GB2295232A

GB2295232A - Continuous multi-parameter monitoring of liquids with a novel sensor cleaning and calibration system

Info

Publication number: GB2295232A
Application number: GB9422996A
Authority: GB
Inventors: Boghos Awanes Manook
Original assignee: Individual
Current assignee: Individual
Priority date: 1994-11-15
Filing date: 1994-11-15
Publication date: 1996-05-22
Anticipated expiration: 2014-11-15
Also published as: GB9422996D0; GB2295232B

Abstract

A multi-parameter monitor 1, with a novel cleaning and calibration system for on-line measurement of various quality parameters of liquid sources at on-site locations, e.g. water in reservoirs or effluent outlets, measures pH, conductivity, temperature, ammonium/ammonia, dissolved oxygen, colour, turbidity and suspended solids etc. The sensors can be individually and/or collectively cleaned and calibrated by spraying warm or cold liquid and/or air mixture on to the face of each sensor. It provides a means of checking and calibrating each individual sensor head to provide an indication of the sensor condition. The data processing means are adapted to calculate and display the multi-parameters of the liquid source. The sampling apparatus (70, Figs. 4, 5), comprises a buoyant sampling head (71) with an inlet port (74) protruding beneath the liquid surface (75), with various filter sizes (77, 78, 79), to a minimum depth of 100mm. <IMAGE>

Description

Continuous Multi-Parameter Monitoring of Liquids With a Novel Sensor Cleaning and Calibration System This invention relates to a Multi-Parameter Monitoring System for measuring various parflmeters of a liquid source, with a novel cleaning system for each individual sensor head, and is of particular application for on-line monitoring of water quality at locations, such as, for example, industrial or water/waste treatment plant effluent outlets, rivers or reservoirs.

A number of instruments are available in the market for determining various measurement parameters such as Suspended Solids concentration Turbidity, Colour, Conductivity, pH, Temperature, Ammonia and Dissolved Oxygen. The measurement methods, based on optical, conventional electrochemistry and/or solid state techniques, of each parameter are well researched and documented. The performance of such monitoring systems can be easily impaired due to sensor fouling. In some cases the sensors need to be cleaned and perhaps calibrated on a daily basis. The cost of ownership of such systems, therefore, can be prohibitive and un-economical. Some instruments employ mechanical cleaning facilities to wipe the face of the sensor head concerned, which others employ air or water based pressurised jet stream for cleaning purposes.

The present invention overcomes the above-mentioned problems associated with the prior art and to provide a novel cleaning system for each individual sensor head, i:1expensive, robust, reliable, low cost of ownership andincorporating a novel cleaning monitor for continuous measurement of multi-parameters, such as Suspended Solids concentration, Turbidity, Colour, Conductivity, pH, Temperature, Ammonia and Dissolved Oxygen, in effluent liquids that can be readily used in a variety of locations and applications.

The present invention provides a novel .method of cleaning the above-mentioned sensor heads in a liquid sample and comprises a series of steps : (a) Emptying the measuring flow-cell chamber from the liquid source whose parameters are being measured.

(b) Projecting a well defined and controlled liquid, such as hot or cold water, detergents or biocides, or air stream je onto the active part of each individual sensor head to remove the fouling deposits in the fortn of a film or otherwise.

(c) Projecting the above said jet from different angles, simultaneously or sequentially, on each individual sensor head and at a programmable time intervals.

(d) Making an assessment to provide an indication of the state of each individual sensor head condition, both in terms of fouling as well as damage.

(e) Determining the calibration cond tion of each individual sensor head, both the zero and/or the range of the above mentioned measurands..

(f) Filling the measuring flow-cell chamber with the liquid source whose parameters are being measured and then proceeding with the above mentioned multi-parameter measurements.

It has been discovered that if a well delined and controlled jet stream is projected, from different angles, onto the active part of each individual measuring sensor head, at regular intervals, then each measuring sensor head can be kept clean and made available for measurement over a prolonged period without the need for human intervention.

The cleaning process in steps of (a) tD (f) may be made either simultaneously and/or sequentially, in any order. The measurements in steps (d) and (e) may be either directly or indirectly.

The present invention also provides apparatus suitable for use in all or part of the method described above. The apparatus comprises firstly a means for monitoring a single parameter or multi-parameter elements in a liquid sample, secondly a means for cleaning the measuring flowcell of each individual sensor head at pre-defined intervals, and thirdly a means for making further checking and calibration of each individual sensor head to provide an indication of the condition of each sensor head as well as the liquid source.

The apparatus may conveniently be provided in a single or separate housing and/or may be portable. The first, second and third means may be provided in a single measuring cell, so as to minimise errors caused due to local fluctuations, for example, in temperature.

Preferably, additional means will be provided for one more additional variables, as outlined above; the processing means may also be used with the measured additional variables for compensation purposes.

For most applications, the processing means are adapted to calculate and display the multiparameters of the liquid source.

The apparatus may be provided with a filtration system, near the apparatus housing, of a suitable pore size preferably not less than 1.5 mm.

The present invention also provides sampling apparatus for withdrawing a sample from the liquid source having a suitable open surface area. The apparatus comprises a buoyant sampling head provided with an inlet port, protruding vertically or at angle beneath the liquid surface, that communicates with a duct for connection to a means of suction. The apparatus is so arranged that, in use, the sampling head floats on the surface of the liquid source and the inlet port protrudes beneath that surface, with a filter across the inlet port not less than 1.5 mm, to a minimum depth of not less than 100 mm. The surface area of the inlet port is preferably substantially greater than the average cross-sectional area of the duct to minimise inlet blockage.

The invention also provides a monitoring, cleaning and control system for use in a method of determining the above mentioned multi-parameters of a liquid source, which system comprises monitoring and cleaning apparatus as described earlier, in combination with the above described sampling apparatus.

One form of multi-parameter of a liquid source, one type of sensor cleaning system, and one type of sampling apparatus for use therewith, constructed in accordance with the invention will now be described, by way of example only, with reference to accompanying drawings, in which: Figure (1) is a partially cut-away schematic view of the mutli-parameter monitoring system; Figure (2) is a schematic sectional view ofthe measuring flow-cell of the multi-parameter monitoring system and the cleaning system; to a larger scale than that of Figure (1); Figures (3a), (3b) and (3c) are, respectively, sectional, side and bottom views of each individual cleaning set for each individual sensor head.

Figure (4) is a side view of the sampling apparatus; and Figures (5a) and (Sb), respectively represent, sectional and bottom views of each sampling head for apparatus.

The multi-parameter measuring system, with the individual sensor cleaning, is capable of being used for on-line, continuous monitoring of liquid quality in a variety of on-site locations, such as, for example rivers, reservoirs or industrial effluent outlets. The monitoring system (1) comprises of a single, weatherproof, portable unit separated into three compartments (2), (3), (4) containing a measuring flow-cell, sensors and their individual cleaning system, and microprocessor based electronics, respectively. The cleaning system apparatus (40), (41), (42), (43). (44), (45), (46), (47), (48), (49), (50), (51), (52), (53) and (54) for each individual sensor head is incorporated with the measuring flow-cell (8). In use, the sampling apparatus (70), as described below, is attached to the monitoring system.

The sampling apparatus is attached to the inlet port (5) ofthe monitor (1), across which port a set of filters (77), (78) and (79) of 5 mrl, 3 mm and 1.5 mm respectively are positioned.

The inlet port (5) is connected to the monitor (1) by suitable tubing to a suction pump (7).

The pump (7) is housed in a separate compartment (2) either within the monitoring system (1) or detached and installed outside the monitoring system (1).

In the main compartment (3), the measuring flow-cell (8) is surrounded by an array of individual sensor heads. Nearest to the inlet (leo) of the flow-cell is the conductivity probe (11), followed by the pH probe (12), followed by the temperature probe (13), followed by the Ammonia/Ammonium probe (14), and followed by the Dissolved Oxygen (DO) probe (15). Two spaced light emitting diodes (LED's) (17), and (20)1 generate light of Blue 410 nm (or white light), and Red (or Infra-Red light ) wavelengths respectively, and colimated via two lenses (18) and (21) penetrating through two suitable glass windows (19), (22), (25) and (28).There are two emerging light beams collected via two lenses (24) and (27) and projected onto two sensitive silicon photodiodes (23) and (26)) in corresponding and opposing positions on the other side of the measuring flow-cell (8). The suspended solids concentration is determined from the Red LED source (20), and the apparent colour is determined from the Blue LED source (19). The light scatter produced by the suspended solids or anything else in the liquid being sampled, penetrating the glass window (31) is collected via the lens (30) and detected with a third silicon photodiode (29) occupying a position at right-angles to the Red LED (20). Ambient air temperature probe (16) measurement is located in the main compartment (3). Both liquid (13) and ambient (16) temperatures are also used for compensation purposes.

Beneath each individual sensor head lies a number of sets of double jetting mechanisms (40 and 40 ), (42 and 43), (44 and 45), (46 and 47),(48 and 49), (50 and 51) and (52, 53 and 54) respectively. Each cleaning set is positioned at suitable angles to project a spray of an appropriate cleaning fluid such as cold/hot water detergents, alcohol or biocides onto the face of each individual sensor head.

The cleaning ofthe sensor heads can be carried out either sequentially, i.e. one sensor head at time via the solenoid valves (90, (91), (92), (93), (94), (95), (96), (97), (98), (99), (100), (102), (103) and (104) respectively, or simultaneously (i.e. all sensor head are cleaned at the same time) via the main solenoid valve (105) only.

The sensor head cleaning sequence is controlled by the microprocessor (38) located in the compartment (4) and can be programmed by the user to defined the cleaning cycle time, for example on a half hourly, hourly or dailybasis.

Each set ofjet mechanics as shown in Figure (3C) comprises a body (60) with an inlet (61) and a narrow tubular opening (62) of different sizes, suitable for each application, with various end (64) geometries, such as rectangulai or circular, allowing the projection of a specific jet spray width with specific pressure exertion on the face of each individual sensor head. Each set ofjet mechanics (60) will also contain a means of non-retum valve (63) to prevent the liquid source from entering the cleaning fluid. The inlet connector of the jet set (61) is linked to a solenoid valve (65) via a flexible tube.

The sampling apparatus is for use with the monitor in a location where the liquid source presents an open, accessible surface, as shown in figure (4), (Sa) and (Sb).

The sampling apparatus (70) comprises a buoyant sampling head (71) attached to the lower end of a pipe (72), the upper end of which is pivotally mounted on a support (73), which is raised above the surface (75) of the liquid source. A flexible tube (76) leads from the upper end of the pipe (70) to the inlet (5) of the monitor (1).

The sampling head (71) comprises a hollow truncated sphere mounted on the lower end of the pipe (72) by means of a screw joint. Inside the sphere an internal pipe (74), protrudes into the liquid source to a minimum depth of 100 mm below the lower part of the buoyant body (71), and leads to an inlet port (80). A set of graduating mesh filters (77), (78) and (79), are secured onto the rim ofthe protruding pipe (74), and are provided with various holes 1.5mm (81), 3 mm (82) and 5mm (83) in diameter and secured onto the lower part of the body of the inlet pipe (74).

When the monitor (1) is operating, the pump draws a continuous sample, at a minimum rate of 1 litre per minute, from beneath the-surface of the liquid source (75) via the sampling head through the holes ofthe mesh (81), (82), and (83) via the inlet port (80) into the flexible pipe (72). The pivotal mounting allows the sampling head (71) to float freely on the surface (75) of the liquid source, so that the inlet port (80) is alto immersed.

Inside the measuring flow-cell (8) the various probes (11), (12), (13), (14), (15), (16), (17,23), (20, 26) and (20, 29) measure the liquid source quality. The pH probe (12) is used in the calculation algorithm for the Ammonium and Ammonia measurement, along with the Ammonia probe (14). Both the liquid (13) and ambient (16) temperatures probes are used for compensation purposes ofthe other probes, by the microprocessor (38) as well as to be shown on the display (37).

Figures (2) and (3b) show narrow but colimated beams of Blue and Red from the light emitting diodes (17) and (20) are transmitted through the optical lenses (18) (21) and windows (19) (22) into the liquid sample. The intensity ofthe emergent beams from the optical windows (25) (28), are focused, via the lenses (24) (27) onto and measured by the photodiodes (23) and (26). The Red light wavelength is used to determine the suspended solids concentration in the liquid sample while the Blue light wavelength is used, after being compensated by the Red light using an algorithm, to determine the apparent colour of the liquid sample. The analysis and display is carried out by the microprocessor (38); situated in the compartment (4).

The third photodiode (29) detects the scattered focused (30) Red light at 90 to the beam direction, to determine and display the turbidity present in the liquid sample, using the microprocessor (38).

The microprocessor (38) processes the. data received from the various probes in order to determine the conductivity, pH, liquid and ambient temperatures, ammonia and/or ammonium content, Dissolved Oxygen concentration, Suspended Solids concentration, Turbidity and apparent colour of the liquid sample. Each of the parameters can be displayed bv operation of the keypad (37), situated in the compartment (4).

In contrast to some of the existing monitors, the microprocessor calculates each individual parameter mentioned above, using suitable algorithms, which are expanded below : a) Temperature compensation is implemented by the microprocessor (38) on the conductivity measurement c carried out by the probe (11).

c) Temperature compensation is implemented by the microprocessor (38) on the pH measurement carried out by the probe (12) d) Liquid temperature (13) and pH (12) compensation is implemented an algorithm resident in the microprocessor (38) to measure Ammonia (NH3) and/or Ammonium (NH4) carried outt the probe (14).

e) Temperature compensation is implemented by the microprocessor (38) on the Dissolved Oxygen (DO) measurement carried out by the probe (15). The effect of salinity is compensated for, using the conductivity probe (11), by an algorithm resident in the microprocessor (38).

f) The suspended solids concentration measurement is calculated by the microprocessor (38) using the Infra-Red or Red wavelength (20). The light source and the photodiodes, (26), are temperature compensated.

f) The Turbidity measurement is calculated by the microprocessor (38) using the Infra-Red or Red wavelengths (20). The photodiode, (29j, is temperatJ.re compensated.

g) The apparent colour measurement is calculated by the microprocessor using two wavelengths, Blue (17) and Infra-red or Red (18). The light sources and the photodiodes, (17) (23) and (20) (26) respectively, are temperature compensated.

The effect of the particulate matters on the apparent colour measurement is also compensated for by an algorithm resident in the microprocessor (38).

In contrast also to existing monitors, the microprocessor (38) implements suitable checking procedures algorithms on each individual sensor head mentioned above, and controls the cleaning system (40) to (54) using which are expanded below : a) Empty the measuring flow-cell (8) by draining the liquid sample via multi-way valve (9) and then check if the flow-cell (8) is empty.

b) After step (a) is completed, fill the measuring flow-cell (8) with an appropriate fluid, such as distilled or tap water, and check either individually or collectively all the sensor heads and optical windows (11, 12, 13, 14, 15, 23, 26) conditions and store these information if any ofthe sensor head requires cleaning (i.e. cleaning flags) to execute the cleaning procedures accordingly.

c) Empty the measuring flow-cell (8) by-draining the fluid, mentioned in (b) above, via the multi-way valve (9) and then check if the flow-cell (8) is emptied) d) Fill the the measuring flow-cell with the appropriate standard solution to calibration the appropriate sensor head concerned. Empty the measuring flow-cell (8) by the draining the above mentioned solution via the multi-way valve (9).

e) After the step (b and c) is completed and checked (the cleaning flag) if the conductivity sensor (11) head requires cleaning a jet stream is project (such as cold/hot water, suitable detergents, alcohol, or biocide in diluted forms or otherwise) on the face of the active part of the probe, by opening the valves (40 and 41) either simultaneously or alternately. During the cleaning action, the fluid is contiguously drained via the multi-way valve (9). The above action is repeated until the cleaning algorithm, resident in the microprocessor (38), is completed fully and satisfactorily. After the cleaning process is completed apply step (d) if necessary.

f) After the step (b and c) is completed and checked (the cleaning flag) if the pH sensor head (12) requires cleaning a jet-stream is projected (such as cold/hot water, suitable detergents, alcohol or biocide in diluted forms or otherwise) on the face of the active part of the probe, by opening the valves (42 and 43) either simultaneously or alternately. Daring the cleaning action, the fluid is continuously drained via the multi-way valve (9) to waste. The above action is repeated until the cleansing algorithm, resident in the microprocessor (38), is completed fully and satisfactorily. After the cleaning process is completed apply step (d) if necessary.

g) After the step (b and c) is completed a jet-stream is projected (such as cold/hot water, suitable detergents or biocide in diluted forms or otherwise) on the face of the active part of the temperature probe (13) , by opening the valves (44 and 45) either simultaneously or alternately. During the cleaning action, the fluid is continuously drained via the multi-way valve (9) to waste. The above action is repeated until the cleaning algorithm, resident in the microprocessor (38), is completed fully and satisfactorily. After the cleaning process is completed apply step (d) if necessary.

h) After the step (b and c) is completed and checked (the cleaning flag) if the Ammonia sensor (14) head requires cleaning a jet-stream is projected (such as cold/hot water, suitable detergents or biocide in diluted forms or otherwise) on the face of the active part of the probe, by opening the valves (46 and 47) either simultaneously or alternately. Duping the cleaning action, the fluid is contiguously drained via the multi-way valve (9) to waste. The above action is repeated until the cleaning algorithm, resident in the microprocessor (38), is completed fully and satisfactorily. After the cleaning process is completed apply step (d) if necessary.

i) After the step (b and c) is completed and checked (the cleaning flag) if the Dissolved Oxygen (DO) sensor (15) head requires cleaning a jet-stream is projected (such as cold/hot water, suitable detergents or biocide in diluted forms or otherwise) on the face of the active part of the probe, by opening the valves (48 and 49) either simultaneously or alternately. During the cleaning action, the fluid is continuously drained via the multi-way valve (9). The above action is repeated until the cleaning algorithm, resident in the microprocessor (38), is completed fully and satisfactorily. After the cleaning process is completed apply step (d) if necessary.

j) After the step (b and c) is completed and checked (the cleaning flag) if the optical windows (19 and 25) of the Blue wavelength requires cleaning a jet stream is projected (such as cold/hot water, suitable detergents, alcohol or biocide in diluted forms or otherwise) on.the face ofthe active part of the probe, by opening the valves (50 and 51) either simultaneously or alternately. During the cleaning action, the fluid is continuously drained via the multi-way valve (9). The above action is repeated until the cleaning algorithm, resident in the microprocessor (38), is completed fully and satisfactorily. After the cleaning process is completed apply step (d) if necessary.

k) After the step (b and c) is completed and checked (the cleaning flag) if the optical windows (22, 28 and 31)) of the Infra-Red or Red wavelength requires cleaning a jet stream is projected (such as cold/hot water, suitable detergents, alcohol or biocide in diluted forms or otherwise) on the face of the active part of the probe, by opening the valves (52, 53 and 54) either simultaneously or sequential. During the cleaning action the fluid is continuously drained via the multi-way valve (9). The above action is repeated until the cleaning algorithm, resident in the microprocessor (38), is completed fully and satisfactorily. After the cleaning process is completed apply step (d) if necessary.

The cleaning and calibration procedures mentioned above (from c to k) can be implemented either sequentially, using individual cleaning fluids, for each sensor head or collectively by cleaning all the sensor heads simultaneously. The cleaning cycle as well as period can be programmed to suit the user requirements. During the cleaning period zero calibration of each sensor head can also be established and stored for future data calculations of various parameters.

The monitor may be modified to suit particular applications. For example, the use of optical fibres with white light source can be used instead of the conventional LED's to determine the true colour using suitable optical diffraction gratings. Similarly, the use of thick or thin film based sensors for pH, conductivity, temperature, Ammonia and Dissolved Oxygen can be used.

Other sensor heads can be added to suit .some.applications, such as flowmeter to determine the gross pollution. The measuring flow-cell (8) can also be adapted to incorporate level switches for ensuring that the flow-cell (8) is empty or full.

Claims

I.A method for determining the various measurement parameters such as Suspended Solids concentration, Turbidity, Colour, Conductivity, pH, Temperature, Ammonia/Ammonium and Dissolved Oxygen (DO) in a liquid source comprising the following steps : (a) making a measurement to provide indication of the conductivity of the liquid sample.

(b) making a measurement to provide indication of the pH of the liquid sample (c) making a measurement to provide indication of the temperature of the liquid sample.

(d) making a measurement to provide indication of the Ammonia/Ammonium concentration of the liquid sample.

(e) making a measurement to provide indication of the Dissolved Oxygen (DO) of the liquid sample.

(f) making a measurement to provide indication of the ambient temperature.

(g) making a measurement to provide indication of the absorption by the liquid sample of a Blue light.

(h) making a measurement to provide indication of the absorption by the liquid sample of either Infra-Red or Red light.

(i) making a measurement to provide indication of the scatter of Infra-Red or Red light, at a particular angle, caused by the presence of particles present in the liquid sample.
2 As claimed in claim 1, wherein (a) the conductivity probe technology used in (a) can be conventional, thick-film, or thin-film based.

(b) the pH probe technology-used in (b) can be conventional, thick-film, thin-film or fibre optics based.

(c) the liquid sample temperature probe technology used in (c) can be conventional, thick-film, thin-film or fibre optics based.

(d) the Ammonia probe technology used in (d) can be conventional membrane type Ion Selective Electrode, thick-film, thin-film or fibre optic based.

(e) the Dissolved Oxygen (DO) probe technology used in (e) can be conventional membrane type, thick-film, or t:lin-film based.

(f) the ambient temperature probe technology used in (f) can be conventional, thick - film, thin-film or fibre optics based.

(g) the visible light used in (g) can be based on conventional or fibre based optics.

(h) the visible light used in (h and i) can be based on conventional or fibre based optics.
3. A method as claimed in claim 1 or 2, wherein steps (a) to (g) are carried out on the same sample under the same conditions.
4. A method claimed in any of claims 1 to 3, wherein the liquid sample is filtered prior to steps (a) to (i).
5 A method as claimed in claim 4, wherein the filtering system accepts rernoves particles of less than about 1.5 mm.
6. A method as claimed in one of claims 1 to 5, including an additional step of measuring one or more additional variable(s).
7. A method as claimed in claims 6, wherein the additional variable is measured for compensation purposes.
8 A method as claimed in claims 4 and 7, wherein the additional step is carried out on the same sample under the same conditions as steps (a) to (i).
9. A method as claimed in any one of claims 1 to 8, wherein both the ambient and the liquid temperatures are used for compensation purposes on the other variables.
10. A method as claimed in any one claims of 1 to 9, wherein the pH probe measurement is used in conjunction with the Ammonia probe measurement to determine the amount of Ammonia and/or Ammonium concentration in the liquid sample.
11. A method as claimed in any one claims of 1 to 9, wherein the conductivity probe measurement is used in conjunction with the Dissolved Oxygen (DO) probe measurement to compensate for the effect of the salinity on the DO probe.
12. A method as claimed in claims 1 to 9 wherein steps (g) and (h) are carried out to determine the apparent colour of the liquid sample.
13. A method as claimed in claims 1 to 9, wherein steps (h) and (i) are carried out tO determine the suspended solids concentration and turbidity of the liquid sample
14. A method as claimed in claims 1 to 13, wherein the active part of each individual probe or optical window, for each individual parameter, is cleaned by projecting a jet-stream of a suitable cleaning fluid.
15- A method as claimed in claims 1 to 14, wherein the active parts of all the probes or optical windows in steps (a) to (i) are cleaned either sequentially or simultaneously.
16. A method as claimed in claims 1 to 15, wherein a number ofjet-streams are projected from different angles onto the active part of each individual probe or optical window either sequentially or simultaneously, for cleaning purposes.
17. A method as claimed in claims 1 to 16, wherein one, or more probes are calibrated during the cleaning cycle using either tap/distilled water or special fluids.
18. A method is claimed in claims 1 to 17, wherein the condition each individual sensor head is necked and identified.
19 A method is claimed in claims 1 to 18, wherein each individual sensor head is calibrated using it own standard solutions.
20. Apparatus for determining the various water quality parameters in a given liquid sample, the apparatus comprising firstly a means for monitoring a single parameter or multi-parameter eiements in a liquid sample, secondly a means for cleaning the measuring flow-cell of each individual sensor head at pre-defined intervals, and thirdly a means for making further checking and calibration of each individual sensor head to provide an indication of the condition of each sensor head as well as the liquid source.
21. Apparatus as claimed in claim 20, including processing means for determining the conductivity, py Ammonia/Ammonium, Dissolved Oxygen, Apparent Liquid Colour, Turbidity and Suspended Solids Concentration parameters.
22. Apparatus as claimed in claims 20 to 21, wherein the temperature is used for the compensation of the above mentioned parameters.
23 Apparatus as claimed in claims 20 to 22, wherein the Ammonia/Ammonium is adjusted in accordance with the pH measurement values.
21. Apparatus as claimed in claims 20 X 23, wherein the Dissolved Oxygen (DO) is compensated for salinity in accordance with rhe conductivity measurement vaiues.
25 Apparatus is claimed in claims 20 to 24, wherein the apparent liquid sample colour is adjusted for the suspended solids concentration in accordance with the absorption measurement of the Infra-Red or Red Light.
26 Apparatus as claimed in claims 20 to 25, wherein a cleaning system is provided for each individual sensor head.
27- Apparatus as claimed in claims 20 to 26, wherein each cleaning set can project a jetstream of a cleaning fluid from different angles onto the active part of each sensor head or optical window.
28. Apparatus as claimed in claims 20 to 27, wherein each cleaning set have their own non-return valve to prevent the liquid sample poisoning the cleaning fluid.
29. Apparatus as claimed in claims 2Q to 28, wherein standard calibration solutions can be transferred in the measuring flow-cell for the calibration of each sensor head.
30. Apparatus as claimed in claims 20 to 29, wherein the processing means checks the condition of each sensor head or optical window.
31. Apparatus as claimed in claims 20 to 30, wherein the processing means calibrates each individual sensor head using either single or varied standards.
32. Sampling apparatus for withdrawing a sample from a liquid source have an open surface, which apparatus comprises a buoyant sampling head provided with an inlet port that communicates with a duct for connection to suction means, the apparatus being so arranged that, in use, the sampling head floats on the surface of the liquid source and has an the inlet port immersed beneath the surface, at a suitable angle to avoid build up of raggs, to a depth of not less than 100 mm.
33. Apparatus as claimed in claim 32, wherein a set of filters, with a pore size ranging from l.5mm to maximum 5 mm, are disposed across the inlet port.
34. Apparatus as claimed in claim 33 wherein the surface area ofthe filter set is substantially larger than the average cross-sectional area of the duct.
35. A method of withdrawing a sample fro:n a liquid source having an open surface, which method involves the use of sampling apparatus as claimed in any one of claims 32 to 34
36. A monitoring system, with automatic cleaning of each individual sensor head and optical window, for determining the various quality parameters in a liquid source, which system comprises apparatus claimed in any one claims 20 to 31 in combination with sampling apparatus as claimed in one claims in 31 to 35.
37. The use as claimed in 36 of a monitoring system, wherein the system is used on a longtern and/or continuous basis.