US20050079079A1

US20050079079A1 - Dilution system

Info

Publication number: US20050079079A1
Application number: US10/960,813
Authority: US
Inventors: Sigvard Wahlin; Lynn Egan; Edmund McDonagh
Original assignee: Hach Co
Current assignee: Hach Co
Priority date: 2003-10-09
Filing date: 2004-10-07
Publication date: 2005-04-14

Abstract

A dilutor has a control interface to receive control signals and a block having an orifice. The dilutor has a single piston at least partially within the block, and there is not another piston within the block. The dilutor has a motor and drive configured, in response to the control signals, to automatically move the single piston away from the orifice to aspirate fluid and to move the single piston toward the orifice to dispense the aspirated fluid. The dilutor has a first valve coupled to the orifice and configured, in response to the control signals, to automatically couple the orifice either to a sample line or to a diluent line.

Description

RELATED APPLICATIONS

This application claims the benefit of U.S. provisional application No. 60/510,076 filed on Oct. 9, 2003 entitled “Dilution System,” which hereby is incorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention is related to the field of dilution, and in particular, to a dilution system where the dilutor uses a single-piston design.
2. Statement of the Problem
FIG. 1 illustrates dilutor 100 in an example of the prior art. Dilutor 100 includes first piston 101, second piston 102, block 103, spring drive 104, multi-link drive 105, and stepper motor 106. Block 103 includes egress orifice 108 and ingress orifice 109. Dilutor 100 is typically coupled to other components to form a dilution system, where such components may include a sampler, diluent supply, pump, analyzer, and computer.
Stepper motor 106 operates multi-link drive 105 to push second piston 102 up against first piston 101 to compress spring drive 104. Valve action then connects a sample line to ingress orifice 109. Stepper motor 106 operates multi-link drive 105 to lower second piston 102 to a first point. This action allows spring drive 104 to push first piston down 101 down against second piston 102. This action also increases the empty volume within block 103 to generate a vacuum that draws a specific amount of sample through ingress orifice 109 into block 103. Valve action then connects a diluent, such as water, to ingress orifice 109. Stepper motor 106 operates multi-link drive 105 to lower second piston 102 to a second point that is below the first point. This second action allows spring drive 104 to push first piston 101 to its maximum low point where first piston 101 is stopped by a tab. This second action lowers the top of second piston 102 below the bottom of stopped first piston 101 to further increase the empty volume within block 103. Thus, the second action also generates a vacuum that draws a specific amount of diluent through ingress orifice 109 into block 103. The amount of sample and diluent that are aspirated into block 103 is based on the coordination of: 1) the interior volume of block 103; the respective volumes of pistons 101 and 102, where second piston 102 is typically larger then first piston 101; and the movement of second piston 102 by multi-link drive 105 and stepper motor 106.
Unfortunately, dilutor 100 exhibits several problems.
When the two pistons move together to a lower position from the top, the two pistons can separate before the top piston is stopped. The piston separation is caused by friction, the differently sized pistons, and other system imperfections. The unwanted piston separation changes the volume in the block to aspirate more sample fluid than expected. The unexpected aspiration can cause serious errors.
The interior of the block is restricted in size relative to the small piston that is used to aspirate sample. Thus, the block may not be large enough to hold enough sample or diluent for a given dilution. This may result in having to repeat aspiration cycles just to obtain enough sample or diluent. Multiple aspiration cycles for a single fluid is complex and time consuming.
The interior of the block tends to hold bubbles that introduce error into the system.
The multi-link drive uses belt and lever linkages that introduce error and backlash into the system.
Prior dilution systems are described in U.S. Pat. Nos. 4,941,808; 5,366,904; 5,183,765; and 5,383,372.

SUMMARY OF THE SOLUTION

Examples of the invention include diluters, dilution systems, and their methods of operation. Some examples of the invention include a dilutor that comprises:

- a control interface configured to receive control signals;
- a block having an orifice; a piston at least partially within the block, wherein there is not another piston within the block;
- a motor and drive configured, in response to the control signals, to automatically move the piston away from the orifice to aspirate fluid and to move the piston toward the orifice to dispense the aspirated fluid; and
- a first valve coupled to the orifice and configured, in response to the control signals, to automatically couple the orifice either to a sample line or to a diluent line.

DESCRIPTION OF THE DRAWINGS

The same reference number represents the same element on all drawings.
FIG. 1 illustrates a dilutor in an example of the prior art.
FIG. 2 illustrates a dilution system in an example of the invention.
FIG. 3 illustrates a dilution system in an example of the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 2-3 and the following description depict specific examples to teach those skilled in the art how to make and use the best mode of the invention. For the purpose of teaching inventive principles, some conventional aspects have been simplified or omitted. Those skilled in the art will appreciate variations from these examples that fall within the scope of the invention. Those skilled in the art will appreciate that the features described below can be combined in various ways to form multiple variations of the invention. As a result, the invention is not limited to the specific examples described below, but only by the claims and their equivalents.
Dilution System
FIG. 2 illustrates dilution system 200 in an example of the invention. Dilution system 200 includes dilutor 201, sampler 202, sample 203, diluent 204, dilution receptacle 205, flush 206, pump 207, analyzer 208, and computer 209. Sampler 202 includes dual probe 210 that has two separate probes. As indicated by the dashed lines and arrows, sampler 202 can move dual probe 210 to sample 203 or dilution receptacle 205. Diluent 204 and flush 206 could be deionized water. Sampler 202 can control the speed of probe movement (in response to computer 209 instructions if desired). Slower probe movement may be desired for some fluids to allow unwanted fluid and drips to fall away from the exterior of probe 210.
Dilutor 201 is coupled to sampler 202 by fluid lines 211-212. Sampler 202 couples each one of fluid lines 211-212 to a respective one of the probes in dual probe 210. Fluid line 211 can hold at least 8 milliliters. Dilutor 201 is coupled to diluent 204 by fluid line 213. Dilutor 201 is coupled to flush 206 by fluid line 214. Dilutor 201 is coupled to pump 207 by fluid line 215. Pump 207 is coupled to analyzer 208 by fluid line 216. The fluid lines can be sized to match the diameter of the component orifices to reduce the negative effects of sizing mis-match on fluid flow.
Computer 209 stores and executes control software. When executed, the control software directs computer 209 to send instructions over communication links 217 to dilutor 201, sampler 202, pump 207, and analyzer 208. Dilutor 201, sampler 202, pump 207, and analyzer 208 operate in response to the instructions. The control exerted by computer 209 results in the following operations.
To perform the dilution:

1. Diluter 201 aspirates a slug of air into dual probe 210.
2. Sampler 202 moves dual probe 210 into sample 203.
3. Diluter 201 aspirates a precise amount of sample 203 through sampler 202 and into line 211.
4. Sampler 202 removes dual probe 210 from sample 203.
5. Dilutor 201 aspirates another slug of air, so the aspirated sample has a slug of air at each end in line 211.
6. Diluter 201 aspirates a precise amount of diluent 204 through line 213.
7. Sampler 202 moves dual probe 210 from sample 203 into the wash, and then to dilution receptacle 205.
8. Dilutor 201 dispenses the aspirated sample and diluent into dilution receptacle 205 through line 211, sampler 202, and probe 210.
9. Sampler 202 moves dual probe 210 from dilution receptacle 205 into the air.
10. Dilutor 201 aspirates air into probe 210.
11. Sampler 202 moves probe 210 into dilution receptacle 205.
12. Dilutor 201 dispenses the air through probe 210 into dilution receptacle 205 to mix the diluted sample and diluent. (Steps 9-12 may be repeated).
13. Diluter 201 decouples line 214 from line 215 and couples line 212 to line 215.
14. Pump 207 draws the mixed dilution from dilution receptacle 205 to analyzer 208 through probe 210 (using the other one of the dual probes), sampler 202, line 212, dilutor 201, line 215, pump 207, and line 216.
15. Analyzer 208 receives and analyzes the mixed dilution.

During the above sequence, some events may occur simultaneously to save time. For example, dilutor 201 returns its single piston to its home position and/or switches valves while sampler 202 moves probe 210.
Dilutor
FIG. 3 illustrates dilutor 201 in an example of the invention. Dilutor includes block 301, piston 302, nut 303, stepper motor 304, screw 305, valve 306, valve 307, and control interface 308. Nut 303 is coupled to piston 302. Block 301 includes orifice 309 that is coupled to fluid line 311.
Control interface 308 is coupled to communication links 217 to receive instructions from computer 209. Control interface 308 could be comprised of conventional communications components, software, and processing circuitry. Control interface controls stepper motor 304 and valves 306-307 in response to the instructions.
In response to the instructions, valve 306 can couple line 311 to either line 211 (sample) or line 213 (diluent), and valve 307 can couple line 215 (pump/analyzer) to either line 214 (flush) or line 212 (mixed dilution). Valve control is carried out to affect the line couplings described above for dilution system 200.
In response to the instructions, stepper motor turns screw 305 within the threads of nut 303. The turning action moves nut 303, and nut 303 moves piston 302. Thus, stepper motor 304 can move piston 302 up and down within block 301 through the action of screw 305 and nut 303. The home position of piston 302 is at the top of block 301. Stepper motor 304 could have 29,000 half-steps or 14,500 full steps to provide thousands of aspiration increments within a total fluid volume of 8 milliliters. The cavity formed by block 301 has a total volume of approximately 9.2 milliliters, but a maximum aspiration amount is approximately 8 milliliters. Nut 303 could be comprised of plastic, such as Delrin.
To aspirate sample 203 through probe 210, valve 306 couples lines 211 and 311. Stepper motor 304 then turns screw 305 to lower nut 303 and piston 302. This movement creates a vacuum that draws sample 203 into line 211. To dispense the aspirated sample from line 211, valve 306 couples lines 211 and 311. Stepper motor 304 then turns screw 305 to raise nut 303 and piston 302. This movement creates pressure that forces the aspirated sample from line 211. Aspiration and dispensation of air or diluent 204 through probe 210 would be similar.
To aspirate diluent 204 through line 213, valve 306 couples lines 311 and 213. Stepper motor 304 turns screw 305 to lower nut 303 and piston 302. This movement creates a vacuum that draws diluent 204 through line 213, line 311, and orifice 309 into block 301. To dispense the aspirated diluent through probe 210, valve 306 couples lines 211 and 311. Stepper motor 304 then turns screw 305 to raise nut 303 and piston 302. This movement creates pressure that forces the aspirated diluent from block 301 through line 311 and into line 211.
Although not shown for clarity, block 301 may be tilted so that the point where orifice 309 meets the interior of block 301 is higher than other points in the interior of block 301. This tilt effectively puts the egress point of block 301 at its highest point to assist in the evacuation of unwanted air bubbles from block 301.
Advantages
Dilution system 200 and diluter 201 provide several advantages over the prior art. The dilutor is faster, smaller, and more accurate than prior dilutors. When implemented properly, the diluter provides a wide range of dilution (1:1.6 to 4000:1) in total volume of 8 milliliters with less than 5% error. In field tests, error is far less than 5%. The dilution range operates from 1:1.6 to 100:1 in a single pass and from 100:1 to 4000:1 using a serial dilution process.
The new dilution system is faster because fewer cycles are needed to produce a dilution. Prior dilution systems often had to go through multiple cycles just to aspirate the desired amount of a single fluid. For a total volume of 8 milliliters, the dilutor can provide a mixed dilution with only a single aspiration of sample and diluent. The new dilution system is also faster because some actions occur simultaneously.
The use of a single piston eliminates the piston separation problem described above. The dilutor simply does not introduce error because of undesired piston separation. The single piston provides smaller performance from system to system due to fewer mechanical imperfections for a single piston as opposed to two pistons. The single piston provides more room in the block for fluid. The single piston also simplifies the control calculations, because prior dilutors had to perform complex calculations for two moving pistons each having different volumes.
The stepper motor can have a much higher resolution than motors used in previous dilution systems. The higher resolution translates into more flexibility and more precise dilutions.
The direct screw/nut drive has fewer linkages than the multi-link belt/lever drive used by previous dilution systems. The direct drive exhibits far less mechanical error, and virtually eliminates backlash from the system.
The play between the screw and nut contribute to system error. With heavy use, the nut and screw wear, and the wear typically causes even more error. The plastic nut provides a softer surface that reduces wear on the screw. The plastic nut also tends to shrink around the screw as it wears to maintain the same fit between the nut and screw over time, which better maintains system accuracy.
The diluter and computer can automatically supply the diluted samples to the analyzer. The diluter also controls the flush of the analyzer line to reduce air and contaminants that contribute error.
The dilution system is designed to produce a mixed dilution having 8 milliliters in total volume. Conveniently, this is the size of test tubes used by common samplers.
The dilutor design maintains relatively low pressure (6 P.S.I) in the block during aspiration and dispensation. The low pressure reduces influence on fluid flow and improves system accuracy.
Slowing probe movement reduces the unwanted fluid clinging to the exterior of the probe. The reduction of unwanted fluid improves system accuracy.
The bigger fluid lines are tuned to component orifices to prevent cavitation.
This tilt of the diluter block assists in the evacuation of unwanted air bubbles from the block to improve system accuracy.

Claims

1. A diluter, comprising:

a body having an outside surface, the body forming a cavity having an inside surface and a top end;

an orifice positioned to connect the inside surface of the cavity with the outside surface of the body;

a single piston configured to fit inside the cavity;

a motor and drive configured to move the single piston away from the orifice to aspirate fluid and to move the single piston toward the orifice to dispense the aspirated fluid.

2. The dilutor of claim 1 wherein the drive comprises a nut and a screw, wherein the nut is directly coupled to the single piston, and wherein the motor is configured to directly turn the screw within the nut.

3. The dilutor of claim 2 wherein the nut comprises plastic.

4. The dilutor of claim 1 wherein the cavity and the single piston are cylindrical in shape.

5. The diluter of claim 1 where the orifice is positioned at the top end of the cavity.

6. The diluter of claim 5 where the block is configured such that the orifice connects the highest point of the cavity with the outside surface of the block.

7. The diluter of claim 1 where the single piston essentially fills the cavity when the single piston is in a position closest to the top end of the cavity.

8. The dilutor of claim 1 where the motor is a stepper motor having at least 29,000 half-steps corresponding to a full range of the piston movement.

9. The dilutor of claim 1 wherein the cavity is configured to hold approximately 9.2 milliliters.

10. The dilutor of claim 1 wherein the diluter can aspirate and dispense two fluids having a combined total volume of 8 milliliters and a dilution range between 1:1.6 and 1:4000.

11. The diluter of claim 1 where the single piston forms a seal with respect to the inside surface of the cavity.

12. The diluter of claim 1 further comprising:

a gasket attached to the single piston and forming a seal between the single piston and the inside surface of the cavity.

13. The diluter of claim 1 further comprising:

a valve connected to the orifice, the valve connecting the orifice to a first fluid source when the valve is in a first position;

a controller configured to switch the valve to a second position, where the valve connects the orifice to a probe when the valve is in the second position.

14. The diluter of claim 13 where the probe is a dual probe.

15. A method for diluting a fluid, comprising:

drawing a first fluid into a conduit by moving a single piston inside a cavity, away from an orifice, where the orifice connects the cavity to the conduit;

drawing the second fluid into the conduit by moving the single piston away from the orifice;

pushing the two fluid out of the conduit into a dilution receptacle by moving the single piston towards the orifice.

16. The method of claim 15 where the single piston and the cavity are cylindrical in shape.

17. The method of claim 15 further comprising:

drawing air into the conduit by moving the single piston away from the orifice;

mixing the two fluids in the dilution receptacle by blowing the air out of the conduit into the two fluids by moving the single piston towards the orifice.

18. The method of claim 15 further comprising:

drawing air into the conduit between the first fluid and the second fluid by moving the single piston away from the orifice.

19. The method claim 15 where the orifice is positioned at a top end of the cavity and the single piston essentially fills the cavity when the single piston is in a position closest to the orifice.

20. A diluter, comprising:

a fluid holding means;

a means for drawing a first fluid into the fluid holding means using a single piston;

a means for drawing a second fluid into the fluid holding means using the single piston

a means for dispensing the two fluids from the fluid holding means using the single piston.