GB2072852A - Gas leakage detectors - Google Patents
Gas leakage detectors Download PDFInfo
- Publication number
- GB2072852A GB2072852A GB8008380A GB8008380A GB2072852A GB 2072852 A GB2072852 A GB 2072852A GB 8008380 A GB8008380 A GB 8008380A GB 8008380 A GB8008380 A GB 8008380A GB 2072852 A GB2072852 A GB 2072852A
- Authority
- GB
- United Kingdom
- Prior art keywords
- gas
- gas leakage
- leakage detector
- detector according
- voltage
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 238000001514 detection method Methods 0.000 claims abstract description 30
- 229910044991 metal oxide Inorganic materials 0.000 claims abstract description 12
- 239000007787 solid Substances 0.000 claims abstract description 11
- 239000000126 substance Substances 0.000 claims abstract description 5
- 238000010521 absorption reaction Methods 0.000 claims abstract description 3
- 239000007789 gas Substances 0.000 claims description 134
- 230000010349 pulsation Effects 0.000 claims description 14
- 239000003990 capacitor Substances 0.000 claims description 7
- 239000000463 material Substances 0.000 claims 1
- 230000035945 sensitivity Effects 0.000 description 14
- 230000004397 blinking Effects 0.000 description 5
- 238000010586 diagram Methods 0.000 description 4
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 4
- 230000001105 regulatory effect Effects 0.000 description 4
- 229920003051 synthetic elastomer Polymers 0.000 description 4
- 239000005061 synthetic rubber Substances 0.000 description 4
- 238000007599 discharging Methods 0.000 description 3
- 239000011521 glass Substances 0.000 description 3
- 239000007788 liquid Substances 0.000 description 3
- 229910052751 metal Inorganic materials 0.000 description 3
- 239000002184 metal Substances 0.000 description 3
- 150000004706 metal oxides Chemical class 0.000 description 3
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 3
- 238000007796 conventional method Methods 0.000 description 2
- 230000008878 coupling Effects 0.000 description 2
- 238000010168 coupling process Methods 0.000 description 2
- 238000005859 coupling reaction Methods 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 230000006641 stabilisation Effects 0.000 description 2
- XOLBLPGZBRYERU-UHFFFAOYSA-N tin dioxide Chemical compound O=[Sn]=O XOLBLPGZBRYERU-UHFFFAOYSA-N 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 239000001273 butane Substances 0.000 description 1
- 230000003750 conditioning effect Effects 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 229920001971 elastomer Polymers 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- XUCNUKMRBVNAPB-UHFFFAOYSA-N fluoroethene Chemical group FC=C XUCNUKMRBVNAPB-UHFFFAOYSA-N 0.000 description 1
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 1
- 239000003915 liquefied petroleum gas Substances 0.000 description 1
- IJDNQMDRQITEOD-UHFFFAOYSA-N n-butane Chemical compound CCCC IJDNQMDRQITEOD-UHFFFAOYSA-N 0.000 description 1
- OFBQJSOFQDEBGM-UHFFFAOYSA-N n-pentane Natural products CCCCC OFBQJSOFQDEBGM-UHFFFAOYSA-N 0.000 description 1
- 239000003345 natural gas Substances 0.000 description 1
- 229910052697 platinum Inorganic materials 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
- 239000005060 rubber Substances 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- 239000008149 soap solution Substances 0.000 description 1
- 230000001960 triggered effect Effects 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M3/00—Investigating fluid-tightness of structures
- G01M3/02—Investigating fluid-tightness of structures by using fluid or vacuum
- G01M3/04—Investigating fluid-tightness of structures by using fluid or vacuum by detecting the presence of fluid at the leakage point
- G01M3/20—Investigating fluid-tightness of structures by using fluid or vacuum by detecting the presence of fluid at the leakage point using special tracer materials, e.g. dye, fluorescent material, radioactive material
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
- G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
- G01N27/14—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of an electrically-heated body in dependence upon change of temperature
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
- G01N33/0004—Gaseous mixtures, e.g. polluted air
- G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
- G01N33/0062—General constructional details of gas analysers, e.g. portable test equipment concerning the measuring method or the display, e.g. intermittent measurement or digital display
- G01N33/0063—General constructional details of gas analysers, e.g. portable test equipment concerning the measuring method or the display, e.g. intermittent measurement or digital display using a threshold to release an alarm or displaying means
Landscapes
- Chemical & Material Sciences (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- Engineering & Computer Science (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Medicinal Chemistry (AREA)
- Food Science & Technology (AREA)
- Combustion & Propulsion (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)
- Emergency Alarm Devices (AREA)
Abstract
A gas leakage detector comprises a solid state gas sensor (3) having a sintered metallic oxide block operative to change thermal conductivity by chemical absorption thereto and a wire to transfer the change of said thermal conductivity to an electrical signal. A gas sensing part of the gas sensor (3) is disposed in a gas intake path (4, 5). A suction pump (7) is connected to the gas intake path in a manner to draw a gas to be detected into the gas intake path thereby to contact the gas sensor (3). A voltage to frequency converter (VFC) produces output pulses at a frequency responsive to an input voltage from the gas sensor (3). The pulses from the converter (VFC) trigger an off- delay timer (ODT) which controls an oscillator (OSC) connected to an alarm LED (10) and a speaker (12) whereby the detection of gas causes the generation of light and sound alarms which pulsate at a frequency proportional to the gas concentration. <IMAGE>
Description
SPECIFICATION
Gas leakage detectors
The present invention relates to gas leakage detectors.
Hitherto, several types of gas leakage detector have been proposed, but almost of them, for example one known as a frame ionization detector, are large stationary types which cannot readily be carried, for example by a single hand. Therefore, such apparatuses are not generally useful as portable apparatus to be carried by service personnel. Accordingly, a simple conventional method of gas leakage detection has been to a detection liquid, such as a soap solution to form bubbles at a gas leakage position, but its limit of detection is about 5 x 1 0-4 cm3/sec.
Furthermore, even if the conventional apparatus is capable of measuring a small concentration of leaking gas, the conventional apparatus, which has an ammeter or sevensegment figure indicators to indicate the
measured concentration, is not very useful in finding the location of the gas leakage, since the operator of the apparatus has to carefully watch both the indicator and the position of the gas leakage to be detected. Accordingly, a pulsating sound alarm or pulsating light alarm type solid state electronised gas detector has been proposed, but the conventional electronised
detector still has the problems of long warm-up time and that the change of pulsation may give
rise to unnoticeable excessively high frequencies
or to inconvenient excessively low frequencies thereby to produce a possibility of erroneous
determination of detection.
According to the present invention there is
provided a gas leakage detector comprising:
a solid state gas sensor having a sintered
metallic oxide block operative to change thermal
conductivity by chemical absorption thereto and a
wire to transfer the change of said thermal conductivity to an electrical signal;
a gas intake path in which a gas sensing part of
said gas sensor is disposed;
a suction pump connected to said gas intake
path in a manner to draw a gas to be detected into
said gas intake path whereby the gas contacts the
gas sensor;
a variable frequency oscillator operative to
provide output pulses which change frequency in
response to an input voltage from the solid state
gas sensor; and a sound and/or light alarm indicator which is controlled to pulsate by the output pulses of the variable frequency oscillator.
Preferably, the sound and/or light provided by
the alarm indicator is controlled to pulsate in such
a manner that the frequency of pulsation can
change between a predetermined lower limit,
which corresponds to a lower limit of
concentration of gas to be detected, and a
predetermined higher limit, which corresponds to
a higher level of concentration of gas to be
detected, and the periods of time during which light and/or sound are provided are uniform irrespective of changing of the pulsation frequency thereby making the light and/or sound continuous at said higher limit.
A preferred embodiment of the present invention described hereinbelow provides an improved handy, portable and practically useful gas leakage detector which can detect gas leakages with high sensitivity, high stability and a quick response time, and is easy to operate.
The invention will now be further described, by way of illustrative and non-limiting example, with reference to the accompanying drawings, in which:
Figure 1 is a perspective view showing the overall appearance of a gas leakage detector embodying the present invention;
Figure 2 is a side view of the detector of Figure 1 with a case cover removed and showing a fragmental side view of attachments;
Figure 3 is a fragmental plan view of the detector of Figure 1;
Figure 4 is a fragmental side view of a drain filter serving as an attachment of the detector;
Figure 5(a) is a perspective view of an attachment to detect gas leakage from a pipe and
Figure 5(b) is a perspective view of the manner of using the attachment of Figure 5(a);
Figure 5(c) is a perspective view of an attachment to detect gas leakage from a wall or floor;;
Figure 6 is a block diagram showing the electrical parts of the detector shown in Figures 1 to 4; Figure 7 is a waveform chart showing waveforms of signals present at various parts of the circuit of Figure 6;
Figure 8 is a circuit diagram of a V-F converter of Figure 6;
Figure 9 is a waveform chart showing waveforms of various parts of the circuit of Figure 9; and
Figure 10 is a graph showing an example of the relationship of gas concentration and the pulsation frequency of alarm light and sound provided by the illustrated detector.
A gas leakage detector or detection apparatus constituting a preferred embodiment of the present invention will now be described with reference to the accompanying drawings.
Figure 1 is a perspective view showing the overall appearance of the embodiment, Figure 2 is a side view of the apparatus of Figure 1 with a case cover removed and showing a fragmental side view of attachments, and Figure 3 is a fragmental plan view. As shown in these figures, the apparatus has a case 1 on which a gas intake connector 2 is disposed at one end.The case contains the following components and parts:
a solid state gas sensor 3 comprising a small block of sintered metallic oxide to be heated to a temperature of over 300 C by an electric heater constituted by platinum wires;
a gas intake path 4, 5 which is connected to an input end of the gas intake connector 2, the solid state gas sensor 3 being disposed in an expanded part 5 of the gas intake path;
a suction pump 7 connected to an output end 6 of the gas intake path 4, 5 and driven by a small battery-driven electric motor 8;
a printed circuit board 9 mounting thereon a
variable frequency oscillator which changes the
frequency of output pulses thereof in response to
an input voltage from the solid state sensor 3;;
at least a lamp 10 or a small speaker 12 which
acts as an alarm indicator and which is energised
by a current controlled by the variable frequency oscillator in such a manner that the speaker 12 periodically emits sounds (e.g. buzzing or ringing) or the lamp 10 is periodically illuminated at a frequency responsive to the gas concentration measured by the gas sensor 3; and
primary or secondary batteries 13 to energise the electric circuit mounted on the printed circuit board 9 and all the other above-mentioned electrical components.
Beside the above-mentioned components, a variable resistor 14 for setting a detection level is fixed on a wall 1 ' of the case 1 and a knob 14' of the variable resistor 14 is mounted outside the
case wall. Furthermore, a power switch 15 to switch on or off the electrical components energised by the batteries 13, a battery check light 1 a buzzer switch 1 5 and a selection switch 17 for conditioning the apparatus to work with different kinds of gases are provided on the case wall 1'.
The solid state gas sensor 3 comprises a sintered metallic oxide-coated wire type sensor having an element 31, wherein a non-oxidisable metal wire such as platinum wire is coated with a sintered block of a metallic oxide such as SnO2 and the metallic oxide block is heated to a predetermined temperature of over 3000C by energising it with a current, thereby producing a change of thermal conductivity of the metal oxide block by chemisorption of gas to be detected and consequently obtaining a change of resistance of the metal wire due to the change of temperature thereof, which change of resistance is measured by means of an electrical circuit.The metallic oxide coated wire type gas sensor has the advantage that: the time elapsing from switchingon to stabilisation of detection sensitivity is only two or three seconds, which is far shorter than the corresponding time of several tens of minutes for
a gas sensor untilising a change of resistance of a semiconductor body; that sensitivity of the metal
oxide coated wire type element is high, especially for low concentration gases and for inflammable
(combustible! gases, such as CH4 or liquid
petroleum gas, or gases that are easily absorbed,
for example NO2CI2 or some kinds of fluoroethylene; and that only a low voltage supply
is required. The metallic oxide coated wire type
gas sensor has a logarithmic gas
concentration/output voltage characteristic.These features are especially important for portable high
sensitivity gas detectors which are switched on and off very frequently and in which high sensitivity detection must be attained in a short time with a quick response. The element 31 is mounted in a net or mesh case and is disposed in the expanded part 5 of the gas intake path 4, 5, which is formed in a sensor mounting block 51 made of metal, to which the gas sensor 3 is mounted via an O-ring 52. The sensor mounting block 51 has an exhaust path 53 leading therethrough to an outlet piece 54 fixed on the case wall 1'.
The suction pump 7 comprises a diaphragm 71 made of synthetic rubber which is mounted on a face of the sensor mounting block 51 in a manher to cover a first port 72 leading to the output end 6 of the gas intake path 4, 5 and a second port 73
leading to the exhaust path 53. The first port 72
and the second port 73 respectively comprise known pump valves. One end of a driving frame 74 comprising a pair of permanent magnets 75 and 76 is fixed to a moving top part of thediaphragm 71 and the other end of the driving frame 74 is movably held by a movable holder 77 made of, for example, flexible rubber.A cylindrical permanent magnet 78 mounted on a shaft of the motor 8 is disposed in such a manner that poles of the cylindrical permanent magnet 78 face the poles of the above-mentioned pair of permanent magnets 75 and 76 and thereby reciprocatingly drive the latter by virtue of attractive and repulsive forces generated between the magnets when the cylindrical permanent magnet 78 is rotated by means of the motor 8. Accordingly, when the motor 8 is driven by current fed from the batteries
13, the diaphragm 71 is subjected to reciprocating movement whereby gas is drawn in from the intake connector 2 through the intake path 4, 5 and is exhausted from the exhaust path 53, so that the gas contacts the element 31 of the gas
sensor 3. The suction pump 7 is desirably capable
of a suction rate of 100 to 400 cm3/min for
obtaining a high detection sensitivity and a
suitable response speed.
For ordinary use, a plug 23 is connected to the
gas intake connector 2 by coupling an internal
screw thread 24 thereof to an external screw
thread 22 of the gas intake connector 2 with an, O-ring 21 in between for gas-tight coupling, and a
nozzle 26 made of a synthetic rubber and having a
through-hole 27 is connected to the plug 23 by
inserting a top or end tube part 25 of the plug 23
into the through-hole 27. The inside diameter of
the through-hole 27 in the nozzle 26 (or other long
attachment) is preferably 2 to 4 mm in order to
ensure adequare response speed and sensitivity.
Figure 4 shows a drain filter 231 for use in
place of the plug 23 when drops of water or
various other liquid or muddy substances, which
may be harmful to the sensor 3, are present at the
place where the gas is to be detected. The drain
filter 231 comprises a transparent or translucent
glass tube 234 between a top or end part 232, of
the same shape as the plug 23, and a bottom or
end part 233 having an internal screw thread
233'. The ends of the glass tube 234 are tightly
sealed to the top part 232 and the bottom part 233 with O-rings in between them. A disposable fine filter 235 is mounted between the glass tube 234 and the bottom part 233 to stop drops of water, oil or muddy substance.
Figure 5(a) is a perspective view of an adapter 261 for use in place of the nozzle 26. The adapter 261 has an arc-shaped recess 262 on an expanded end thereof for making good contact with a gas pipe 269 (Figure 5(b)) whose gas leakage is to be detected. The adapter 261 has a mesh filter 263 in the recess 262 in order to stop rust or any other stains on the pipe 269 from being drawn in. The body and a connecting end 264 of the adapter 261 are preferably made of synthetic rubber for good fitting to the pipe 269 as well as to the top or end tube part 25 of the plug 23 (Figure 2).
Figure 5(c) shows another adapter 265 for use in detecting gas leakage from a wall or floor of the like in which a gas pipe is buried. The adapter 265 has an intake opening 267 at an expanded end thereof, a narrow connecting end 266 at the opposite end, and a mesh filter 268 near an opening 267 of the expanded end. The body and the connecting end 266 of the adapter 265 are preferably made of synthetic rubber for good fitting to the wall or floor as well as to the top or end tube part 25 of the plug 23.
As shown in Figures 1 to 3, a gas outlet cap 99 is mounted on the exhaust pipe 54 on the wall 1 in order to exhaust the gas in a desired directlon.
Figure 6 is a block diagram of the electrical circuitry and other electrical components of the apparatus, the main parts of which circuitry are mounted on the printed circuit board 9.
As shown in Figure 6, the batteries 1 3 feed power through the power switch 1 5 to an output transistor Q3, in the collector circuit of which is connected the alarm lamp 10, which is in the form of an LED. The small speaker 12, acting as an alarm buzzer, is connected via the buzzer switch
16 across the LED 10. If desired, an ear phone socket 121 can be connected across the contacts of the buzzer switch 1 6, so that the user can use an ear phone 122 in a very noisy place. Power is also fed from the batteries 13 to a transistor Q2 which constitutes, together with a known voltage comparator Q1 and a variable resistor VR2 for voltage setting, a known regulated power supply to feed a constant voltage to a line RPL. A semifixed variable resistor VR3 is connected across the positive and negative terminals of the batteries
13.A second LED acting as the battery check indication lamp 11 and a known voltage comparator circuit Q4 are connected in series across the regulated power supply line RPL and the slider of the variable resistor VR3.
The regulated power supply line RPL further feeds power to the pump 7, to the heater wires of the gas sensor 3 and to the below-mentioned voltage-frequency converter (hereinafter VF converter) VFC, off-delay timer ODT and oscillator OSC. The variable resistor 14 for alarm setting and a zero adjusting variable resistor VR5 are connected across the regulated power supply line
RPL and the negative terminal (earth) of the power source (batteries 13). The heater wires of the gas sensor 3 consist of the detector wire in the gas detection element 31 exposed to the gas and a reference wire, which is in a reference element 39 not exposed to the gas but connected in series with and disposed in close proximity to the detection wire of the detection element 31 ,for compensation against the influence of ambient temperature.The junction point X between the detection wire and the reference wire is connected to a first input terminal of the VF converter VFC.
The slider Y of the variable resistor 14 is connected to the moving contact of the selection switch 1 7. Fixed contacts of the selection switch
17 are connected, respectively, through semi-fixed variable resistors VR6 and VR7 for alarm range setting, to a second input terminal of the VF converter VFC, and further to the slider of the variable resistor VR5. An output terminal of the VF converter VFC is connected to an input terminal of the off-delay timer ODT, and an output of the offdelay timer ODT is connected to an input of the oscillator OSC, which has an output connected to the base of the output transistor Q3.
The operation of the circuit shown in Figure 6 will now be described with reference to the waveform chart of Figure 7, which shows signals present at several position in the block diagram of
Figure 6.
When the power switch 15 is turned on, the battery indication lamp 11 is lit if the batteries 13 show a proper terminal voltage. At the same time, the transistor Q2 feed the voltage-reguiated power to the line RPL, and hence the pump 7 is energised and draws gas into the gas-intake path 5 and the platinum wire heater of the gas sensor 3 is energised to heat the element to a predetermined temperature of more than 3000 C.
When combustible gas contacts the gas sensor 3, the thermal conductivity of the metal oxide film on the heater wire of the gas detection element 31 becomes small, and therefore, due to an increase of heat conduction, the temperature of the wire is lowered, and hence the resistitivity of the heater wire increases. Therefore, the potential at the junction point X is raised. For example, a 20 mV voltage change in obtained for a gas concentration of 100 ppM of butane. When the gas concentration increases, the input voltage difference Vin between the first and second input terminals increases as shown in the waveform (Vin) of Figure 7, and hence, the VF converter VFC increases its output frequency as shown by the waveform (VFC) of Figure 7. The off-delay timer
ODT produces square waves of uniform duration or width, which are triggered by the output pulses of the VF converter VFC.Therefore, the output waveform of the VF converter VFC becomes continuous for values of the input voltage difference Vin above a predetermined level LV2.
The oscillator OSC oscillates to provide an audio frequency waveform of, for example, 1000 Hz, which is amplitude-modulated by 100% -- as shown by Figure 7 (OSC) - by the input signal from the off-delay timer ODT as shown by Figure 7 (ODT). In other words, the 1000 Hz signal is issued only in blocks of time when the output signal of the off-delay timer ODT is at a high level 'H'. The output transistor Q3 amplifies the output signal of the oscillator OSC and, therefore, the waveform shown at (OSC) in Figure 7 is fed to the alarm LED 10 and, when the switch 16 is closed, to the speaker 12, thereby to provide an alarm indicating the detection of gas.Accordingly, as is shown by Figure 7 (ODT') and (OSC), the current flowing through the LED 10 and the speaker 12 is a pulsating current which intermittently stops and flow at a frequency of, for example, 1 to 20 times per second. Therefore, the LED 10 emits light (blinks) and the speaker 12 emits sound at a frequency of 1 to 20 times per second, depending on the gas concentration. Though the light is also blinking at 1000 Hz, such a high frequency is not noticeable by the human eye, whereby only the blinking at 1 to 20 times per second is observed.
Experiments shows that the human eye and ear cannot notice pulsation (blinking) of light and pulsation of sound at more than 20 times per second, and therefore the upper limit of frequency at which the alarm lamp 10 and speaker 12 are pulsated is preferably about 20 Hz. The inventors found that for the present portable gas leakage apparatus, wherein detection of gas leakage of a
predetermined concentration range is sufficient, the mode of indication is preferably simple in order to obtain reliable and quick detection.
Therefore, for concentrations exceeding a
predetermined high level, there is no need to
gradually change the mode (i.e. pulsation frequency) of the alarm. Therefore, it is sufficient that a highest noticeable pulsation frequency, for
example 20 Hz, is set to correspond to the
predetermined high level LV2 of the input voltage
difference Vin of Figure 7 (Vin). That is, for concentrations higher than such predetermined
high level, it is preferable, for easy use of the
apparatus to provide continuous alarm light and
alarm sound, instead of further raising the
pulsation frequency in vain. In order to meet such
requirement. the waveform of the control signal to
be give to the input terminal of the oscillator OSC
is designed in such a manner that the widths of
the pulses are uniform and only the spacing
between the pulses changes in response to the
gas concentration.Such control signal is produced
by feeding the output signal of the VF converter
VFC to the off-delay time; ODT and appropriately selecting the pulse width of the off-delay timer
ODT, for example 25 ms. The off-delay timer ODT
can be replaced by a known one-shot
multivibrator, since the former and the latter
function similarly.
The inventors studied the question of indicating the lower limit of gas concentration to provide easy use of the apparatus, and their study showed that a pulsation frequency of less than 1 Hz is not suitable in the use of the portable detector.
Therefore, the lower limit of the output frequency of the VF converter VFC should preferably be set to such desired selected value. This is achieved by employing the circuit shown in Figure 8 for the VF converter VFC.
The VF converter VFC shown in Figure 8 comprises a comparator CMP whose output terminal Vout is fed to the output terminal of the
VF converter VFC. The input voltage difference signal Vin is applied between an input terminal X and an earth terminal E. A resistor Ri is connected between the input terminal X and the negative input terminal "-" of the comparator CMP, and a resistor R2 and a diode D are connected in series between the negative input terminal "-" and the output terminal Vout, which is connected through a resistor R5 to the positive power supply line RPL.
A capacitor C1 is connected between the negative input terminal "-" and the earth terminal E. A resistor R4 is connected between the output terminal Vout and the positive input terminal "+" of the comparator CMP, and a resistor R3 is connected between the positive input terminal "+"
and a reference input terminal Vref, to which a
predetermined reference voltage V1 is applied.
The resistors R3 and R4 are for providing positive feedback.
Operation of the VF converter of Figure 8 is as
follows:
At first, the capacitor C1 is changed to the voltage of Vin through the resistor R1.
When the input voltage Vin is lower than the
voltage V3, the output terminal Vout is at a high
level "H".
As the gas concentration increases and hence
the input voltage Vin increases, charging the
capacitor Cl, the potential at the negative input
terminal "-" becomes higher than the potential
at the positive input terminal "+". The comparator CMP then becomes OFF and the output terminal
Vout goes to a low level "L", and accordingly the
charge of the capacitor Cl is discharged through
the resistor R2 and the diode D1 at a rate
determined by the time constant C1 R2. Due to
this discharging, the voltage V3 between the
positive input terminal "+" of the comparator CMP and earth is reduced from V3a to V3b as shown in
the waveform chart of Figure 9 at (Vin), which shows the input voltage Vin.
When the voltage of the capacitor C1 is
reduced by discharging to the level V3b, the
comparator CMP is restored to the OFF state,
making the output terminal Vout go to level "H",
whereby the voltage V3 goes back from the level
V3b to the level V3a of Figure 9 (Vin), and the
capacitor C1 again begins to be charged through
the resistor R1, at a rate determined by the time constant C1 Ri The relationship between the
time constants is selected to be: C1 R2 C1 C1-R1.
When the input voltage Vin becomes higher,
the charging time becomes shorter than the case
for the lower Vin voltage as shown by Figure 9,
(Vin) and (V2), and therefore, the time from the
comparator CMP going OFF to its subsequently becoming ON again becomes short, that is, the duration of the "L" period of the output terminal
Vout becomes short, while the discharging time period defined by the time constant C1 R2 is retained unchanged. This means that the signal at the output terminal Vout becomes as shown in
Figure 9 at (Vout).
In the circuitry of Figure 8, by suitably selecting the hysteresis gap V3a-V3b of the comparator CMP, which is determined by the resistances of the resistors R3 and R4, the longest period of the above-mentioned operation of the circuit can be selected to be a desired value, for example, 1 second.In one example, the condition for obtaining the longest period of 1 second is as follows:
hysteresis gap (V3a-V3b) is about mV
and V3a -- V1 '.40mV 40 mV = V1 =Vi -V3b, where CMP is an LM339 device made by Intersil
Inc. of USA R1 = 47 kQ, R2 = 4.7 kS?, R3 = 10 kQ, R4 = 220 kQ, R5 = 4.7 kS?, C1 = 1,uF, and the voltage between RPL and the earth is 5V.
The circuit of Figure 8 has the feature that, because the comparator CMP is employed as the active element, the change of the "L" period is equally obtainable either by changing the input signal level Vin or by changing the reference voltage Vref, which is the potential of the slider Y of the variable resistor 14 in Figure 6. Accordingly, the slider Y of the variable resistor 14 is usable to set the level of the gas concentration, for example, 50 ppm, for which an alarm signal with the lower pulsation frequency, for example 1 Hz, is to be issued. Such adjustment is necessary to attain detection of the gas leakage with as high a sensitivity as possible in relation to the level of background contamination of the atmosphere.
The circuit described above with reference to
Figure 8 has a small number of components and yet is still very advantageous.
Use of the apparatus for obtaining the highest possible sensitivity of detection is effected as follows:
After a lapse of 3 to 4 seconds from switching on of the power switch 15, to permit stabilisation of the detection sensor 3, the knob 14' of the variable resistor 14 is turned so that its slider Y is moved to its very low position, so that the VF converter VFC ceases to provide its output signal.
Thereafter, the knob 14' of the variable resistor
14 is carefully adjusted to move its sliding
terminal Y upwardly and find a critical position
where the VF converter start to issue a pulsating
output signal of a lowest frequency, for example
1 Hz. Then, from the critical position, the position
of the slider Y is again lowered by a predetermined
very narrow increment of one unit to a position
where the VF converter VFC does not issue the
pulse signal. By following the above procedure, the apparatus is now adjusted to a very sensitive
waiting condition to detect gas leakage. Between
different kinds of gas, for example, between
manufactured gas and natural gas, the detection
range is considerably different.Therefore, in order
to obtain high detection sensitivity with a similar
position of the slider Y of the variable resistor 14
for both kinds of gas, the detection range is
switched by use of the switch 1 7 to select the
series resistor VR6 and VR7 to be connected
between the point Y and the input terminal of the
VF converter VFC.
Figure 10 shows an overall characteristic curve
of one example of the apparatus embodying the
invention. The curve A shows the case when the
alarm set knob is suitably adjusted. As shown by
the graph, the apparatus has a good logarithmic
characteristic with respect to gas concentration,
which implies applicability for very wide ranges of
gas concentration. In the area of the pulsation or
blinking frequencies, above 20 Hz, which is for a
concentration value of above 0.35 volume %, the
light and sound alarm signals are made
continuous. In the lower area of the blinking
frequencies, below 1 Hz, which is for a
concentration value of about 0.01 volume %, the
light and sound alarm signals are stopped.
As the slider Y of the variable resistor 14 is slid
upwardly or downwardly, the curve A of Figure 10
shifts rightwardly, for example, to the curve C, or
leftwardly, for example to the curve B. By carefully
sliding the slider Y down from the above
mentioned critical position, thereby shifting the
curve leftwardly to a very highly sensitive position,
when the ambient atmosphere is very clean, a
small leakage of about 50 ppm or lower can be
reliably detected.
The gas intake rate in the intake path is
preferably slow for the sake of high sensitivity
detection in the case of a small leakage amount.
However, the intake rate should not be too small
in order not to lose the quick response
characteristic of the apparatus embodying the
present invention.
Provided that all of the leakage gas can be
taken in the gas intake path, which draws in air at
the rate of 200 cm3/min, and provided that the
leakage rate of the gas is 3.3 x 10-4 cm3/sec, ther
the concentration of the gas in the gas intake path
is 100 ppm, which is sufficiently within the stable detection range of the apparatus. This means that the apparatus can detect with higher sensitivity than the conventional method utilising a detection liquid, the maximum sensitivity of which method is about 5 x 10-4 cm3/sec.
If the circumstances (for example, ambient atmosphere) permit, the lowest detectable concentration is 1.6 x 10-4 atom cm3/sec, which corresponds to a concentration of 50 ppm.
In view of hydrodynamic resistance, the gas intake path and the attachment should have an inside diameter of 3 mm or larger; and for an inside diameter of 3 mm, the suction rate of the pump 7 should be about 200 cm3/min, in order to ensure a reasonable response speed of about 2 seconds for an extended attachment having a length of about 1 m. The suction rate of the suction pump 7 is preferably in the range of 100 to 400 cm3/min in order to obtain good results.
The average inside diameter of tubular parts of the attachment and the gas-intake path is preferably between 2 and 4 mm. When the suction rate of the pump 7 is over 400 cm3/min or the inside diameter is below 2 mm, the gas flow speed becomes too fast, thereby decreasing the detection sensitivity. When the suction rate is under 100 cm3/min or the insider diameter is over 4 mm, the detection response speed becomes too slow for this kind of apparatus.
Claims (14)
1. A gas leakage detector comprising:
a solid state gas sensor having a sintered metallic oxide block operative to change thermal conductivity by chemical absorption thereto and a wire to transfer the change of said thermal conductivity to an electrical signal;
a gas intake path in which a gas sensing part of said gas sensor is disposed;
a suction pump connected to said intake path in
a manner to draw a gas to be detected in said gas
intake path whereby the gas contacts the gas
sensor;
a variable frequency oscillator operative to
provide output pulses which change frequency in
response to an input voltage from the solid state
gas sensor; and
a sound and/or light alarm indicator which is
controlled to pulsate by the output pulses of the
variabie frequency oscillator.
2. A gas leakage detector according to claim 1,
wherein the sound and/or light provided by the
alarm indicator is controlled to pulsate in such a
manner that the frequency of pulsation can
change between a predetermined lower limit,
which corresponds to a lower limit of
concentration of gas to be detected, and a predetermined higher limit, which corresponds to
a higher level of concentration of gas to be detected, and the periods of time during which
light and/or sound are provided are uniform irrespective of changing of the pulsation frequency thereby making the light and/or sound continuous at said higher limit.
3. A gas leakage detector according to claim 2, wherein said lower limit is substantially equal to
1 Hz and said higher limit is substantially equal to 20 Hz.
4. A gas leakage detector according to claim 2 or claim 3, wherein said variable frequency oscillator is operative to issue an output signal to an off-delay timer or a one-shot multivibrator operative to control the output signal of an audiofrequency oscillator to produce a pulsating sound alarm signal.
5. A gas leakage detector according to claim 4, wherein said off-delay timer or one-shot multivibrator is operative to produce a pulse train wherein the on-period of each pulse is substantially equal to 25 ms.
6. A gas leakage detector according to any one of claims 2 to 5, wherein the variable frequency oscillator comprises a voltage-frequency converter having a first input terminal connected to receive said input voltage from the solid state gas sensor and a second input terminal connected to receive a reference voltage from a variable voltage source comprising a variable resistor to adjust said reference voltage and therefore to adjust the level of detection.
7. A gas leakage detector according to claim 6, wherein the voltage-frequency converter includes a comparator comprising:
an input terminal connected by a first resistor to said first input terminal of the voltage-frequency converter, by a capacitor to one terminal of a power source and by the series combination of a second resistor and a diode to an output terminal thereof; and
another input terminal connected by a third resistor to said second input terminal of the voltage-frequency converter and by a fourth resistor to said output terminal, which is connected by a fifth resistor to another terminal of said power source.
8. A gas leakage detector according to claim 6 or claim 7, which further comprises a range switching circuit for different types of gases connected between said second input terminal and said variable voltage source, said range switching circuit comprising a change-over switch and a plurality of semi-variable resistors connected thereto.
9. A gas leakage detector according to any one of the preceding claims, wherein a series combination of a sound alarm indicator and a switch is connected in parallel with a light alarm indicator.
10. A gas leakage detector according to any one of the preceding claims, wherein the suction pump comprises:
an electric motor capable of being driven by a battery;
a rotatable permanent magnet fixed on a shaft of said motor;
a pair of permanent magnets disposed on opposite sides of the rotatable permanent magnet and fixed on a reciprocatingly movable frame;
a diaphragm covering a closed space and having a movable part connected to the reciprocatingly movable frame; and
a pair of valves respectively mounted on a first port which is in said closed space and leads to said gas intake path and on a second port which is in said closed space and leads to an exhaust path.
11. A gas leakage detector according to any one of the preceding claims, wherein the suction rate of the suction pump is substantially in the range of 100 to 400 cm3/min and the overage inside diameter of an elongate tubular part of the gas intake path is substantially in the range of 2 to 4 mm.
12. A gas leakage detector according to any one of the preceding claims, which comprises an attachment releasably connectable to a gas intake connector which is disposed on a wall of a case of the detector and leads to the gas intake path, the inside diameter of said attachment being substantially in the range of 2 to 4 mm.
13. A gas leakage detector according to claim 12, wherein said attachment has an elongate nozzle.
14. A gas leakage detector according to claim 12, wherein said attachment has an extended part having an arc-shaped recess to fit the side of a tubular object.
1 5. A gas leakage detector according to claim 12, wherein said attachment has a conical extended end part having a flat opening to fit against a flat surface.
1 6. A gas leakage detector according to claim 14 or 15, wherein said end part has a mesh.
1 7. A gas leakage detector according to claim 12, wherein said attachment has a short tubular body of transparent or translucent material and a fine filter at its downstream end part.
1 8. A gas leakage detector substantially as herein described with reference to the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8008380A GB2072852B (en) | 1980-03-12 | 1980-03-12 | Gas leakage detectors |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8008380A GB2072852B (en) | 1980-03-12 | 1980-03-12 | Gas leakage detectors |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2072852A true GB2072852A (en) | 1981-10-07 |
| GB2072852B GB2072852B (en) | 1984-07-11 |
Family
ID=10512042
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8008380A Expired GB2072852B (en) | 1980-03-12 | 1980-03-12 | Gas leakage detectors |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2072852B (en) |
Cited By (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0224628A1 (en) * | 1985-11-26 | 1987-06-10 | Controfugas S.R.L. | Electronic correction circuit for a tracing element of an inflammable-gas leak detector |
| EP0327089A2 (en) * | 1988-02-04 | 1989-08-09 | Figaro Engineering Inc. | Gas detecting device |
| US5277057A (en) * | 1992-08-06 | 1994-01-11 | Yazaki Corporation | Gasoline detecting device |
| WO2003008923A3 (en) * | 2001-07-13 | 2003-12-31 | Inficon Gmbh | Sniffing leak detector and method for operation thereof |
| US7779675B2 (en) | 2005-03-03 | 2010-08-24 | Inficon Gmbh | Leak indicator comprising a sniffer probe |
| US7874201B2 (en) | 2005-09-13 | 2011-01-25 | Inficon Gmbh | Leakage search assembly having a sniffing probe |
| DE102016217891A1 (en) | 2016-09-19 | 2018-03-22 | Inficon Gmbh | Filling probe attachment with elongated gas-conducting element |
| CN110346417A (en) * | 2019-07-28 | 2019-10-18 | 北京交通大学 | A kind of tunnel inverted arch quality nondestructive testing instrument |
| CN113866351A (en) * | 2021-08-31 | 2021-12-31 | 应急管理部上海消防研究所 | Detection device for industrial flue gas emission |
-
1980
- 1980-03-12 GB GB8008380A patent/GB2072852B/en not_active Expired
Cited By (16)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0224628A1 (en) * | 1985-11-26 | 1987-06-10 | Controfugas S.R.L. | Electronic correction circuit for a tracing element of an inflammable-gas leak detector |
| EP0327089A2 (en) * | 1988-02-04 | 1989-08-09 | Figaro Engineering Inc. | Gas detecting device |
| EP0327089A3 (en) * | 1988-02-04 | 1990-12-19 | Figaro Engineering Inc. | Gas detecting device |
| US5277057A (en) * | 1992-08-06 | 1994-01-11 | Yazaki Corporation | Gasoline detecting device |
| GB2269456A (en) * | 1992-08-06 | 1994-02-09 | Yazaki Corp | Gasoline detecting device |
| GB2269456B (en) * | 1992-08-06 | 1996-05-01 | Yazaki Corp | Gasoline detecting device |
| EP2270457A1 (en) * | 2001-07-13 | 2011-01-05 | Inficon GmbH | Sniffing leak detector and method for operation thereof |
| WO2003008923A3 (en) * | 2001-07-13 | 2003-12-31 | Inficon Gmbh | Sniffing leak detector and method for operation thereof |
| US7159445B2 (en) | 2001-07-13 | 2007-01-09 | Inficon Gmbh | Sniffing leak detector and method for operation thereof |
| US7779675B2 (en) | 2005-03-03 | 2010-08-24 | Inficon Gmbh | Leak indicator comprising a sniffer probe |
| US7874201B2 (en) | 2005-09-13 | 2011-01-25 | Inficon Gmbh | Leakage search assembly having a sniffing probe |
| DE102016217891A1 (en) | 2016-09-19 | 2018-03-22 | Inficon Gmbh | Filling probe attachment with elongated gas-conducting element |
| US11841300B2 (en) | 2016-09-19 | 2023-12-12 | Inficon Gmbh | Fill probe attachment with elongated gas-guiding element |
| CN110346417A (en) * | 2019-07-28 | 2019-10-18 | 北京交通大学 | A kind of tunnel inverted arch quality nondestructive testing instrument |
| CN113866351A (en) * | 2021-08-31 | 2021-12-31 | 应急管理部上海消防研究所 | Detection device for industrial flue gas emission |
| CN113866351B (en) * | 2021-08-31 | 2024-04-12 | 应急管理部上海消防研究所 | Detection device for industrial flue gas emission |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2072852B (en) | 1984-07-11 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4369647A (en) | Gas leakage detector | |
| KR930008366B1 (en) | Optical indication and operation monitoring unit for vacuum cleaner | |
| US4550615A (en) | Fluid flowmeter | |
| GB2072852A (en) | Gas leakage detectors | |
| US4124793A (en) | Aquarium water heater | |
| US4010650A (en) | Apparatus for generating an electrical signal indicative of liquid level | |
| US3889247A (en) | Device for detecting the presence of liquids | |
| GB1578527A (en) | Apparatus for detecting water in oil | |
| IL106196A0 (en) | Methods and circuits for measuring the conductivity of solutions | |
| ES8307051A1 (en) | Apparatus for monitoring the level of liquid by resistive wire | |
| CA2305402A1 (en) | Battery capacity measurement circuit | |
| US4592147A (en) | Electrically actuated angular orientation indicating device | |
| JPS602614B2 (en) | Liquid concentration detection device | |
| US5311130A (en) | Electromagnetic field radiation detector having audible and visual indicators for detecting frequencies within the range of five hertz to four hundred kilohertz | |
| US4074562A (en) | Method and apparatus for measuring fluid specific gravity | |
| US3441737A (en) | Radiation sensitive sludge level testing device | |
| US3959108A (en) | System for automatically measuring and controlling the sulfate content of a chromium plating solution | |
| US3805224A (en) | Method and apparatus for monitoring biological activity | |
| KR890008564A (en) | Ultrasonic Handheld Refrigerator Leak Detector | |
| JPS5772010A (en) | Flow rate meter | |
| US5111188A (en) | Electronic fluid-level sensor with three state indicator | |
| CA1072184A (en) | Apparatus and method for detecting a substance in a fluid medium | |
| GR3019408T3 (en) | Blood coagulation time measurement | |
| GB2119932A (en) | Low pressure sensor for monitoring respiration | |
| JP2004024514A (en) | Pickup implement for measuring biomedical signal and biomedical signal measuring instrument |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PE20 | Patent expired after termination of 20 years |
Effective date: 20000311 |