Abstract:
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.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/645,789, filed on May 11, 2012. The entire disclosure of the above application is incorporated herein by reference. 
    
    
     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 
     This section provides background information related to the present disclosure which is not necessarily prior art. 
     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 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     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. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG. 1  is a schematic of a circuit topology of an ultrasonic electrolyte sensor in accordance with an aspect of the present disclosure; 
         FIG. 2  is a perspective view showing the ultrasonic electrolyte sensor of  FIG. 1  mounted to a case of a battery cell; 
         FIGS. 3A and 3B  are oscilloscope traces showing the reflection of an ultrasonic signal from an interface between an inner wall of a battery cell and electrolyte in a battery cell when the battery cell has a full electrolyte level and from an interface between an inner wall of the battery cell and air when the battery cell has a low electrolyte level; 
         FIG. 4  is a flowchart illustrating various operations that may be performed by the system of  FIG. 1  during a calibration procedure; and 
         FIG. 5  is a flowchart illustrating various operations that may be performed by the system in determining if an electrolyte level of the battery it is being used to monitor is at least at a predetermined acceptable level. 
     
    
    
     DETAILED DESCRIPTION 
     Example embodiments will now be described more fully with reference to the accompanying drawings. 
       FIG. 1  is a schematic of an illustrative circuit topology for an ultrasonic electrolyte level sensor system  10  (hereinafter “the system  10 ”) in accordance with an aspect of the present disclosure. The system  10  of  FIG. 1  may illustratively include a printed circuit board  12  propagated with a plurality of components for creating a highly sensitive, ultrasonic electrolyte sensor. 
     The components of the system  10  may include a data input port  14  and a data output port  16   s . The input and output ports  14  and  16 , respectively, may be RJ-11 ports or they may take any other suitable form. The system  10  also may include a controller, for example a microcontroller  18 , having an analog-to-digital converter (“ADC”)  18   a  and a random access memory (“RAM”)  18   b . The microcontroller  18  may be in communication with the ports  14  and  16 . The microcontroller  18  may have a built in temperature sensor  20 , the operation of which will be described in greater detail in the following paragraphs. 
     The microcontroller  18  may be in communication with an ultrasonic receiver circuit  22  and with an ultrasonic transmitter circuit  24 . The ultrasonic receiver circuit  22  includes an ultrasonic transducer  26 , such as a 400 kHz piezo electric ultrasonic transducer, and the ultrasonic transmitter circuit includes an ultrasonic transducer  28 , such as a 400 kHz piezo electric ultrasonic transducer. The ultrasonic receiver circuit  22  may also include an echo detection circuit  22   a  and an envelope follower circuit  22   b . A calibration pushbutton  32  may be provided to enable an individual to initiate a calibration procedure for the system  10 . A voltage regulator  34  is included to supply a regulated DC voltage to the components of the system  10  that require electrical power for their operation. 
       FIG. 2  shows the system  10  mounted to a case (i.e., housing)  36  of a battery cell  38 . It will be appreciated that the case  36  will typically have a “Low” and “High” electrolyte level markings on it, identified in  FIG. 2  by reference numbers  36   a  and  36   b , respectively that allow an individual to visually determine what level the electrolyte level is at. The system  10  may include a suitable housing  40  in which the PCB board  12  and its associated components are housed. The system  10  may be mounted to the battery cell case  36  so that the ultrasonic receive transducer  26  and the ultrasonic transmit transducer  28  face the battery cell  38  case at a desired position on a sidewall of the case  36  to be able to detect a low electrolyte level condition within the battery cell  38 . In one specific implementation this may be accomplished by providing a line  40   a  ( FIG. 2 ) or other demarcation on the housing  40  which may be aligned with the “Low” electrolyte level marking when the housing  40  is physically secured to the case  36 . The line  40   a  is at a location on the housing  40 , relative to the positioning of the transmit and receive transducers  26  and  28 , which is predetermined to result in a “Low” electrolyte level signal from the system  10  if the electrolyte level in the battery case  36  falls to (or below) the “Low” level marking  36   a  on the battery case  36 . The housing  40  may be secured to the battery case  36  by 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 transducers  26  and  28  may themselves be secured with a suitable adhesive tape, such as VHB 4910, to an interior surface of the housing  40  of the system  10 . Whatever means is used to secure the housing  40  to the battery case  36 , as well as the transducers  26  and  28  to the interior surface of the housing  40 , 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 housing  40  to housing  36  connection. 
     The microcontroller  18  of the system  10  may 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&#39;s and microprocessor systems. The system  10  may include a “monitoring” mode where it tests the electrolyte level in the battery cell  38  to see if it is at or below a “low” level (i.e., below “Low” level mark  36   a  on the battery case  36 ). The system  10  may also include a “calibration” mode where it establishes a signal that corresponds to a “norm” condition for the battery cell  38 . The norm condition may be represented by a reflected ultrasonic signal that is present when the electrolyte level corresponds to the “Full” level marking  36   b  on the battery case  36 . Thus, the norm condition may be viewed as a “Full” condition for the electrolyte level in the battery  38 . 
     In the monitoring mode the system  10  periodically tests the battery cell  38  to determine if the electrolyte level in the battery cell has fallen below the Low mark  36   a  on the battery case  36 . For example, the system  10  may test the battery cell  38  every 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 system  10  tests the battery cell  38  it generates a short ultrasonic test signal that is transmitted by the ultrasonic transmit transducer  28 . The ultrasonic signal from the ultrasonic transmit transducer  28  is directed at the battery cell case  36  so that the ultrasonic signal irradiates a swath between the High electrolyte level mark  36   b  and the Low electrolyte level mark  36   a . 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 case  36  and received by the ultrasonic receive transducer  26 . The received ultrasonic signal may be used by the microcontroller  18  to determine if the electrolyte level is low. In the embodiment of  FIG. 1 , the transmit and receive ultrasonic transducers  28  and  26 , 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&#39;s plastic case  36 , the echo rejection circuit  22   a  and the envelope follower circuit  22   b  may 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 case  36 . The reflected ultrasonic signal from the electrolyte within the battery case  36  (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 microcontroller  18 . If the reflected ultrasonic signal deviates sufficiently from the norm, the microcontroller  18  determines 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 case  36  of the battery cell  38  may be a plastic case. When the electrolyte level in the battery cell  38  is at or above the norm level (i.e., the Full level  36   b ), 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 cell  38 . When the battery cell  38  has a low electrolyte level, there will be a plastic/air interface at the inner wall of the battery cell case  36  that 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 transducer  26 . Conversely, the comparatively higher reflection coefficient of the plastic/air interface results in more ultrasonic energy being reflected back to the ultrasonic receive transducer  26  and less energy being transmitted forward into the battery cell  38 . Thus, the ultrasonic signal reflected by the interface at the inner wall of the battery cell case  36  has more energy when the battery cell  38  has 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 case  36  when the battery cell has a full electrolyte level. 
       FIG. 3A  shows an ultrasonic signal  50  reflected by the interface at the inner wall/electrolyte interface of the battery cell case  36  when the battery cell  38  has a full electrolyte level.  FIG. 3B  shows an ultrasonic signal  52  generated by the interface of the inner wall of the battery cell case  36  and air when the battery cell  38  has a low electrolyte level. The microcontroller  18  thus determines that the electrolyte in the battery cell  38  is 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 microcontroller  18  determines that the electrolyte level in the battery cell  38  is 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 microcontroller  18  determines that the electrolyte level in the battery cell  38  is 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” level  36   a ). 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 transducer  26  may be amplified, demodulated, and presented to the ADC  18   a , which may be part of the microcontroller  18  or it may be an independent component. For convenience, the ADC  18   a  is shown in  FIG. 1  as being part of the microcontroller  18 . A plurality of samples are taken with the ADC  18   a  to obtain a plurality of digital test data points and the resulting digital test data points stored in a memory, such as the RAM  18   b  of the microcontroller  18 . 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 cell  38  in a known good (i.e., electrolyte “Full” condition). If the test signature deviates sufficiently from the signature corresponding to the norm condition, the microcontroller  18  determines that the electrolyte level in the battery cell  38  is low. The test signature for the norm condition may be programmed into the microcontroller  18  (i.e., stored in the RAM  18   b ) 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 cell  38  obtained 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 ADC  18   a  every 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 system  10  has 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 sensor  20  associated with the microcontroller  18  may be used to sense the temperature of the microcontroller  18  and/or the ambient environment in which the system  10  is being used, and to provide a sensed temperature value to the microcontroller  18  that 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 sensor  20  embedded in the microcontroller  18  to 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 microcontroller  18  may 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 microcontroller  18 . The fault level sensitivity adjustment may be used to compensate for excessive humidity or dryness that the sensor  10  is experiencing that would otherwise affect the magnitude of the reflected ultrasonic signal that is received by the receive ultrasonic transducer  28 . 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 housing  40  and the battery case  36 . 
     Referring to  FIG. 4 , a flowchart  100  illustrates 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 cell  38  is in a known good condition, that is, having its electrolyte level at least at the predetermined acceptable level, as indicated at operation  102 . At operation  104  the calibration mode may then be entered by pressing the calibration pushbutton  32  shown in  FIG. 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&#39;s  10  housing  40  and the housing  36  of the battery cell  38 . During the coupling test mode a check is made of the magnitude of the reflected signal emitted from the ultrasonic transmit transducer  28 . If the magnitude of the reflected signal received by the receive transducer  26  is 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” LED  56  may be turned on, which indicates that the physical coupling between the housing  40  and the battery case  36  is 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 cell  38  as indicated at operation  106 . A first data sample is then obtained at operation  108 . During operation  108  the reflected ultrasonic signal representing the first data sample is amplified, demodulated, and presented to the ADC  18   a . The data sample thus is converted to a corresponding digital value. The just-obtained data sample may then be stored in memory (e.g., RAM  18   b ), as indicated at operation  110 . A check may then be made if the desired number of data samples has been obtained, as indicated at operation  112 . If not, then a counter is incremented at operation  114  and operations  108 - 112  are repeated. If the check at operation  112  indicates that the desired number of data samples has been obtained (in this example 7 such data samples), then a check is made at operation  116  to 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 operation  118  and operations  106 - 112  are re-performed for the next generated ping. 
     If the check at operation  116  indicates that the predetermined number of ultrasonic pings has been performed, then the collected data samples are averaged together at operation  120 . This may involve averaging all of the 1 st  data samples collected after each ultrasonic ping to obtain an average of the 1 st  group of data samples, and then averaging all of the 2 nd  data samples collected after each ultrasonic ping to obtain an average of all the 2 nd  data 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, operation  120  would 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 cell  38  in 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 system  10  for 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 microcontroller  18  may 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 cell  38  is shown in the flowchart  200  of  FIG. 5 . When testing the battery cell  38 , the microcontroller  18  may 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 operation  202 . At operation  204  the microcontroller  18  may 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 microcontroller  18  at operation  206 . If not, then a check may be made by the microcontroller  18  if all of the data samples (seven in this example) have been checked, as indicated at operation  208 . If the check at operation  208  produces a “No” answer, then n is incremented and operations  202 - 204  are repeated by the microcontroller  18  with the next averaged data sample for each of the test and calibration signatures. 
     If the test at operation  208  indicates 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 microcontroller  18  to determine if the test counter is at or exceeds a predetermined value, which in this example is “3” or higher. The microcontroller  18  determines 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 microcontroller  18  may generate a signal that illuminates the fault LED  56  to indicate a “Low Electrolyte” level. However, if the check at operation  212  indicates that the test counter is not at a value of three or higher, then the microcontroller  18  may clear the test counter and set the data sample n value back to “1”, as indicated at operation  216 . The microcontroller  18  may then wait a predetermined time period (e.g., 10 minutes), as indicated at operation  218 , before repeating the entire test sequence shown in the flowchart  200 . 
     As long as the system  10  is receiving power, the green LED  58  may be powered on. During normal monitoring the green LED  58  may be controlled by the microcontroller  18  to blink at a first rate or frequency. As a measurement is being obtained by the system  10 , the green LED  58  may be controlled to remain illuminated. This provides an immediate visual clue to the user that the system  10  is 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 LED  56  has been described as being red in color, although any other color could be used. The fault LED  56  alerts a user to the fault condition. If the electrolyte level is determined to be at least at the norm condition, then the fault LED  56  remains off. The microcontroller  18  may also transmit data, such as the test signatures and fault status, to a host via the data output transmission port  16 . 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.