GB2544868A

GB2544868A - A non-intrusive fluid level monitoring system and method

Info

Publication number: GB2544868A
Application number: GB1616859.3A
Authority: GB
Inventors: David Scott Nigel; Baxter Fry George; Malcolm Jones Dennis
Original assignee: Custom And Contract Power Solutions Ltd
Current assignee: Custom And Contract Power Solutions Ltd
Priority date: 2015-09-21
Filing date: 2016-10-04
Publication date: 2017-05-31
Also published as: WO2017051204A1; GB201616859D0

Abstract

A non-intrusive fluid level monitoring system, and associated method, is disclosed suitable for monitoring electrolyte fluid levels 13 within flooded lead-acid battery cells. The system comprises a reservoir 9 for containing electrolyte fluid 13; a sensor array including at least two emitter-receiver sensor pairs 16, 17; and a processor (see figs. 7, 8) connected to the sensor array. The respective emitter-receiver sensor pairs 16, 17 are coupled one above the other to an external wall of the reservoir and each emits signals towards the internal wall 10. Reflected signals are received, compared and converted by the processor into information representative of fluid level flux within the reservoir. The processing may comprise determining the difference between the outputs of adjacent sensor receivers in the array. An alarm may be triggered if the difference exceeds a threshold. By employing at least two emitter-receiver sensor pairs 16, 17, distortions arising from external factors such as ambient light, temperature variations, gassing bubbles in the electrolyte, debris shed by the lead plates, etc. can be eliminated. The emitter-receiver sensor pairs may use infrared sensor technology. Capacitance or ultrasound sensor alternatives are also suggested.

Description

A Non-intrusive Fluid Level Monitoring System and Method

The present invention relates to a non-intrusive fluid level monitoring system and associated method. Particularly, though not exclusively, the non-intrusive fluid level monitoring system and method is used to monitor electrolyte levels within flooded lead-acid battery cells. However, the invention is equally applicable to non-intrusively monitoring other fluid levels within other types of reservoirs.

In order to ensure that flooded battery cells can deliver the energy required when called upon to do so, and to maintain cells in optimum condition, it is imperative to maintain the acid electrolyte above the level of the lead plates and internal group/bus bars or separators. At present, the most effective method of determining the level of the electrolyte in flooded cell batteries is by visual inspection. For example, a probe may be inserted into the cell or electrolyte to determine the level of the electrolyte by electrical conductivity, or similar methods.

This method, while reliable within the boundaries of human intervention, is costly in time and resources. It requires personnel to examine each cell perhaps once per month. In certain harsh environments visits may have to be made more often. In an operation with many hundreds, perhaps many thousands, of such batteries in many different locations, maintaining reliable operations by physically visiting each site and physically checking every cell can be an expensive procedure in cost and resources.

Additionally, legislative requirements in some countries require the acid electrolyte level of such batteries to be known on a continuous basis.

Non-intrusive sensors, of which there are not many, may take the form of a variety of sensors using different technologies, e.g. ultrasound, capacitance or infrared (IR). All the above have several drawbacks. For example, whilst capacitive and ultrasound sensing can work well in certain cells, where the plates or group bars are adjacent to the container wall the capacitive sensor will have difficulty in differentiating between the electrolyte and the lead plates.

As for infrared (IR) sensors, there are also numerous difficulties associated with their use to detect liquid levels. For example, the principle is that the IR light irradiated by the emitter diode is reflected from the inner surface of the container and collected by the receiver diode. However, it is usually not possible to know in advance what the thickness of the battery reservoir wall will be. Larger batteries have thicker reservoir walls and smaller batteries have thinner walls. Consequently, for the same output, the amount of received infrared radiation will change significantly between different reservoirs thus making it extremely difficult to predict, for all cells, the receiver output level corresponding to a certain condition, e.g. a drop in fluid levels.

Ambient light can also have a significant effect on the levels of received IR. This is because ambient light itself inherently contains infrared wavelengths. Therefore if an environment, such as a room, is well lit during installation and calibration of an IP sensor output, there is a high likelihood of a false reading occurring once the lights are subsequently switched off, i.e. the level of output current at the receiver initially selected as representing an alarm condition will likely no longer be valid. Infrared filtering is not always successful in overcoming this problem.

Further problems can be experienced by all sensor technologies as a consequence of variations in cell temperature and/or ambient temperature; the proximity of lead plates and group bars to the external reservoir wall; the presence of gassing bubbles in the electrolyte; and the presence of debris shed by the lead plates.

The present invention seeks to provide a solution to one or more of the foregoing problems by providing a means of remotely detecting and continuously monitoring electrolyte levels within flooded battery cells. Whilst the detection and monitoring system and method described below is implemented using infrared sensor technology, it will be appreciated that suitable alternatives are possible, e.g. capacitance or ultrasound based sensor technology.

Throughout the following description, the terms "cell", "gassing voltage”, and IR sensor are intended to have the following meanings: "Cell"-: a single lead-acid electrochemical voltage/current generator and energy storage unit with a nominal terminal voltage of 2 volts. Multiple individual cells may be contained in the same overall enclosure. "Gassing voltage” (also known as the charge overvoltage)-: The difference between the open circuit voltage of a fully charged cell and the float voltage developed across the cell by the float current. The gassing voltage, if improperly set, can cause excess gassing in the cells, forming hydrogen bubbles in the electrolyte on the inner surface of the container. "IR sensor”-: A matched pair of diodes, which operate by means of infrared light, i.e. light of a particular wavelength just above the red scale in the electromagnetic radiation spectrum. One diode is the emitter, which emits infrared light, proportional to the amount of current passing through it; the other is a receiver, a diode which, on receiving infrared light, allows a current, proportional to the amount of received light, to flow in the electronic circuit. The combined sensor pair operates by projecting IR light from the emitter diode which is reflected from objects placed in front of it; the amount of reflected light controls the output of the receiver diode.

According to a first embodiment of the present invention there is provided a non-intrusive fluid level monitoring system comprising: (i) a reservoir for containing a fluid; (ii) a sensor array including at least two emitter-receiver sensor pairs; and (iii) a processor connected to the sensor array; wherein the sensor array is positionable proximate an external wall of the reservoir for emitting signals through said wall; and wherein the processor is operative to process signals received by the sensor array and convert same into user-perceptible information representative of fluid level flux within the reservoir.

According to a second embodiment of the present invention there is provided a method of non-intrusively monitoring a fluid level within a reservoir comprising: (i) providing a reservoir containing a fluid; (ii) positioning a sensor array, including at least two emitter-receiver sensor pairs proximate an external wall of the reservoir; and (iii) providing a processor connected to the outputs of the receivers; (iv) emitting a signal from the emitters through said wall; (v) receiving a signal at the receivers from the reservoir; and (vi) processing the received signals to convert same into user-perceptible information representative of fluid level flux within the reservoir.

This innovative solution provided by the present invention is achieved by utilising a sensor array comprising of at least two sensor pairs, each consisting of an emitter and a receiver, one pair situated above the other within a single sensor/transducer.

The emitters of both pairs are powered by the same power source at the same current; this means that, within tolerances, both receivers should receive the same amount of reflected IR light from an object in front of them, in this case an acid electrolyte. The output of both sensor pairs, i.e. the current output from the receivers, are connected to the input of a detection circuit, set to remain at zero output until a significant difference is seen on its inputs, at which point the detection circuit will output a signal, reflecting this difference. This innovative step has the benefit of addressing the problems described above.

The methodology of the present invention employs two IR sensor emitter-receiver pairs to detect the liquid level in a reservoir (e.g. within a flooded lead-acid battery cell) which is at least partially transparent to infrared wavelengths.

In one embodiment, the present invention utilises two IR sensor pairs arranged in a simple electronic circuit with a detection circuit monitoring the outputs of each receiver pair and detecting a significant difference in their respective outputs via a detector circuit. The output of the detection circuit may be routed to a processor, microcontroller or other device programmable to trigger an audio and/or visual alarm signal to any overview system when a significant difference between the two sensor pairs is detected above a predetermine threshold.

The detection circuit may be an analogue circuit, or may be structured to convert the emitter and receiver output currents to digital data and inputting the data to a processor or microcontroller, pre-programmed to make a decision on the level of difference of the two inputs. Both methods may be termed detection circuits.

As mentioned above, of the main problems with using IR sensors to detect liquid electrolyte in a battery cell is that of ambient light. Different levels of ambient light alter the amount of light perceived by the receiver of the IR sensor, and thus the output of the sensor. For example, fitting an IR sensor to a battery cell will normally take place in a room with high ambient light levels; once the installation is complete the room may be closed and the ambient light switched off.

In a standard IR sensor arrangement this makes it very difficult to set a reliable level for the detection of the electrolyte, since the level depends on the amount of reflected IR at the receiver, which can be affected by the ambient light levels which often contains IR wavelengths. Using IR filter material to cover the receiver diode, thus excluding most of the ambient light, is not always successful, particularly for large ambient light changes, and also has the effect of reducing the amount of reflected IR experienced by the receiver.

By arranging two IR sensor pairs on the reservoir, one above the other, and connecting the output of the receivers of each pair into a detection circuit, the inherent uncertainties introduced by external conditions (i.e. outside the reservoir) in determining a baseline level are eliminated. Instead, it is merely necessary to determine the difference between two identical IR pairs, thus bringing the control of the measurement conditions within a closed system.

When the IR sensor pairs are installed on the reservoir, both the upper and lower pair are arrange below the level of the electrolyte within the cell reservoir. In doing so, the output of both receivers will be the same, or closely similar, and of reduced current due to refractive losses at the reservoir-electrolyte boundary. It will be appreciated that external conditions, such as the presence or absence of ambient light, will affect both receivers equally.

Therefore, a discernible difference between the output of the upper and lower receivers will only arise once the electrolyte level descends to a level lying below that of the upper receiver, but above that of the lower receiver. The absence of any electrolyte at the level of the upper receiver significantly reduces, or substantially eliminates, refractive losses at the inner reservoir wall boundary. Consequently, a greater level of irradiance is reflected into the receiver creating a significant step change in current output sufficient to be detected by the detection circuit and trigger an alarm condition via the processor. The increase in current output may, for example, be greater than 100%. This change will be more than.

As noted above, another shortcoming associated with existing single sensor detection systems is that they are incapable of taking into account differing wall thicknesses within different battery reservoirs. Since the level of reflected irradiance varies with wall thickness, it is not possible for any a single sensor detection system to provide reliable results when used on different batteries. Since the wall thickness of the cell is unknown at the time of manufacture, the amount of current output generated by the receiver diode in the single sensor cannot be anticipated. Consequently, an accurate baseline current output from the receiver diode for the purpose of triggering an alarm cannot be established.

Again, by arranging two IR sensor pairs on the reservoir wall this problem is eliminated. This is because both the upper and lower sensor pairs are arranged on reservoir walls having the same wall thickness. Therefore, regardless of the actual thickness, the same level of IR irradiance emitted by the respective emitters is received by the corresponding receivers. Consequently, the input to the detection circuit remains the same from both receiver pairs, unless the incident IR irradiance from the upper sensor pair changes relative to that of the lower sensor pair due to a reduction in the level of electrolyte below that of the upper sensor pair. A further problem encountered by existing non-intrusive methods of electrolyte level detection is that of gassing. Brisk gassing, sometimes due to overcharging, can create large hydrogen bubbles within the electrolyte and these can adhere to the reservoir wall, corrupting the measurements necessary to determine the level of the electrolyte liquid. Once again, by arranging two IR sensor pairs on the reservoir wall this problem is significantly alleviated. This is because both the upper and lower sensor pairs are arranged in relatively close proximity such that they will experience substantially the same degree of gassing bubbles at their reservoir-electrolyte boundary. Consequently, the input to the detection circuit remains the same, or substantially similar, from both receiver pairs unless a fluid level reduction occurs. A further advantage associated with a system which compares the output of two IR emitter-receiver pairs is that the effects of variation in ambient temperature and occlusion of the electrolyte due to floating debris are also cancelled out.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Fig. 1 is a schematic of a flooded electrochemical cell, showing the desired electrolyte levels;

Fig. 2 is a schematic illustration the principle of object detection by infrared [IR] sensors;

Fig. 3 is a schematic illustration showing the reflection of emitted IR light when an emitter-receiver pair are arranged in close proximity to an optically transparent glass or plastic container;

Fig. 4 is a schematic illustration showing the reflection of emitted IR light when an emitter-receiver pair are arranged in close proximity to a fluid-filled optically transparent glass or plastic container;

Figs 5 and 6 are schematic illustrations showing the effects of different wall thicknesses of containers on the available angles of IR reflection from the inner wall surface of the container;

Figs. 7 and 8 are block diagrams proving an overview of the electrical circuit of the fluid level monitoring system; and

Figs. 9 and 10 are schematic illustrations showing the IR reflection and refraction of light associated with two emitter-receiver sensor pairs arranged vertically on a reservoir wall when the fluid within the reservoir is at different levels.

With reference to Fig. 1, a battery enclosure or reservoir (1) is formed from an optically transparent material such as clear plastic or glass. In order to ensure optimal and safe performance, the electrolyte level within the reservoir (1) cannot be permitted to fall below a lower threshold level (2), or above an upper threshold level (3). Also shown in Fig. 1 are the lead plates or electrodes (4) and the group bars or separators joining then together.

Fig. 2 shows a sensor pair consisting of an emitter diode (5) and a receiver diode (6). The emitter diode (5) emits infrared (IR) light (7) which is reflected off any near object (8) and is received by the receiver diode (6).

As shown in Fig. 3, the sensor pair of Fig. 2 can be attached to, or arranged proximate, a battery enclosure or reservoir (9). With no electrolyte present within the reservoir (9), incident IR light (7) from the emitter (5) is strongly reflected from the inner boundary surface (10) and is received by the receiver (6). By contrast, when electrolyte (13) is present within the reservoir (9) and in contact with its inner boundary surface (10), a significant proportion (11) of the incident IR light (7) from the emitter (5) is refracted through the electrolyte (13) considerably reducing the irradiance level of reflected light (12) reaching the receiver diode (6).

Figs. 5 and 6 demonstrate the relative effect of the reservoir wall thickness on the irradiance levels of IR light (7) reflected from the inner boundary surface of the reservoir and received by the receiver diode (6). In particular, a relatively thin wall (14) restricts the amount of IR light (7) received by the receiver diode (6); whereas a relatively thick wall (15) permits a greater amount of IR (7) to be reflected to the receiver diode (6).

Circuit diagrams are shown in Figs. 7 and 8 where two IR sensor pairs (16, 17) each consist of an emitter diode (5) and a receiver diode (6) having outputs (22) which are connected to the input of either an analogue detection circuit (18) - as shown in Fig. 7 - or an analogue-to-digital converter (26) - as shown in Fig. 8. The emitter diodes (5) of both IR sensor pairs (16, 17) are supplied with the same common controlled current (21) by a processor or microcontroller (19), either directly via pulse width modulation, or via a controlled transistor or other suitable means. If the two IR outputs (22) from the respective receiver diodes (6) into the detection circuit (18, 26) are balanced, then no output is generated by the detection circuit (18, 26). However, if the two IR outputs (22) differ by more than a predetermined threshold level the detection circuit (18, 26) will output a signal to the processor or microcontroller (19). The processor or microcontroller (19) then communicates a signal (20) to an external overview system (not shown), e.g. by providing an audio and/or visual alarm.

With reference to Figs 9 and 10, the structure of the non-intrusive fluid level monitoring system of the present invention can be further understood. The two IR sensor pairs (16, 17) are situated on the exterior side wall of the cell reservoir (9), one above the other. In Fig. 9, the electrolyte fluid level (13) exceeds the lower threshold level (2) mentioned above such that both IR sensor pairs are situated below the level of the electrolyte (13). In this arrangement, if both IR sensor emitters (6) are supplied with the same current (21) then both receivers (6) will register approximately the same value after experiencing similar refractive losses (24) at the inner wall boundary surface (10). The outputs (22) of the receiver diodes (6) will therefore be approximately the same, and the output of the detection circuit (18, 26) will be zero.

In Fig. 10 the electrolyte fluid level (13) is reduced such that the upper IR sensor pair (16) is now above the level of the electrolyte (13). The absence of any electrolyte (13) opposite the upper IR sensor pair (16), and its replacement with air (23), alters the optical behaviour of the IR light when it reaches the inner wall boundary surface (10). In particular, the proportion of reflected IR light (25) at the level of the upper IR sensor pair (16) is significantly increased relative to that of the lower IR sensor pair (17). Indeed, since the optical behaviour of the IR light at the level of the lower IR sensor pair (17) remains unchanged, the outputs (22) of the detection circuit (18, 26) will be non-zero and therefore produce an output to the processor (19).

Modification and improvements may be made to the foregoing without departing from the scope of the invention as defined by the accompanying claims.

Claims

1. A non-intrusive fluid level monitoring system comprising: (i) a reservoir for containing a fluid; (ii) a sensor array including at least two emitter-receiver sensor pairs; and (in) a processor connected to the sensor array; wherein the sensor array is positionable proximate an external wall of the reservoir for emitting signals through said wall; and wherein the processor is operative to process signals received by the sensor array and convert same into user-perceptible information representative of fluid level flux within the reservoir.

2. A non-intrusive fluid level monitoring system according to claim 1, wherein all emitters within the sensor array have a common current supply, and hence produce equal irradiance levels.

3. A non-intrusive fluid level monitoring system according to claim 1 or 2, wherein the outputs of all receivers within the sensor array are connected to the input(s) of a detection circuit adapted to detect current differentials exceeding a predetermined threshold level.

4. A non-intrusive fluid level monitoring system according to claim 3, wherein the detection circuit comprises only analogue circuitry.

5. A non-intrusive fluid level monitoring system according to claim 3, wherein the detection circuit comprises one analogue to digital converter per emitter-receiver sensor pair.

6. A non-intrusive fluid level monitoring system according to any of claims 3 to 5, wherein an output of the detection circuit is connected to an input of said processor.

7. A non-intrusive fluid level monitoring system according to any preceding claim, wherein an output of said processor is connected to an audio and/or visual alarm.

8. A non-intrusive fluid level monitoring system according to any preceding claims, wherein multiple identical emitter-receiver sensor pairs are arranged vertically on an external wall of the reservoir.

9. A non-intrusive fluid level monitoring system according to any preceding claim, wherein the fluid to be measured is a battery electrolyte.

10. A method of non-intrusively monitoring a fluid level within a reservoir comprising: (i) providing a reservoir containing a fluid; (ii) positioning a sensor array, including at least two emitter-receiver sensor pairs proximate an external wall of the reservoir; and (iii) providing a processor connected to the outputs of the receivers; (iv) emitting a signal from the emitters through said wall; (v) receiving a signal at the receivers from the reservoir; and (vi) processing the received signals to convert same into user-perceptible information representative of fluid level flux within the reservoir.

11. A method of non-intrusively monitoring a fluid level according to claim 10, wherein the sensor array comprises multiple identical emitter-receiver sensor pairs arranged vertically on said external wall of the reservoir.

12. A method of non-intrusively monitoring a fluid level according to claim 10 or 11, further comprising determining, via a detector circuit, a current differential between the outputs of adjacent receivers within the sensor array.

13. A method of non-intrusively monitoring a fluid level according to claim 12, wherein an output of said processor triggers an audio and/or visual alarm when a current differential determined by the detection circuit exceeds a predetermined threshold level.

14. A method of non-intrusively monitoring a fluid level according to any of claims 10 to 13, wherein the reservoir is a battery casing containing an electrolyte.