U.S. patent application number 09/893097 was filed with the patent office on 2003-01-02 for method at detection of presence of hydrogen gas and measurement of content of hydrogen gas.
Invention is credited to Enquist, Fredrik, Hebo, Peter.
Application Number | 20030000285 09/893097 |
Document ID | / |
Family ID | 25401028 |
Filed Date | 2003-01-02 |
United States Patent
Application |
20030000285 |
Kind Code |
A1 |
Enquist, Fredrik ; et
al. |
January 2, 2003 |
METHOD AT DETECTION OF PRESENCE OF HYDROGEN GAS AND MEASUREMENT OF
CONTENT OF HYDROGEN GAS
Abstract
The present invention relates to a method at detection of
presence of hydrogen gas and measurement of content of hydrogen
gas. The detection is performed by means of a hydrogen gas
sensitive semiconductor sensor, whose output signal is used for
determination of the content of hydrogen gas in the gas sample. The
semiconductor sensor is exposed to the gas sample during a
detection interval, which is preceded by a time interval during
which the semiconductor sensor is exposed to a surrounding gas
atmosphere. The invention is characterized in that the gas
atmosphere contains a negligible amount of oxygen and carbon
monoxide compared to the gas sample and that the time interval is
many times longer than the detection interval.
Inventors: |
Enquist, Fredrik;
(Linkoping, SE) ; Hebo, Peter; (Linkoping,
SE) |
Correspondence
Address: |
MERCHANT & GOULD PC
P.O. BOX 2903
MINNEAPOLIS
MN
55402-0903
US
|
Family ID: |
25401028 |
Appl. No.: |
09/893097 |
Filed: |
June 27, 2001 |
Current U.S.
Class: |
73/31.06 |
Current CPC
Class: |
G01N 33/0026 20130101;
G01N 33/005 20130101 |
Class at
Publication: |
73/31.06 |
International
Class: |
G01N 009/00; G01N
007/00 |
Claims
1. Method at detection of hydrogen gas and measurement of content
of hydrogen gas in a gas sample by means of a hydrogen gas
sensitive semiconductor sensor, whose output signal is used for
determination of the content of hydrogen gas in the gas sample, at
which the detection is performed by exposing the semiconductor
sensor to the gas sample during a detection period, which is
preceded by a preconditioning period during which the semiconductor
sensor is exposed to a surrounding gas atmosphere, characterized
in, that the gas atmosphere contains negligibles amount of oxygen
and carbon monoxide compared to the gas sample and that the highest
sensitivity of the semiconductor sensor is achieved when the
preconditioning period is considerably longer than the detection
period.
2. Method according to claim 1, characterized in, that the length
of the detection period is between 0.01 s and 10 s.
3. Method according to claim 1 or 2, characterized in, that the
length of the preconditioning period is between 1 s and 1 h.
4. Method according to any of the preceding claims for measurement
of the content of hydrogen gas in the gas sample, characterized in,
that the maximum value of the time derivative of the output signal
is used for determination of the content of hydrogen gas in the gas
sample.
5. Method according to any of the preceding claims, characterized
in, that the gas atmosphere consists of an inert gas, preferably
nitrogen.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a method according to the
preamble of claim 1.
[0002] There are a large number of different methods, which can be
used at detection of presence of gases and measurement of gas
concentrations. A common factor for these methods is that they
generate a value as a measure of the presence or concentration of a
gas. At applications when the detection and measurement will be
performed continuously or at a number of successive occasions, it
is preferred to use a device, a so-called sensor, which transforms
the gas concentration into an electric signal.
[0003] The sensors known today include all types of sensors from
complex technical systems, like for example mass spectrometers and
gas chomatographs, to small and relatively simple sensors, like for
example sensors measuring the thermal conductivity of a gas. Most
of these sensors measure physical or chemical properties of the
atoms or molecules of a gas.
[0004] Another type of sensor, which instead measures the presence
of molecules of a gas is described in SE-7411342-4. This sensor,
which is a semiconductor sensor, exhibits advantages, such as very
high sensitivity to and selectivity for hydrogen gas, moderate
energy consumption, small size and possibility for rational
manufacturing. The term "semiconductor sensor" refers herein to the
type of sensor described in SE-7411342-4 but includes also other
structures of catalytic metals and semiconductors working along the
principles described below.
[0005] The semiconductor sensor comprises a catalytic metal layer,
which captures hydrogen molecules and decomposes these molecules
into hydrogen atoms, which diffuse through the metal layer and give
rise to an electric signal in the semiconductor structure. The
amount of hydrogen atoms within the metal and the amount of
hydrogen gas in the surroundings of the metal, equilibrate after a
certain time. Thus, the output signal from the semiconductor sensor
is dependent of the hydrogen gas concentration in its surroundings.
The output signal is also depending on the relationship between the
content of oxygen gas and hydrogen gas in the surroundings, which
will be described below.
[0006] As previously known, the semiconductor sensor provides
greater signals for hydrogen gas when the measurements are
performed in an environment free of oxygen compared to measurements
in an environment containing oxygen. Oxygen in the surroundings of
the semiconductor sensor influences the measurements by producing
an adsorbed oxygen layer on the metal surface of the semiconductor
sensor. The higher the concentration of oxygen gas in the
surroundings of the semiconductor sensor, the greater the number of
molecules and atoms of oxygen adsorbed on the metal surface. This
implies, that the number of sites, which molecules of hydrogen gas
can be adsorbed to, is being reduced concurrently with the number
of molecules and atoms of oxygen being increased on the metal
surface. Furthermore, oxygen reacts with hydrogen adsorbed to the
metal surface under production of water and hydrogen is thereby
removed from the metal surface without having influenced the output
signal.
[0007] Most gas samples subject to analysis regarding hydrogen,
contains air and/or oxygen and as it is relatively difficult and
complicated to purify gas samples from oxygen in an effective and
reproducible way, there has been no practical way to take full
advantage of the sensitivity of semiconductor sensors. Purification
of gas samples from oxygen also results in that the total analysis
time will be considerable lengthened, as this requires an extra
step of sample preparation.
[0008] Consequently, oxygen is counteracting the sensitivity of the
semiconductor sensor for hydrogen gas and influences both the
equilibrium signal, i e the output signal when equilibrium between
the amount of hydrogen gas in the surroundings and hydrogen within
the metal is obtained and the time derivative of the output signal,
i e the rate with which the output signal increases at increased
hydrogen gas concentration. When interpreting the output signal of
the semiconductor sensor, it is previously known to, either use the
equilibrium signal or the time derivative of the output signal.
[0009] The aforementioned interactions between oxygen and a
semiconductor sensor are also valid for carbon monoxide, which also
is present in many gas samples.
SUMMARY OF THE INVENTION
[0010] The object of the present invention is to provide an
increased sensitivity for hydrogen gas of the semiconductor sensor.
This is achieved according to the method of the invention by means
of the measurements indicated in the characterizing par of claim
1.
BRIEF DESCRIPTION Of THE DRAWING
[0011] In the following the invention will be explained in more
detail by means of an example of an embodiment of the present
invention and with reference to the accompanying drawing.
[0012] FIG. 1 illustrates a sensor system for detection and
measurement of content of hydrogen gas in a gas sample.
[0013] In the drawing designation 1 indicates a semiconductor
sensor, to which a measuring instrument 2 is connected. A
controller unit 3 controls valve 4, which is connected to the
semiconductor sensor 1 and which has an inlet 5 for a gas sample
and an inlet 6 for another gas.
DESCRIPTION OF THE INVENTION
[0014] At detection and measurement of the content of hydrogen gas
in a gas sample, the semiconductor sensor 1 is exposed to a gas
sample during a certain detection period. As previously described,
the catalytic metal layer of the semiconductor sensor 1 decomposes
molecules of hydrogen into atoms of hydrogen, which diffuse through
the metal layer and generate an electric signal in the
semiconductor sensor 1. The electric signal is measured by the
measuring instrument 2.
[0015] The valve 4 and the two inlets 5 and 6 are according to the
present invention arranged in the sensing system in order to make
it possible to supply different gases to the semiconductor sensor
1. The supply of gas to the semiconductor sensor 1 is controlled by
the controller unit 3, which controls the position of the valve 4,
so that gas may pass from either of the inlets 5 or 6 through the
valve 4 to the semiconductor sensor 1. During the detection period
the gas sample is supplied through inlet 5 to the semiconductor
sensor 1.
[0016] According to the present invention there is a
preconditioning period before each detection period. The length of
the detection period is preferably between 0.01 s and 10 s and the
length of the preconditioning period is between 1 s and 1 h and the
preconditioning and detection periods may be repeated at regular
intervals. The semiconductor sensor 1 is during the preconditioning
period kept in an environment free of oxygen and carbon monoxide.
Then the controller unit 3 controls the valve 4, so that a gas free
of oxygen and carbon monoxide, preferably nitrogen, may pass from
inlet 6 through the valve 4 to the semiconductor sensor 1. The
exposure of a gas free of oxygen and carbon monoxide aims to remove
oxygen and carbon monoxide molecules, which may be adsorbed to the
metal surface of the semiconductor sensor 1 and thereby influence
the output signal. In order to obtain as high sensitivity as
possible the preconditioning period should be so long that a state
of equilibrium between the amount of oxygen and carbon monoxide
molecules adsorbed on the metal surface of the semiconductor sensor
1 and those present in the surroundings of the semiconductor sensor
1 is obtained, i e such that the metal surface is obtained
essentially free of oxygen and carbon monoxide. The highest
sensitivity is achieved when the preconditioning period is much
longer than the detection period, i e when the relationship
preconditioning period/detection period is high. Furthermore the
semiconductor sensor is kept in an environment free of oxygen and
carbon monoxide before the first measurement.
[0017] When the surface layer of the semiconductor sensor 1 is
essentially free of oxygen and carbon monoxide, the measurements
may be performed on a gas sample including carbon monoxide and/or
oxygen, because the detection period is so short that the
measurement is terminated before oxygen and carbon monoxide are
able to influence the sensitivity of the sensor.
[0018] Consequently, the measurement is performed according to the
present invention after the exposure of the semiconductor sensor 1
to the gas free of oxygen and carbon monoxide during a detection
period. The content of hydrogen gas in the gas sample is determined
in the present invention in an actually known way by using the
maximum rate by which the output signal from the semiconductor
sensor 1 increases, i e the maximum of the time derivative of the
output signal.
[0019] It is apparent for anyone skilled in the art that the
present invention is not restricted to the above described
embodiment. For example, argon or helium may be used as the inert
gas instead of nitrogen.
* * * * *