Ultrasonic electrolyte sensor

A system is disclosed for monitoring an electrolyte level in a battery cell and generating an indication of a fault condition when the electrolyte level drops below a predetermined acceptable level. The system may make use of a controller, an ultrasonic transmit circuit for transmitting an ultrasonic signal into an interior area of the battery cell, and an ultrasonic receive circuit for receiving the ultrasonic signal after it has been reflected from the interior area of the battery cell. The controller may use the reflected ultrasonic signal and a predetermined calibration signal representing the predetermined acceptable level of the electrolyte to determine when the electrolyte level has dropped below the predetermined acceptable level.

FIELD

The present disclosure relates to battery testing, and more particularly to an ultrasonic sensor for detecting an electrolyte level in a battery cell.

BACKGROUND

Battery cells have plates surrounded by an electrolyte. When the level of electrolyte in the battery cell drops sufficiently, known as dry out, failure of the battery cell can occur. In battery cells allowing for electrolyte to be added, the battery cells are typically checked periodically and electrolyte added to replace any lost electrolyte. One such type of battery is the lead-acid battery and water is added as needed to keep the electrolyte level at a full level.

Sealed batteries, as the name implies, are sealed and do not allow electrolyte to be added to make up for lost electrolyte. A common type of sealed battery is the valve-regulated lead-acid (VRLA) battery.

It is desirable to monitor the electrolyte level of a battery as a low electrolyte level is an indicator of early dry out of the battery making it more likely that the battery will fail. Also, in batteries where electrolyte can be added, monitoring the electrolyte level allows a user to be alerted when electrolyte needs to be added.

Typical approaches for monitoring electrolyte levels in battery cells are intrusive as they are installed within the cells of the batteries. The inside of a battery cell is a highlight corrosive environment, requiring that the components of the monitoring device installed within the cells be made of material that can withstand this environment. Also, the mechanical design of that part of the monitoring device that is installed within a battery cell is specific to the configuration of the battery cell thus requiring differing mechanical designs for battery cells with different configurations.

Ohmic measurements and capacity testing are other technologies that are used to determine dry out of battery cells. Ohmic measurements often cannot identify that dry out is occurring until it has become severe. Capacity testing is often considered the best method of determining dry out, but the equipment tends to be expensive and the process time consuming.

SUMMARY

In one aspect the present disclosure relates to a system for monitoring an electrolyte level in a battery cell and generating an indication of a fault condition when the electrolyte level drops below a predetermined acceptable level. The system may comprise a controller, an ultrasonic transmit circuit for transmitting an ultrasonic signal into an interior area of the battery cell, and an ultrasonic receive circuit. The ultrasonic receive circuit may be used for receiving the ultrasonic signal after it has been reflected from the interior area of the battery cell. The controller may be configured to use the reflected ultrasonic signal and a predetermined calibration signal representing the predetermined acceptable level of the electrolyte to determine when the electrolyte level has dropped below the predetermined acceptable level.

In another aspect the present disclosure relates to a system for monitoring an electrolyte level in a battery cell and generating an indication of a fault condition when the electrolyte level drops below a predetermined acceptable level. The system may comprise a microcontroller, an ultrasonic transmit circuit for transmitting ultrasonic signal pulses into an interior area of the battery cell, and an ultrasonic receive circuit. The ultrasonic receive circuit may be used for receiving the ultrasonic signal pulses after the electronic signal pulses have been reflected from the interior area of the battery cell. The microcontroller may be configured to perform a plurality of operations that involve converting each one of the reflected ultrasonic signal pulses into a calibration data sample during a calibration procedure to construct a calibration signature waveform; converting each one of the reflected ultrasonic signal pulses into a test data sample during a test procedure to construct a test signature waveform; and using the reflected ultrasonic signal to create a predetermined calibration signature waveform. The predetermined calibration signature waveform may represent the predetermined acceptable level of the electrolyte. The microcontroller may also use the received ultrasonic signal to construct a test signature waveform representative of a real time electrolyte level within the battery cell. The microcontroller may use the test and calibration signature waveforms to detect, in real time, when the electrolyte level within the battery has dropped below the predetermined acceptable level.

In still another aspect the present disclosure relates to a method for monitoring an electrolyte level in a battery cell and generating an indication of a fault condition when the electrolyte level drops below a predetermined acceptable level. The method may comprise transmitting a first plurality of ultrasonic signals and receiving a first plurality of reflected ultrasonic signals. The first plurality of reflected ultrasonic signals may be used to construct a calibration signature representative of a condition where the electrolyte level is at least at the predetermined acceptable level. A second plurality of ultrasonic signals may be transmitted and received to create a second plurality of reflected ultrasonic signals. The second plurality of reflected ultrasonic signals may be used to construct a test signature representative of an actual level of the electrolyte within the battery cell. The calibration and test signatures may be used to determine when the electrolyte level in the battery cell drops below the predetermined acceptable level.

DETAILED DESCRIPTION

FIG. 1is a schematic of an illustrative circuit topology for an ultrasonic electrolyte level sensor system10(hereinafter “the system10”) in accordance with an aspect of the present disclosure. The system10ofFIG. 1may illustratively include a printed circuit board12propagated with a plurality of components for creating a highly sensitive, ultrasonic electrolyte sensor.

The components of the system10may include a data input port14and a data output port16s. The input and output ports14and16, respectively, may be RJ-11 ports or they may take any other suitable form. The system10also may include a controller, for example a microcontroller18, having an analog-to-digital converter (“ADC”)18aand a random access memory (“RAM”)18b. The microcontroller18may be in communication with the ports14and16. The microcontroller18may have a built in temperature sensor20, the operation of which will be described in greater detail in the following paragraphs.

The microcontroller18may be in communication with an ultrasonic receiver circuit22and with an ultrasonic transmitter circuit24. The ultrasonic receiver circuit22includes an ultrasonic transducer26, such as a 400 kHz piezo electric ultrasonic transducer, and the ultrasonic transmitter circuit includes an ultrasonic transducer28, such as a 400 kHz piezo electric ultrasonic transducer. The ultrasonic receiver circuit22may also include an echo detection circuit22aand an envelope follower circuit22b. A calibration pushbutton32may be provided to enable an individual to initiate a calibration procedure for the system10. A voltage regulator34is included to supply a regulated DC voltage to the components of the system10that require electrical power for their operation.

FIG. 2shows the system10mounted to a case (i.e., housing)36of a battery cell38. It will be appreciated that the case36will typically have a “Low” and “High” electrolyte level markings on it, identified inFIG. 2by reference numbers36aand36b, respectively that allow an individual to visually determine what level the electrolyte level is at. The system10may include a suitable housing40in which the PCB board12and its associated components are housed. The system10may be mounted to the battery cell case36so that the ultrasonic receive transducer26and the ultrasonic transmit transducer28face the battery cell38case at a desired position on a sidewall of the case36to be able to detect a low electrolyte level condition within the battery cell38. In one specific implementation this may be accomplished by providing a line40a(FIG. 2) or other demarcation on the housing40which may be aligned with the “Low” electrolyte level marking when the housing40is physically secured to the case36. The line40ais at a location on the housing40, relative to the positioning of the transmit and receive transducers26and28, which is predetermined to result in a “Low” electrolyte level signal from the system10if the electrolyte level in the battery case36falls to (or below) the “Low” level marking36aon the battery case36. The housing40may be secured to the battery case36by any suitable means, but in one preferred form is secured with an adhesive. One specific adhesive that may be preferred is VHB 4910 bonding tape available from 3M Corporation. Similarly the ultrasonic transducers26and28may themselves be secured with a suitable adhesive tape, such as VHB 4910, to an interior surface of the housing40of the system10. Whatever means is used to secure the housing40to the battery case36, as well as the transducers26and28to the interior surface of the housing40, a highly important consideration is that an excellent “coupling” is achieved to minimize reflections of the ultrasonic signal that is reflected back as a result of the housing40to housing36connection.

The microcontroller18of the system10may be programmed to control the overall operation of the system, as described below. It should be understood that control devices other than microcontrollers could be used, such as ASIC's and microprocessor systems. The system10may include a “monitoring” mode where it tests the electrolyte level in the battery cell38to see if it is at or below a “low” level (i.e., below “Low” level mark36aon the battery case36). The system10may also include a “calibration” mode where it establishes a signal that corresponds to a “norm” condition for the battery cell38. The norm condition may be represented by a reflected ultrasonic signal that is present when the electrolyte level corresponds to the “Full” level marking36bon the battery case36. Thus, the norm condition may be viewed as a “Full” condition for the electrolyte level in the battery38.

In the monitoring mode the system10periodically tests the battery cell38to determine if the electrolyte level in the battery cell has fallen below the Low mark36aon the battery case36. For example, the system10may test the battery cell38every 5-30 seconds, and in one preferred implantation every 10 seconds. It should be understood that ten seconds is just one example, and other time intervals could just as easily be used.

When the system10tests the battery cell38it generates a short ultrasonic test signal that is transmitted by the ultrasonic transmit transducer28. The ultrasonic signal from the ultrasonic transmit transducer28is directed at the battery cell case36so that the ultrasonic signal irradiates a swath between the High electrolyte level mark36band the Low electrolyte level mark36a. The ultrasonic test signal may be a strong 400 kHz signal, illustratively a burst between 2.5 and 10 microseconds. It may be, for example, a 2.5 microsecond burst, which is one cycle. The ultrasonic test signal may be referred to herein as a “ping.” The transmitted ultrasonic signal is reflected back by the electrolyte within the battery cell case36and received by the ultrasonic receive transducer26. The received ultrasonic signal may be used by the microcontroller18to determine if the electrolyte level is low. In the embodiment ofFIG. 1, the transmit and receive ultrasonic transducers28and26, respectively, are preferably separate transducers to reduce residual ringing in their respective ultrasonic transmit elements. It should be understood, however, that the same ultrasonic transducer can be used as both the ultrasonic transmit transducer and the ultrasonic receive transducer. To eliminate the “echo” that may result from the transmitted ultrasonic signal being reflected back from the sensor's plastic case36, the echo rejection circuit22aand the envelope follower circuit22bmay be used to remove, for example, the first 10 μs of the reflected ultrasonic signal that is detected by the ultrasonic receive transducer. This early echo is high in amplitude and could have a significant impact on the envelope obtained. The echo rejection needs to be performed before the envelope is obtained in order to acquire an envelope that corresponds only to the signal reflected from the electrolyte or air interface with the battery cell case36. The reflected ultrasonic signal from the electrolyte within the battery case36(with any echo component removed) is then compared to the value representing the norm, which may be stored in a memory such as an EEPROM, so it can be used after a power or reset cycle associated with the microcontroller18. If the reflected ultrasonic signal deviates sufficiently from the norm, the microcontroller18determines that the electrolyte level in the battery cell is at or below a predetermined acceptable level (i.e., at or below the predetermined “Low” level).

The case36of the battery cell38may be a plastic case. When the electrolyte level in the battery cell38is at or above the norm level (i.e., the Full level36b), there will be a plastic/electrolyte interface at an inner wall of the battery cell case that is impinged by the transmitted ultrasonic test signal directed at the battery cell38. When the battery cell38has a low electrolyte level, there will be a plastic/air interface at the inner wall of the battery cell case36that is impinged by the ultrasonic test signal transmitted at the battery cell. The plastic/electrolyte interface has a lower reflection coefficient compared to the plastic/air interface, resulting in more ultrasonic energy being transmitted forward into the battery and less ultrasonic energy being reflected back to the ultrasonic receive transducer26. Conversely, the comparatively higher reflection coefficient of the plastic/air interface results in more ultrasonic energy being reflected back to the ultrasonic receive transducer26and less energy being transmitted forward into the battery cell38. Thus, the ultrasonic signal reflected by the interface at the inner wall of the battery cell case36has more energy when the battery cell38has a low electrolyte level and will have a higher magnitude than the ultrasonic signal reflected by the interface at the inner wall of the battery cell case36when the battery cell has a full electrolyte level.

FIG. 3Ashows an ultrasonic signal50reflected by the interface at the inner wall/electrolyte interface of the battery cell case36when the battery cell38has a full electrolyte level.FIG. 3Bshows an ultrasonic signal52generated by the interface of the inner wall of the battery cell case36and air when the battery cell38has a low electrolyte level. The microcontroller18thus determines that the electrolyte in the battery cell38is low when the magnitude of the reflected ultrasonic signal is a certain predetermined percentage above the magnitude that corresponds to the previously determined signal value for the norm (i.e., “Full) condition, as described above. Illustratively, the microcontroller18determines that the electrolyte level in the battery cell38is low when the reflected ultrasonic signal is at least fifty percent above the signal level that has been predetermined for the norm electrolyte level. In an example, the microcontroller18determines that the electrolyte level in the battery cell38is low when the reflected signal is at least 300 millivolts above the signal level that has been predetermined to correspond to the norm condition. In this example, then, the 300 mv value would correspond to the predetermined acceptable level of the electrolyte (i.e., the “Low” level36a). It should be understood that the predetermined voltage level may be determined heuristically and may be higher or lower than fifty percent or 300 millivolts.

The reflected ultrasonic signal received by the receive ultrasonic transducer26may be amplified, demodulated, and presented to the ADC18a, which may be part of the microcontroller18or it may be an independent component. For convenience, the ADC18ais shown inFIG. 1as being part of the microcontroller18. A plurality of samples are taken with the ADC18ato obtain a plurality of digital test data points and the resulting digital test data points stored in a memory, such as the RAM18bof the microcontroller18. The digital test data points represent a signature of the actual reflected ultrasonic signal. This test signature (that is, the digital test data points) is then compared to the signature that corresponds to the norm condition. Again, the norm condition is represented by a signature of a reflected ultrasonic signal of the battery cell38in a known good (i.e., electrolyte “Full” condition). If the test signature deviates sufficiently from the signature corresponding to the norm condition, the microcontroller18determines that the electrolyte level in the battery cell38is low. The test signature for the norm condition may be programmed into the microcontroller18(i.e., stored in the RAM18b) or it may be obtained by a calibration routine, discussed below. As discussed in more detail below, the norm condition may be represented by a set of digital data points that collectively represent a signature of a reflected ultrasonic wave of the battery cell38obtained by testing the battery cell when it is in a known, full electrolyte condition.

The reflected ultrasonic signal (after amplification and demodulation and echo removal) may be sampled with the ADC18aevery 11.5 microseconds to obtain a suitable number of test samples, and in this example seven such test samples. Sampling may illustratively start 10 microseconds after the ping. It should be understood that sampling can occur at periods of other than 11.5 microseconds and that other than seven samples can be taken. Also, a test may include a plurality of pings and subsequent test samples. By way of example and not of limitation, a test may include sixteen pings with seven samples taken after each ping. The corresponding samples taken after each ping may then be averaged to generate a set of seven test data points, also referred to as a test signature, with each test data point being the average of the corresponding samples taken after each of the sixteen pings. That is, the first sample obtained after each of the sixteen pings are averaged, the second sample obtained after each of the sixteen pings are averaged, and so on.

In an aspect, the system10has a calibration mode in which it is calibrated to obtain the norm, illustratively a calibration signature, against which the comparison of the test data is made. The temperature sensor20associated with the microcontroller18may be used to sense the temperature of the microcontroller18and/or the ambient environment in which the system10is being used, and to provide a sensed temperature value to the microcontroller18that it may use to compensate for temperature conditions that may affect the magnitude of the reflected ultrasonic signal. There is a high correlation between the surrounding temperature and the amplitude of the reflected signal. By using the temperature sensor20embedded in the microcontroller18to acquire the temperature, the signal amplitude is compensated for every sample in real-time. This compensation is performed for the test signal as well as for the calibration (or normal) signal. The microcontroller18may also include firmware that includes a suitable algorithm for making an automatic noise level determination, which in turn allows an automatic fault level sensitivity adjustment to be made by the microcontroller18. The fault level sensitivity adjustment may be used to compensate for excessive humidity or dryness that the sensor10is experiencing that would otherwise affect the magnitude of the reflected ultrasonic signal that is received by the receive ultrasonic transducer28. In this regard it will be appreciated that the magnitude of the reflected signal may be affected by extremes of humidity or dryness, which effectively influences the quality of the “coupling” that is achieved between the sensor housing40and the battery case36.

Referring toFIG. 4, a flowchart100illustrates one example of various operations that may be performed during the calibration mode. The calibration mode is only initiated after visually verifying that the battery cell38is in a known good condition, that is, having its electrolyte level at least at the predetermined acceptable level, as indicated at operation102. At operation104the calibration mode may then be entered by pressing the calibration pushbutton32shown inFIG. 1. The calibration mode may involve initially executing a coupling test pursuant to a coupling test mode. The coupling test mode makes a preliminary check of the quality of the acoustic coupling between the sensor's10housing40and the housing36of the battery cell38. During the coupling test mode a check is made of the magnitude of the reflected signal emitted from the ultrasonic transmit transducer28. If the magnitude of the reflected signal received by the receive transducer26is too far above a predetermined upper limit (e.g., 520 mv) then a full calibration operation is not performed. In this instance a red “Fault” LED56may be turned on, which indicates that the physical coupling between the housing40and the battery case36is unsatisfactory to enable a proper calibration to be performed. If the magnitude of the reflected signal is below the predetermined upper limit, then the calibration mode will continue.

During calibration the ultrasonic ping described above is generated and transmitted into the battery cell38as indicated at operation106. A first data sample is then obtained at operation108. During operation108the reflected ultrasonic signal representing the first data sample is amplified, demodulated, and presented to the ADC18a. The data sample thus is converted to a corresponding digital value. The just-obtained data sample may then be stored in memory (e.g., RAM18b), as indicated at operation110. A check may then be made if the desired number of data samples has been obtained, as indicated at operation112. If not, then a counter is incremented at operation114and operations108-112are repeated. If the check at operation112indicates that the desired number of data samples has been obtained (in this example 7 such data samples), then a check is made at operation116to determine if the predetermined number of ultrasonic pings has been performed. If not, then the data sample counter is reset to “1” as indicated at operation118and operations106-112are re-performed for the next generated ping.

If the check at operation116indicates that the predetermined number of ultrasonic pings has been performed, then the collected data samples are averaged together at operation120. This may involve averaging all of the 1stdata samples collected after each ultrasonic ping to obtain an average of the 1stgroup of data samples, and then averaging all of the 2nddata samples collected after each ultrasonic ping to obtain an average of all the 2nddata samples collected, and so forth. When the averaging is completed an average data sample value will exist for each of the data samples collected. So if seven data samples were collected after each ultrasonic ping, operation120would create seven average data sample values, with each average value representing the average of those data samples collected at specific points in the data collection sequence.

The digital data points corresponding to the stored data samples are used to construct a signature that is used to represent the norm condition, that is, a signature that represents the battery cell38in a known good condition. It should be understood that preferably the same number of pings are made and samples taken in the calibration procedure as in actual testing. Thus in the above described example in which four pings are used followed by seven data samples (and where the corresponding samples after each of the four pings are averaged) after each ping, this preferably occurs both in the calibration mode and then when an actual test is conducted. The calibration mode allows a “calibration signature” (i.e., waveform) to be created that represents the norm condition and which takes into account the electrical characteristics of the particular battery cell, and thus “calibrates” the system10for use with the particular battery cell that it is being used to monitor. When this same sequence of operations is performed during actual testing, a “test signature” is created (i.e., a waveform represented by the collected data samples obtained). It will also be appreciated that when a calibration is initiated, the microcontroller18may also clear any fault conditions and any previous calibration signature may be replaced with a new calibration signature.

One example of a test sequence for the battery cell38is shown in the flowchart200ofFIG. 5. When testing the battery cell38, the microcontroller18may initially obtain a first one of the averaged data samples used to construct the calibration waveform, as well as a first one of the averaged data samples used to construct the just-obtained test signature, as indicated at operation202. At operation204the microcontroller18may perform a comparison of the magnitudes of the first averaged test samples of each of the calibration and test signatures to determine if the data sample of the test signature exceeds that of the calibration signature by at least a minimum predetermined amount (e.g., 300 mv or more). If so, a software test counter may be incremented by the microcontroller18at operation206. If not, then a check may be made by the microcontroller18if all of the data samples (seven in this example) have been checked, as indicated at operation208. If the check at operation208produces a “No” answer, then n is incremented and operations202-204are repeated by the microcontroller18with the next averaged data sample for each of the test and calibration signatures.

If the test at operation208indicates that all of the averaged data samples have been considered (i.e., in this example all seven averaged data samples), then a check is made by the microcontroller18to determine if the test counter is at or exceeds a predetermined value, which in this example is “3” or higher. The microcontroller18determines that the electrolyte level is below the norm condition when, for example, three of the seven comparisons described above show that the averaged data sample of the test signature is higher by the predetermined amount (e.g., 300 mv) than the corresponding averaged data sample of the calibration signature. When this condition is present the microcontroller18may generate a signal that illuminates the fault LED56to indicate a “Low Electrolyte” level. However, if the check at operation212indicates that the test counter is not at a value of three or higher, then the microcontroller18may clear the test counter and set the data sample n value back to “1”, as indicated at operation216. The microcontroller18may then wait a predetermined time period (e.g., 10 minutes), as indicated at operation218, before repeating the entire test sequence shown in the flowchart200.

As long as the system10is receiving power, the green LED58may be powered on. During normal monitoring the green LED58may be controlled by the microcontroller18to blink at a first rate or frequency. As a measurement is being obtained by the system10, the green LED58may be controlled to remain illuminated. This provides an immediate visual clue to the user that the system10is functioning as intended.

It should also be understood that different comparison sequences could be implemented other than the “three of seven” comparison sequence described above, when making the determination if the electrolyte level is at the norm condition. The fault LED56has been described as being red in color, although any other color could be used. The fault LED56alerts a user to the fault condition. If the electrolyte level is determined to be at least at the norm condition, then the fault LED56remains off. The microcontroller18may also transmit data, such as the test signatures and fault status, to a host via the data output transmission port16.