FI108866B - Method of dosing a detergent product - Google Patents

Description

108866

A method for dispensing a detergent product. - Förfarande för dosering av en detergentprodukt.

The present invention relates to a method for dispensing a detergent product 5 into a washing solution in an industrial washing machine, in particular an institutional machine; ware washing machine.

In prior art scrubbing systems, the detergent concentration of a wash solution is usually detected by measuring the electrical conductivity of the wash solution between at least two electrical electrodes immersed in the wash solution.

In this respect, the electrical conductivity can simply be determined by the ability of the solution to pass an electric current. In a conventional conductivity sensor, the solution is contacted with two or more electrodes and a small alternating current flows between them. This current is proportional to the conductivity of solution i. '20

Conductivity measurement is generally accomplished by the electrodes and conductivity amplifier described above, which activates the detergent dosing pump whenever the washing solution: v: electrical conductivity (and consequently detergent concentration) • · .v. 25 falls below a predetermined threshold value until * «· threshold level is reached again. Since the conductivity amplifier can operate with high accuracy, it is possible to ensure under all circumstances that the detergent content and the washing efficiency are adequate, i. so that the detergent concentration remains 30 above a predetermined level.

: However, it has been found that the detergent content of the prior art washing systems usually exceeds significantly _ ··. a threshold that results in perfect purity. This overdose of '! '35 detergent product can be up to tens of percent, thus causing considerable additional operating costs | 'That's it.

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GB-A-2,217,050 identifies this problem associated with conventionally used detergent overdosage. Thus, this document describes a method for reducing this overdose by periodically adding detergent product in small portions and allowing it to mix with and dissolve in the wash solution after a predetermined period of time, thereby ensuring that no insoluble detergent material that affects the result at the start of the dosing cycle, and then that the measured conductivity corresponds very closely to the actual detergent concentration of the wash solution.

Systems for controlling detergent concentration in a wash solution using a pair of electrodes immersed in the wash solution are known to have shortcomings. For example! Therefore, the electrodes in the measuring cell are susceptible to noise nanoparticle (scumming), m.p. the electrodes may be film-coated when used to monitor hard water solution, and may result in an acceptable level of conductivity when, in fact, the conductivity, and thus the detergent concentration of the wash solution, is unacceptably high. In addition, food stains in the washing solution are likely to cause electrode contamination, which can • adversely affect the accuracy of the conductivity measurement. Finally, the electrodes have been found to be sensitive to scale build-up, leading to erroneous k * * !! '.> Measurements and, consequently, increased product wear and operating costs.

. 30 • | ·

Because the aforementioned conditions leading to erroneous V * measurements (i.e., slag formation, contamination and dandruff formation) occur in the washing solution and the electrode. interface has been developed so-called. inductive • 35 measuring systems comprising electrode-free conductivity measurement sensors. The type of sensor used in these inductive systems * 'usually comprises two toroidal 108866 3 coils and when these sensors are immersed in the monitored wash solution, said solution provides an electrical connection between the coils.

US-A-4,733,798 describes a device for controlling the concentration of a washing solution, wherein the conductivity of said solution is measured using an inductive measuring system comprising an electrode-free sensor.

However, commercially available inductive measuring systems suitable for monitoring electrical conductivity and thus detergent solution detergent concentration are so far extremely expensive. In addition to coils contamination by food stains may prevent the determination of a homogeneous distribution of the detergent product in a prolonged wash solution, particularly near coils. Other drawbacks of inductive measuring systems are as follows: (i) for inductive measuring techniques, a certain minimum distance between the coils and the inner wall of the container for the detergent solution to be monitored is required. Thus, this measurement technique is not applicable in size; '·· in reduced tanks or pipes; (ii) since the signal produced on the coils is weak, the length of the cables 25 between the coils and the conductivity amplifier must be>; ·· | limited.

* · · F ·; ·. It is therefore an object of the present invention to provide a method for detergent concentration in a washing solution. 30, which utilizes a cheap and simple measuring system and does not have the above-mentioned '' 'and disadvantages. It is also an object of the invention to provide a method for controlling the detergent content of a detergent solution which minimizes detergent consumption and provides a constant cleaning performance.

• ». It has now surprisingly been found that these and other objects 4 '08866 can be achieved by carrying out a method according to the present invention by which the conductivity of a monitored wash solution is measured by a measuring cell containing electrodes.

5

The present invention provides a method of dispensing a detergent product into an industrial washing machine wash solution comprising measuring the conductivity of a solution containing water and detergent material using a measuring cell containing one or more electrodes having a conductivity relative to the detergent concentration of said wash solution, below a conductivity threshold corresponding to a preset threshold concentration of said detergent material in said 15 detergent solution, characterized by (a) dispensing, upon filling the washing machine with clean water, a predetermined amount of detergent product to achieve said preservative concentration, with water 20; (b) measuring the conductivity of the wash solution thus obtained after a mixing time of less than 2 minutes; and I '* · (c) storing said measured conductivity as said conductivity threshold value in a memory of the control unit which:: 25 units is connected to the measuring cell and controls the detergent product ·; ··; dosing as a function of measured conductivity.

t * · »*»

As a result of the process of the present invention, the problems associated with the use of electrodes are largely eliminated. 30 degree. This is achieved by measuring the conductivity of the wash solution; at the beginning of the washing cycle to obtain a preset conductivity threshold of • 1 · '* [* corresponding to a preset detergent concentration in the solution;

35 As a result of conductivity measurement, electrode contamination, dandruff formation, and slag formation, which has accumulated during previous washing cycles, cannot adversely affect the detergent concentration control of the washing solution. This accumulation of electrode fouling can be stretched over a period of months depending on the frequency of maintenance periods at the plant in question.

5

As a result of the process according to the invention, a constant detergent content can be achieved during the life of the electrodes and with minimal detergent consumption. Other advantages of the method of the invention are the secure constant cleaning performance using a relatively inexpensive system containing measuring cells containing one or more electrodes, and improved reliability resulting in a reduced number of maintenance visits. In addition, the system used is usually fully automated.

15

In order to reduce hardware and installation costs, a measuring cell containing only one electrode is preferred. In this case, the second "counter electrode" is formed by the inner wall of the container containing the washing solution to be monitored.

; It is desirable that the mixing time before conductivity is measured is as short as possible. When applied to the · ': process of the invention to monitor the detergent concentration of detergent solutions in multi-container laundry machines, this mixing time is generally less than 2 minutes,,, 1, preferably less than 1 minute. Alternative, 1 I 1 !!! In particular, when the method of the invention is applied to monitor detergent content in single-wash detergent solutions, this mixing time is generally less than 1 minute, preferably less than 30 * seconds, with a mixing time of 5 to 15 seconds being preferred.

In order to achieve optimal detergent consumption, the steps of the present invention are preferably repeated; every time the washing machine is filled with clean water.

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To dispense the correct amount of detergent product when filling the washing machine with clean water, it is desirable to calculate this amount by determining the volume of water inside the washing machine used. The method of the invention has proven to be particularly suitable for controlling detergent concentration in detergent solutions in institutional washers.

An alarm-10 function may be incorporated into the method of the invention, indicating that the electrodes used are contaminated to such an extent and that, as a result, their sensitivity is impaired to such an extent that proper operation of these electrodes is no longer possible. This alarm function is usually adjustable to provide a visual or auditory signal when the sensitivity of the electrodes is reduced to a level within the range of 50-70% of their lifetime; the sensitivity value at the moment. The specific adjustment of the alarm function depends on the required concentration control accuracy: when higher accuracy is required, the alarm can be adjusted to a higher 20% of the initial sensitivity. In other words: in this case, less overlapping of the electrodes is tolerated.

The invention will now be further described by means of the following preferred embodiment and with reference to the accompanying drawing, in which Figure 1 schematically illustrates a system for carrying out the method of the invention.

This figure shows a block diagram of this system, including a conductivity amplifier / controller 1 connected to the measuring electrodes 3 and 4, one of which may be the inner wall of a container containing the washing solution monitored by said system. These electrodes are embedded in a suitable location in the wash solution. This place is not critical; However, a measuring point located near the detergent supply point will more quickly recognize the effect of the detergent product supplied. The conductivity amplifier / controller 1 108866 7 measures the electrical conductivity of the wash solution between the measuring electrodes 3 and 4 and outputs an activation signal AKT as the measured conductivity drops below a preset conductivity threshold. This preset value is measured during the start of the wash cycle 5 and subsequently stored in memory 3.

The output of the conductivity amplifier / controller 1 is connected to the control input of the detergent dose control unit 2. This control unit 2 only switches on the dosing pump if the AKT signal is generated.

10

The invention is illustrated by the following non-limiting examples.

i

Examples 1, 2, 3. Comparative Examples A, B, C

15

A detergent product having the following composition was tested on an industrial machine dishwasher containing a measuring cell with a pair of conductivity electrodes: 20 Component

Sodium hydroxide (50%) 35.5

Bayhibit AM (1) 3.0; Norasol LMW 45 N (2) 3.0; Demineralized water 58.8! · '·. 25, * where:,! > f, (1) Bayhibit AM: phosphono-1,2,4-butane-tricarboxylic acid ;;; (50%), Bayer'1 ta t * '· * (2) Norasol LMW 45 N: Sodium salt of polyacrylic acid, from Norsohaas.

«V t J * * I · I» '* First, three mechanical dishwashing cycles were performed with a clean conductivity sensor at various dosing levels> to achieve the indicated detergent product level in the respective' 35 order of 1.5 g / l, 2.0 g / l and 3.5 g / 1. Next

/ 4 S

; at each of these dosing levels, two cycles of dishwashing were performed with a desiccated conductivity sensor: one cycle using a preset conductivity threshold according to the method of the present invention and a second reference cycle without using said preset conductivity threshold. In other words, according to the invention, the meek-5 during the dishwashing cycles was compensated for the delamination effect of the sensor, while said compensation was not performed during the reference cycles. During all dishwashing cycles, the actual detergent level in the washing solution was measured.

10

The following true product concentrations were observed in mechanical dishwashing solutions (g / l):

Example 1_ A

15 Addressed Detergent - Pure Decayed Sensor Product Level Sensor Compensated Uncompensated 1.5 g / 1 1.5 1.5 2.2

Example '2 B

20 Detergent Detergent - Pure Decayed Sensor Product Level Sensor Compensated Non-Compensated 2.0 g / 1 2.0 2.0 2.8 t · • ·

Example 3. C

'• '25 Detergent Indicated- Pure Decayed Sensor Product Level Sensor Compensated Uncompensated L: 3.5 g / 1 3.5 3.5 4.3

It can be seen that at all dosage levels tested. . '. 30 actually used more detergent products than • · ·. ·. ·. demonstrated when using an uncompensated scaled conductivity sensor. On the other hand, the actual concentration of detergent product in the wash solution was found to be equivalent to * I * relative to the indicated product level when compensated-damped sensors were applied.

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Claims (7)

108866 9 A method for dispensing a detergent product into a washing solution of an industrial washing machine, comprising measuring the conductivity of a solution containing water and detergent material using a measuring cell containing one or more electrodes having a conductivity relative to the detergent concentration of said detergent and increasing the detergent product the value drops below a conductivity threshold corresponding to a preset threshold concentration of said detergent material in a detergent solution, the method comprising the steps of: (a) dispensing, upon filling the washing machine with clean water, a predetermined amount of (b) measuring the conductivity of the wash solution thus obtained after less than 2 minutes of agitation; characterized by (c) storing a measured conductivity as a conductivity threshold in a memory of the control unit, which control unit is connected to a measuring cell and controls the dispensing of the detergent product as a function of the measured conductivity. 20 Method according to claim 1, characterized in that the measuring cell has two electrodes. 4 · '1. 3. A method according to claim 1 or 2, characterized in that the washing 4 4 4 1 4 1. The conductivity of 25 solutions is measured after a mixing time of less than 1 minute. »· 4 1 · Method according to one of the preceding claims, characterized in that the steps mentioned in claim 1 are repeated each time * · ·; Fill the washing machine with clean water. '·; : 30 A method according to any one of the preceding claims, characterized in that, to achieve a preset threshold concentration, it is dispensable; the amount of detergent product is calculated by determining the volume of water inside the washing machine. 35 108866 10 S Method according to one of the preceding claims, characterized in that said method is carried out in an industrial dishwasher. Method according to one of the preceding claims, characterized in that an alarm element is used which indicates when the sensitivity of the electrodes has been reduced to a level within the range of 50-70% of the sensitivity at the start of their service life. i! ♦ · · * t * ♦ «· 1» t · * t | 108866 11