Abstract:
A method of conveying information to/from an impact sensor. The method includes the steps of producing a signal representative of an impact detected by the impact sensor; and altering a conveying of the signal on a single signal line if the impact has a characteristic that violates a preselected value.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a non-provisional application based upon U.S. provisional patent application Ser. No. 61/789,258, entitled “IMPACT SENSOR AND PROGRAMMER”, filed Mar. 15, 2013, which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to impact sensors, and, more particularly, to methods of programming and obtaining information from impact sensors. 
         [0004]    2. Description of the Related Art 
         [0005]    Many industrial and commercial processes involve large forces or velocities during operation. Many means have been developed to control these forces and velocities. A specific example would be cushions and shock absorbers applied to pneumatically operated equipment. Failure of these energy-controlling components can result in rapid damage to equipment and product. As a result, these components are often replaced on a scheduled basis before they actually begin to fail, causing unnecessary expense. 
         [0006]    Measuring impacts allow the user to monitor these components to know when operating conditions have changed so that replacement can be made only when necessary but before damage occurs. One traditional way to measure impact would be to use a conventional accelerometer sensor, power supply, signal conditioner, and analog signal input to the control system. Another approach is to convert the vibration signal from a sensor mounted to the relatively stationary surface that the moving component strikes to indicate when the impact force is too high. The first approach requires the user to integrate several components and requires an analog input plus control system processing to interpret the signal. Analyzing the data from the sensor will require a great deal of the control system&#39;s processing power, especially if more than a few points must be monitored. The second approach has the disadvantage of offering low sensitivity if the surface impacted is significantly more massive than the moving component. 
         [0007]    Shock and impact sensors are types of inertial sensors, which include accelerometers and vibration sensors. Accelerometers can be and often are designed to measure shock as well as acceleration. Shock and impact sensors are designed to detect instances of sudden impact or severe vibration in order to output a value associated with the detected impact or vibration. 
         [0008]    Accelerometers have a multitude of applications in industry and science. Sensitive accelerometers are used as components of inertial navigation systems for the navigation of aircraft and guidance of missiles to a target. Accelerometers are also used to detect and monitor vibration in rotating and cyclical machinery. Accelerometers are additionally used in tablet computers and digital cameras so that images on their screens are displayed in an upright manner. 
         [0009]    Single- and multi-axis accelerometers are available to detect the magnitude and the direction of the acceleration, with this information being useful in the orientation of an image or an effected device. Micro-machined accelerometers are often used in portable electronic devices and video game controllers, to detect the orientation of the device and/or provide for input from the device. 
         [0010]    One problem associated with the prior art is that the devices are not easily configured. 
         [0011]    What is needed in the art is an easy to program impact sensor having a simple controlling signal as an output. 
       SUMMARY OF THE INVENTION 
       [0012]    The present invention provides a system and a method of conveying information from an impact sensor. 
         [0013]    The invention in one form is directed to a method of conveying information from an impact sensor. The method includes the steps of producing a signal representative of an impact detected by the impact sensor; and stopping a conveying of the signal on a single signal line if the impact has a characteristic that is above a first preselected value. 
         [0014]    The invention in another form is directed to an impact sensor system including a structural element and an impact sensor. The impact sensor is coupled to the structural element. The impact sensor includes an impact detector configured to produce a signal representative of an impact experienced by the structural element. The impact sensor also includes a single signal line for conveying the signal. 
         [0015]    The invention in yet another form is directed to an impact sensor including an impact detector and a single signal line. The impact detector is configured to produce a signal representative of an impact experienced by the impact sensor. The single signal line is configured to convey the signal. 
         [0016]    An advantage of the present invention is that only a single signal line is needed to receive information from the sensor. 
         [0017]    Another advantage of the present invention is that it has two preselected levels that serve as a warning level and a trip level. 
         [0018]    Yet another advantage of the present invention is that the sensor produces a digital time based signal thereby reducing the processing required within a controller that receives the signal. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
           [0020]      FIG. 1  is a perspective view of an embodiment of an impact sensor according to the present invention; 
           [0021]      FIG. 2  is a front view of a programming device for interfacing with the impact sensor of  FIG. 1 ; 
           [0022]      FIG. 3  is a perspective view of a mounting method of the impact sensor of  FIG. 1  to a structural element to form an impact sensor system; 
           [0023]      FIG. 4  is a perspective view of another mounting method of the impact sensor of  FIG. 1  to another structural element to form an impact sensor system; 
           [0024]      FIG. 5  is a schematic view of inputs to, and responses of, the impact sensor of  FIGS. 1 ,  3  and  4  to those inputs; 
           [0025]      FIG. 6  is another schematic view of other inputs to, and responses of, the impact sensor of  FIGS. 1 ,  3  and  4  to those inputs; 
           [0026]      FIG. 7  is a schematical block diagram of the functions of the impact sensor of  FIGS. 1 ,  3  and  4 ; 
           [0027]      FIG. 8  is a functional schematic of the impact sensor of  FIGS. 1 ,  3  and  4 ; and 
           [0028]      FIG. 9  is a flow diagram illustrating a method in which the impact sensor of  FIGS. 1 ,  3  and  4 , works and is programmed to vary parameters therein. 
       
    
    
       [0029]    Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0030]    Referring now to the drawings, and more particularly to  FIG. 1  there is illustrated an embodiment of an impact sensor apparatus  10  of the present invention. 
         [0031]    Definitions of abbreviations used herein include:
       I/O—Input/output, specifically as applied to the terminals of common automated industrial control devices.   LED—Light emitting diode, a semiconductor device that converts electrical power into light.   MEMS—Micro-electromechanical system, typically fabricated using the same processes used to create miniature electronic components.   PLC—Programmable logic controller, a common control device used in industry to control automated machines and processes.       
 
         [0036]    Impact sensor apparatus  10  includes an impact sensor device  12 , a cable  14  incorporating a single signal line  16 , and a connector  18  (although not separately illustrated sensor device  12  may not have a connector  18  and simply have cable  14 , which is then directly electrically terminated). Impact sensor device  12  includes a visual indicator  20 , which may be in the form of a LED  20 . LED  20  displays a status of an output signal of impact sensor device  12  as either red or green, and may use a dynamic of switching between red and green. LED  20  will typically use the colors red and green during normal operation; however, LED  20  also uses several other colors to enhance the user interface aspects of the present invention. 
         [0037]    Now, additionally referring to  FIG. 2 , there is illustrated an embodiment of an interface device  22  that is connectable to impact sensor apparatus  10  by way of connectors  24  or by way of a singular connector above connectors  24 , which is configured to connect to connector  18 . As can be seen in  FIG. 2 , connectors  24  and thus cable  14  may have three wires, two to supply power to impact sensor device  12  and a single signal line  16 . Single signal line  16  denotes that only a single line is provided for receiving a signal from impact sensor device  12 . Interface device  22  also includes a display  26 , controls  28  and a slot  48 . To program or configure impact sensor device  12 , it is slid into slot  48 , which is shaped to receive impact sensor device  12  in a select orientation. Within interface device  22  there is a light sensor proximate to where LED  20  is positioned in slot  48  and two electromagnetic coils proximate to where Hall devices  42 - 1  and  42 - 2 , discussed later, are located. Display  26  displays information from impact sensor device  12  during programming or reading of impact sensor device  12 . Controls  28  allow information to be selected for display and to allow the programming of impact sensor device  12 . For example preselected impulse levels can be sent to impact sensor device  12  for signal comparison purposes. 
         [0038]    Now, additionally referring to  FIGS. 3 and 4  are illustrations of ways of mounting impact sensor device  12 . Similar items in  FIGS. 3 and 4  may have 100 added to thereby indicate while they may be depicted in a different fashion the items have a similar function. There is illustrated an impact sensor system  30  having an impact sensor device  12  coupled to a structural element  32  by way of a clamp  34 . The clamping of impact sensor device  12  to structural element  32  ensures that the movement and impacts encountered by structural element  32  are detected by impact sensor device  12 . 
         [0039]    The impact sensor device  12  of the present invention (also referred to as the “KG impact sensor” herein) provides a simple, inexpensive way to monitor impacts within modern machinery. It was specifically designed for, but not limited to, use with medium to large pneumatic applications that require flow controls, cushions, or shock absorbers for proper operation but may also be applied in other applications. 
         [0040]    Impact sensor device  12  is intended to open new applications to impact sensing, not to replace instrumentation. In particular, the sensor  12  can signal problems with flow controls, cushions, and shock absorbers before expensive actuator damage occurs. The KG impact sensor uses MEMs and micro-controller technology to provide a complete sensing solution in a small package requiring only three wires: two for power plus a single digital output signal wire. This eliminates the need more expensive analog circuitry and simplifies wiring. 
         [0041]    Impact sensor device  12  combines an accelerometer, signal conditioner, analog to digital converter, set point comparison, and configurable output circuits into a small, IP67 rated device. Its output signal is buffered and then sent to the analog to digital converter. After conversion, the result is compared to the two set points. If an action is indicated, the output signal is set accordingly. The micro-controller software allows the user to easily configure the sensor and converts the complex analog impact signal into a single, simple output signal that requires only a single digital input from the user&#39;s machine control circuitry. The software allows the user to utilize accelerometer technology without needing to learn the details of acceleration sensors, signal conditioning circuits, and special power supplies. 
         [0042]    The output signal is fail-safe, meaning a normally closed “on” signal is provided during normal operating conditions. Absence of the signal indicates an impact has exceeded a set point or a connection problem. This allows detection of a wire break or continuity error so the application remains protected. The single digital output can indicate two different internal set points. These set points are called “trip” and “warn” and are latching and non-latching, respectively. The KG impact sensor may use both set points “Dual Point Mode” or each one separately “Single Point Mode”. 
         [0043]    An impact exceeding the “warn” (non-latching) set point causes the output to turn “off” for 50 milliseconds and then to automatically turn back on. During this period, the LED  20  will appear to blink red. The sensor continues to monitor the accelerometer during this short period to see if the second set point is reached. If the impact exceeds the “trip” (latching) set point, the signal is permanently turned “off”. LED  20  will remain red. Impact sensor device  12  continues to monitor the accelerometer for a brief period after a “trip” is detected. The largest value recorded during that period is saved in the sensor as “LAST IMPACT”. This can be read directly by the KG Programmer  22  or with a manual technique. The LED  20  will remain red until power is cycled, which resets impact sensor device  12 . 
         [0044]    KG Impact Sensor  12  constantly monitors impacts of the mass  32  to which it is attached. It provides a time-based signal driven by one or more user-defined set points indicating excessive impact or erratic operation. The “warn” or “trip” signal can be interpreted by a device, which then performs an appropriate function. Functions include, but are not limited to: Operator alert devices (illuminated lights, audible alarms) and machine stoppage (preventing catastrophic failure, bad product manufacture). 
         [0045]    The user is able to digitally configure the set point values specific to their application and whether these points are monitored together or individually. The KG Impact Sensor is available preset from the factory or set on-site by the user using programming interface  22 . Set point values can be modified at any time. The KG Impact Sensor  12  is also able to measure an impact and relay that value to the user. This is helpful for diagnostics or during initial set up of the KG Impact Sensor  12 . Impacts and set points are indicated in g-force. 
         [0046]    Use of the optional KG Programmer  22  unlocks the total potential and flexibility of the KG Impact Sensor  12 . With the programmer  22 , the end user is able to modify the circuit type (SINK/NPN or SOURCE/PNP), whether sensor  12  is in Dual or Single Point Mode, and the value of the set point(s). In addition, the KG Programmer  22  simplifies setting up the KG Impact Sensor  12 . Lastly, a single programmer has the ability to service an unlimited number of impact sensors throughout an entire plant. 
         [0047]    Impact Sensor  12  Features
       Bi-directional single axis sensitivity   Single or dual point operation   User defined, rewriteable set-points   Attaches easily to moving mass   Multi-color LED for visual monitoring   Fail-safe output signal   Available preset or field programmable   3 pin quick connect option   Optional programmer available       
 
         [0057]    Impact Sensor Uses
       Predictive maintenance device   Detects changes in impact force   Can help to reduce unanticipated downtime   Minimizes unnecessary preventive maintenance   Maintenance tripwire   Flags personnel of a machine crash   Can stop production of bad parts when a severe crash is detected   Prevents/detects product damage by detecting abnormal machine operation   Benchmarking   Measures impact   Provides an input for an event counter of impacts or extreme vibration   Monitors centripetal forces       
 
         [0070]    Now, additionally referring to  FIG. 5 , there is illustrated signals  50  including multiple impacts  52  that are sensed, a preselected value non-latching point (Warn)  54 , a preselected value latching point (Trip)  56 , sensor signal  58  shown here as impact sensor output  58  and LED status  60 . As normal impacts  52  increase and exceed the non-latching point  54 , the fail-safe signal  58  drops for 50 milliseconds with every excessive impact. A programmable logic controller (PLC) that is monitoring the signal  58  can utilize timer logic to issue an appropriate action, alert, or warning depending upon signal  58 . When the impact  52  increases beyond the latching point  56 , the fail-safe signal  58  permanently drops and the PLC can determine the appropriate action to protect the machine and products made by the machine. 
         [0071]    Now, additionally referring to  FIG. 6 , in the case of constant acceleration or centripetal motion where the profile is flat or has an extended duration, the fail-safe signal  58  remains low, returning high 50 ms (or other predetermined time) after the force falls below the non-latching point  54 . If the latching point  56  is exceeded, the fail-safe signal  58  permanently drops, until reset. 
         [0072]    To reset impact sensor device  12  from a latched condition, power must be cycled to sensor  12 . An allowance of 200 ms for sensor initialization before returning to normal operation is typically required. 
         [0073]    LED status  60  may indicate that the low condition may indicate the LED  20  is green and the high may indicate LED  20  is red. Other signaling scenarios are contemplated such as different colors, blinking sequences, and intensity levels to name a few. 
         [0074]    Proper cable management is critical to the operation of the impact sensor. All cabling must be secured as not to influence the motion of the sensor  12  in any way. 
         [0075]    Now, additionally referring to  FIG. 7 , further details of sensor  12  are illustrated. The present invention overcomes the problems encountered with the prior art. Sensor  12  combines an acceleration sensor  36 , power conditioning, signal conditioning and processing circuits  38 , timing and control functions  40 , user inputs  42 , a parameter memory  44 , and output functions  46  into a small, robust, environmentally protected housing. This low mass assembly may be easily mounted to the moving component, as illustrated in  FIGS. 3 and 4 , to provide accurate measurement of the moving assembly itself instead of inferring forces from a secondary mass via impact vibration. It also interprets the internal, rapid analog signals against the user&#39;s predefined settings to provide a simple, time based, digital output. This digital output may be used directly (to activate a relay, for example), or supplied to an input terminal of the PLC controlling the machine on which the components are mounted. The output signal  58  uses time to indicate a measured value relative to the user settings and may be easily interpreted by almost any PLC program using the input timer function. The unit draws only a small amount of power increasing its utility in this type of application. By powering the unit from one of the PLC outputs and reading its signal  58  with one of the PLC inputs, it may be completely controlled, including its reset function, using only two PLC I/O lines. 
         [0076]    Sensor  12  uses a MEMS accelerometer  36  to sense impacts. This type of device is commonly used to detect impact and is used in other impact sensing applications such as automotive airbag deployment. The signal from the accelerometer  36  is adjusted to improve accuracy and the output therefrom is compared to the set points selected by the user. 
         [0077]    Timing and control function  40  coordinates the interpretation of the sensor signal, the comparison to the user settings memory  44 , the monitoring of the user inputs  42 , and the setting of the output  46  conditions. To guarantee reliable operation and predictable performance for both impact sensing and the user interface, the control function scans continuously at a rate significantly faster than the response rate of the MEMS accelerometer  36  to assure timely updates to the output signal  58 . 
         [0078]    The output function  46  provides both electrical and visual indication of the sensor status during operation. It also provides feedback to the user or the programmer during user interface activities such as reading or setting parameters. 
         [0079]    The user input function  42  incorporates logic and circuitry to prevent unintended transition to the user interface mode and allows the user to change settings, configure output condition, and read recent status from the device memory  44 . 
         [0080]    A preferred embodiment of the impact sensor  12  provides several useful features in addition to sensing impact. The user interface is by way of magnetic sensors  42 - 1  and  42 - 2  and a multicolor LED  20  allowing sensor  12  to be small and hermetically sealed for use in environments contaminated with fluids and dirt. This interface also permits use by a human using a simple magnet or by way of an optional programming device  22 . An illustration of the preferred embodiment is shown in  FIG. 1 . 
         [0081]    Now, additionally referring to  FIG. 8 , there is illustrated a simplified schematic of the preferred embodiment. Diodes D 1  through D 4  and current limiter F 1  protect the electrical connections of the impact sensor  12 . Semiconductor switches Q 1  and Q 2  provide a user configurable output signal  58 . Power regulator U 1  provides regulated voltage for powering the components as well as the reference voltage for the analog to digital conversion. Microcontroller U 2  provides the timing and control functions  40  as well as configurable memory  44  to store user parameters. User output is provided by a red-green-blue light emitting diode  20 . User input is by way of Hall switches U 3  ( 42 - 2 ) and U 4  ( 42 - 1 ). The MEMS accelerometer U 5  ( 36 ), provides a low current ratiometric signal to buffer amplifier U 6 . The buffered signal is then delivered to an analog to digital converter peripheral contained within microcontroller U 2 . 
         [0082]    The user configurable output  16  may either push (source) or pull (sink) current. This allows the device be used with nearly any common industrial programmable logic controller. Many industrial sensors do not feature this advantage, forcing the user to select the appropriate type when ordering and requiring the manufacturer to inventory two versions to support their customers. The output also uses additional components (D 1  through D 4 , and F 1 ) to protect against reversed connections, transient voltages, and sustained excessive current common in the environment where this type of sensor is employed. 
         [0083]    Two magnetically sensitive Hall switches U 3  and U 4  provide the user input interface via a magnet. The Hall switches are physically separated within sensor  12 , to make it easy for the user to select either Hall switch separately. For example, Hall switch U 3  may be on one end of sensor  12  and Hall switch U 4  may be on an opposite end of sensor  12  with LED  20  being between them. Many different techniques could be used to allow user input, even conventional push button switches. However, the Hall switches are robust, inexpensive and may be completely sealed to protect them from the environment. For the purposes of this description, user input  2  ( 42 - 2 ) is located nearest to the end of the housing with the cable connection, while user input  1  ( 42 - 1 ) is near the opposite end of the unit. 
         [0084]    The Microcontroller U 2  performs all timing and control functions  40  and also stores the user settings and operating information in static memory so that the settings are maintained in the absence of a power source. 
         [0085]    Now, additionally referring to  FIG. 9 , there is illustrated a high level state diagram of the software of the preferred embodiment of the present invention. Much of the functionality of the impact sensor is derived from its software. The operation of the software by way of the different states will be described below and essentially proceeds through  FIG. 9  from top to bottom. 
         [0086]    Upon microcontroller startup, either due to power up or internal reset, the unit checks non-volatile memory to see if this is the very first application of power. If it is the first power up, the unit enters the CALIBRATION state to improve accuracy. One specific function of the CALIBRATION state is to correct the offset error of the specific MEMS accelerometer  36  used in the assembly. This correction is permanently saved to non-volatile memory  44 . 
         [0087]    Once the CALIBRATION state is finished, or on any subsequent startup, the microcontroller enters an INITIALIZE state. In this state, the microcontroller peripheral registers are set and mathematical functions convert user variables into register values to speed computation during normal operation. In the event of a defined error, the microcontroller will enter a SYSTEM FAULT state. 
         [0088]    The SYSTEM FAULT state flashes LED indicator  20  red. The flashing distinguishes this state from the continuous red indication of the TRIP state. The only way to clear this state is to cycle the power to sensor  12 . If the system fault clears itself, sensor  12  will return to normal operation. 
         [0089]    Following successful initialization, the microcontroller will enter the OPERATE state. In this state the sensor monitors the signal from accelerometer  36  and one of the user inputs. It also controls the output signal  58  based on the user configuration. Predefined errors occurring within the OPERATE state can cause the microcontroller to enter the SYSTEM FAULT state. The sensor uses a “normally closed” type of output to provide “fail safe” operation. The output  16  is “on” during normal operation. Output  16  turns “off” to indicate that the warning or trip set points have been reached or exceeded. Should the output signal wire  16  or connection fail, it will appear as a loss of output signal  58  to the control system. 
         [0090]    The signal from accelerometer  36  caused by impact  52  is compared to the user set points  54  and  56  stored in non-volatile memory  44 . If the “warning” set point  54  is reached the output signal  58  is turned off for 50 milliseconds and then turned on again. While the output  58  is off, the normally green LED  20  changes to red. The signal from accelerometer  36  is still sampled during the “warning” signal event. The output signal  58  remains off as long as the signal is above the “warning” set point  54 . When the signal from accelerometer  36  drops below the “warning” set point  54 , the output signal  58  is maintained off for an additional 50 milliseconds and then returns to normal. If the signal from accelerometer  36  reaches the “trip” set point  56  at any time, the unit leaves the OPERATE state and enters the TRIP state. The behavior of the output  58  is shown graphically in  FIGS. 5 and 6 . 
         [0091]    The TRIP state sets the output  58 , changes the LED indicator  20 , saves the highest impact value, and provides a means for the user to display that value. As soon the TRIP state is entered, the output is turned off and the LED indicator  20  is set to red. The microcontroller continues to monitor the accelerometer for a brief period after entering the TRIP state and saves the highest impact value during that time period to memory  44 . Without this feature, the recorded value would be identical or very close to the user setting. By sampling beyond the set point, the value saved will be closer to the maximum impact. The user can manually read this value while in the TRIP state by simultaneously activating both user input sensors  42 - 1  and  42 - 2 . The LED indicator  20  will flash the measured value using different colors and then revert to the steady red indication. The user may repeat this action as many times as desired while the unit is in the TRIP state. The user may also use programmer  22  to read this value at any time. Changing the set points will serve to reset this value to zero. To return the unit to normal operation, the power to the unit must be turned off and then restored. This resets the unit as described at the beginning of this section. The behavior of the output is shown graphically in  FIGS. 5 and 6 . 
         [0092]    The OPERATE state also continuously scans user input  1  ( 42 - 1 ), the first of two user input sensors. In the preferred embodiment, these inputs incorporate Hall sensor technology and respond to magnetic fields. However, these could be any technology that allows the user to interact with the device, such as pushbutton, inductive, or light sensing devices. If the user input remains active for a specified length of time, the microcontroller will enter the USER INTERFACE REQUEST state. 
         [0093]    The USER INTERFACE REQUEST state confirms that a user interface request is valid while maintaining the protection of the OPERATE mode. In this state, the accelerometer signal is still scanned and the output signal  58  is controlled based on the user set points  54  and  56 . The LED indicator  20  changes from green to purple to indicate the state change from OPERATE. In order to prevent accidentally entering the USER INTERFACE state, a special sequence is required that would be very unlikely to occur during normal operation. In the preferred embodiment, this sequence is a long activation of user input  1  ( 42 - 1 ), then three separate brief activations of user input  2  ( 42 - 2 ), concluding with a final long activation of user input  1  ( 42 - 1 ). This sequence must occur within a predetermined time period (approximately 30 seconds) or the unit will return to the OPERATE state. If the sequence is entered in time, the microcontroller enters the USER INTERFACE state. Other activation sequences are also contemplated. 
         [0094]    The USER INTERFACE state allows the user to display or change the set points  54  and  56  and output configuration of the sensor. Upon entering the USER INTERFACE state, the LED indicator  20  turns blue, scanning of the accelerometer signal and comparison of it to set points  54  and  56  is stopped, and the output  58  is turned off. Activating user input  1  ( 42 - 1 ) briefly will cause the LED indicator  20  to flash different colors that display the values for the trip set point, the output configuration, and the warning set point in order. If user input  1  ( 42 - 1 ) activation is maintained, this sequence will begin but will then quickly return to the normal operating state. This provides a means for the user to quickly return to the OPERATE state. The USER INTERFACE state will also automatically return to the OPERATE state after a predetermined time period with no user activity. 
         [0095]    The user may also change the settings of the sensor by briefly selecting user input  2  ( 42 - 2 ). Each selection of user input  2  ( 42 - 2 ) advances to the next selection, which is indicated by a color change of the LED indicator  20 . To enter a different value for a setting, user input  1  ( 42 - 1 ) is briefly selected. If the setting has only two values, such as the output configuration, each brief selection of user input  1  ( 42 - 1 ) will alternate between these values, indicated by two different colors of the LED indicator  20 . When the desired value is indicated, the user simply selects user input  2  ( 42 - 2 ) briefly to move to the next selection. If the selection requires a numeric value, the LED indicator  20  will display a very rapid flash to indicate the starting value of zero. Each brief selection of user input  1  ( 42 - 1 ) increments the value by one. The LED also flashes off briefly at each increment for user feedback. The counter recycles at the end of the allowable input range and returns to zero. This allows the user to easily return to zero and restart if he is uncertain of his entry. A specific setting of a numeric selection, such as zero, can allow its function to be intentionally disabled. To move to the next selection, user input  2  ( 42 - 2 ) is briefly selected, the LED  20  color changes to indicate the new selection. If the user advances through a selection without changing it, it retains its previous value. 
         [0096]    When the user has advanced through all the available selections, the LED  20  rapidly alternates between red and yellow to indicate the end of the selection set. At this point, any changes have not been saved to non-volatile memory  44 . If the user waits until the USER INTERFACE state time period expires, approximately one minute, the unit will revert to the OPERATE state without saving the changes. The user may also select user input  1  ( 42 - 1 ) if he wishes to return to the OPERATE state without saving his changes. In this case, the LED  20  will start slowly flashing blue. The speed of the flash will increase until the blue color is constant and then the unit will enter the OPERATE state. If the user wishes to save his changes, user input  2  ( 42 - 2 ) is selected and held. The LED will begin to slowly flash green. The speed of the flash will increase until the green color is constant and then the unit will save the values to non-volatile memory and perform a software reset. The unit will then automatically restart with the new values. 
         [0097]    In one embodiment, a programming device  22  is available to automate the display and setting process described above to simplify these processes for the user. This device is illustrated in  FIG. 2  and is used to perform the functions described above. Sensor  12  is slid into slot  48  and electromagnets control inputs  42 - 1  and  42 - 2 , with the output of LED  20  being received by a light sensitive sensor. Controls  28  are used to select options displayed on display  26  to read the status of sensor  12  and to configure the set points, by triggering the electromagnets and receiving the light output of LED  20 , in a user-friendly manner. 
         [0098]    While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.