粉丝: 5
- 资源: 955
我的内容管理
展开
最新资源
- BGP协议首选值(PrefVal)属性与模拟组网实验
- C#实现VS***单元测试coverage文件转xml工具
- NX二次开发：UF_DRF_ask_weld_symbol函数详解与应用
- 从机FIFO的Verilog代码实现分析
- C语言制作键盘反应力训练游戏源代码
- 简约风格毕业论文答辩演示模板
- Qt6 QML教程：动态创建与销毁对象的示例源码解析
- NX二次开发函数介绍：UF_DRF_count_text_substring
- 获取inspect.exe：Windows桌面元素查看与自动化工具
- C语言开发的大丰收游戏源代码及论文完整展示
- 掌握NX二次开发：UF_DRF_create_3pt_cline_fbolt函数应用指南
- MobaXterm：超越Xshell的远程连接利器
- 创新手绘粉笔效果在毕业答辩中的应用
- 学生管理系统源码压缩包下载
- 深入解析NX二次开发函数UF-DRF-create-3pt-cline-fcir
- LabVIEW用户登录管理程序：注册、密码、登录与安全
资源上传下载、课程学习等过程中有任何疑问或建议，欢迎提出宝贵意见哦~我们会及时处理！
点击此处反馈
