WO2003069325A1

WO2003069325A1 - Determination of solution concentration

Info

Publication number: WO2003069325A1
Application number: PCT/AU2003/000186
Authority: WO
Inventors: John Panok; Mark Parsons
Original assignee: Airservices Australia
Priority date: 2002-02-15
Filing date: 2003-02-14
Publication date: 2003-08-21
Also published as: WO2003069325A9; AUPS059002A0

Abstract

A concentration meter including a device for measuring a parameter of a mixture containing a substance and water, calibration means for calibrating the device from a measurement of a known sample concentration, and stored data relating said parameter to said substance concentration. A processor is able to process the data obtained by the measuring device, compare the measured parameter with the stored data and convert the measured parameter into a reading of substance concentration. The substance is preferably foam, and the parameter is preferably conductivity. The invention extends to a method of determining the concentration of a substance in a mixture. The device and method have particular application in compliance testing of foam produced in fire trucks.

Description

Determination of solution concentration

Field of the invention

This invention relates to methods and apparatus for determining one or more parameters of a test sample. Aspects of the invention have particular relevance in the field of testing foam containing mixtures produced from fire fighting vehicles although it will be apparent to the skilled reader that the invention is not limited thereto.

Background of the invention

In the field of aviation fire fighting, industry standards require the percentage of foam in an aqueous solution pumped out by the fire fighting vehicle to be within a very strict tolerance. Vehicles must be regularly tested to ensure compliance with this standard. However, prior art methods of testing, in particular using refractometers, have proved to be highly inaccurate, with identical tests often producing different and inconsistent results which affected both efficiency and operational safety. Furthermore, the refractometers themselves are fragile, regularly unserviceable and expensive to repair. There have been various attempts in the past to ensure that foam produced in a fire fighting vehicle is of the correct foam/water ratio. For example, US Patents 5,823,219 and 5,284,174 describe a system in which a pair of probes carried on the vehicle measure the conductivity of the foam concentrate and the foam being generated by the vehicle. A control signal is generated which is representative of the difference between a measured conductivity and a desired conductivity, and the foam mixture is adjusted in response to the control signal, hi other words, the systems described in these patents are in-situ metering systems, requiring two probes.

US 6,456,903 and US 6,454,540 both describe in situ systems for regulating foam percentage in the outflow of a foam dispenser. Both systems rely on multiple conductivity probes for measuring the conductivity of the water, the pure foam and/or the foam mixture.

US 3,739,795 relates to a system in which a conductivity measurement is used to measure the height of a foam mixture in a mixing tank to determine the foamability of the foam. Multiple conductivity probes are used at different heights within the tank to determine the height of the foam mixture.

Probes carried by the vehicle are susceptible to malfunction, and if malfunction results in an incorrect variation of the foamwater ratio, the foam produced by the vehicle could be of inferior quality leading to potentially catastrophic results. Also, if the foam/water ratio is to be adjusted in-situ this requires an extremely precise adjustment mechanism to be included in the foam supply line. The adjustment mechanism would itself be prone to malfunction, and need to be regularly serviced.

None of the prior art systems referred to above provide a simple yet effective method of determining the concentration of a parameter in a sample which is able to eliminate errors in measurement which might arise due to in-situ measuring conditions, or other causes of false reading.

Summary of the invention

In the first aspect the invention provides a method of determining a parameter of a test sample including: obtaining one or more control samples in which said parameter is known; measuring said parameter in said one or more control samples with an instrument adapted to measure said parameter; calibrating said instrument from said control sample measurements; obtaining at least one test sample in which said parameter is unknown; measuring said parameter of said test sample using said calibrated instrument. hi one preferred embodiment, the measured parameter is converted to another parameter using data stored in said instrument. i one embodiment, the method includes testing the purity of an ingredient from which said test sample is derived. hi one embodiment, the test sample is a mixture containing a foam agent. The parameter of interest may be the concentration of the foam agent in the mixture. In a further preferred embodiment the measurement of the concentration of foam agent in the mixture depends on the conductivity of the test sample, and the instrument is adapted to measure conductivity of a solution.

In a preferred embodiment the first control sample may consist of water, e.g. fresh water. A second control sample may comprise an aqueous solution having a known concentration of a foam agent.

The instrument preferably stores data relating a response of said instrument, eg a conductivity measurement, to a sample concentration. i a second aspect of the invention there is provided a foam concentration meter including at least one device for measuring a parameter of a mixture containing foam, calibration means for calibrating said at least one device from a measurement of a known sample concentration, and stored data relating said parameter to a foam concentration, wherein said foam concentration meter measures said parameter in a mixture and converts said measured parameter into a reading of foam concentration. According to another aspect of the invention, there is provided a method of establishing the concentration of an ingredient in a sample, said method including the steps of

1) providing a processor programmed with an algorithm which maps how a parameter of said sample varies with the concentration of said ingredient in said sample; 2) linking said processor to a device adapted to measure said parameter;

3) calibrating said processor by measuring said parameter with said device in one or more control samples containing a known concentration of said ingredient;

4) measuring for said parameter with said device in a test sample containing an unknown concentration of said ingredient; and 5) causing said processor to determine the concentration of said ingredient using said measured parameter from said test sample and said algorithm. According to a further aspect of the invention, there is provided a method of establishing the concentration of an ingredient in a sample, said method including the steps of :

1) preparing a series of solutions, each with a different but known concentration of said ingredient;

2) measuring a parameter of each of said samples in order to establish a parameter/concentration relationship for said ingredient;

3) storing data relating to said relationship in a processor;

4) measuring said parameter in a sample containing an unknown concentration of said ingredient;

5) providing said measured parameter to said processor; and

6) causing said processor to determine the concentration of said ingredient in said unknown sample from said measured parameter using said stored data.

Preferably the processor is calibrated prior to step 4 by measuring said parameter in at least one sample of known concentration. Optionally the processor is calibrated prior to step 4 by measuring said parameter in at least two solutions of known concentration.

In one preferred form of the invention the parameter is the conductivity of the sample and measurement is undertaken with a conductivity meter. Brief description of the drawings

The invention will now be described by way of example only with reference to preferred embodiments and to the accompanying figures in which: -

Fig. 1 is a flow chart showing the steps of a method according to the present invention; Fig. 2 is a schematic diagram of a water/foam system fitted to a fire vehicle;

Fig. 3 is a graph of sample data relating conductivity to foam concentration;

Fig. 4 is a schematic diagram of a modified water/foam system; and Fig. 5 is a schematic diagram of a percentage foam meter according to the present invention.

Detailed description of preferred embodiments

In the environment of aviation rescue and fire fighting, fire vehicles are required to dispense fire retardant foam mixture in which the percentage of foam in the solution must be within very strict tolerances, for example, 5.5% to 7%. Fire fighting vehicles must be regularly tested to ensure that the mixture which they output complies with this standard.

With reference to Fig. 2, a typical fire vehicle 20 includes a foam reservoir 21 and a water reservoir 22. The output of the water reservoir 22 feeds to a pump 23 via a pump suction conduit 26, and then to an output nozzle 24 through a pump delivery conduit 25. The pump delivery conduit 25 is branched between the pump 23 and the nozzle 24, and connected via a propelling conduit 29 to allow the supply of pressurised fluid to the inlet port of a foam inductor 28 (eg venturi, eductor, nozzle, etc). The outlet port of the foam inductor 28 is connected via a mixing conduit 31 to a branch between the water reservoir

22 and the pump 23. The output from the foam reservoir is connected via a foam supply conduit 27 to the vacuum port of the foam inductor 28. Flow of liquid through the foam inductor 28 creates a vacuum in the vacuum port of the foam inductor 28, thus inducing foam into the mixing conduit 31. The foam inductor circuit acts to mix water and foam together which is then supplied to the suction side of the pump. An adjustable metering valve 30 in the foam supply conduit 27 between the foam reservoir 21 and foam inductor 28 determines the relative amount of foam added to the solution. Operation of the pump

23 causes a solution of foam in water to be produced through nozzle 24.

In one preferred embodiment, the method of the present invention is implemented using a Percentage Foam Meter (PFM) of the type illustrated in Fig. 5. The PFM 50 incorporates a conductivity meter 51, for example, the N-250 gemini conductivity meter produced by Amalgamated Instrument Co Pty Limited which has a four electrode epoxy probe 52 and automatic temperature compensation thyristor (not shown). The percentage foam meter (PFM) has a memory 53 storing data relating solution conductivity to foam concentration. Operation of the PFM is controlled through an interface 54 having control buttons, dials etc 55 and display 56.

Referring now to the flow chart of Fig. 1, a method of testing the output of the water/foam system will now be described. Prior to testing the foam percentage produced by the water/foam system, the foam purity is determined. At step 100, a sample of foam is taken from the foam reservoir of the fire vehicle and allowed to settle to test room temperature. A probe of the PFM is then inserted in the sample and a reading of temperature and conductivity are taken 102. For acceptable foam purity, the conductivity reading must be within the range specified in Table 1 at the specified test temperature. Table 1 is an example of the conductivities for two common aqueous film forming foam agents.

Note 1 - Ansul Ansulite ICAO B 15590-22 Note 2 - 3M Lightwater FC3003

Table 1

If the indication from the PFM is that the foam purity is outside the acceptable range then the foam reservoir has been contaminated in some way and is discarded from use for fire fighting purposes 103.

If the foam purity is acceptable then the process continues with the foam percentage test. At step 104 the pure foam sample obtained previously is mixed with water from the water reservoir of the fire vehicle to make a known 6% concentration control sample. A further water sample is obtained from the water reservoir to provide a 0% control sample. At step 106 the PFM is placed in a calibration mode and set to take a 0% reading. The probe is placed in the obtained water sample and the measurement taken. Next the PFM is set to take a known 6% measurement and the probe is placed in the known 6% sample. The PFM then compares the measured 0% and 6% readings with the stored calibration data and adjusts the probe response appropriately, thereby calibrating the instrument 107. At step 108 the pump of the fire vehicle is operated to produce a foam mixture that is collected and allowed to settle to test room temperature. The PFM is set into a test mode and the probe is placed into the obtained pump sample. The PFM measures the conductivity of the test sample 110 and using functional relationships stored in the calibrated instruments, converts the conductivity measurement into a reading of the percentage foam concentration of the test sample. The foam concentration reading is displayed on the PFM display, eg a calculation of 5.9% is displayed as 5.9.

If the concentration measurement is within acceptable limits, then the fire vehicle can be certified as complying with requirements 112. However, if the PFM indicates a concentration outside these allowable limits then the valve 30 on the foam reservoir output can be adjusted 111 as appropriate and the steps of sampling 108 and testing 110 repeated until the pump is operating within the allowable requirements.

Whilst the foam tank purity testing is conducted using a sample from the vehicle foam tank, the method may additionally or alternatively incorporate the step of testing the foam purity from the supplier drum. The 6% sample is obtained by mixing six parts of the pure foam sample obtained previously with 94 parts water obtained from the water reservoir. To provide greater accuracy of measurement and to avoid contamination of samples, the probe is washed with deionised water and blotted dry in between measurements. Samples may be stirred with the probe to ensure measurement of a homogenous mixture is obtained. Conductivity readings for known sample concentrations covering the full range of concentrations have been obtained by the present inventors, with particular sampling in the concentrations of interest, ie from approximately 0-10% foam concentration. A graph of conductivity verses foam concentration is shown in Fig. 3. The graph was obtained by firstly testing the conductivity of a large number of samples in a range of different temperature environments. It was found that for a particular temperature the relationship between concentration and conductivity followed the form of curve depicted in Fig 3. Curve matching software was then applied to the data in order to achieve a mathematical expression of the curve which could then be stored in the processor of the PFM to define the functional relationship between concentration and conductivity, hi other words, the functional relationship is stored in the PFM and used in converting the measured conductivity of the foam into a reading of foam concentration in an unknown sample.

In a further aspect the fire vehicle arrangement can be modified to provide in situ testing and adjustment of the fire vehicle output. Referring to Fig. 4, the water/foam system arrangement 20 further includes a probe 41 in pump suction conduit 26, a probe 42 in foam supply conduit 27 and a probe 43 in pump delivery conduit 25. The probes

41, 42, 43 each obtain conductivity readings relating to pure water, pure foam and an unknown mixture respectively. The readings of the probes 41, 42, 43 can be combined at the PFM 50 to determine the foam concentration being output through pump delivery conduit 25. The water/foam system 20 may further include a feedback circuit 46 from the PFM 50 that automatically adjusts the metering valve 30 as required to make the water/foam system produce a foam mixture having the required percentage of foam. The probes 41, 42, 43 may be removed from their respective conduits for calibration.

Whilst the invention has been described with particular reference to aviation rescue vehicles, the invention should not be limited thereto. In other preferred embodiments, the PFM may be used in testing foam from other foam making equipment such as vehicle or ship pumps or static pumps such as in refineries etc.

It will be understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.

The foregoing describes embodiments of the present invention and modifications, obvious to those skilled in the art can be made thereto, without departing from the scope of the present invention.

Claims

Claims:

1 A method of determining a parameter of a test sample including: obtaining one or more control samples in which said parameter is known; measuring said parameter in said one or more control samples with an instrument adapted to measure said parameter; calibrating said instrument from said control sample measurements; obtaining at least one test sample in which said parameter is unknown; measuring said parameter of said test sample using said calibrated instrument.

2 A method according to claim 1 wherein the measured parameter is converted to another parameter using data stored in said instrument.

3 A method according to either preceding claim which includes the step of testing the purity of an ingredient from which said test sample is derived.

4 A method according to any preceding claim wherein the test sample is a mixture containing a foam agent. 5 A method according to claim 4 wherein the parameter of interest is the concentration of the foam agent in the mixture.

6 A method according to claim 5 wherein the measurement of the concentration of foam agent in the mixture depends on the conductivity of the test sample, and the instrument is adapted to measure conductivity of a solution. 7 A method according to any preceding claim 6 wherein the first control sample consists of water.

8 A method according to claim 7 wherein second control sample is used which comprises an aqueous solution having a known concentration of a foam agent.

9 A method according to any preceding claim wherein the instrument stores data relating a response of said instrument. 10 A method according to claim 9 wherein the response which is stored by the instrument is a conductivity measurement relating to sample concentrations.

11 A method of establishing the concentration of an ingredient in a sample, said method including the steps of: 1) providing a processor programmed with an algorithm which maps how a parameter of said sample varies with the concentration of said ingredient in said sample;

2) linking said processor to a device adapted to measure said parameter;

3) calibrating said processor by measuring said parameter with said device in one or more control samples containing a known concentration of said ingredient; 4) measuring for said parameter with said device in a test sample containing an unknown concentration of said ingredient; and

5) causing said processor to determine the concentration of said ingredient using said measured parameter from said test sample and said algorithm.

12 A method of establishing the concentration of an ingredient in a sample, said method including the steps of :

2) measuring a parameter of each of said samples in order to establish a parameter/concentration relationship for said ingredient; 3) storing data relating to said relationship in a processor;

5) providing said measured parameter to said processor; and

6) causing said processor to determine the concentration of said ingredient in said unknown sample from said measured parameter using said stored data. 13 A method according to claim 12 wherein the processor is calibrated prior to step 4 by measuring said parameter in at least one sample of known concentration.

14 A method according to claim 12 wherein the processor is calibrated prior to step 4 by measuring said parameter in at least two solutions of known concentration. 15 A method according to claim 14 wherein the parameter is the conductivity of the sample and measurement is undertaken with a conductivity meter.

16 A concenfration meter including at least one device for measuring a parameter of a mixture containing a substance and water, calibration means for calibrating said at least one device from a measurement of a known sample concentration, and stored data relating said parameter to said substance concentration, wherein said concentration meter measures said parameter in a mixture and converts said measured parameter into a reading of substance concentration.

17 A concentration meter according to claim 16 wherein said parameter is the conductivity of said mixture, and said device comprises a conductivity probe. 18 A concentration meter according to claim 16 or 17 wherein the stored data comprises an algorithm that relates concentration and conductivity over a wide range of concentrations of said mixture.

19 A concenfration meter according to any one of claims 16 to 18 which is adapted to measure the concentration of foam concentrate mixed in water. 20 A method of establishing the concentration of an ingredient in a sample substantially as hereinbefore described with reference to the drawings.

21 A concentration meter substantially as hereinbefore described, with reference to the drawings.