GB2107061A

GB2107061A - Electrical carbon monoxide detecting devices

Info

Publication number: GB2107061A
Application number: GB08127274A
Authority: GB
Inventors: Willem Godijn
Original assignee: SESTO RES INST BV; RESEARCH INSTITUUT SESTO BV
Current assignee: SESTO RES INST BV; RESEARCH INSTITUUT SESTO BV
Priority date: 1981-09-02
Filing date: 1981-09-09
Publication date: 1983-04-20
Also published as: GB2107061B; DE3134692A1; BE890185A

Abstract

A CO detecting device comprises a column (1) through which a quantity of gas to be inspected flows, preferably under the action of a pump (2). A CO sensor is located within the column (1) and is supported by a holder (11). The CO sensor comprises a filament (12) and measuring electrodes. The arrangement of the sensor being such that only a portion of the gas flowing within the column (1) flows within the sensor, in order to reduce the cooling effect of the gas flow upon the sensor. Means (6, 7, 13) are provided within the column (1), upstream of the sensor for ensuring a uniform distribution of gas flow within the column (1) and for maintaining the humidity of the gas flow at an equal value throughout the distribution of the gas flow. Circuit means connected to the sensor provide a visual display of the CO concentration and also an alarm when a critical concentration is exceeded for longer than a threshold period of time. <IMAGE>

Description

SPECIFICATION A CO-detecting device The invention relates to a CO-detecting device provided with a CO-detector element (sensor) of the type consisting of a house with two oppositely located central passage openings and with contacts for the connection of an internal filament and of two internal measuring electrodes, the filament being heated by a voltage source and between the measuring electrodes and electric resistance being measured which is dependent on the CO concentration of the gas mixture flowing through the house of the CO detector element, said measuring electrodes being connected with an electronic circuit which converts resistance values into voltage values for the visual read-out of the CO concentration and which is equipped to activate one or more alarm devices.

Such a CO detecting device is already being used, though not at a large scale, for signalling a dangerous CO construction in rooms in which CO gas can be formed by incomplete combustion as a result of insufficient air supply, in certain factories (e.g. for processing synthetic materials), garages and in poorly ventilated rooms in which much people is present and in which people smoke.

The CO gas problem also occurs in greehhouse horticulture, where use is made of flue gases for the CO2 fertilization for promoting the growth of certain plants. The CO2 gas, which is innocent in itself, is normally present in air, which can be considered as a gas mixture of 78% of nitrogen, 21% of oxygen and circa 0.03% of CO2, among other gases. When the installation supplying the CO2 gas to the greenhouse does not work satisfactorily in certain circumstances, inadmissible concentrations of CO gas can occur in addition to the CO2 gas, which not only causes irreparable damage to the plants in the greenhouse, but also presents a risk of life to the persons who have to do their work in the greenhouse.

The dangers of the colourless and odourless carbon monoxide gas should not be underestimated. It is known that a CO concentration in the air of 0.2% (2000 particles per million or 2000 ppm) already presents a risk of life and that a CO concentration of 0.005% (50 ppm) is already dangerous. It may serve as an example that the exhaust gases of petrol engines normally contain 5 to 10% (50,000 to 100,000 ppm) of CO gas.

It is of essential importance that a CO detecting device is reliable in all respects. Many test of commercially available CO detecting devices, however, have shown that this is not the case at all.

It is therefore the purpose of the present invention to provide a CO detecting device of the type described in the preamble, which assures a very reliable functioning, of which the measuring results are accurate and reproducable, of which the construction is simple and little expensive and which can be adapted to certain requirements, to be made e.g. by the authorities.

According to the invention, it is therefore a characteristic of the CO detecting device that the voltage source for the heating of the filament of the CO sensor supplies a constant direct current, that the CO sensor is accommodated in a holder in a channel along which the gas mixture, of which the CO concentration must be determined, is kept flowing by means of a pump, the holder being washed by the greater part of this gas mixture flow and the CO sensor letting through the remaining part of this gas mixture flow only at a limited speed in order to prevent the cooling of the filament, that through means for the equal spreading of the gas mixture flow the humidity state of the part of the gas mixture flow which passes by the CO sensor, is kept equal to the prevailing humidity state of the gas mixture, and that the electronic circuit is fed by a constant direct current and is provided among other things, with a circuit which only allows the visual readout of CO concentrations above a first value (relevant value) as well as circuits in order to activate a direct alarm when the CO concentration considerably exceeds a critical value and to prevent that the alarm is made when during a certain period of time the CO concentration exceeds the critical value only slightly once or several times, during a short period.

In order to enable the use of one single or only a few detectors for monitoring large buildings, such as e.g. parking garages, it may be provided, according to an embodiment of the invention, that to the supply opening of the house are connected a number of lines running to different parts of a building, which lines by means of valves can be brought subsequently into connection with the house for measuring the CO concentration at a number of places in the building, means being provided for opening and closing the valves according to a certain cycle and, if necessary, for storing the values of the CO concentration measured at the different places in a memory for a certain time.

According to the invention the device may then be carried out in such a way, that after the observation of a CO concentration above a first value, ventilators or the like with a certain capacity are switched on and the exceeding of this value is recorded in the memory, that after the observation of a CO concentration above a second value ventilators of the like with a certain higher capacity are switched on and the exceeding of this value is recorded in the memory, that after the observation of a CO concentration above the critical value the alarm is activated and the means for opening and closing the valves according to a certain cycle are put out of operation in such a way that the device keeps measuring at the place where the critical value of the CO concentration was exceeded until the CO concentration has dropped under the critical value and the alarms have been switched off.

The invention will now be explained with reference to the drawing, in which Figure 1 schematically shows components of an embodiment of a CO detecting device according to the invention, and Figure 2 shows a block diagram of the electronic circuit and of stabilization circuits for the feeding of the circuits of this circuit and of the filament of the CO sensor.

The mechanical components, shown in figure 1, of the CO detecting device comprise a vertically arranged condensor column 1, an electrically driven suction pump 2 and a depression switch 3 for the alarming (not shown) as soon as the functioning of the pump stagnates for one reason or another.

The condensor column 1, of preferably a circular section, comprises two essentially closed chambers 4 and 5, separated by a partition 6 with a central opening 7.

The upper chamber 4 comprises at the upper end an exhaust tube 8, which is connected by a line 9, e.g. of synthetic material, with the suction pump 2. The suction pump 2, which is connected with an exhaust line 10, provides in the condensor column 1 a depression of circa 12 mm of water column. In the upper chamber 4 a holder 11 is mounted to the inside wall, in which holder a CO detecting element (sensor) 12 is accommodated with the connection contacts for the filament and the measuring electrodes directed upwards.

Parallel to the partition 6 a fine-meshed grid, e.g.

of gauze, is provided, the surface of which is limited by the side wall of the condensor column.

This grid not only serves to retain any pollutions such as soot particles but also, as will be explained later, to realize an equal spreading of the gas mixture flow in the upper chamber 4. In the side wall of the upper chamber there is between the partition 6 and the grid 13 a connecting tube 14, which is connected through a line 15, e.g. of synthetic material, with the depression switch 3.

The lower chamber 5 is closed at the lower end by a water lock 16, which-already before the putting into operation has been filled with water (circa 20 ml) and which is provided with an exhaust tube 17, put through the lateral wall, for evacuating superfluous condensation water through a line 18. In the side wall of the lower chamber 5 is provided above the water lock 1 6 a supply tube 19 for supplying the sucked in gas mixture of which the CO concentration must be determined. The supply tube 19 is connected through a line 20, e.g. of synthetic material, which runs down so that condensation water can flow down to the water lock, with a metal pipe 21, e.g.

of copper. The pipe 21 can be placed at any place in the space around the CO detecting device, but in the case of greenhouse horticulture it is of importance that this pipe in the flue gas channel is placed as close to the CO2 producing boiler as possible.

In order to assure a stable working and extremely accurate and reproducable measuring results of the CO detecting device, the following measures have been taken according to the invention.

a) The holder 11 of the CO detector element 12 has a special shape. The holder, which is placed axially in the upper chamber 4, has a cylindrical part which entirely encloses the cylindrical house of the CO detecting element 12.

This cylindrical part becomes funnel-shaped at the lower side and ends in a straight tube with an opening 22. The gas mixture, which is kept flowing by the suction pump 2, of which the CO concentration must be determined, washes the outer wall of the cylindrical part of the holder for the greater part, as is shown by arrows in Figure 1. The detector element receives the remaining part of the gas mixture flow through the opening 22 in the holder at a relatively low flow speed. It has appeared in practice, that a low flow speed causes no noticeable cooling of the filament of the detector element, which assures a stable working of the detector element.

b) By an equal spreading of the gas mixture flow in the upper chamber 4, the humidity state of the part of the gas mixture flow through the detector element 12 is kept equal to the prevailing humidity state of the gas mixture, of which the CO concentration must be determined The gas mixture sucked in through the line 20 first passes the opening 7 in the partition 6 and subsequently the grid 1 3. An efficient spreading is obtained in this way. As the measuring results of CO detector elements of the above-mentioned type are dependent on the humidity state of the gas mixture to be measured, it is prevented by said spreading of the gas mixture that, even when the humidity state of the gas mixture remains constant and the CO concentration does not change, the CO detector element would give deviating measuring results.

c) The filament of the CO detector element 12 is heated by a constant direct current. Also the electronic circuit, which converts the resistance values observed between the measuring electrodes of the CO detector element into voltage values, is fed by a constant direct current.

Figure 2 shows a block diagram of the electronic circuit consisting of several circuits and of stablization circuits for feeding this circuit and the filament of the CO detector element 12. In the present case the supply voltages are taken from the electricity network. By transformation, rectification, smoothing and stabilization in the circuits 23 and 24, the desired constant direct currents are obtained, namely 12 Volts for the circuits of the electronic circuit and 5 Volts for the filament of the CO detector element 12. A pilot lamp 25 burns only when both supply voltages are present. Of course the constant supply voltages can also be obtained from a battery, so that in that case the CO detecting device will be completely insensitive to temporary or prolonged interruptions of the network supply.

Figure 2 shows that the measuring electrodes of the CO detector element 12 are connected with a measuring bridge 26. The resistance between the measuring electrodes of the element 12, which resistance depends on the CO concentration and which amounts to some dozens of Ohms, is converted by the measuring bridge 26 into a voltage value. By means of a test button 27 the measuring bridge can be deranged intentionaliy, so that all following circuits of the electronic circuit are tested for their proper functioning. By a separation amplifier 28, which has a high resistance input impedance, it is prevented that the measuring bridge 26 is loaded and thereby becomes inaccurate by the following circuits.

There is a meter 29, which only gives a visual indication at gas concentrations above a certain value (15 ppm), the so-called relevant value. The threshold serving that purpose is provided by a threshold circuit 30. Therefore, fluctuations in the gas concentration remaining below 1 5 ppm cannot be read. Thus a psychological fixation on an irrelevant meter reading is avoided. The meter 29 indicates to which extent the critical value (50 ppm) has been exceeded or has not yet been reached.

A second threshold circuit cuts off concentration values below 50 ppm, so that only values above 50 ppm are fed to the integrator circuit 32. The integrator circuit 32 integrates theoverconcentration towards the time, so that a slight exceeding of the critical value will take considerably more time to activate the alarm than an important exceeding. The alarm obtained in this way signals real danger. The time delay also assures that short exceedings of the critical value, e.g. at the switching on of a heating boiler, do not cause the alarm to go off.

A zero-setting circuit 33 becomes active and brings the integration process to an end as soon as the gas concentration has dropped slightly below the critical value, i.e. has reached a value of 45 ppm. Thus it is avoided that when during a certain period of time, e.g. a day or a week, the CO concentration slightly exceeds the critical value for a short time once or several times the alarm is activated after all.

When by the integration process in the integrator 32 a certain voltage value has been reached, a level detection circuit 34 will react thereto. In this case the circuit 34 activates a holding circuit 35 comprising a trigger, whereby the alarm is switched on. The alarm continues, even when the CO concentration is low again, until the holding circuit 35 has been re-set by means of the re-set button 36. A second zero setting circuit 37 assures that the integrator circuit 32 is inactive and that the holding circuit 35 remains in the re-set position during the warming-uptime (5 minutes) of the filament of the CO detector element 12. Thus it is avoided that already at the putting into operation of the CO detecting device an alarm, in this case a false alarm, is given.

The alarm can be given in different ways, namely through a relay circuit 38, visually by means of a lamp 39 and acoustically by means of a loud-speaker 40. Besides giving the alarm, the relay circuit can carry out several other functions, such as closing and or opening valves, switching on ventilators, air conditioning installations and the like. The intervals of the visual and acoustic alarm are determined by an interruption circuit 41 which is connected with the lamp 39 and with the loud-speaker 40 through a circuit 42 which supplies an acoustic signal.

The components of all circuits shown in figure 2, with the exception of a network transformer in circuit 23, can be mounted on a printed conductor pattern on a plate of insulating material of small dimensions.

As already observed above, a single device can also be used for detecting the CO concentration at a number of points inside a building.

On the line 20, shown in Figure 1, can then be connected a number of parallel-connected electrically operated valves which are connected with lines running to the places concerned in the building, so that the gas mixture to be measured can be sucked from those placed by subsequently opening and closing the valves in a certain cycle.

When at a certain place the CO concentration exceeds a first value, this is signalled, e.g. by means of a signal lamp, and a ventilator or an air conditioning installation is switched on in order to try to reduce the CO concentration. The signal lamp keeps burning until the following measurement is carried out at the place concerned. If the CO concentration has dropped below the first value, then the signal lamp goes out and the original condition re-establishes itself.

When the concentration exceeds a second value, the ventilator or the air conditioning installation is switched to a higher capacity, or more of such devices are switched on and a signal lamp lights up as a sign that the measurement has been stored in the memory.

When the concentration exceeds a third, critical value, then the alarm situations will begin after a certain period of time, e.g. of two minutes, in that the holding circuit 35 is activated, as described above. From that moment on the measurement cycle is interrupted and measurements are made only at the place where the alarm situation occurred. The original situation can be repaired only after a drop of the CO concentration until below the critical value and after the re-set button 36 has been operated.

It will be obvious that the above-described device requires a number of additional electronic circuits with respect to the block diagram shown in Figure 2, but these additional electronic circuits want no further explanation.

Experiments have demonstrated that the CO -detecting device according to the invention is very reliable and provides accurate and reproducable measuring results. It will be obvious that within the framework of the invention the level and threshold values which determine when and at which CQ concentration values the alarm must be activated, can be modified according to the need.

Finally it is observed that, as is the case with all CO detecting devices, the CO detecting device according to the invention reacts mainly, but not exclusively, to CO gas.

Claims

1. A CO-detecting device provided with a CO detector element (sensor) of the type consisting of a house with two oppositely located central passage openings and with contacts for the connection of an internal filament and of two internal measuring electrodes, the filament being heated by a voltage source and between the measuring electrodes an electric resistance being measured which is dependent on the CO concentrations of the gas mixture flowing through the house of the CO detector element, said measuring electrodes being connected with an electronic circuit which converts resistance values into voltage values for the visual read-out of the CO concentration and which is equipped to activate one or more alarm devices, characterized in that the voltage source for heating the filament of the CO detector element supplies a constant direct current, that the CO detector element is accommodated in a holder in a channel along which the gas mixture, of which the CO concentration must be determined, is kept flowing by means of a pump, the holder being washed bs the greater part of this gas mixture flow and the CO detector element letting through the remaining part of this gas mixture flow only ata limited speed in order to prevent the cooling of the filament, that through means for equal spreading of the gas mixture flow the humidity state of the part of the gas mixture flow which passes by the CO detector element, is kept equal to the prevailing humidity state of the gas mixture, and that the electronic circuit is fed by a constant direct current and is provided, among other things, with a circuit which only allows the visual read-out of CO concentrations above a first value (relevant value), as well as circuits in order to activate a direct alarm when the CO concentration considerably exceeds critical value and to prevent that the alarm is made when during a certain period of time the CO concentration exceeds the critical value only slightly once or several times, during a short period.

2. A detecting device according to Claim 1, characterized by a vertically arranged condensor column consisting of two essentially closed chambers, which are separated by a partition with a central opening, the upper chamber having at the upper end an exhaust tube for connection to a suction pump and being provided with the holder with the CO detector element enclosed therein, as well as with a fine-meshed grid parallel to the partition, which acts as a filter and serves for the equal spreading of the gas mixture flow, the lower chamber at the lower end being closed by a water lock, which has been filled with water already before its putting into operation and which has an exhaust tube for superfluous condensation water, and having in the side wall above this water lock a supply tube for the supply of the sucked gas mixture of which the CO concentration must be determined.

3. A detecting device according to Claim 1 or 2, characterized in that the holder of the CO detector element is placed axially in the condensor column and has the shape of a cylinder, which laterally encloses the detector element entirely and which at the lower side becomes funnel-shaped and ends in a straight tube.

4. A detecting device according to Claims 1,2 or 3 characterized in that the side wall of the upper chamber between the partition and the grid has a connecting tube for a connection with a depression switch in order to be able to give the alarm when the pump function stagnates.

5. A detecting device according to Claims 1,2, 3 or 4, characterized in that the supply tube for the gas mixture to be measured is connected with a supply line which runs downward, so that condensation water can flow to the water lock.

6. A detecting device according to anyone of the preceding Claims, characterized in that the electronic circuit comprises a circuit which, when the detecting device is put into operation, prevents that the alarm is given during the warming up time of the filament of the CO detector element.

7. A detecting device according to anyone of the preceding Claims, characterized in that on the supply opening of the house are connected a number of lines running to different places of a building, which lines can be brought subsequently into connection with the house by means of valves for measuring the CO concentration at a number of places in the building, means being provided for opening and closing the valves according to a certain cycle and, if necessary, for storing the CO concentration valves measured at the different places in a memory for a certain time.

8. A detecting device according to Claim 7, characterized in that after the observation- of a CO concentration above a first value, ventilators or the like with a certain capacity are switched on and the exceeding of this value is stored in the memory, that after the observation of a CO concentration above a second value, ventilators or the like with a certain higher capacity are switched on and the exceeding of this value is stored in the memory, that after the observation of a CO concentration above the critical value, the alarm is activated and the means for opening and closing the valves according to a certain cycle are put out of operation in such a way, that the device keeps measuring at the place where the critical value of the CO concentration was exceeded until the CO concentration has dropped below the critical value and the alarm has been switched off.

9. A CO detecting device having a CO sensor comprising a housing through which gas to be monitored passes, an internal filament and two measuring electrodes for detecting the CO concentration of the gas, wherein the CO sensor is positioned within a column in which the gas flows, the arrangement of the sensor being such that only a portion of the gas flowing within the column flows through the sensor, so as to reduce cooling of the filament by the gas flow, means being provided within the column, downstream of the sensor, for ensuring a uniform distribution of gas flow within the column and for maintaining the humidity of the gas flow at an equal value throughout the distribution of the gas flow and circuit means responsive to the sensor for providing a visual display of the CO concentration and for providing an alarm when a critical concentration is exceeded for longer than a threshold period of time.

1 0. A detecting device substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.