WO2011132200A2

WO2011132200A2 - A level sensing device

Info

Publication number: WO2011132200A2
Application number: PCT/IN2011/000255
Authority: WO
Inventors: Prethiviraj Balaji; Rajendran Rajmohan; Frank Gottwald
Original assignee: Robert Bosch Engineering And Business Solutions Limited; Robert Bosch Gmbh
Priority date: 2010-04-19
Filing date: 2011-04-15
Publication date: 2011-10-27
Also published as: WO2011132200A3

Abstract

A device to determine level of a solution in a tank is disclosed. The solution has the property that the specific resistance of the device varies over a period of time. The device comprises a conducting element having at least one gap. The gap is bridged with resistor R1 of defined value. A look up table containing a set of ranges of resistance values, each range of resistance value being indicative of specific level of the solution in the tank and a control means adapted to determine the level of the solution depending upon the resistance across the contact points of the conducting element and the range of resistance values stored in the look up table.

Description

Title : A LEVEL SENSING DEVICE

Applicant's Name : Robert Bosch Engineering and Business Solutions Limited and Robert Bosch GmbH

FIELD OF INVENTION:

The invention relates to a device to sense level of a fluid in a tank. BACKGROUND OF THE INVENTION:

Electrically resistive fluid level sensors are known generally for measuring conductive and partially conductive fluid levels. EP-A-0962751 discloses fluid level sensors comprising resistive film elements disposed in a _. container. The conductive fluid in the container provides a relatively low resistance, or short circuit, path between the resistive elements, thus forming a series connection. The resistance of the resistive elements varies continuously in proportion to the changing fluid level in the container. A corresponding change in a voltage output measured across the series resistive elements is indicative of the fluid level in the container

ADVANTAGES OF THE INVENTION:

The invention proposes a device and a method to measure the level of a fluid in a tank, especially for a fluid whose resistance varies over a period of time.

The invention uses a simple resistor network and a table containing a set of range of values for comparing the measured resistance with, each range indicating a specific level of the fluid. By selecting the appropriate values for the resistors and determining the range of values for the measured resistance to indicate different levels of the fluid, the level of the fluid is sensed unambiguously even if the specific resistance of the fluid is varying over a period of time. BRIEF DESCRIPTION OF THE DRAWINGS:

Figure 1 Shows the schematic of the invention;

Figure 2 Shows the schematic of another embodiment of the invention; and

Figure 3 Shows a detailed setup of the embodiment of figure 2.

DESCRIPTION OF THE INVENTION:

Shown in fig. 1 is a device 10 used to sense the level of the liquid 12 in the tank 14. The liquid 12 can be any kind of liquid, which is conductive or partially conductive, but the invention particularly describes the application for an AdBlue® solution. The AdBlue® is a 32.5 % aqueous urea solution which is used to inject into the exhaust channel of a vehicle to reduce harmful gases. The property of the AdBlue® solution is such that the specific resistance of the AdBlue® solution changes over a period of time. The specific resistance of the AdBlue® solution is known to vary by a factor of 40 over a period of time. With this property of the AdBlue® solution, it is not possible to use a continuous resistive element to measure the level of the AdBlue® solution, because the resistance read from the resistive element will vary over a period of time even if the level of the AdBlue® solution is constant as the specific resistance of the AdBlue® solution varies.

The device 10 shown in fig. 1 comprises a conductive element 16, a set of resistors R1 , R2 and R3, and an evaluation unit 8. The evaluation unit 18 further comprises a look up table 20 and a computation means 22. The conductive element 16 has gaps and the gaps are bridged with the resistors R1 , R2 and R3. In the example embodiment, three resistors R1, R2 and R3 are shown, each resistor used to indicate a specific level i.e. L, M, H respectively, the level L indicating Low level, the level M indicating Middle level and the level H indicating High level. Also there is a level Έ' indicating the tank is empty. It is to be understood that if the device has to detect N levels, then N resistors need to be connected in the network. A resistance Rs is shown as representing the resistance provided by AdBlue® solution in parallel to each of the resistors R1 , R2 and R3. The resistance Rs is provided by the AdBlue® solution when the corresponding resistors get submerged in the AdBlue® solution.

The look up table 20 contains a set of ranges of resistance values against which the read resistance is compared with.

In one exemplary application of the invention, the solution 14 is AdBlue® solution. The device 10 may be used more generally in any application where it is desirable to sense or to control, fluid level in a tank. The conductive element and the resistors are preferably disposed vertically in the tank. When the tank is completely empty or near empty, none of the resistors are submerged in the AdBlue® solution. In other conditions where some AdBlue® solution is present in the tank, either one or two or all the three resistors are submerged in the AdBlue® solution depending upon the quantity of the AdBlue® solution in the tank. The AdBlue® solution offers a parallel path of resistance with its specific resistance, for the resistors R1 , R2 and R3 whenever the resistors get submerged in the AdBlue® solution.

For an exemplary embodiment, the values of the resistors selected are as given below:

R1 = 7.5 K Ohm

R2 = 6 K Ohm

R3 = 10 K Ohm

Rs = 25 Ohm to 1 K Ohm

The values stored in the look up table 20 are given below for the above resistors R1 , R2 and R3.

Range 1 : Lower limit 16.03 K Ohm; Upper limit 16.88 KOhm.

Range 2 : Lower limit 10,05 K Ohm; Upper limit 11.74 KOhm.

Range 3 : Lower limit 0.07 K Ohm; Upper limit 2.65 KOhm. Range 1 , Range 2 and Range 3 are indicative of Low level, Middle level and High level respectively.

Generally, an input signal or input voltage is applied to the conductive element 16. An output or the resistance across the two contact points of the conductive element is measured. The measured resistance R across the contact points 24 of the conducting element 16, varies with the changing level of the AdBlue® solution in the tank, and is indicative of the level therein, as discussed further below. In the exemplary embodiment of Fig. 1 , for example, an input voltage signal V is applied to the conductive element 16. The resistance R is measured across the contact points 24. ·

For the example shown in fig. 1 , the device 10 provides three discrete level measurements apart from an empty indication. The discrete levels are explained as examples below:

Tank Empty: When the tank is empty, the resistance R measured across the contact points 24 of the conductive element is: R1+R2+R3.

Low level: When the level of the AdBlue® solution is such that only the bottom most resistors (R1) is submerged in the AdBlue® solution, the level is treated as Low level. When only R1 is submerged into the AdBlue® solution, the combined resistance R measured across the two contact points 24 of the conductive element 16 is given as:

R = (R1 II Rs) + (R2) + (R3).

As the specific resistance of the AdBlue® solution varies over a period of time for the same level of the AdBlue® solution in the tank, the R also varies. To account the variation in the specific resistance of the AdBlue® solution, a range for resistance value is pre-computed and stored into the look up table 20, taking into account the maximum and minimum specific resistance Of the AdBlue® solution. For the example shown in fig. 1 , the range of the resistance values when only R1 submerged into the AdBlue® solution is found to be from 16.03 K Ohm to 16.88 K Ohm. The lower limit 16.03 K Ohm corresponds to a minimum specific resistance of the AdBlue® solution and the upper limit 16.88 K Ohm corresponds to maximum specific resistance of the AdBlue® solution.

The computation means 22 determines the combined resistance R. Then the value of R is compared with the ranges stored in the look table. Based on in which range the value of R falls, the level of the AdBlue® solution is determined.

For the above case where only R1 is submerged in the AdBlue® solution, the R falls within the range of 16.03 K Ohm to 16.88 K Ohm. Hence the computation means 22 finds from the look up table that the R for the above case falls in Range 1 which is indicative of Low level.

Middle level: When the level of the AdBlue® solution is such that the two bottom most resistors (R1 and R2) are submerged in the AdBlue® solution, the level is treated as Middle level. When R1 and R2 are submerged in the AdBlue® solution, the combined resistance R measured across the two contact points 24 is given as:

R = (R1|| Rs) + (R2|| Rs) + (R3).

For the example shown in fig. 1, the range of the resistance R value when R1 and R2 are submerged in the AdBlue® solution is found to be between 10.05 K Ohm and 11.74 K Ohm. The lower limit 10.05 K Ohm corresponds to a minimum specific resistance of the AdBlue® solution and the upper limit 11.74 K Ohm corresponds to maximum specific resistance of the AdBlue® solution.

The computation means 22 determines the combined resistance R. Then the value of R is compared with the ranges stored in the look table.

For the above case where R1 and R2 are submerged in the AdBlue® solution, the R falls within the range of 10.05 K Ohm to 11.74 K Ohm. Hence the computation means 22 finds from the look up table 20 that the R for the above case falls in Range 2 which is indicative of Middle level.

High level: When the level of the AdBlue® solution is such that all the three resistors are submerged in the AdBlue® solution, the level is treated as High level. When all the three resistors are submerged into the AdBlue® solution, the combined resistance R at the two contact points 24 is given as:

R = (R1 II Rs) + (R2|| Rs) + (R3|| Rs)

For the example shown in fig. 1 , the resistance R when all the 3 resistors are submerged into the AdBlue® solution is found to be between 0.07K Ohm and 2.65 K Ohm. The lower limit 0.07 K Ohm corresponds to a minimum specific resistance of the AdBlue® solution and the upper limit 2.65 K Ohm corresponding to maximum specific resistance of the AdBlue® solution.

For the above case where R1 , R2 and R3 are submerged in the AdBlue® solution, the R falls within the range of 0.07 K Ohm to 2.65 K Ohm. Hence the computation means finds from the look up table that the R for the above case falls in Range 3 which is indicative of High level.

As explained in the above three cases, it is observed that the level of the AdBlue® solution in the tank is detected unambiguously even when the specific resistance of the AdBlue® solution varies by a large factor, for example a factor of 40 over a period of time. This is achieved by selecting the appropriate values for the resistors R1 to R3 and also using appropriate ranges Range 1 , Range 2 and Range 3 for the resistance values to compare the read resistance R, the ranges being non-overlapping for any two levels.

To detect more levels than explained above, an additional resistor needs to be introduced for every additional level and appropriate range needs to be stored in the look table for each additional level, to compare the read resistance R with. Thus by introducing more resistors and more data into the look up table for ranges, the device can detect more levels of the AdBlue® solution in the tank , thereby increasing the resolution of the measurement.

In accordance with another embodiment of this invention the resistor component of the level sensing device are replaced by metallic elements M. The metallic elements provide the similar functionality as the resistors used in the aforementioned embodiment. The metallic elements used may be in the form of strips, disc, plate and the like. Figure 2 shows the schematic of this embodiment of the invention. As seen from figure 1 the resistances R1 , R2 and R3 which are located in the gaps provided in the conducting element 16 are replaced by the metallic elements. The metallic elements M are chosen such that metallic resistance offers resistance to the flow of current and helps measure the level of the Adblue 12 in the tank 14. The metallic elements M may be clipped, screwed, clinched, clamped, riveted, wrapped around or welded in the gaps provided in the conducting element 16.

Figure 3 shows a detailed setup of the metallic elements in accordance with the embodiment of figure 2. The metal used in the manufacture of the metallic elements M is non-corrosive iron sheet. A non-corrosive iron sheet is used so that there is no reaction between the Adblue and the metallic elements M. Further to protect the conducting elements assembly and the metallic elements from having any type of reaction with the Adblue, the conducting elements 16 and the metallic elements M are provided with an injection molded housing 26. At least some part of the metallic elements M which are required to be in contact with the Adblue solution are not a part of the injection molded housing. The injection molded housing can further be provided with an arrangement which allows the housing to be fitted into the tank containing the Adblue solution.

The working principle of the level sensing device is similar to that of the embodiment shown in figure 1. The metallic elements M which replace the resistors R1 , R2 and R3 have the same resistance value. Thus while all the metallic elements M used are used as a series cascade set of resistances. Thus the total resistance offered by the metallic elements is the sum of the individual resistance offered by each of the metallic elements M. When the Adblue is in contact with at least one part of the metallic element located in which is not in the injection molded housing 26, the total resistance value would vary. This variation in the resistance value is compared with the range of the resistance values stored in the look up table. Depending on the range of resistance value obtained from the comparison an indication as to the level of the Adblue in the tank is determined.

Claims

CLAIMS:

1. A device 10 to determine a level of a solution 12 in a tank 14, the said solution 12 having a property of varying specific resistance over a period of time, the said device 10 comprising:

- a conducting element 16 having at least one gap, the said gap being bridged with resistor R1 of defined value

- a look up table 20 containing a set of ranges of resistance values, each range of resistance value being indicative of a specific level of the said solution.

-a control means 22 adapted to determine the level of the solution 12 depending upon the resistance R across the contact points 24 of the conducting element 16 and the said range of resistance values stored in the said look up table 20.

2. A device according to claim 1 , wherein, if more than one resistors are used, each resistor (R1 , R2 and R3) indicates a specific level.

3. A device according to claim 1 , wherein the resistors (R1 , R2 and R3) are

connected in series.

4. A device according to claim 1 , wherein the solution 12, whose level is being determined, is AdBlue® solution.

5. A device according to claim 1 , wherein depending upon the quantity of the solution in the tank, different resistors get submerged into the solution.

6. A device according to claim 1 , wherein resistor is a metallic element.

7. A device according to claim 1 and 6, wherein said metallic element M is fitted to said conducting element 16 by clipping, screwing, clinching, clamping, riveting, wrapping around or welding the metallic element M in said at least one gap in said conducting element 16.

8. A device according to claim 1 and 6, wherein said conducting elements 16 and the metallic element M are provided in a injection molded housing, at least a portion of the said metallic element M is in contact with said Adblue.