US20010046051A1

US20010046051A1 - Turbidimeter array system

Info

Publication number: US20010046051A1
Application number: US09/900,560
Authority: US
Inventors: Ashim Banerjee
Original assignee: Hach Co
Current assignee: Hach Co
Priority date: 1999-11-19
Filing date: 2001-07-06
Publication date: 2001-11-29
Also published as: WO2001036940A2; EP1230534A2; JP2003515124A; AU772363B2; KR20020063576A; WO2001036940A3; AU1603901A; US6307630B1; CA2391979C; CA2391979A1

Abstract

A turbidimeter array system for measuring the turbidity of each of a plurality of liquid samples. The system includes a plurality of sample chambers, a single light source and a single detector. The light source directs a light beam into the liquid sample and the detector detects light scattered by the liquid sample.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation-in-part of my copending application Ser. No. 09/444,061, filed Nov. 19, 1999.[0001]

FIELD OF THE INVENTION

This invention relates to turbidimeters and their use in monitoring the turbidity of water (e.g. drinking water). More particularly, this invention relates to the use of a turbidimeter to monitor the effluent from membrane filters.

BACKGROUND OF THE INVENTION

Many water plants which are used to produce drinking water utilize membrane filters (e.g. micro-filtration, ultra-filtration, and nano-filtration). Typical ultra-filtration membranes have an effective pore size of less than 0.1 micron which means that not only do they completely remove most bacteriological pathogens, but they also have the capability to filter out most viruses. The California Department of Health and other state and federal agencies are considering means by which they can offer virus removal credit to water plants which adopt ultra-filtration technology. If adopted, water plants will be able to save very significant amounts of money by avoiding the costs associated with chemical disinfection of drinking water.

A serious disadvantage associated with the use of filtration membranes is the periodic failure or rupture of a membrane. Typically there are thousands of relatively small diameter elongated membrane fibers contained in a parallel arrangement in a single cartridge, with numerous cartridges (e.g. 1000 or more in racks of 20 to 50) being used simultaneously in a single water plant. Presently, the operator of the plant periodically (e.g. every four hours or so) takes each rack off-line and passes air through one end while the other end is submerged in water. Below a certain air pressure, air should not be able to pass through a membrane, unless the membrane has been punctured or has ruptured. If the membrane has ruptured or been punctured, a stream of bubbles will be detected from that membrane at the submerged end. The failed membrane can then be identified and mechanically plugged, after which the cartridge can be put back into service. The main problem with this approach is that it allows for a four to six hour period during which undesirable material could pass through the cartridge and enter into the effluent water.

Although manufacturers have provided turbidimeters and particle counters for on-line monitoring of water quality, those instruments generally lack sensitivity to sub-micron particles. Furthermore, a full scale water plant would require several hundred membrane cartridges, and the instrumentation costs for monitoring the effluent of each membrane would be prohibitive.

The prior art has several references to apparatus that uses a single light source and detector for measuring light absorption. For example, U.S. Pat. No. 4,549,809 (Minekane et al.) describes a photometric apparatus which is indicative of light absorption in a liquid sample. For such an instrument to work, the sample must be free of particulate matter which would scatter light. The light source and the detector are arranged such that the light from the source passes through the sample on its way to the detector. U.S. Pat. No. 4,534,651 (Minikane) also describes a light absorption instrument similar to that of Minekane et al.

U.S. Pat. No. 4,888,484 (Harvey) describes a spectrophotometer for light absorption. This instrument is very similar to the light absorption system described by Minekane. The main difference is the presence of two separate sample chambers with moving mirrors to deflect the beam into each chamber.

U.S. Pat. No. 4,509,856 (Lee) describes a photometric analyzer using a rotor for centrifugal fast analyzers. The instrument is designed to be used for measuring fluorescence and as such is limited to measuring samples that are tagged with fluorescent markers.

U.S. Pat. No. 6,134,000 (Schmid) describes apparatus using optical fibers to simultaneously make multiple optical measurements on samples that are undergoing rapid thermal cycling (for biological samples).

U.S. Pat. No. 4,826,319 (Namba et al.) describes a system for measuring light scattered from antibody-antigen reactions. This system employs fiber optics with multiple light sources and multiple detectors to measure light scattered from a plurality of sample cells along a reaction line. Fiber optics are used to collect light from different positions within the same cell. Also described is a system where multiple sample cells are moved across a single light source and a single detector. The light scattered from the sample is analyzed using a Fourier transform to obtain a power spectrum of the signal.

There has not heretofore been provided a system for accurately and efficiently monitoring the effluent of multiple membranes used for ultra-filtration of water.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a turbidimeter system for efficiently monitoring the effluent of a plurality of membrane cartridges comprising a membrane filtration plant.

To accomplish the foregoing and other objects, the present invention provides a turbidimeter array system comprising a plurality of sample chambers for containing a liquid sample to be tested, and wherein the system includes a single light source and a single detector means. In other words, the system includes a plurality of sample chambers which share a single light source and a single detector when a turbidity measurement is made of the liquid in a particular chamber.

In one embodiment, a single light source is adapted to sequentially direct a light beam into each of the sample chambers, and the detector means is adapted to detect light which is scattered by the liquid sample in each of the sample chambers.

The system of this invention enables efficient monitoring of the turbidity of a plurality of liquid samples contained in a plurality of separate chambers, without requiring a separate light source and separate detector for each sample chamber. Rather, in a preferred embodiment the system utilizes a common light source, detector means, associated control electronics, display, etc.

Other advantages and features of the turbidimeter array system of the invention will be apparent from the following detailed description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in more detail hereinafter with reference to the accompanying drawings wherein like reference characters refer to the same parts throughout the several views and in which: [0017]
FIG. 1 is a schematic diagram showing an array of [0018] 16 separate sample chambers which share a common light source, detector means, and control electronics;
FIG. 2 illustrates one embodiment of a sample chamber of the array shown in FIG. 1; [0019]
FIG. 3 illustrates one embodiment of the invention in which a first optical fiber transmits light from the light source to a sample chamber, and a second optical fiber transmits scattered light from the sample chamber to a detector means; [0020]
FIG. 4 is a front elevational view of a rotatable disk in which the ends of a set of optical fibers are supported, with each optical fiber being associated with a separate sample chamber; [0021]
FIG. 5 illustrates the use of a calibration system in the present invention.[0022]

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a number of embodiments in which a single light source and a single detector means are shared for turbidity testing of a plurality of liquid samples contained in a plurality of separate chambers or cells. FIG. 1 is a schematic diagram illustrating this concept. There is shown an array comprising 16 separate sample chambers, with one [0023] light source station 100, one detector station 200, and one control electronics station 300.
In this embodiment, a separate optical fiber extends between the light source and each of the sample chambers. Also, a separate optical fiber extends between each sample chamber and the detector. The chambers each include appropriate inlet and outlet windows, as required, to enable the light beam to be transmitted into the chamber and to enable scattered light to be transmitted out of the chamber. The chambers preferably each include appropriate inlet and outlet ports for the liquid (e.g. water) which is being tested in each chamber. [0024]
When it is desired to measure the turbidity of the sample in [0025] chamber 1, light from the light source is directed through the optical fiber 101 extending to chamber 1. See also FIG. 2 where the light beam from fiber 101 is shown being transmitted into chamber 1 where it proceeds through the sample. Light which is scattered by the sample in chamber 1 is transmitted via an optical fiber 201 to the detector station. The conventional control electronics is able to convert the signal generated by the detector into a turbidity value and cause it to be displayed or recorded.
A similar situation occurs when it is desired to measure the turbidity of a sample in [0026] chamber 2 using optical fiber 102 to transmit light from the light source 100 and optical fiber 202 to transmit scattered light to the detector. The same technique is used with respect to each of the separate sample chambers. Because each chamber can be tested using the same light source and the same detector and control electronics, the array system is very efficient.
The light source used in this invention may be, for example, a laser or a laser diode. Other light sources could also be used, if desired. [0027]
The detector means used in this invention may be any conventional light detector such as a photomultiplier tube, photodiode, or avalanche photodiode. [0028]
There are a variety of ways to utilize a single light source and single detector in combination with an array of separate sample chambers in accordance with this invention. One of these is illustrated in FIGS. 3 and 4. Each sample chamber has an optical fiber (e.g. [0029] 101) which terminates at one end at the chamber inlet window and terminates at its opposite end in rotatable disk 150 adjacent light source 100 (as shown). The rotatable disk 150 can be selectively rotated by means of stepper motor 160 so as to position the end of any desired optical fiber adjacent to the light source.
Each sample chamber also has an optical fiber (e.g. [0030] 201) which terminates at one end at the chamber outlet window and terminates at the opposite end in rotatable disk 250 adjacent detector 200. The disk 250 can be rotated by means of stepper motor 260 so as to position the end of the desired fiber 201 adjacent to the detector. When fibers 101 and 201 are adjacent to the light source and the detector, respectively, then the turbidity of the sample in chamber 1 can be determined. Appropriate rotation of disks 150 and 250 enable similar testing of all of the samples in the other chambers in the array. Although only 16 separate chambers are illustrated in FIGS. 1-4, there may be any desired number of separate chambers for separate samples to be tested.
FIG. 5 illustrates a [0031] sample chamber 30 which is designed to enable verification of the calibration of the unit. The chamber 30 includes a light trap section 32 comprising a sloped or angled floor 32A beneath a horizontal floor 32B in which there is provided an aperture 32C. On top of the measurement chamber 30 there is located a calibration chamber or section 31. The light beam from the light source (e.g. laser fiber optics) first passes through a beam splitter BS which transmits about 90% of the beam and reflects about 10% into the calibration path. The main beam L1 which is transmitted passes through shutter S1, diffuser D, then through the sample in the chamber 30 and through aperture 32C into the light trap 32.
When it is desired to verification the calibration of the unit, shutter S[0032] 1 is closed and shutter S2 is opened. This enables the light from beam splitter BS to pass through neutral density filter ND (which attenuates the light beam about 1000 times) and two polarizers P1 and P2 to reach mirror M where it is reflected through open shutter S2 and diffuser D and into the sample chamber 30 as beam L2. This calibration beam is factory adjusted using the two polarizers such that it reads as a known amount of turbidity. During verification, the instrument looks for a turbidity reading corresponding to this predetermined value. If the turbidity reading is within preset limits then the insturment is deemed to be functioning properly. If the measured reading is not within the preset limits, then a calibration is performed using the available signal. Alternatively, verification of the calibration can be performed with both shutters S1 and S2 open. In such case, the instrument looks for an increase in the turbidity reading by an amount corresponding to the factory preset calibration signal.
A calibration verification system of the type described above is shown in U.S. Pat. No. 5,912,737, incorporated herein by reference. [0033]
Other variants are possible without departing from the scope and spirit of this invention. [0034]

Claims

What is claimed is:

1. A turbidimeter array system for measuring the turbidity of each of a plurality of liquid samples, the system comprising a plurality of sample chambers each including a liquid sample to be tested, wherein said system includes a single light source and a single detector means, wherein said light source directs a light beam into said liquid sample and said detector means detects light scattered by said liquid sample.

2. A turbidimeter array system for measuring the turbidity of each of a plurality of liquid samples, the system comprising:

(a) a plurality of sample chambers each including a liquid sample to be tested;

(b) a single light source means for sequentially directing a light beam into each of said sample chambers; and

(c) detector means for sequentially detecting light scattered by said liquid sample in each of said sample chambers.

3. A system in accordance with

claim 2

, wherein each said sample chamber includes a light inlet window and a light outlet window.

4. A system in accordance with

claim 2

, wherein said sample chambers are aligned in a side-by-side manner.

5. A system in accordance with

claim 3

, further comprising first optical fiber means positioned between said light source and said light inlet window for transmitting light to said sample chamber, and further comprising second optical fiber means positioned between said light outlet window for transmitting scattered light from said outlet window to said detector means.

6. A system in accordance with

claim 5

, wherein said first optical fiber means includes a first end positioned at said light inlet window and a second end positioned in a rotatable disk adjacent said light source, wherein rotation of said disk enables said light source to transmit light through a desired one of said first optical fiber means.

7. A system in accordance with

claim 5

, wherein said second optical fiber means includes a first end positioned at said light outlet window and a second end positioned in a rotatable disk adjacent said detector means, wherein rotation of said disk enables said detector means to detect light transmitted by a desired one of said second optical fiber means.

8. A system in accordance with

claim 2

, wherein said detector means comprises a photomultiplier tube, a photodiode or an avalanche photodiode.

9. A system in accordance with

claim 2

, further comprising calibration verification means operatively associated with each said chamber, wherein said calibration verification means comprises:

(a) a beam splitter for splitting the light from said light source into first and second beams;

(b) polarizer means for polarizing the light in said second beam and controlling the amount of light passing through said polarizer means, and

(c) shutter means for controlling transmittance of said second beam into said chamber.

10. A turbidimeter array system comprising:

(d) a plurality of sample chambers each including a liquid sample to be tested;

(e) light source means operatively associated with each said sample chamber;

(f) a single detector means adapted to sequentially detect light scattered by said liquid sample in each of said sample chambers.