Patent Publication Number: US-7592888-B2

Title: Low cost user adjustment, resistance to straying between positions, increased resistance to ESD, and consistent feel

Description:
RELATED APPLICATION 
   The present application claims the benefit of U.S. Provisional Application No. 60/831,006, filed Jul. 14, 2006, titled “Motor Circuit Protector,” which is hereby incorporated by reference in its entirety. 

   FIELD OF THE INVENTION 
   This invention is directed generally to a user adjustment switch for use in an electrical apparatus, and, more particularly, to a low cost mechanical adjustment button that resists straying between positions and has increased resistance to electrostatic discharge and a consistent feel. 
   BACKGROUND OF THE INVENTION 
   As is well known, a circuit breaker is an automatically operated electro-mechanical device designed to protect a load from damage caused by a power overload or a short circuit. A circuit breaker may be tripped by an overload or short circuit causing an interruption of power to the load. A circuit breaker can be reset (either manually or automatically) to resume power flow to the loads. One type of circuit breaker that provides instantaneous short circuit protection to motors and/or motor control centers (“MCC”) is called a motor circuit protector (MCP). A typical MCP includes a temperature-triggered overload relay, a circuit breaker, and a contactor. An MCP circuit breaker must meet National Electric Code (“NEC”) requirements when installed as part of a UL-listed MCC to provide instantaneous overload protection. 
   Mechanical circuit breakers energize an electro-magnetic device such as a solenoid to trip a breaker instantaneously due to large surges in current such as by a short circuit. The solenoid is tripped when current exceeds a certain threshold. In order to provide protection over different types of motors, different MCP circuit breakers that match the operating parameters of the particular motor must be designed for each current rating. Each MCP circuit breaker is designed with specific trip point settings for a given current rating. MCPs must protect against fault currents while avoiding tripping on in-rush motor currents or locked-rotor currents, but these current levels vary by motor. Existing MCPs have a relatively limited operating range, so they are suitable for protecting motor circuits within the MCP&#39;s operating range. For motor circuits outside of a particular MCP&#39;s operating range, a different MCP must be designed for the operating parameters of those motor circuits. 
   It is costly to design a different MCP device for different current ratings, and it is also costly to inventory and distribute many different MCP devices. What is needed is an MCP device with user-adjustable and automatically configurable trip point settings over a broad range of current ratings. What is also needed is a circuit protection device that couples a mechanical adjustment button and a potentiometer for adjusting trip levels of an electrical circuit. 
   SUMMARY OF THE INVENTION 
   Aspects of the present invention improves conventional techniques of translating user-adjustable trip unit settings to pickup levels. These aspects enable a fail-safe operation mode where user adjustments can revert to greater or any other predetermined protective levels. Overall system performance is improved with lower-cost components without requiring switch calibration. Switch performance is verified during the production test process with quantitative techniques. 
   The MCP according to aspects of the present invention includes a user adjustment assembly for adjusting the tripping levels of the MCP. The user adjustment assembly includes a mechanical button with switch-like stop and detent features corresponding to mechanical orientation angles that are translated to a potentiometer mechanical orientation via a user adjustment circuit. The user adjustment circuit may include a potentiometer and is configured to present a percentage of an A/D&#39;s full-scale voltage to an A/D input pin, which converts the scaled voltage to a corresponding digital value that determines the button position. 
   The user adjustment circuit is a cheaper alternative to existing mechanical solutions by substantially eliminating the number of mechanical parts required to translate mechanical switch positions to meaningful data. 
   Software embedded in the MCP and executed by a controller in the MCP implements a switch detection algorithm that includes a failure mode detection. Mechanical button positions are determined via the controller&#39;s A/D converter, and changes to the mechanical button positions are sensed by the A/D converter and the MCP&#39;s trip levels are automatically adjusted based upon the new position. The failure mode detection reverts to predetermined protective levels. 
   The user adjustment assembly according to aspects of the present invention eliminates the need for calibration. Position thresholds are determined by producing a statistical distribution of data corresponding to the switch settings, and as each user adjustment assembly is produced, the position thresholds and user adjustment assembly performance are monitored and stored. 
   In an embodiment of the present invention, a user adjustment assembly for adjusting tripping levels of an electrical trip unit includes a potentiometer and an adjustment button. The potentiometer is positioned inside a protective cover of the electrical trip unit and has a top surface. The adjustment button is coupled to the potentiometer for mechanically adjusting the potentiometer and has an insulation disc for increasing resistance to electrostatic discharge. The adjustment button is dimensioned and located so that it covers the potentiometer. 
   In another alternative embodiment of the present invention, an electrical circuit breaker has adjustable tripping levels and includes an enclosing cover, a potentiometer, and an adjustment button. The enclosing cover has a button hole. The potentiometer is coupled to a voltage source and is mounted to a printed wire assembly in an interior area of the enclosing cover. The adjustment button has an insulation disc for protecting the potentiometer from electrostatic discharge. The adjustment button is dimensioned and located so that it covers the potentiometer. 
   Additional aspects of the invention will be apparent to those of ordinary skill in the art in view of the detailed description of various embodiments, which is made with reference to the drawings, a brief description of which is provided below. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may best be understood by reference to the following description taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  is perspective view of a motor circuit protector according to the present application; 
       FIG. 2  is a functional block diagram of the motor circuit protector in  FIG. 1 ; 
       FIG. 3  is a functional block diagram of the operating components of a control algorithm of the motor circuit protector in  FIG. 1 ; 
       FIG. 4A  is a functional electrical schematic of an user adjustment switch for use with the motor circuit protector of  FIG. 1 ; 
       FIG. 4B  is an illustration of an electromechanical orientation for adjustment in accordance with the diagram of  FIG. 4A ; 
       FIG. 4C  is a flowchart diagram for setting an operating trip curve of the motor circuit protector of  FIG. 1  by adjusting a mechanical switch; 
       FIG. 5A  is a perspective view of a trip unit assembly according to an alternative implementation of the present application; 
       FIG. 5B  is an enlarged view of a top portion of the trip unit assembly of  FIG. 5A ; 
       FIG. 6  is a cross-sectional view showing a portion of the trip unit assembly of  FIG. 5A  at a rotational center of an adjustment switch; 
       FIG. 7A  is a top perspective view of the adjustment switch of  FIG. 6 ; 
       FIG. 7B  is a bottom perspective view of the adjustment switch of  FIG. 6 ; 
       FIG. 8A  is a perspective view of a printed wire assembly including two potentiometers according to another alternative implementation of the present application; 
       FIG. 8B  is a perspective view of the printed wire assembly of  FIG. 8A  including two adjustment switches coupled to the two potentiometers; 
       FIG. 9A  is an enlarged view showing the adjustment switch inserted into a cover of the trip unit assembly of  FIG. 5A ; 
       FIG. 9B  is an enlarged bottom perspective view illustrating a hole in the cover of the trip unit assembly of  FIG. 5A ; 
       FIG. 9C  illustrates a cross-sectioned portion of the adjustment switch of  FIG. 6  inserted into the hole of  FIG. 9B ; 
       FIG. 10  illustrates another cross-sectioned portion of the adjustment switch of  FIG. 6  inserted into the hole of  FIG. 9B ; 
       FIG. 11A  illustrates a top perspective view of an adjustment switch having a insulative skirt according to yet another alternative implementation of the present application; and 
       FIG. 11B  illustrates a bottom perspective view of the adjustment switch of  FIG. 11A . 
   

   DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS 
   Although the invention will be described in connection with certain preferred embodiments, it will be understood that the invention is not limited to those particular embodiments. On the contrary, the invention is intended to include all alternatives, modifications and equivalent arrangements as may be included within the spirit and scope of the invention as defined by the appended claims. 
   Turning now to  FIG. 1 , an electronic motor circuit protector  100  is shown. The motor circuit protector  100  includes a durable housing  102  including a line end  104  having line terminals  106  and a load end  108  having load lugs or terminals  110 . The line terminals  106  allow the motor circuit protector  100  to be coupled to a power source and the load terminals  110  allow the motor circuit protector  100  to be coupled to an electrical load such as a motor as part of a motor control center (“MCC”). In this example the motor circuit protector  100  includes a three-phase circuit breaker with three poles, although the concepts described below may be used with circuit protectors with different numbers of poles, including a single pole. 
   The motor circuit protector  100  includes a control panel  112  with a full load ampere (“FLA”) dial  114  and an instantaneous trip point (“I m ”) dial  116  which allows the user to configure the motor circuit protector  100  for a particular type of motor to be protected within the rated current range of the motor circuit protector  100 . The full load ampere dial  114  allows a user to adjust the full load which may be protected by the motor circuit protector  100 . The instantaneous trip point dial  116  has settings for automatic protection (three levels in this example) and for traditional motor protection of a trip point from 8 to 13 times the selected full load amperes on the full load ampere dial  114 . The dials  114  and  116  are located next to an instruction graphic  118  giving guidance to a user on the proper settings for the dials  114  and  116 . In this example, the instruction graphic  118  relates to NEC recommended settings for the dials  114  and  116  for a range of standard motors. The motor circuit protector  100  includes a breaker handle  120  that is moveable between a TRIPPED position  122  (shown in  FIG. 1 ), an ON position  124  and an OFF position  126 . The position of the breaker handle  120  indicates the status of the motor circuit protector  100 . For example, in order for the motor circuit protector  100  to allow power to flow to the load, the breaker handle  120  must be in the ON position  124  allowing power to flow through the motor circuit protector  100 . If the circuit breaker is tripped, the breaker handle  120  is moved to the TRIPPED position  122  by a disconnect mechanism, causing an interruption of power and disconnection of downstream equipment. In order to activate the motor circuit protector  100  to provide power to downstream equipment or to reset the motor circuit protector  100  after tripping the trip mechanism, the breaker handle  120  must be moved manually from the TRIPPED position  120  to the OFF position  126  and then to the ON position  124 . 
     FIG. 2  is a functional block diagram of the motor circuit protector  100  in  FIG. 1  as part of a typical MCC configuration  200  coupled between a power source  202  and an electrical load such as a motor  204 . The MCC configuration  200  also includes a contactor  206  and an overload relay  208  downstream from the power source  202 . Other components such as a variable speed drive, start/stop switches, fuses, indicators and control equipment may reside either inside the MCC configuration  200  or outside the MCC configuration  200  between the power source  202  and the motor  204 . The motor circuit protector  100  protects the motor  204  from a short circuit condition by actuating the trip mechanism, which causes the breaker handle  120  to move to the TRIPPED position when instantaneous short-circuit conditions are detected. The power source  202  in this example is connected to the three line terminals  106 , which are respectively coupled to the primary windings of three current transformers  210 ,  212  and  214 . Each of the current transformers  210 ,  212  and  214  has a phase line input and a phase load output on the primary winding. The current transformers  210 ,  212  and  214  correspond to phases A, B and C from the power source  202 . The current transformers  210 ,  212  and  214  in this example are iron-core transformers and function to sense a wide range of currents. The motor circuit protector  100  provides instantaneous short-circuit protection for the motor  204 . 
   The motor circuit protector  100  includes a power supply circuit  216 , a trip circuit  218 , an over-voltage trip circuit  220 , a temperature sensor circuit  222 , a user adjustments circuit  224 , and a microcontroller  226 . In this example, the microcontroller  226  is a PIC16F684-E/ST programmable microcontroller, available from Microchip Technology, Inc. based in Chandler, Ariz., although any suitable programmable controller, microprocessor, processor, etc. may be used. The microcontroller  226  includes current measurement circuitry  241  that includes a comparator and an analog-to-digital converter. The trip circuit  218  sends a trip signal to an electromechanical trip solenoid  228 , which actuates a trip mechanism, causing the breaker handle  120  in  FIG. 1  to move from the ON position  124  to the TRIPPED position  122 , thereby interrupting power flow to the motor  204 . In this example, the electro-mechanical trip solenoid  228  is a magnetic latching solenoid that is actuated by either stored energy from a discharging capacitor in the power supply circuit  216  or directly from secondary current from the current transformers  210 ,  212  and  214 . 
   The signals from the three current transformers  210 ,  212  and  214  are rectified by a conventional three-phase rectifier circuit (not shown in  FIG. 2 ), which produces a peak secondary current with a nominally sinusoidal input. The peak secondary current either fault powers the circuits  216 ,  218 ,  220 ,  222 , and  224  and the microcontroller  226 , or is monitored to sense peak fault currents. The default operational mode for current sensing is interlocked with fault powering as will be explained below. A control algorithm  230  is responsible for, inter alia, charging or measuring the data via analog signals representing the stored energy voltage and peak current presented to configurable inputs on the microcontroller  226 . The control algorithm  230  is stored in a memory that can be located in the microcontroller  226  or in a separate memory device  272 , such as a flash memory. The control algorithm  230  includes machine instructions that are executed by the microcontroller  226 . All software executed by the microcontroller  226  including the control algorithm  230  complies with the software safety standard set forth in UL-489 SE and can also be written to comply with IEC-61508. The software requirements comply with UL-1998. As will be explained below, the configurable inputs may be configured as analog-to-digital (“A/D”) converter inputs for more accurate comparisons or as an input to an internal comparator in the current measurement circuitry  241  for faster comparisons. In this example, the A/D converter in the current measurement circuitry  241  has a resolution of 8/10 bits, but more accurate AID converters may be used and may be separate and coupled to the microcontroller  226 . The output of the temperature sensor circuit  222  may be presented to the A/D converter inputs of the microcontroller  226 . 
   The configurable inputs of the microcontroller  226  include a power supply capacitor input  232 , a reference voltage input  234 , a reset input  236 , a secondary current input  238 , and a scaled secondary current input  240 , all of which are coupled to the power supply circuit  216 . The microcontroller  226  also includes a temperature input  242  coupled to the temperature sensor circuit  222 , and a full load ampere input  244  and an instantaneous trip point input  246  coupled to the user adjustments circuit  224 . The user adjustments circuit  224  receives inputs for a full load ampere setting from the full load ampere dial  114  and either a manual or automatic setting for the instantaneous trip point from the instantaneous trip point dial  116 . 
   The microcontroller  226  also has a trip output  250  that is coupled to the trip circuit  218 . The trip output  250  outputs a trip signal to cause the trip circuit  218  to actuate the trip solenoid  228  to trip the breaker handle  120  based on the conditions determined by the control algorithm  230 . The microcontroller  226  also has a burden resistor control output  252  that is coupled to the power supply circuit  216  to activate current flow across a burden resistor (not shown in  FIG. 2 ) and maintain regulated voltage from the power supply circuit  216  during normal operation. 
   The breaker handle  120  controls manual disconnect operations allowing a user to manually move the breaker handle  120  to the OFF position  126  (see  FIG. 1 ). The trip circuit  218  can cause a trip to occur based on sensed short circuit conditions from either the microcontroller  226 , the over-voltage trip circuit  220  or by installed accessory trip devices, if any. As explained above, the microcontroller  226  makes adjustment of short-circuit pickup levels and trip-curve characteristics according to user settings for motors with different current ratings. The current path from the secondary output of the current transformers  210 ,  212 ,  214  to the trip solenoid  228  has a self protection mechanism against high instantaneous fault currents, which actuates the breaker handle  120  at high current levels according to the control algorithm  230 . 
   The over-voltage trip circuit  220  is coupled to the trip circuit  218  to detect an over-voltage condition from the power supply circuit  216  to cause the trip circuit  218  to trip the breaker handle  120  independently of a signal from the trip output  250  of the microcontroller  226 . The temperature sensor circuit  222  is mounted on a circuit board proximate to a copper burden resistor (not shown in  FIG. 2 ) together with other electronic components of the motor circuit protector  100 . The temperature sensor circuit  222  and the burden resistor are located proximate each other to allow temperature coupling between the copper traces of the burden resistor and the temperature sensor. The temperature sensor circuit  222  is thermally coupled to the power supply circuit  216  to monitor the temperature of the burden resistor. The internal breaker temperature is influenced by factors such as the load current and the ambient temperatures of the motor circuit protector  100 . The temperature sensor  222  provides temperature data to the microcontroller  226  to cause the trip circuit  218  to actuate the trip solenoid  228  if excessive heat is detected. The output of the temperature sensor circuit  222  is coupled to the microcontroller  226 , which automatically compensates for operation temperature variances by automatically adjusting trip curves upwards or downwards. 
   The microcontroller  226  first operates the power supply circuit  216  in a startup mode when a reset input signal is received on the reset input  236 . A charge mode provides voltage to be stored for actuating the trip solenoid  228 . After a sufficient charge has been stored by the power supply circuit  216 , the microcontroller  226  shifts to a normal operation mode and monitors the power supply circuit  216  to insure that sufficient energy exists to power the electro-mechanical trip solenoid  228  to actuate the breaker handle  120 . During each of these modes, the microcontroller  226  and other components monitor for trip conditions. 
   The control algorithm  230  running on the microcontroller  226  includes a number of modules or subroutines, namely, a voltage regulation module  260 , an instantaneous trip module  262 , a self protection trip module  264 , an over temperature trip module  266  and a trip curves module  268 . The modules  260 ,  262 ,  264 ,  266  and  268  generally control the microcontroller  226  and other electronics of the motor circuit protector  100  to perform functions such as governing the startup power, establishing and monitoring the trip conditions for the motor circuit protector  100 , and self protecting the motor circuit protector  100 . A storage device  270 , which in this example is an electrically erasable programmable read only memory (EEPROM), is coupled to the microcontroller  226  and stores data accessed by the control algorithm  230  such as trip curve data and calibration data as well as the control algorithm  230  itself. Alternately, instead of being coupled to the microcontroller  226 , the EEPROM may be internal to the microcontroller  226 . 
     FIG. 3  is a functional block diagram  300  of the interrelation between the hardware components shown in  FIG. 2  and software/firmware modules  260 ,  262 ,  264 ,  266  and  268  of the control algorithm  230  run by the microcontroller  226 . The secondary current signals from the current transformers  210 ,  212  and  214  are coupled to a three-phase rectifier  302  in the power supply circuit  216 . The secondary current from the three-phase rectifier  302  charges a stored energy circuit  304  that supplies sufficient power to activate the trip solenoid  228  when the trip circuit  218  is activated. The voltage regulation module  260  ensures that the stored energy circuit  304  maintains sufficient power to activate the trip solenoid  228  in normal operation of the motor circuit protector  100 . 
   The trip circuit  218  may be activated in a number of different ways. As explained above, the over-voltage trip circuit  220  may activate the trip circuit  218  independently of a signal from the trip output  250  of the microcontroller  226 . The microcontroller  226  may also activate the trip circuit  218  via a signal from the trip output  250 , which may be initiated by the instantaneous trip module  262 , the self protection trip module  264 , or the over temperature trip module  266 . For example, the instantaneous trip module  262  of the control algorithm  230  sends a signal from the trip output  250  to cause the trip circuit  218  to activate the trip solenoid  228  when one of several regions of a trip curve are exceeded. For example, a first trip region A is set just above a current level corresponding to a motor locked rotor. A second trip region B is set just above a current level corresponding to an in-rush current of a motor. The temperature sensor circuit  222  outputs a signal indicative of the temperature, which is affected by load current and ambient temperature, to the over temperature trip module  266 . The over temperature trip module  266  will trigger the trip circuit  218  if the sensed temperature exceeds a specific threshold. For example, load current generates heat internally by flowing through the current path components, including the burden resistor, and external heat is conducted from the breaker lug connections. A high fault current may cause the over temperature trip module  266  to output a trip signal  250  ( FIG. 2 ) because the heat conducted by the fault current will cause the temperature sensor circuit  222  to output a high temperature. The over temperature trip module  266  protects the printed wire assembly from excessive temperature buildup that can damage the printed wire assembly and its components. Alternately, a loose lug connection may also cause the over temperature trip module  266  to output a trip signal  250  if sufficient ambient heat is sensed by the temperature sensor circuit  222 . 
   The trip signal  250  is sent to the trip circuit  218  to actuate the solenoid  228  by the microcontroller  226 . The trip circuit  218  may actuate the solenoid  228  via a signal from the over-voltage trip circuit  220 . The requirements for “Voltage Regulation,” ensure a minimum power supply voltage for “Stored Energy Tripping.” The trip circuit  218  is operated by the microcontroller  226  either by a “Direct Drive” implementation during high instantaneous short circuits or by the control algorithm  230  first ensuring that a sufficient power supply voltage is present for the “Stored Energy Trip.” In the case where the “Stored Energy” power supply voltage has been developed, sending a trip signal  250  to the trip circuit  218  will ensure trip activation. During startup, the power supply  216  may not reach full trip voltage, so a “Direct Drive” trip operation is required to activate the trip solenoid  228 . The control for Direct Drive tripping requires a software comparator output sense mode of operation. When the comparator trip threshold has been detected, the power supply charging current is applied to directly trip the trip solenoid  228 , rather than waiting for full power supply voltage. 
   The over-voltage trip circuit  220  can act as a backup trip when the system  200  is in “Charge Mode.” The control algorithm  230  must ensure “Voltage Regulation,” so that the over-voltage trip circuit  220  is not inadvertently activated. The default configuration state of the microcontroller  226  is to charge the power supply  216 . In microcontroller control fault scenarios where the power supply voltage exceeds the over voltage trip threshold, the trip circuit  218  will be activated. Backup Trip Levels and trip times are set by the hardware design. 
   The user adjustments circuit  224  accepts inputs from the user adjustment dials  114  and  116  to adjust the motor circuit protector  100  for different rated motors and instantaneous trip levels. The dial settings are converted by a potentiometer to distinct voltages, which are read by the trip curves module  268  along with temperature data from the temperature sensor circuit  222 . The trip curves module  268  adjusts the trip curves that determine the thresholds to trigger the trip circuit  218 . A burden circuit  306  in the power supply circuit  216  allows measurement of the secondary current signal, which is read by the instantaneous trip module  262  from the peak secondary current analog-to-digital input  238  (shown in  FIG. 2 ) along with the trip curve data from the trip curves module  268 . The self-protection trip module  264  also receives a scaled current (scaled by a scale factor of the internal comparator in the current measurement circuitry  241 ) from the burden resistor in the burden circuit  306  to determine whether the trip circuit  218  should be tripped for self protection of the motor circuit protector  100 . In this example, fault conditions falling within this region of the trip curve are referred to herein as falling within region C of the trip curve. 
   As shown in  FIGS. 2 and 3 , a trip module  265  is coupled between the trip circuit  218  and the voltage regulation module  260 . Trip signals from the instantaneous trip module  262 , the self protection trip module  264 , and the over temperature trip module  266  are received by the trip module  265 . 
   Embedded software  230  is provided for switching a trip unit, such as the motor circuit protector  100 , when detecting a failure mode in the trip unit. The software  230  implements switch detection algorithms that include failure mode detection. The algorithm  230  can be used on any trip unit system that accesses calibrated trip pick-up data, including the motor circuit protector  100 . As described in more detail in connection with  FIGS. 4A and 4B , the software translates user-adjustable trip unit settings to pick-up levels by accessing stored calibrated trip data in a data table. Specifically, the translation technique includes data compression of trip point data, diagnostic checksums, switch to trip point memory mapping, and extension of data settings to elevated temperatures. Normalized templates including normalized trip point data are used as a starting point for calibrating the embedded software. 
   Aspects of the present invention enable a fail-safe operation mode where user adjustments (such as adjustments of the full load ampere dial  114  and/or the instantaneous trip point dial  116 ) can revert to predetermined protective levels. An electronic circuit for a potentiometer is configured to present a percentage of a microcontroller&#39;s analog/digital (“A/D”) full scale to an A/D input pin, where one channel is used for each user adjustment position. 
   The user adjustment circuit  224  can be used as a switch for detecting an open contact fault, a short-to-ground fault, and/or a short to a supplied or reference voltage. As described in more detail below in reference to  FIGS. 5A-11B , the potentiometer is coupled with an adjustment button, which is generally a mechanical button, that includes switch-like stop and detent features for translating mechanical orientation angles to a potentiometer mechanical orientation. The user adjustment circuit  224  can be adjusted by rotating a dial similar to the full load ampere dial  114  and/or the instantaneous trip point dial  116 . 
   Aspects of the present invention provide numerous improvements and benefits. In an example, the potentiometer&#39;s vulnerability to electrostatic discharge (“ESD”) is decreased by increasing an over-surface distance of the adjustment button. The adjustment button interacts with a cover to increase the likelihood that the adjustment button will easily rotate only to a designed switch position, not to an unintended in-between position. The adjustment button interacts with the cover to have increased consistent feel to a user by incorporating, for example, three detent pressure arms (or spring elements) located symmetrically around the user adjustment button 120 degrees apart. 
   In another example, low cost components can be utilized (while achieving improved over-all system performance), eliminating need for switch calibration, and providing the ability to use quantitative techniques to verify switch performance in a production test process. Trip unit products can be easily and securely updated, independent of embedded software product design. For example, trip point changes in relation to switch settings can be made without changing product software code as long as data points are within a maximum/minimum range. 
   Referring to switch calibration and switch performance, a statistical distribution of data corresponding to switch settings can be used to determine position thresholds. The position thresholds and device performance are monitored for each trip unit. Additionally, automated process techniques can be used during product development to quantitatively monitor user adjustment performance. For example, mechanical torque, angular orientation, and microprocessor data have correlated profiles that can be quantitatively adapted for monitoring user-adjustment performance. This quantitative approach is an improvement over an approach that requires manual inspection of mechanical user adjustment. 
   The automated process technique involves a functional tester with two motors that can rotate the switches  114 ,  116  to any position. The motors are coupled to motor drivers that detect the amount of current needed to drive each switch  114 ,  116  to different positions. A torque can be derived directly from this current, and the rotation (in degrees) can be derived from the torque or from optical decoders in the motors that detect the amount of rotation a motor shaft has turned. The functional tester is coupled to communicate the switch rotation angle to the microcontroller  226 . The automated process technique automatically rotates the switches  114 ,  116  to various positions, measures the corresponding torque required to put the switches into the various positions, calculates the angle of rotation (i.e., the distance traveled by the motor) from the torque or from the optical decoders, and communicates, via the microcontroller  226 , an A/D count that represents the voltage level from a potentiometer  510 . 
     FIGS. 4A and 4B  illustrate an electrical schematic of a user-adjustment button and a plurality of electro-mechanical orientations (i.e., “P 1 ”-“P 9 ”), respectively. Thus, P 1  corresponds to a first position of the user-adjustment button, P 2  corresponds to a second position, and so on. Switch position ranges, P 1  Range through P 9  Range, correspond to respective ranges of mechanical orientation positions of the user-adjustment button. For example, if the user-adjustment button has a mechanical orientation position anywhere within P 1  Range, then its position is P 1 . An important aspect of this implementation is that there is a lack of continuity between switch position ranges. Each position range is continuous with respect to its neighboring position range(s). This avoids having any “deadman” zones wherein the button position cannot be ascertained. A lower limit error range and an upper limit error range define the lower and upper limits, respectively, beyond which invalid positions are found. The electromechanical orientations are generally mechanical switch orientations of a user-adjustment button that are translated to corresponding analog signal levels by way of a resistive potentiometer. The button and the user adjustment circuit are described in more detail below in reference to  FIGS. 5A-11B . 
   The user adjustment circuit is mechanically aligned with the user-adjustment button so that button position “P 5 ”  403  is nominally at 50% resistance. An analog/digital (“A/D”) reference voltage (“Vdd”) is presented to a switch circuit, and each analog voltage converted by the A/D converter into corresponding digital values can be expressed as a percentage of the reference voltage (i.e., “% Vdd”). 
   The mechanical orientation of the switch relative to a resistive element of the potentiometer sets a signal presented to a microcontroller for measurement. According to an implementation of the present invention, the mechanical design of the switch is illustrated as a nine-position switch, with a “Detent” feature in-between positions and “Stop” features at the switch extremes (i.e., “P 1 ” and “P 9 ”). Table 1 shows some of the electromechanical parameters considered in the software design. 
   
     
       
         
             
           
             
               TABLE 1 
             
           
          
             
                 
             
             
               User Adjustment Switch Electro-Mechanical Orientation 
             
          
         
         
             
             
             
             
             
             
             
          
             
               Description 
               Parameter 
               Units 
               Conditions 
               Max 
               Nominal 
               Min 
             
             
                 
             
             
               Number of Switch 
               Pi 
               [dec] 
                 
                9 
               — 
               1 
             
             
               Positions 
             
             
               Switch Angular 
               SW_REF_POS 
               [Position] 
                 
               — 
               P5 
               — 
             
             
               Reference Position 
             
             
               Switch Reference 
                 
               [degree] 
               Orientation 
               220 
               110 
               0 
             
             
               Angles 
                 
                 
               CCW, Center, 
             
             
                 
                 
                 
               CW 
             
             
               Nominal Switch 
               SW_STEP 
               [degree] 
                 
               — 
                24 
               — 
             
             
               Step 
             
             
                 
             
          
         
       
     
   
   The switch positions can be determined from experimental test results of voltages at the microcontroller&#39;s inputs for each of the desired mechanical positions, i.e., A/D inputs also referred to as “FLA” (full load amperes) and “Im” (instantaneous trip point current) inputs. The movement of the switch within a particular position is considered and expressed as a maximum voltage allowable value and a minimum voltage allowable value. These voltage values may be expressed as a percentage of the switch reference voltage or as the equivalent respective 8 bit A/D threshold values, such as, e.g., the threshold values (also referred to as “thresholds”) illustrated below in Table 2. 
   
     
       
         
             
           
             
               TABLE 2 
             
           
          
             
                 
             
             
               Switch Thresholds Expressed As 8 Bit Decimal A/D Thresholds 
             
          
         
         
             
             
             
             
             
             
             
             
          
             
                 
                 
               Software 
                 
                 
                 
                 
                 
             
             
                 
                 
               Logical 
                 
               Mechanical 
             
             
               Description 
               Parameter 
               Position 
               Units 
               Orientation 
               Max 
               Nominal 
               Min 
             
             
                 
             
          
         
         
             
             
             
             
             
             
             
             
          
             
               Switch Low Error 
               P0, FLA, Im 
               Position 1 
               [dec] 
               — 
               3 
               — 
               0 
             
             
               Switch Position 1 
               P1, FLA, Im 
               Position 1 
               [dec] 
               Position 1 
               25 
               15 
               4 
             
             
               Switch Position 2 
               P2, FLA, Im 
               Position 2 
               [dec] 
               Position 2 
               51 
               39 
               26 
             
             
               Switch Position 3 
               P3, FLA, Im 
               Position 3 
               [dec] 
               Position 3 
               79 
               66 
               52 
             
             
               Switch Position 4 
               P4, FLA, Im 
               Position 4 
               [dec] 
               Position 4 
               110 
               95 
               80 
             
             
               Switch Position 5 
               P5, FLA, Im 
               Position 5 
               [dec] 
               Position 5 
               143 
               127 
               111 
             
             
               Switch Position 6 
               P6, FLA, Im 
               Position 6 
               [dec] 
               Position 6 
               173 
               159 
               144 
             
             
               Switch Position 7 
               P7, FLA, Im 
               Position 7 
               [dec] 
               Position 7 
               200 
               187 
               174 
             
             
               Switch Position 8 
               P8, FLA, Im 
               Position 8 
               [dec] 
               Position 8 
               226 
               214 
               201 
             
             
               Switch Position 9 
               P9, FLA, Im 
               Position 9 
               [dec] 
               Position 9 
               249 
               238 
               227 
             
             
               Switch High Error 
               P10, FLA, Im 
               Position 1 
               [dec] 
               — 
               255 
               — 
               250 
             
             
                 
             
          
         
       
     
   
   Switch error detection is accomplished by implementation of a “SW_HIGH_ERR” specification, independently, for both “FLA” and “Im” switches. Is If a switch is oriented past a stop-feature maximum limit, then a switch error will be detected and the switch logic shall revert to a specified position, such as illustrated in Table 2. For example, when the “SW_HIGH_ERR” limit is reached, both the “FLA” and the “Im” switches default to position  1  setting, independently. 
   Analogously, trip points stored in the EEPROM  270  (there are 81 in a specific aspect, which represent high temperature settings) are associated with 27 FLA and Im position combinations. A diagnostic routine periodically adds up all the trip point data values and compares the summed values against a checksum. If the checksum does not match the summed values, a Diagnostics Trip will occur, eventually causing the MCP  100  to trip. Alternately, instead of causing a Diagnostics Trip, the diagnostic routine can revert to predetermined trip point settings. In an aspect, the predetermined settings are set to a low pickup level. In this manner, the integrity of trip points and trip data stored in the EEPROM  270  can be verified. When the verification fails, either tripping can occur, or the trip curve settings can be automatically reverted to predetermined low pickup settings. 
   On start-up, switch positions should be determined before attempting instantaneous (“INST”) trip detection. Optionally, it is permissible to read an adjacent switch position at the minimum/maximum extremes of the mechanical adjustments. However, the software  230  should read the correct switch positions at the nominal (or center) mechanical switch adjustment markings. Labels identifying the adjustment markings should be aligned to mechanical specifications. 
   A user adjusts the switch positions, either from an “Energized” or “De-energized” state. The software design considers one or more of the electrical and software parameters shown below in Table 3. While the application is running, the switch settings are updated at the “Switch Change Perception” rate. A minimum “Switch Change Perception” rate may be specified to spread over time a temperature compensation calculation. 
   
     
       
         
             
           
             
               TABLE 3 
             
           
          
             
                 
             
             
               User Adjustment Switch Electrical Parameters 
             
          
         
         
             
             
             
             
             
             
             
          
             
               Description 
               Parameter 
               Units 
               Conditions 
               Max 
               Nominal 
               Min 
             
             
                 
             
             
               Switch Change 
               SW_UPDATE_TIME 
               [mS] 
                 
               — 
               150 
               — 
             
             
               Perception 
             
             
               Switch &amp; A/D 
               Vdd or FSv 
               [Volts] 
                 
               — 
                5 
               — 
             
             
               Reference Voltage 
             
             
               Switch A/D Resolution 
                 
               [bits] 
                 
               — 
                8 
               — 
             
             
                 
             
          
         
       
     
   
   FSv corresponds to the full-scale voltage of the A/D converter to which the FLA and Im inputs  244 ,  246  are coupled. For example, FSv may correspond to 5 volts (nominal). The A/D converter may be part of the measurement circuit  241  shown in  FIG. 2 . Note, for clarity, the measurement circuit  241  is shown coupled to inputs  232 ,  238 , and  240 . However, it is understood that the measurement circuit may also be coupled to inputs  244 ,  246 . Alternately, the inputs  244 ,  246  may be presented to another AID converter, either in the microcontroller  226  or external to the microcontroller  226 . 
   Switch position settings may determine product trip curve settings. These settings are realized by implementing a switch to an EEPROM  270  trip point lookup algorithm. The same translation algorithm can be implemented in a plurality of circuit breakers. Each switch setting permutation may correspond to a specified pair of “A” and “B/C” trip points as per breaker trip settings specifications. 
   The “A” and “B/C” trip points may be implemented as 16 bit words in 8 bit EEPROM memory  270 . The formatting of “A” and “B” trip data can be identical and 10 bit left justified. The “C” trip points are packed within the “B/C” word and 5 bit right justified. This trip data organization is convenient for implementing the switch translation algorithm, specified by the equations listed below in Table 4. 
   
     
       
         
             
           
             
               TABLE 4 
             
           
          
             
                 
             
             
               Equations for Trip Points “A” and “B/C” 
             
          
         
         
             
             
             
             
          
             
               Description 
               Parameter 
               Units 
               Equation/{Notes} 
             
             
                 
             
             
               Lookup 
               “B/C” 
               [16 bit word] 
               B/C:H = (SW1 − 1) * 18 + (SW2 − 1) * 2 + 54 
             
             
               Thresholds B/C 
                 
               Where: 
               B/C:L = (SW1 − 1) * 18 + (SW2 − 1) * 2 + 55 
             
             
                 
                 
               [B/C] = [B/C:H] + [B/C:L] 
             
             
               Lookup 
               “A” 
               [16 bit word] 
               if (SW1 &lt; 4) 
             
             
               Thresholds A 
                 
               Where:[A] = [A:H] + [A:L] 
               A:H = (SW1 − 1) * 18 + (SW2 − 1) * 2 
             
             
                 
                 
                 
               A:L = (SW1 − 1) * 18 + (SW2 − 1) * 2 + 1 
             
             
                 
                 
                 
               Else (A = B) 
             
             
                 
             
          
         
       
     
   
   Note that in Table 4, the convention “[x:H]” is the high byte of word x, while “[x:L]” is the low byte of word x. Also, the “SW1” and “SW2” variables correspond respectively to the “FLA” and “Im” switch positions,  1  through  9 . 
   As stated above, the trip curve profiles are stored in the EEPROM memory  270 . The various combinations of “FLA”  114  and “Im”  116  adjustments will cause the control algorithm  230  to point to specific pickup values stored in EEPROM memory  270 . The EEPROM values will represent the actual A/D pickup levels for the corresponding settings. 
   In an implementation, there are twenty-seven independent trip regions “A,” for each of the breakers, specifically for the first three “Im” switch  116  positions. For all remaining “Im” switch  116  positions, trip region “A” equals “B” and region “C” exists. Table 5.13.1 shows the storage requirements for trip curve implementation in the EEPROM  270 . 
   
     
       
         
             
             
             
             
           
             
                 
             
             
               Trip Region 
               Size 
               EEPROM Words [16 bit] 
               EEPROM Bytes [8 bit] 
             
             
                 
             
           
          
             
                 
             
          
         
         
             
             
             
             
          
             
               “A” 
               10 bits 
               27 
               54 
             
             
               “B” 
               10 bits 
               81 
               162 
             
             
               “C” 
                5 bits 
               81 
               162 
             
             
                 
             
          
         
       
     
   
   The software trip curve settings are dependent on the combination of “FLA” and “Im” user adjustment switches  114 ,  116 . For example, in an implementation, there are nine different FLA settings, in addition to nine “Im” settings for each of the “FLA” settings. This is equivalent to eighty-one different trip curve profiles for the circuit breaker  100 . Each of the eighty-one different settings correspond to a different trip profile. 
   The following exemplary table lists for each breaker size, the FLA settings corresponding to each of the switch positions  1 - 9  of the FLA dial  114 . For example, the circuit breaker  100  may have a current rating of 30 A rms, 50 A rms, etc. For each current rating, there are different FLA settings as set forth in the table below. 
   Trip Curve Adjustment “FLA” 
   
     
       
         
             
             
           
             
                 
             
             
                 
               Requirement 
             
             
                 
               Switch Positions 1 to 9 
             
             
               Breaker Size [Arms] 
               FLA Settings, “Full Load Amps,” units [Arms] 
             
             
                 
             
           
          
             
                 
             
          
         
         
             
             
          
             
               30 
               1.5, 3, 6, 8, 11, 14, 17, 20, 25 
             
             
               50 
               14, 17, 21, 24, 27, 29, 32, 36, 42 
             
             
               100 
               30, 35, 41, 46, 51, 56, 63, 71, 80 
             
             
               150 
               58, 71, 79, 86, 91, 97, 110, 119, 130 
             
             
               250 
               114, 137, 145, 155, 163, 172, 181, 210, 217 
             
             
                 
             
          
         
       
     
   
   Likewise, for each “Im” (instantaneous trip point current), there is defined a set of auto setting multipliers and manual settings corresponding to FLA multiples. The following table lists examples of such settings. 
   Trip Curve Adjustment “Im” 
   
     
       
         
             
             
           
             
                 
             
             
                 
               Requirement 
             
             
                 
               Switch Positions 1 to 9 
             
             
               Breaker Size [Arms] 
               Manual settings 6× through 13× are FLA multiples 
             
             
                 
             
           
          
             
                 
             
          
         
         
             
             
          
             
               30 
               Auto1, Auto2, 6×, 8×, 9×, 10×, 11×, 12×, 13× 
             
             
               50 
               Auto1, Auto2, 6×, 8×, 9×, 10×, 11×, 12×, 13× 
             
             
               100 
               Auto1, Auto2, 6×, 8×, 9×, 10×, 11×, 12×, 13× 
             
             
               150 
               Auto1, Auto2, 6×, 8×, 9×, 10×, 11×, 12×, 13× 
             
             
               250 
               Auto1, Auto2, 6×, 8×, 9×, 10×, 11×, 12×, 13× 
             
             
                 
             
          
         
       
     
   
   For each FLA-Im combination, there are stored in the EEPROM  270  for each trip curve A, B, C, the peak rms primary current Ip, the peak primary current Ip, and the peak secondary current Is. 
     FIG. 4C  is a flowchart illustrating the coupling of a mechanical button to a user adjustment circuit for setting an operating trip curve in a circuit breaker. The mechanical button is operatively coupled to the potentiometer ( 410 ). For example, the mechanical button can be operatively coupled to the user adjustment circuit as described below in reference to  FIGS. 5A-10 . Accordingly, adjustment of the mechanical button results in adjustment of the user adjustment circuit. 
   The mechanical button is adjusted to a first position ( 412 ). The mechanical adjustment causes a first signal to be received from the user adjustment circuit ( 414 ). The first signal is indicative of a trip curve. The first signal is associated with one of a plurality of trip curves ( 416 ) and a first trip curve is produced in response to the association between the first signal and the plurality of trip curves ( 418 ). An operating trip curve is set to be the first trip curve ( 420 ). 
     FIGS. 5A and 5B  illustrate a trip unit assembly  500  that generally includes one or more copper components to carry electrical current, a set of current transformers (one per phase) to measure the electrical current, and a circuit board to process information. The trip unit assembly  500  is an alternative embodiment of the motor circuit protector  100  and can generally include similar components and operate as described above in reference to  FIGS. 1-3 . The internal components of the trip unit assembly  500  (e.g., copper components, circuit board, etc.) are contained within a base  502  and a cover  504  of the trip unit assembly  500 . In addition, the trip unit assembly  500  includes one or more user adjustment buttons  506  for controlling electrical current trip curves of the trip unit assembly  500 . These buttons  506  may correspond to the FLA dial  114  and the instantaneous trip point dial  116  shown in  FIGS. 1-3 . 
     FIG. 6  illustrates a partial cross-sectional view of the trip unit assembly  500  at a rotational center of one of the adjustment button  506 . The trip unit assembly  500  includes a printed wire assembly  508  to which a potentiometer  510  is attached. The potentiometer  510  has a shaped pocket  511  at a top face of a potentiometer button  512  for receiving snugly the corresponding adjustment button  506 . The potentiometer button  512 , via the shaped pocket  511 , connects the adjustment button  506  and the potentiometer  510  during rotational movement of the button  506 . The cover  504  encapsulates an upper portion of the adjustment button  506 . 
     FIGS. 7A and 7B  illustrate features of the adjustment button  506 . Specifically, the adjustment button  506  includes a spring element  506   a , a rigid base  506   b , a flex member  506   c , a location nipple  506   d , a stop  506   e , a stopping surface  506   f , an insulation disc  506   g , a protrusion  506   h , and a shoulder  506   j . The adjustment button  506  can include any number of features in accordance with the claimed invention. For example, the illustrated adjustment button  506  includes three spring elements  506   a  and two stopping surfaces  506   f.    
   The spring element  506   a  includes the rigid base  506   b , the flex member  506   c , and the location nipple  506   d . The rigid base  506   b  is in direct contact with the shoulder  506   j  and connects two flex members  506   c  of respective adjacent spring elements  506   a . A gap separates the flex member  506   c  and the shoulder  506   j , and the location nipple  506   d  is located generally in a central location of the flex member  506   c.    
   The stop  506   e  is located generally over one of the rigid bases  506   b  and is in contact with the shoulder  506   j . Furthermore, the stop  506   e  includes the two stopping surfaces  506   f , which are symmetrically located at opposing ends of the stop  506   e.    
   The shoulder  506   j  is generally a cylinder centrally located on top of the insulation disc  506   g . The shoulder  506   j  is surrounded by the spring elements  506   a  and the stop  506   e . Starting on a top surface of the shoulder  506   j , an arrow-shaped blind hole  506   k  is provided for receiving a tool when rotational movement of the adjustment switch  506  is required. 
   The insulation disc  506   g  is located at the bottom of the adjustment button  506 , below the shoulder  506   j . The insulation disc  506   g  has a diameter that is greater than the diameter of the shoulder  506   j , to increase resistance to ESD and to provide protection against pollutants entering the cavity located between the insulation disc  506   g  and the printed wire assembly  508 . When a user, such as a customer, touches a top exterior surface of the cover  504 , static electricity carried by the user may try to reach internal electronics through air or over surfaces located between the adjustment button  506  and the cover  504 . The insulation disc  506   g  increases the distance that ESD needs to travel to go from a front face of the adjustment button  506  (e.g., a top surface of the adjustment button  506  in which the arrow-shaped hole  506   k  is located) to the potentiometer  510  and other components on the printed wire assembly  508 . Thus, the insulation disc  506   g  increases ESD protection by increasing through-air or over-surface distance of the adjustment button  506 . In addition, the insulation disc  506   g  protects against pollutants (such as environmental debris, dust, oil, and the like) from entering the cavity between the insulation disc  506   g  and the printed wire assembly  508 , which may interfere with the potentiometer  510 . 
   To increase ESD protection of the potentiometer  510 , a bottom surface of the insulation disc  506   g  is greater than the bottom face of the potentiometer  510 . For example, as more clearly shown in  FIG. 6 , the insulation disc  506   g  has a diameter that  10  is greater than the largest dimension of the potentiometer button  512 . Thus, the bottom surface of the insulation disc  506   g  is shaped and sized such that it exceeds the largest dimension of the potentiometer button  512  to protect the potentiometer  510  from ESD and/or pollutants. The larger size of the insulation disc  506   g  also prevents application of down force on the potentiometer button  512 , thereby protecting the potentiometer button  512  from damage. 
   The protrusion  506   h  is centrally located on a bottom surface of the insulation disc  506   g  and has a cross-shaped profile. The illustrated embodiment of the protrusion  506   h  is also referred to as an “X” style protrusion. 
     FIGS. 8A and 8B  illustrate the printed wire assembly  508  having two potentiometers  510 . Each potentiometer  510  has a rotational center with the pocket  511  on the potentiometer button  512  for receiving a respective protrusion  506   h . Specifically, the pocket  511  is an “X” style pocket for receiving the respective “X” style protrusion  506   h . The adjustment switches  506  are assembled correspondingly on the potentiometers  510 , with the “X” style protrusion  506   h  being snugly inserted into the “X” style pocket  511  of a respective potentiometer button  512 . 
     FIGS. 9A-9C  illustrate the interaction between the adjustment switch  506  and the cover  504  (viewing from inside the cover in  FIGS. 9B and 9C ) at the spring elements  506   a  level. The adjustment switch  506  has been sectioned in  FIG. 9C  to remove the insulation disc  506   g  for more clearly showing the spring elements  506   a  from below. The cover includes a hole  504   e  through which the shoulder  506   j  of the adjustment switch  506  protrudes such that the top surface of the shoulder  506   j  is generally planar with a top surface of the cover  504  (as shown in  FIG. 9A ). The hole  504   e  of the cover  504  includes a bearing surface  504   a , two stop limits  504   b , a plurality of position detents  504   c , a plurality of detent walls  504   d , a plurality of crests  504   f , and a plurality of troughs  504   g.    
   The bearing surface  504   a  defines in part the circular hole  504   e , which locates the adjustment switch  506  and allows rotational movement of the adjustment switch  506 . The shoulder  506   j  has a diameter dimensioned such that a top portion of the shoulder  506   j  can protrude through the hole  504   e.    
   The stop limits  504   b  are located below the bearing surface  504   a . Specifically, each stop limit  504   b  is a surface formed by removing material along the depth of the hole  504   e  such that a partial greater-diameter hole is formed within the hole  504   e.    
   The position detents  504   c  are located below the stop limits  504   b , along the circumference and near the bottom of the hole  504   e  (in the interior of the cover  504 ). Each detent  504   c  is defined by two detent walls  504   d  coupled by a trough  504   g . In addition, each detent  504   c  is connected to another detent  504   c  by a common crest  504   f . Specifically, the crest  504   f  is located at the intersection of two detent walls  504   d  that are not part of the same detent  504   c  and that is a point generally closest to a center axis of the hole  504   e.    
   When the adjustment switch  506  is inserted into the hole  504   e , the flex members  506   c  are generally aligned with the position detents  504   c  along an axial direction of the hole  504   e . Additionally, a center axis of the adjustment switch  506  is generally collinear with the center axis of the hole  504   e . Each of the location nipples  506   d  is located within a corresponding clearance formed by two detent walls  504   d  between two consecutive crests  504   f.    
   When the adjustment switch  506  is rotated relative to the cover  504 , the location nipples  506   d  comes into contact with the detent walls  504   d . The flex member  506   c  of the spring elements  506   a  elastically deforms towards the center axis of the adjustment switch  506  to allow the location nipple  506   d  to move over a crest  504   f  of a position detent  504   c . When the movement forces the location nipple  506   d  of each spring element  506   a  past a respective crest  504   f , the location nipple  506   d  is forced by the flex member  506   c  into a centered position between two detent walls  504   d  that are not joined by a crest  504   f . In the centered position the location nipple  506   d  is generally aligned with the trough  504   g  of a respective detent  504   c.    
   The crests  504   f  are designed such that they reduce the likelihood that a location nipple  506   d  of the adjustment switch  506  will statically stop on top of any crest  504 . For example, the angles and radius sizes of the crests are selected to provide crests that are as small as possible for achieving the current invention. In another example, the detent walls  504   d  should have an angle that allows easy centering of the location nipples  506   d . Accordingly, the design of the position detents  504   c  should reduce, or eliminate, the amount of play that the adjustment switch  506  can move relative to the hole  504   e . The feel and accuracy of the position detents  504   c  movements should take into considerations other factors, such as possible tolerance stack-ups of the potentiometer  510  relative to the printed wire assembly  508 , the “X” style protrusion  506   h  relative to the “X” style pocket  511 , etc. 
     FIG. 10  illustrates the interaction between the adjustment switch  506  and the cover  504  (viewing from inside the cover) at the stop  506   e  level, wherein the adjustment switch  506  has been sectioned to remove features located below the stop  506   e  (e.g., insulation disc  506   g , spring elements  506   a , etc.). The adjustment switch  506  can rotate in either direction (clockwise or counterclockwise) until opposing stops of the two parts make contact. Specifically, the adjustment switch  506  can rotate until either one of its stopping surfaces  506   f  makes contact with a respective stop limit  504   b  of the cover  504 . The contact between the stopping surfaces  506   f  and the stop limits  504   b  ensures that the adjustment switch  506  will not be rotated beyond a design rotation specification. The potentiometer  510  can also have internal stops, which also prevent over-rotation. 
     FIGS. 11A and 11B  illustrate an adjustment switch  1106  according to an alternative aspect of the present invention. The adjustment switch  1106  includes an insulation disc  1106   g  having a skirt  1106   i  around its bottom surface to further increase ESD protection and/or to reduce any pollution from entering a corresponding potentiometer. The skirt  1106   i  is designed to totally encircle the potentiometer. 
   While particular embodiments, aspects, and applications of the present invention have been illustrated and described, it is to be understood that the invention is not limited to the precise construction and compositions disclosed herein and that various modifications, changes, and variations may be apparent from the foregoing descriptions without departing from the spirit and scope of the invention as defined in the appended claims.