GB2165948A - Gas or vapour monitor - Google Patents
Gas or vapour monitor Download PDFInfo
- Publication number
- GB2165948A GB2165948A GB08426766A GB8426766A GB2165948A GB 2165948 A GB2165948 A GB 2165948A GB 08426766 A GB08426766 A GB 08426766A GB 8426766 A GB8426766 A GB 8426766A GB 2165948 A GB2165948 A GB 2165948A
- Authority
- GB
- United Kingdom
- Prior art keywords
- formaldehyde
- humidity
- vapour
- fumigation
- monitor
- 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
- WSFSSNUMVMOOMR-UHFFFAOYSA-N Formaldehyde Chemical compound O=C WSFSSNUMVMOOMR-UHFFFAOYSA-N 0.000 claims abstract description 266
- 238000003958 fumigation Methods 0.000 claims abstract description 25
- 244000005700 microbiome Species 0.000 claims abstract description 18
- 238000000034 method Methods 0.000 claims abstract description 16
- 230000009467 reduction Effects 0.000 claims abstract description 13
- 230000001665 lethal effect Effects 0.000 claims abstract description 9
- 238000005259 measurement Methods 0.000 claims description 8
- 230000001419 dependent effect Effects 0.000 claims description 7
- 239000004065 semiconductor Substances 0.000 claims description 5
- 238000001179 sorption measurement Methods 0.000 claims description 3
- 230000004044 response Effects 0.000 claims description 2
- 230000008569 process Effects 0.000 abstract description 3
- 239000000523 sample Substances 0.000 description 9
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 6
- 230000000694 effects Effects 0.000 description 5
- 238000002474 experimental method Methods 0.000 description 5
- 238000012544 monitoring process Methods 0.000 description 5
- 239000000126 substance Substances 0.000 description 5
- 239000007789 gas Substances 0.000 description 4
- WSFSSNUMVMOOMR-NJFSPNSNSA-N methanone Chemical compound O=[14CH2] WSFSSNUMVMOOMR-NJFSPNSNSA-N 0.000 description 4
- 230000008901 benefit Effects 0.000 description 3
- 230000008859 change Effects 0.000 description 3
- 238000009826 distribution Methods 0.000 description 3
- 230000004048 modification Effects 0.000 description 3
- 238000012986 modification Methods 0.000 description 3
- 241000005398 Figaro Species 0.000 description 2
- 238000004566 IR spectroscopy Methods 0.000 description 2
- 229930040373 Paraformaldehyde Natural products 0.000 description 2
- 238000004364 calculation method Methods 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 230000001276 controlling effect Effects 0.000 description 2
- 238000005202 decontamination Methods 0.000 description 2
- 230000003588 decontaminative effect Effects 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 230000007613 environmental effect Effects 0.000 description 2
- 238000004817 gas chromatography Methods 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 229920002866 paraformaldehyde Polymers 0.000 description 2
- 238000012935 Averaging Methods 0.000 description 1
- 244000063299 Bacillus subtilis Species 0.000 description 1
- 230000004075 alteration Effects 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 238000003556 assay Methods 0.000 description 1
- 238000009833 condensation Methods 0.000 description 1
- 230000005494 condensation Effects 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 238000004320 controlled atmosphere Methods 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 239000012678 infectious agent Substances 0.000 description 1
- 208000015181 infectious disease Diseases 0.000 description 1
- 230000002458 infectious effect Effects 0.000 description 1
- 239000002085 irritant Substances 0.000 description 1
- 231100000021 irritant Toxicity 0.000 description 1
- 231100000518 lethal Toxicity 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 230000000813 microbial effect Effects 0.000 description 1
- 230000002906 microbiologic effect Effects 0.000 description 1
- 230000002093 peripheral effect Effects 0.000 description 1
- 239000004033 plastic Substances 0.000 description 1
- 229920003023 plastic Polymers 0.000 description 1
- 229920000642 polymer Polymers 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- 238000005070 sampling Methods 0.000 description 1
- 239000012047 saturated solution Substances 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 230000004083 survival effect Effects 0.000 description 1
- 239000000725 suspension Substances 0.000 description 1
- XOLBLPGZBRYERU-UHFFFAOYSA-N tin dioxide Chemical compound O=[Sn]=O XOLBLPGZBRYERU-UHFFFAOYSA-N 0.000 description 1
- 229910001887 tin oxide Inorganic materials 0.000 description 1
- 231100000331 toxic Toxicity 0.000 description 1
- 230000002588 toxic effect Effects 0.000 description 1
- 231100000419 toxicity Toxicity 0.000 description 1
- 230000001988 toxicity Effects 0.000 description 1
- 238000009834 vaporization Methods 0.000 description 1
- 238000009423 ventilation Methods 0.000 description 1
Classifications
-
- 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
- G01N33/0027—General constructional details of gas analysers, e.g. portable test equipment concerning the detector
- G01N33/0036—General constructional details of gas analysers, e.g. portable test equipment concerning the detector specially adapted to detect a particular component
- G01N33/0047—Organic compounds
-
- 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
- G01N33/0027—General constructional details of gas analysers, e.g. portable test equipment concerning the detector
- G01N33/0031—General constructional details of gas analysers, e.g. portable test equipment concerning the detector comprising two or more sensors, e.g. a sensor array
- G01N33/0032—General constructional details of gas analysers, e.g. portable test equipment concerning the detector comprising two or more sensors, e.g. a sensor array using two or more different physical functioning modes
Landscapes
- Chemical & Material Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Health & Medical Sciences (AREA)
- Analytical Chemistry (AREA)
- Food Science & Technology (AREA)
- Medicinal Chemistry (AREA)
- Physics & Mathematics (AREA)
- Combustion & Propulsion (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Investigating Or Analyzing Materials By The Use Of Fluid Adsorption Or Reactions (AREA)
- Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)
Abstract
A gas or vapour (e.g. Formaldehyde) monitor senses gas at vapour concentration together with temperature and humidity. By comparison with the known lethal effect of formaldehyde at particular levels of humidity, a fumigation process can be controlled automatically to produce a desired reduction in micro- organism population. Excess usage of formaldehyde can thereby be avoided. <IMAGE>
Description
SPECIFICATION
Formaldehyde monitor
This invention relates to the monitoring of gas or vapour concentration and in one important example to the monitoring of formaldehyde in fumigation or decontamination procedures.
Fumigation of rooms or chambers in laboratories, hospitals, pharmaceutical production areas and the like is used routinely for the reduction of microbial levels. It may take place after known contamination with infectious microorganisms or as a precaution before commencing work requiring "clean" conditions. Formaldehyde vapour is the most commonly employed chemical in microbiological decontamination. It is effective against a wide range of microorganisms and is easily produced as a vapour phase. Formaldehyde is relatively inexpensive and easily available.
There are, however, a number of disadvantages in using formaldehyde. The vapour is irritant and toxic and the low threshold limit value (TLV) which is currently recognised as 2 ppm-is very much lower than the levels required for fumigation. There are difficulties in removing formaldehyde vapour after fumigation as paraformaldehyde polymers are often deposited on surfaces during the fumigation procedure. The gradual vapourization of formaldehyde from these deposits will give a background level of formaldehyde vapour which may exceed the TLV unless excellent ventilation is provided. This situation is complicated by the use of added water to raise the humidity levels during fumigation.It is known that the lethal effect of formaldehyde on microorganisms is usually greater in increased relative humidity but the presence of water vapour increases the tendency for the formaldehyde to polymerise and the presence of condensation may effectively remove the formaldehyde as the vapour is readily soluble in water.
The currently accepted practices for fumigation with formaldehyde involve a calculation of the required amount of formaldehyde from the known room volume. The relative humidity is usually artificially increased but there is little quantitative evidence to support the accepted amounts of formaldehyde per unit volume and little knowledge of the quantitative effects of increasing relative humidity. There is necessarily a tendency to "play safe" and this has resulted in gradually escalating quantities of formaldehyde being used. From a cost viewpoint this is probably not significant but it does severely aggravate the problems arising from the toxicity of the vapour and the difficulties of removing the vapour to return to safe levels as quickly as possible after the end of the fumigation process.
A controlled formaldehyde fumigation system has been suggested (Applied and Environmental
Microbiology March 1980 pages 480-487) in which an electric formaldehyde vapour generator is controlled from the output of an electronic formaldehyde monitor. This monitor is based on a direct adsorption semiconductor sensor, the conductivity of which changes on exposure to reactive vapours such as formaldehyde. Such a monitor has considerable advantages over other assay methods such as direct chemical estimation (with for example Draeger tubes); indirect chemical estimation using air samples collected for later analysis; infra red spectrophotometry and gas chromatography.Chemical estimation, whether direct or indirect, is impractical where continuous monitoring is required, whilst both infra red spectrophotometry and gas chromatography involve the considerable expense of piping samples from the room which is being fumigated to the measuring instrument. Such pipes may need to be heated to avoid polymerisation. A difficulty with the semiconductor sensing device is that the output is dependent upon relative humidity levels. This introduces an error in the monitor output. A further, and more important, disadvantage of this prior system is that no account is taken of the artificially increased relative humidity level on the fumigation process itself. Lack of knowledge of the actual relative humidity level may result in an over-estimate of the formaldehyde level required.
Under certain conditions, excess water may be being added thus unnecessarily aggravating the difficulties mentioned above of polymerisation and solubility of formaldehyde in condensed water.
It is an object of one aspect of this invention to provide an improved formaldehyde monitor for use in fumigation procedures which enjoys the advantages of a direct electrically reading sensor device whilst reducing errors arising from variations in relative humidity.
It is an object of this invention in a further aspect to provide a formaldehyde monitor and control device, and a fumigation method, by which the amount of formaldehyde used may be brought to the minimum consistent with the desired lethal effect of microorganisms, and with operational constraints on humidity and the like.
Accordingly, the present invention consists in one aspect in a formaldehyde monitor for use in fumigation procedures, comprising a formaldehyde sensor device providing an electrical indication of formaldehyde vapour concentration; a humidity measurement device providing an electrical indication of relative humidity; a temperature responsive electrical circuit device and a processor connected to receive inputs from said devices and arranged when calibrated to provide an output value for formaldehyde vapour concentration corrected for humidity and temperature dependent variations in the formaldehyde sensor device.
In another aspect, the present invention consists in a formaldehyde monitor and control device providing an output for the control of a formaldehyde vapour generator in a fumigation procedure effective against microorganisms, comprising a formaldehyde sensor device providing an electrical indication of formaldehyde vapour concentration; a humidity measurement device providing an electrical indication of relative humidity; a temperature responsive electrical circuit device and a processor connected to receive inputs from said devices and arranged when calibrated to provide an output value for formaldehyde vapour concentration corrected for humidity and temperature dependent variations in the formaldehyde sensor device and further arranged to generate a formaldehyde vapour control output derived from the measured formaldehyde vapour concentration value, the measured relative humidity, the previously known lethal effect of the said concentration at the said relative humidity and the predetermined desired reduction in microorganism population.
In yet a further aspect, the present invention consists in a fumigation method for killing microorganisms in a volume, comprising the steps of generating formaldehyde vapour in said volume; measuring the formaldehyde vapour concentration; measuring the relative humidity in said volume; deriving a control signal based on the measured formaldehyde vapour concentration, the measured humidity and the known fumigation effectiveness of formaldehyde at the said humidity level and controlling said vapour generation step in response to said control signal.
Although particularly useful for monitoring formaldehyde, this invention will have application to other gas or vapour monitors where environmental factors introduce errors in the output of an electrical sensor device.
Accordingly, the present invention consists, in yet a further aspect, in a monitor comprising a sensor device providing an electrical indication of a gas or vapour concentration; a humidity measurement device providing an electrical indication of relative humidity; a temperature responsive electrical circuit device and a processor connected to receive inputs from said devices and arranged when calibrated to provide an output value for the said concentration corrected for humidity and temperature dependent variations in the sensor device.
Advantageously, the sensor device comprises a semiconductor sensor.
The invention will now be described by way of example with reference to the accompanying drawings, in which:
Figure 1 shows a formaldehyde monitor and control device according to this invention, partly in block form and partly diagrammatic,
Figures 2a), b) and c) are circuit diagrams of respectively formaldehyde, humidity and temperature measuring circuits contained within the metering unit of Fig. 1,
Figure 3 is a graph showing the decline in population of a microorganism on exposure to formaldehyde,
Figure 4 is a graph showing the variation in lethal effect with formaldehyde concentration of differing relative humidities, and
Figure 5 is a block diagram illustrating a modification to the monitor and control device shown in Fig. 1.
Referring to Fig. 1, a probe 10 is connected through multichannel cable 12 to a metering unit 14. As will be described, the probe 10 contains sensing devices which are connected through the cable 12 with respective measuring circuits in the unit 14. In the practical embodiment the monitor would include a number of identical probes each connected to its own metering unit. In this particular example, five probes are provided, though for clarity only one is shown in the drawing. The five metering units 14 are each connected to a common distribution board 16.
This distribution board serves to connect the various metering units with a power supply unit 18 and a multichannel analogue to digital convertor 20. The power supply unit provides various direct and alternating power supplies details of which are best given in the description of the metering units which follows. The analogue to digital convertor is a commercially available circuit board providing sixteen channels of eight bit analogue to digital conversion.The A/D convertor is connected with a microprocessor 22 which conveniently takes the form of a commercially available microcomputer. This microcomputer is provided with peripherals shown generally at 24 which may include a- VDU, disc storage and a printer.
Referring additionally to Fig. 2a), the formalhyde sensing device 24 is a direct adsorption semiconductor sensor based on sintered tin oxide (Figaro 812 sensor, Figaro Engineering Inc,
Osaka, Japan). Exposure to reactive vapours causes a change in the sensor conductivity which can be used as a measure of vapour concentration. The sensor is not specific for formaldehyde vapour but this is not a problem since the formaldehyde levels to be monitored are normally hundreds of times greater than those of any interferant. The sensor incorporates a heater and receives a regulated five volt heater supply from the power supply unit. This is achieved using a constant current source which minimises the effect of cable resistances. As shown in Fig. 1, the portion of the probe containing the formaldehyde sensing device is separated from the remainder of the probe by a finned heat sink 26. As can be seen in Fig. 2a, the measurement circuit comprises a current/voltage convertor input stage followed by an operational amplifier to increase the output voltage and provide span adjustment. The circuitry has an output range of O to 2.5 volts corresponding to the range 0 to 3000 ppm formaldehyde.
The humidity sensor 28 is of the type formed of specially treated plastics material which undergoes a large change of impedance as the water content of the surrounding air is altered (PCRC 32 Physical Chemical Research Corporation.) The sensor receives a low frequency (60 Hz)
AC supply from the power supply unit and, as shown in Fig. 2b, is connected with a high impedance input stage followed by a precision rectifier and span and zero adjustment stages.
The measurement circuitry gives an output of O to 2.5 volts over the range of humidity from 25% to 100% rH.
The temperature responsive element 30 is an NTC thermistor connected, as shown in Fig. 2c), in a standard bridge circuit. A single operational amplifier stage is used to provide zero and span adjustment and an output range of O to 2.5 volts is provided corresponding with a temperature range of O to 50"C.
The outputs of the Fig. 2a), b) and c) circuits, each comprising a voltage in the range 0 to 2.5
V are passed via the distribution board 16 to respective channels in the A/D convertor 18. In this way the microprocessor receives 8-bit digital signals indicative of apparent temperature, humidity and formaldehyde levels as directly measured at each probe. These digital signals may be referred to as XT, XH and x,.
In the microprocessor, the actual temperature T"C is calculated from the expression: log,, T C T"C=m,x,+C, where mT and CT are slope and intercept constants determined by calibration. With multiple sampling and averaging to reduce errors in the A/D conversion, a resolution of about +/ 0.2"C should be obtainable. The humidity measurement is calibrated using saturated solutions of various organic salts to give humidity controlled atmospheres in the range 33% to 98% rH.
Because of the moderate temperature coefficient of the humidity sensor, it is necessary to repeat the calibrations at a range of temperatures. When calibrated, the microprocessor can calculate the humidity levels rH from the expression: rH%=mHX"+CH+(0.62[25 T C]) The formaldehyde sensing device is calibrated using chemically determined vapour concentrations under controlled humidity and temperature conditions. The concentration of formaldehyde (mgm
HCHO) may be calculated by the microprocessor according to the expression: log",(mgm 3 HCHO)=(mr/rH%+C").X,+C', Using apparatus as described above, experiments can be carried out to determine the effects of differing humidities and formaldehyde levels on the survival of microorganisms.The graph of
Fig. 3 shows the decline in population of B. globigii spores on exposure to a known formaldehyde concentration at a known relative humidity. The curve has an initial plateau followed by a linear section which tails off as the surviving fraction becomes very small. The initial plateau indicates that some time is necessary for formaldehyde to effect cells and this lag phase is found to be most apparent under those conditions which give the highest death rate.
The slope of the logarithmic portion of the graph can be used to calculate the decimal reduction time for the particular conditions of exposure. This is defined as the time required to reduce the population by one logarithmic decade. The logarithmic phase corresponds with the period of maximum death rate during which the decimal reduction time is the shortest; that is to say Dmin. A series of experiments can then be performed and Dmin measured for differing formaldehyde concentrations at different relative humidity levels. The results of one series of such experiments is shown in Fig. 4 where the Dmin value in minutes is plotted against formaldehyde concentration for differing relative humidities.From such work a relationship has been established between Dmin and the formaldehyde concentration:
A D . min= B+mgm 3HCHO where B is a constant and A is related to relative humidity in accordance with the formula: A=a-b rH% Experimental values have been determined as a=12471 b=108
A number of conclusions can be drawn from the experimental work. There is a minimum level below which formaldehyde vapour is not lethal. This level can be calculated to be about 40 mgm3. In practice some small effect is likely but the resulting very long decimal reduction times make the use of such low levels unrealistic. There is then a range of levels of formaldehyde (about 50 to 150 mgm3) over which small changes in concentration give very marked alterations in Dmin.Above 200 mgm 3, the change in Dmin is small with increasing levels of formaldehyde. "Dry formaldehyde" is still effective as a decontaminant at 30% humidity although the Dmin value for a given concentration is longer than for high humidities.
Whiist the quoted experiments have been carried out on only one microorganisms, the biological spore chosen (B. globigli) is more resistant than most infectious agents and use of the relationships given should allow a generous safety margin in relation to other microorganism.
Returning to the apparatus which is shown in Fig. 1, the microprocessor 22 is arranged to calculate values of Dmin at, say, one minute intervals using the measured and corrected values of formaldehyde and relative humidity. The total lethal effect D can then be calculated using the expression
where To is a starting time chosen to exclude the initial lag period and TF is the total exposure time. The value D is then indicative of the reduction achieved in the microorganism population.
Using apparatus according to the invention in one mode, the described continuous monitoring enables a calculation to be made of D for the fumigation procedure. In a preferred mode of operation, a desired value of D is preset in the microprocessor together with information on operational constraints such as limits on humidity and time. The microprocessor provides a signal for controlling a formaldehyde vapour generator which may usefully comprise an oil bath containing a controlled amount of paraformaldehyde powder in suspension. In this way apparatus according to the invention will achieve the desired reduction in microorganism population without using excessive formaldehyde. In, for example, a routine fumigation procedure in a pharmaceutical production area, the desired reduction may be only 3 or 4 log cycles.Apparatus according to this invention will enable that reduction to be achieved with confidence at significantly reduced formaldehyde concentrations, enabling the area to be made ready for use much more quickly. In an area known to be heavily contaminated a reduction in microorganism population of, say 12 to 14 cycies may be necessary. Again, however, the invention enables that reduction to be achieved under optimum conditions.
It is relevant that whilst the experiments that have been described indicte that there is little gain in raising the formaldehyde level above 400 mgm 3, typical calculated values using current recommendations would be between 7000 and 14000 mgm3.
In a modification, illustrated in Fig. 5, a single metering circuit is provided, comprising a formaldehyde measuring circuit 50, a humidity measuring circuit 52 and a temperature measuring circuit 54. Each measuring circuit receives its input from a respective analogue multiplexer 56 which is in turn connected to the appropriate probe sensing devices. Each multiplexer receives a channel select signal from the processor on line 58.
This modified embodiment will be advantageous where there are many probes and also has the benefit of requiring only a three channel analogue to digital converter.
This invention has been described by way of example only and a variety of modifications are possible without departing from the scope of the invention as set forth in the accompanying claims. Thus, whilst the invention has been described with particular reference to formaldehyde, the skilled man will appreciate that it has application to other gases or vapours monitored with the same or similar detection devices.
Claims (8)
1. A formaldehyde monitor for use in fumigation procedures, comprising a formaldehyde sensor device providing an electrical indication of formaldehyde vapour concentration; a humidity measurement device providing an electrical indication of relative humidity; a temperature responsive electrical circuit device and a processor connected to receive inputs from said devices and arranged when calibrated to provide an output value for formaldehyde vapour concentration corrected for humidity and temperature dependent variations in the formaldehyde sensor device.
2. A monitor according to Claim 1 wherein the formaldehyde sensor comprises a direct adsorption semiconductor sensor.
3. A monitor according to Claim 1 or Claim 2 further comprising a processor adapted to calculate an indication D of the lethal effect of the fumigation according to
4. A formaldehyde monitor and control device providing an output for the control of a formaldehyde vapour generator in a fumigation procedure effective against microorganisms, comprising a formaldehyde sensor device providing an electrical indication of formaldehyde vapour concentration; a humidity mesurement device providing an electrical indication of relative humidity; a temperature responsive electrical circuit device and a processor connected to receive inputs from said devices and arranged when calibrated to provide an output value for formaldehyde vapour concentration corrected for humidity and temperature dependent variations in the formaldehyde sensor device and further arranged to generate a formaldehyde vapour control output derived from the measured formaldehyde vapour concentration value, the measured relative humidity, the previously known lethal effect of the said concentration at the said relative humidity and the predetermined desired reduction in microorganism population.
5. A fumigation method for killing microorganisms in a volume, comprising the steps of generating formaldehyde vapour in said volume; measuring the formaldehyde vapour concentration; measuring the relative humidity in said volume; deriving a control signal based on the measured formaldehyde vapour concentration, the measured humidity and the known fumigation effectiveness of formaldehyde at the said humidity level and controlling said vapour generation step in response to said control signal.
6. A monitor comprising a sensor device providing an electrical indication of a gas or a vapour concentration; a humidity measurement device providing an electrical indication of relative humidity; a temperature responsive electrical circuit device and a processor connected to receive inputs from said devices and arranged when calibrated to provide an output value for said concentration corrected for humidity and temperature dependent variations in the sensor device.
7. A formaldehyde monitor and control device substantially as hereinbefore described with reference to and as shown in Figs. 1 and 2 or Figs. 2 and 5 of the accompanying drawings.
8. A fumigation method substantially as hereinbefore described with reference to the drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB08426766A GB2165948B (en) | 1984-10-23 | 1984-10-23 | Formaldehyde monitor |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB08426766A GB2165948B (en) | 1984-10-23 | 1984-10-23 | Formaldehyde monitor |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB8426766D0 GB8426766D0 (en) | 1984-11-28 |
| GB2165948A true GB2165948A (en) | 1986-04-23 |
| GB2165948B GB2165948B (en) | 1988-12-07 |
Family
ID=10568606
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB08426766A Expired GB2165948B (en) | 1984-10-23 | 1984-10-23 | Formaldehyde monitor |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2165948B (en) |
Cited By (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4730478A (en) * | 1985-06-18 | 1988-03-15 | Icor Ab | Gas analyzer |
| FR2616226A1 (en) * | 1987-06-05 | 1988-12-09 | Mine Safety Appliances Co | MOISTURE COMPENSATION DEVICE FOR A PHOTO-IONIZATION DETECTOR, AND APPARATUS FOR IMPLEMENTING SAME |
| US4817414A (en) * | 1986-07-03 | 1989-04-04 | Dragerwerk Aktiengesellschaft | Measuring arrangement for detecting the level of combustible gases mixed with air |
| GB2219397A (en) * | 1988-05-24 | 1989-12-06 | Sando Bela Nagy | Gas analysis |
| EP0701123A1 (en) * | 1994-09-10 | 1996-03-13 | United Kingdom Atomic Energy Authority | Formaldehyde vapour detector |
| GB2293015A (en) * | 1994-09-10 | 1996-03-13 | Atomic Energy Authority Uk | Formaldehyde vapour detector |
| WO1998000176A1 (en) * | 1996-07-03 | 1998-01-08 | American Sterilizer Company | Monitoring and control of sterilization processes with semiconductor sensor modules |
| GB2331810A (en) * | 1997-11-28 | 1999-06-02 | Taiyo Toyo Sanso Co Ltd | Temperature and humidity compensation for a semiconductor gas sensor |
| FR2790088A1 (en) * | 1999-02-23 | 2000-08-25 | Daimler Chrysler Ag | METHOD FOR CORRECTING THE INFLUENCE OF WATER ON THE SIGNAL OF A SENSOR TO DETECT THE CONCENTRATION OF REDUCER IN THE EXHAUST GAS OF AN ENGINE |
| WO2001067092A2 (en) * | 2000-03-09 | 2001-09-13 | Electricite De France Service National | Continuous analyzer of volatile organic compounds, device and method for continuously assessing the quality of inside ambient air and use of said device for monitoring a ventilation installation |
| WO2002068953A1 (en) * | 2001-02-28 | 2002-09-06 | Basf Aktiengesellschaft | Method and device for detecting fumigants in air samples |
| EP2012837A1 (en) | 2006-04-28 | 2009-01-14 | Infection Control B.V. | Method and device for disinfecting a space |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112415141B (en) * | 2020-11-06 | 2022-02-08 | 珠海格力电器股份有限公司 | Compensation method and compensation device for formaldehyde measurement concentration display value |
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-
1984
- 1984-10-23 GB GB08426766A patent/GB2165948B/en not_active Expired
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| GB953665A (en) * | 1961-03-02 | 1964-03-25 | Gas Detector S P A | Method and apparatus for detecting the presence of hydrogen-containing combustible gases or vapors |
| GB1412026A (en) * | 1972-12-26 | 1975-10-29 | Borg Warner | Anti-evasion system for a breath alcohol tester |
| GB1425685A (en) * | 1973-06-08 | 1976-02-18 | Sybron Corp | Sterility analyzer |
| GB1505726A (en) * | 1974-05-27 | 1978-03-30 | Philips Ltd | Sensor for gas or smoke detection |
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| EP0031156A1 (en) * | 1979-12-24 | 1981-07-01 | Matsushita Electric Industrial Co., Ltd. | Cooking oven with a ceramic humidity sensor |
| EP0056752A1 (en) * | 1981-01-21 | 1982-07-28 | Allied Corporation | Titania oxygen sensor with chrome oxide compensator |
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| EP2012837A1 (en) | 2006-04-28 | 2009-01-14 | Infection Control B.V. | Method and device for disinfecting a space |
| US9616148B2 (en) | 2006-04-28 | 2017-04-11 | Infection Control B.V. | Method and device for disinfecting a space |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8426766D0 (en) | 1984-11-28 |
| GB2165948B (en) | 1988-12-07 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19921023 |