Abstract:
An ionization system for a predefined area includes a plurality of emitter modules spaced around the area, a system controller for individually addressing and monitoring the emitter modules and communication lines for electrically connecting the plurality of emitter modules with the system controller. Each emitter module has an individual address and including at least one electrical ionizer.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of application Ser. No. 12/136,114, filed Jun. 10, 2008, entitled “LOW VOLTAGE MODULAR ROOM IONIZATION SYSTEM,” currently pending, which is a divisional of application Ser. No. 11/555,949, filed Nov. 2, 2006, entitled “LOW VOLTAGE MODULAR ROOM IONIZATION SYSTEM,” now U.S. Pat. No. 7,391,599 which is a divisional of application Ser. No. 10/626,300, filed Jul. 24, 2003 entitled “LOW VOLTAGE MODULAR ROOM IONIZATION SYSTEM,” now U.S. Pat. No. 7,161,788 which is a continuation of application Ser. No. 10/299,499, filed Nov. 19, 2002 entitled “LOW VOLTAGE MODULAR ROOM IONIZATION SYSTEM,” now U.S. Pat. No. 6,643,113, which is a continuation of application Ser. No. 10/024,861 filed Dec. 18, 2001 entitled “LOW VOLTAGE MODULAR ROOM IONIZATION SYSTEM,” now U.S. Pat. No. 6,507,473, which is a continuation of application Ser. No. 09/852,248 filed May 9, 2001 entitled “CIRCUIT FOR AUTOMATICALLY INVERTING ELECTRICAL LINES CONNECTED TO A DEVICE UPON DETECTION OF A MISWIRED CONDITION TO ALLOW FOR OPERATION OF DEVICE EVEN IF MISWIRED,” now U.S. Pat. No. 6,417,581, which is a continuation of application Ser. No. 09/287,935 filed Apr. 7, 1999 entitled “LOW VOLTAGE MODULAR ROOM IONIZATION SYSTEM,” now U.S. Pat. No. 6,252,756, which claims the benefit of U.S. Provisional Application No. 60/101,018, filed Sep. 18, 1998, entitled “LOW VOLTAGE MODULAR ROOM IONIZATION SYSTEM,” the entire contents of all of which are incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     Controlling static charge is an important issue in semiconductor manufacturing because of its significant impact on the device yields. Device defects caused by electrostatically attracted foreign matter and electrostatic discharge events contribute greatly to overall manufacturing losses. 
     Many of the processes for producing integrated circuits use non-conductive materials which generate large static charges and complimentary voltage on wafers and devices. 
     Air ionization is the most effective method of eliminating static charges on non-conductive materials and isolated conductors. Air ionizers generate large quantities of positive and negative ions in the surrounding atmosphere which serve as mobile carriers of charge in the air. As ions flow through the air, they are attracted to oppositely charged particles and surfaces. Neutralization of electrostatically charged surfaces can be rapidly achieved through the process. 
     Air ionization may be performed using electrical ionizers which generate ions in a process known as corona discharge. Electrical ionizers generate air ions through this process by intensifying an electric field around a sharp point until it overcomes the dielectric strength of the surrounding air. Negative corona occurs when electrons are flowing from the electrode into the surrounding air. Positive corona occurs as a result of the flow of electrons from the air molecules into the electrode. 
     To achieve the maximum possible reduction in static charges from an ionizer of a given output, the ionizer must produce equal amounts of positive and negative ions. That is, the output of the ionizer must be “balanced.” If the ionizer is out of balance, the isolated conductor and insulators can become charged such that the ionizer creates more problems than it solves. Ionizers may become imbalanced due to power supply drift, power supply failure of one polarity, contamination of electrodes, or degradation of electrodes. In addition, the output of an ionizer may be balanced, but the total ion output may drop below its desired level due to system component degradation. 
     Accordingly, ionization systems incorporate monitoring, automatic balancing via feedback systems, and alarms for detecting uncorrected imbalances and out-of-range outputs. Most feedback systems are entirely or primarily hardware-based. Many of these feedback systems cannot provide very fine balance control, since feedback control signals are fixed based upon hardware component values. Furthermore, the overall range of balance control of such hardware-based feedback systems may be limited based upon the hardware component values. Also, many of the hardware-based feedback systems cannot be easily modified since the individual components are dependent upon each other for proper operation. 
     A charged plate monitor is typically used to calibrate and periodically measure the actual balance of an electrical ionizer, since the actual balance in the work space may be different from the balance detected by the ionizer&#39;s sensor. 
     The charged plate monitor is also used to periodically measure static charge decay time. If the decay time is too slow or too fast, the ion output may be adjusted by increasing or decreasing the preset ion current value. This adjustment is typically performed by adjusting two trim potentiometers (one for positive ion generation and one for negative ion generation). Periodic decay time measurements are necessary because actual ion output in the work space may not necessarily correlate with the expected ion output for the ion output current value set in the ionizer. For example, the ion output current may be initially set at the factory to a value (e.g., 0.6 μA) so as to produce the desired amount of ions per unit time. If the current of a particular ionizer deviates from this value, such as a decrease from this value due to particle buildup on the emitter of the ionizer, then the ionizer high voltage power supply is adjusted to restore the initial value of ion current. 
     A room ionization system typically includes a plurality of electrical ionizers connected to a single controller.  FIG. 1  (prior art) shows a conventional room ionization system  10  which includes a plurality of ceiling-mounted emitter modules  12   1 - 12   n  (also, referred to as “pods”) connected in a daisy-chain manner by signal lines  14  to a controller  16 . Each emitter module  12  includes an electrical ionizer  18  and communications/control circuitry  20  for performing limited functions, including the following functions: 
     (1) TURN ON/OFF; 
     (2) send an alarm signal to the controller  16  through a single alarm line within the signal lines  14  if a respective emitter module  12  is detected as not functioning properly. 
     One significant problem with the conventional system of  FIG. 1  is that there is no “intelligent” communication between the controller  16  and the emitter modules  12   1 - 12   n . In one conventional scheme, the signal line  14  has four lines; power, ground, alarm and ON/OFF control. The alarm signal which is transmitted on the alarm line does not include any information regarding the identification of the malfunctioning emitter module  12 . Thus, the controller  16  does not know which emitter module  12  has malfunctioned when an alarm signal is received. Also, the alarm signal does not identify the type of problem (e.g., bad negative or positive emitter, balance off). Thus, the process of identifying which emitter module  12  sent the alarm signal and what type of problem exists is time-consuming. 
     Yet another problem with conventional room ionization systems is that there is no ability to remotely adjust parameters of the individual emitter modules  12 , such as the ion output current or balance from the controller  16 . These parameters are typically adjusted by manually varying settings via analog trim potentiometers on the individual emitter modules  12 . (The balances on some types of electrical ionizers are adjusted by pressing (+)/(−) or UP/DOWN buttons which control digital potentiometer settings.) A typical adjustment session for the conventional system  10  having ceiling mounted emitter modules  12  is as follows: 
     (1) Detect an out-of-range parameter via a charged plate monitor; 
     (2) Climb up on a ladder and adjust balance and/or ion output current potentiometer settings; 
     (3) Climb down from the ladder and remove the ladder from the measurement area. 
     (4) Read the new values on the charged plate monitor; 
     (5) Repeat steps (1)-(4), if necessary. 
     The manual adjustment process is time-consuming and intrusive. Also, the physical presence of the operator in the room interferes with the charge plate readings. 
     Referring again to  FIG. 1 , the signal lines  14  between respective emitter modules  12  consist of a plurality of wires with connectors crimped, soldered, or otherwise attached, at each end. The connectors are attached in the field (i.e., during installation) since the length of the signal line  14  may vary between emitter modules  12 . That is, the length of the signal line  14  between emitter module  12   1  and  12   2  may be different from the length of the signal line  14  between emitter module  12   3  and  12   4 . By attaching the connectors in the field, the signal lines  14  may be set to exactly the right length, thereby resulting in a cleaner installation. 
     One problem which occurs when attaching connectors in the field is that the connectors are sometimes put on backwards. The mistake may not be detected until the entire system is turned on. The installer must then determine which connector is on backwards and must fix the problem by rewiring the connector. 
     The conventional room ionization system  10  may be either a high voltage or low voltage system. In a high voltage system, a high voltage is generated at the controller  16  and is distributed via power cables to the plurality of emitter modules  12  for connection to the positive and negative emitters. In a low voltage system, a low voltage is generated at the controller  16  and is distributed to the plurality of emitter modules  12  where the voltage is stepped up to the desired high voltage for connection to the positive and negative emitters. In either system, the voltage may be AC or DC. If the voltage is DC, it may be either steady state DC or pulse DC. Each type of voltage has advantages and disadvantages. 
     One deficiency of the conventional system  10  is that all emitter modules  12  must operate in the same mode. Thus, in a low voltage DC system, all of the emitter modules  12  must use steady state ionizers or pulse ionizers. 
     Another deficiency in the conventional low voltage DC system  10  is that a linear regulator is typically used for the emitter-based low voltage power supply. Since the current passing through a linear regulator is the same as the current at its output, a large voltage drop across the linear regulator (e.g., 25 V drop caused by 30 V in/5 V out) causes the linear regulator to draw a significant amount of power, which, in turn, generates a significant amount of heat. Potential overheating of the linear regulator thus limits the input voltage, which in turn, limits the amount of emitter modules that can be connected to a single controller  16 . Also, since the power lines are not lossless, any current in the line causes a voltage drop across the line. The net effect is that when linear regulators are used in the emitter modules  12 , the distances between successive daisy-chained emitter modules  12 , and the distance between the controller  16  and the emitter modules  12  must be limited to ensure that all emitter modules  12  receive sufficient voltage to drive the module-based high voltage power supplies. 
     Accordingly, there is an unmet need for a room ionization system which allows for improved flexibility and control of, and communication with, emitter modules. There is also an unmet need for a scheme which automatically detects and corrects the miswire problem in an easier manner. There is also an unmet need for a scheme which allows individualized control of the modes of the emitter modules. The present invention fulfills these needs. 
     BRIEF SUMMARY OF THE INVENTION 
     Methods and devices are provided for balancing positive and negative ion output in an electrical ionizer having positive and negative ion emitters and positive and negative high voltage power supplies associated with the respective positive and negative ion emitters. A balance reference value is stored in a software-adjustable memory. During operation of the electrical ionizer, the balance reference value is compared to a balance measurement value. At least one of the positive and negative high voltage power supplies are automatically adjusted if the balance reference value is not equal to the balance measurement value. The adjustment is performed in a manner which causes the balance measurement value to become equal to the balance reference value. Also, during a calibration or initial setup of the electrical ionizer, the actual ion balance is measured in the work space near the electrical ionizer using a charged plate monitor. The balance reference value is adjusted if the actual balance measurement shows that the automatic ion balance scheme is not providing a true balanced condition. 
     The balance reference value may be adjusted by a remote control device or by a system controller connected to the electrical ionizer. 
     The present invention also provides an ionization system for a predefined area comprising a plurality of emitter modules spaced around the area, a system controller for monitoring and/or controlling the emitter modules, and a communication medium or electrical lines which electrically connect the plurality of emitter modules with the system controller. 
     In one embodiment of the ionization system, each emitter module has an individual address and the system controller individually addresses and controls each emitter module. The balance reference value and an ion output current reference value of each emitter module may be individually adjusted, either by the system controller or by a remote control transmitter. 
     In another embodiment of the ionization system, each emitter module is provided with a switching power supply to minimize the effects of line loss on the electrical lines. 
     In another embodiment of the ionization system, a power mode setting is provided for setting each emitter module in one of a plurality of different operating power modes. 
     The present invention also comprises a method of balancing positive and negative ion output in an electrical ionizer having positive and negative ion emitters and positive and negative high voltage power supplies associated with the respective positive and negative ion emitters. The method includes storing a balance reference value in a software-adjustable memory located in the electrical ionizer, comparing the balance reference value to a balance measurement value during operation of the electrical ionizer, and automatically adjusting at least one of the positive and negative high voltage power supplies if the balance reference value is not equal to the balance measurement value by ramping up or ramping down the at least one of the positive and negative power supplies at a first predetermined rate. The adjustment is performed in a manner which causes the balance measurement value to become equal to the balance reference value. 
     The present invention also comprises an electrical ionizer having positive and negative ion emitters and positive and negative high voltage power supplies associated with the respective positive and negative ion emitters. The electrical ionizer includes a software-adjustable memory for storing a balance reference value and a comparator for comparing the balance reference value to a balance measurement value, and an automatic balance adjustment circuit for adjusting at least one of the positive and negative high voltage power supplies if the balance reference value is not equal to the balance measurement value. The adjustment is performed in a manner which causes the balance measurement value to become equal to the balance reference value. The adjustment circuit is configured to ramp up or ramp down the at least one of the positive and negative power supplies at a first predetermined rate. 
     The present invention also comprises a method of balancing positive and negative ion output in an electrical ionizer having positive and negative ion emitters and positive and negative high voltage power supplies associated with the respective positive and negative ion emitters. The electrical ionizer includes receiver circuitry for receiving adjustments to at least one ionizer reference value. The method includes storing a balance reference value in a software-adjustable memory, comparing the balance reference value to a balance measurement value during operation of the electrical ionizer, automatically adjusting at least one of the positive and negative high voltage power supplies if the balance reference value is not equal to the balance measurement value by ramping up or ramping down the at least one of the positive and negative power supplies at a predetermined rate. The adjustment being performed in a manner which causes the balance measurement value to become equal to the balance reference value. The method also includes measuring the actual ion balance in the work space near the electrical ionizer during operation of the electrical ionizer and adjusting the balance reference value if the balance measurement value is equal to the balance reference value and the actual measured ion balance is not zero. The adjustment is performed in a manner which causes the actual measured ion balance to become equal to zero. The adjustment is performed by communicating the adjustment value to the receiver circuitry of the electrical ionizer, which, in turn, communicates the adjustment value to the software-adjustable memory. 
     The present invention also comprises an electrical ionizer having positive and negative ion emitters and positive and negative high voltage power supplies associated with the respective positive and negative ion emitters. The electrical ionizer includes receiver circuitry for receiving adjustments to at least one ionizer reference value, including a balance reference value stored in a software-adjustable memory, a comparator for comparing the balance reference value to a balance measurement value, an automatic balance adjustment circuit for adjusting at least one of the positive and negative high voltage power supplies if the balance reference value is not equal to the balance measurement value. The adjustment is performed in a manner which causes the balance measurement value to become equal to the balance reference value. The adjustment circuit is configured to ramp up or ramp down the at least one of the positive and negative power supplies at a predetermined rate. The electrical ionizer also includes means in communication with the receiver circuitry for adjusting the balance reference value. The balance reference value is adjusted if the balance measurement value is equal to the balance reference value and an actual measured ion balance measured in the work space near the electrical ionizer is not zero. The adjustment is performed in a manner which causes the actual measured ion balance to become equal to zero. 
     The present invention also comprises a method of balancing positive and negative ion output in an electrical ionizer having positive and negative ion emitters and positive and negative high voltage power supplies associated with the respective positive and negative ion emitters. The method includes storing a balance reference value in a software-adjustable memory located in the electrical ionizer and ramping up the output of at least one of the positive and negative high voltage power supplies at predetermined rate upon initiation of the operation of the electrical ionizer, thereby avoiding sudden changes in positive or negative ion output or potential overshoot of the balanced state. the method also includes comparing the balance reference value to a balance measurement value during operation of the electrical ionizer and automatically adjusting at least one of the positive and negative high voltage power supplies if the balance reference value is not equal to the balance measurement value. The adjustment is performed in a manner which causes the balance measurement value to become equal to the balance reference value. 
     The present invention also comprises an electrical ionizer having positive and negative ion emitters and positive and negative high voltage power supplies associated with the respective positive and negative ion emitters. The electrical ionizer includes a software-adjustable memory for storing a balance reference value, a comparator for comparing the balance reference value to a balance measurement value, and an automatic balance adjustment circuit for adjusting at least one of the positive and negative high voltage power supplies if the balance reference value is not equal to the balance measurement value. The adjustment is performed in a manner which causes the balance measurement value to become equal to the balance reference value. The adjustment circuit being configured to ramp up the output of at least one of the positive and negative power supplies at a predetermined rate upon initiation of the operation of the electrical ionizer, thereby avoiding sudden changes in positive or negative ion output or potential overshoot of the balanced state. 
     The present invention also comprises a method of balancing positive and negative ion output in an electrical ionizer having positive and negative ion emitters and positive and negative high voltage power supplies associated with the respective positive and negative ion emitters. The method includes automatically adjusting at least one of the positive and negative high voltage power supplies by ramping up or ramping down the at least one of the positive and negative power supplies at a predetermined rate. 
     The present invention also comprises a method of balancing positive and negative ion output in an electrical ionizer having positive and negative ion emitters and positive and negative high voltage power supplies associated with the respective positive and negative ion emitters. The method includes automatically adjusting at least one of the positive and negative high voltage power supplies by ramping up the at least one of the positive and negative power supplies at a predetermined rate upon initiation of the operation of the electrical ionizer. 
     The present invention also comprises an electrical ionizer having positive and negative ion emitters and positive and negative high voltage power supplies associated with the respective positive and negative ion emitters. The electrical ionizer includes an automatic balance adjustment circuit for adjusting at least one of the positive and negative high voltage power supplies, the adjustment circuit being configured to ramp up the output of at least one of the positive and negative power supplies at a predetermined startup rate upon initiation of the operation of the electrical ionizer, thereby avoiding sudden changes in positive or negative ion output or potential overshoot of the balanced state. 
     The present invention also comprises a method of balancing positive and negative ion output in an electrical ionizer having positive and negative ion emitters and positive and negative high voltage power supplies associated with the respective positive and negative ion emitters. The method includes automatically adjusting at least one of the positive and negative high voltage power supplies by ramping down the at least one of the positive and negative power supplies at a predetermined rate upon termination of the operation of the electrical ionizer. 
     The present invention also comprises an electrical ionizer having positive and negative ion emitters and positive and negative high voltage power supplies associated with the respective positive and negative ion emitters. The electrical ionizer includes an automatic balance adjustment circuit for adjusting at least one of the positive and negative high voltage power supplies, the adjustment circuit being configured to ramp down the output of at least one of the positive and negative power supplies at a predetermined rate upon termination of the operation of the electrical ionizer, thereby avoiding sudden changes in positive or negative ion output or potential overshoot of the balanced state. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The following detailed description of preferred embodiments of the present invention would be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the present invention, there is shown in the drawings embodiments which are presently preferred. However, the present invention is not limited to the precise arrangements and instrumentalities shown. In the drawings: 
         FIG. 1  is a prior art schematic block diagram of a conventional room ionization system; 
         FIG. 2  is a schematic block diagram of a room ionization system in accordance with the present invention; 
         FIG. 3A  is a schematic block diagram of an infrared (IR) remote control transmitter circuit for the room ionization system of  FIG. 2 ; 
         FIGS. 3B-1  and  3 B- 2 , taken together (hereafter, referred to as “FIG.  3 B”), are a detailed circuit level diagram of  FIG. 3A ; 
         FIG. 4  is a schematic block diagram of an emitter module for the room ionization system of  FIG. 2 ; 
         FIG. 5  is a circuit level diagram of a miswire protection circuit associated with  FIG. 4 ; 
         FIG. 6  is a schematic block diagram of a system controller for the room ionization system of  FIG. 2 ; 
         FIG. 7A  is a schematic block diagram of a balance control scheme for the emitter module of  FIG. 4 ; 
         FIG. 7B  is a schematic block diagram of a current control scheme for the emitter module of  FIG. 4 ; 
         FIG. 8  is a perspective view of the hardware components of the system of  FIG. 2 ; 
         FIG. 9  is a flowchart of the software associated with a microcontroller of the emitter module of  FIG. 4 ; and 
         FIG. 10  is a flowchart of the software associated with a microcontroller of the system controller of  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Certain terminology is used herein for convenience only and is not to be taken as a limitation on the present invention. In the drawings, the same reference letters are employed for designating the same elements throughout the several figures. 
       FIG. 2  is a modular room ionization system  22  in accordance with the present invention. The system  22  includes a plurality of ceiling-mounted emitter modules  24   1 - 24   n  connected in a daisy-chain manner by RS-485 communication/power lines  26  to a system controller  28 . In one embodiment of the present invention, a maximum of ten emitter modules  24  are daisy-chained to a single system controller  28 , and successive emitter modules  24  are about 7-12 feet apart from each other. Each emitter module  24  includes an electrical ionizer and communications/control circuitry, both of which are illustrated in more detail in  FIG. 4 . The system  22  also includes an infrared (IR) remote control transmitter  30  for sending commands to the emitter modules  24 . The circuitry of the transmitter  30  is shown in more detail in  FIGS. 3A and 3B . The circuitry of the system controller  28  is shown in more detail in  FIG. 6 . 
     The system  22  provides improved capabilities over conventional systems, such as shown in  FIG. 1 . Some of the improved capabilities are as follows: 
     (1) Both balance and ion output of each emitter module  24  can be individually adjusted. Each emitter module  24  may be individually addressed via the remote control transmitter  30  or through the system controller  28  to perform such adjustments. Instead of using analog-type trim potentiometers, the emitter module  24  uses a digital or electronic potentiometer or a D/A converter. The balance and ion current values are stored in a memory location in the emitter module and are adjusted via software control. The balance value (which is related to a voltage value) is stored in memory as B REF , and the ion current is stored in memory as C REF . 
     (2) The balance and ion output adjustments may be performed via remote control. Thus, individual emitter modules  24  may be adjusted while the user is standing outside of the “keep out” zone during calibration and setup, while standing close enough to read the charged plate monitor. 
     (3) The emitter modules  24  send identification information and detailed alarm condition information to the system controller  28  so that diagnosis and correction of problems occur easier and faster than in conventional systems. For example, the emitter module  24   3  may send an alarm signal to the system controller  28  stating that the negative emitter is bad, the positive emitter is bad, or that the balance is off. 
     (4) A miswire protection circuitry built into each emitter module  24  allows for the installer to flip or reverse the RS-485 communication/power lines  26 . The circuitry corrects itself if the lines are reversed, thereby eliminating any need to rewire the lines. In conventional signal lines, no communications or power delivery can occur if the lines are reversed. 
     (5) The mode of each emitter module  24  may be individually set. Thus, some emitter modules  24  may operate in a steady state DC mode, whereas other emitter modules  24  may operate in a pulse DC mode. 
     (6) A switching power supply (i.e., switching regulator) is used in the emitter modules  24  instead of a linear regulator. The switching power supply lessens the effects of line loss, thereby allowing the system controller  28  to distribute an adequate working voltage to emitter modules  24  which may be far apart from each other and/or far apart from the system controller  28 . The switching power supply is more efficient than a linear power supply because it takes off the line only the power that it needs to drive the output. Thus, there is less voltage drop across the communication/power line  26 , compared with a linear power supply. Accordingly, smaller gauge wires may be used. The switching power supply allows emitter modules  24  to be placed further away from each other, and further away from the system controller  28 , than in a conventional low voltage system. 
     Specific components of the system  22  are described below. 
       FIG. 3A  shows a schematic block diagram of the remote control transmitter  30 . The transmitter  30  includes two rotary encoding switches  32 , four pushbutton switches  34 , a 4:2 demultiplexer  36 , a serial encoder  38 , a frequency modulator  40  and an IR drive circuit  42 . The rotary encoder switches  32  are used to produce seven binary data lines that are used to “address” the individual emitter modules  24 . The four pushbutton switches  34  are used to connect power to the circuitry and create a signal that passes through the 4:2 demultiplexer  36 . 
     The 4:2 demultiplexer  36  comprises two 2 input NAND gates and one 4 input NAND gate. Unlike a conventional 4:2 demultiplexer which produces two output signals, the demultiplexer  36  produces three output signals, namely, two data lines and one enable line. The “enable” signal (which is not produced by a conventional 4:2 demultiplexer), is produced when any of the four inputs are pulled low as a result of a pushbutton being depressed. This signal is used to turn on a LED, and to enable the encoder and modulator outputs. 
     The seven binary data lines from the rotary encoder switches  32 , and the two data lines and the enable line from the demultiplexer  36 , are passed to the serial encoder  38  where a serial data stream is produced. The modulator  40  receives the enable line from the demultiplexer  36  and the serial data from the encoder  38 , and creates a modulated signal. The modulated signal is then passed to the IR diode driver for transmitting the IR information. 
       FIG. 3B  is a circuit level diagram of  FIG. 3A . 
       FIG. 4  shows a schematic block diagram of one emitter module  24 . The emitter module  24  performs at least the following three basis functions; produce and monitor ions, communicate with the system controller  28 , and receive IR data from the transmitter  30 . 
     The emitter module  24  produces ions using a closed loop topology including three input paths and two output paths. Two of the three input paths monitor the positive and negative ion current and include a current metering circuit  56  or  58 , a multi-input A/D converter  60 , and the microcontroller  44 . The third input path monitors the ion balance and includes a sensor antenna  66 , an amplifier  68 , the multi-input A/D converter  60 , and the microcontroller  44 . The two output paths control the voltage level of the high-voltage power supplies  52  or  54  and include the microcontroller  44 , a digital potentiometer (or D/A converter as a substitute therefor), an analog switch, high-voltage power supply  52  or  54 , and an output emitter  62  or  64 . The digital potentiometer and the analog switch are part of the level control  48  or  50 . 
     In operation, the microcontroller  44  holds a reference ion output current value, C REF , obtained from the system controller  28 . The microcontroller  44  then compares this value with a measured or actual value, C MEAS , read from the A/D converter  60 . The measured value is obtained by averaging the positive and negative current values. If C MEAS  is different than C REF , the microcontroller  44  instructs the digital potentiometers (or D/A&#39;s) associated with the positive and negative emitters to increase or decrease their output by the same, or approximately the same, amount. The analog switches of the positive level controls  48 ,  50  are controlled by the microcontroller  44  which turns them on constantly for steady state DC ionization, or oscillates the switches at varying rates, depending upon the mode of the emitter module. The output signals from the analog switches are then passed to the positive and negative high voltage power supplies  52 ,  54 . The high voltage power supplies  52 ,  54  take in the DC signals and produce a high voltage potential on the ionizing emitter points  62 ,  64 . As noted above, the return path for the high voltage potential is connected to the positive or negative current metering circuits  56 ,  58 . The current metering circuits  56 ,  58  amplify the voltage produced when the high voltage supplies  52 ,  54  draw a current through a resistor. The high voltage return circuits then pass this signal to the A/D converter  60  (which has four inputs for this purpose). When requested by the microcontroller  44 , the A/D converter  60  produces a serial data stream that corresponds to the voltage level produced by the high voltage return circuit. The microcontroller  44  then compares these values with the programmed values and makes adjustments to the digital potentiometers discussed above. 
     Ion balance of the emitter module  24  is performed using a sensor antenna  66 , an amplifier  68  (such as one having a gain of 34.2), a level adjuster (not shown), and the A/D converter  60 . The sensor antenna  66  is placed between the positive and negative emitters  62 ,  64 , such as equidistant therebetween. If there is an imbalance in the emitter module  24 , a charge will build up on the sensor antenna  66 . The built-up charge is amplified by the amplifier  68 . The amplified signal is level shifted to match the input range of the A/D converter  60 , and is then passed to the A/D converter  60  for use by the microcontroller  44 . 
     A communication circuit disposed between the microcontroller  44  and the system controller  28  includes a miswire protection circuit  70  and a RS-485 encoder/decoder  72 . 
     The miswire protection circuit allows the emitter module  24  to function normally even if an installer accidentally inverts (i.e., flips or reverses) the wiring connections when attaching the connectors to the communication/power line  26 . When the emitter module  24  is first powered on, the microcontroller  44  sets two switches on and reads the RS-485 line. From this initial reading, the microcontroller  44  determines if the communication/power line  26  is in an expected state. If the communication/power line  26  is in the expected state and remains in the expected state for a predetermined period of time, then the communication lines of the communication/power line  26  is not flipped and program in the microcontroller  44  proceeds to the next step. However, if the line is opposite the expected state, then switches associated with the miswire protection circuit  70  are reversed to electronically flip the communication lines of the communication/power line  26  to the correct position. Once the communication/power line  26  is corrected, then the path for the system controller  28  to communicate with the emitter module  24  is operational. A full-wave bridge is provided to automatically orient the incoming power to the proper polarity. 
       FIG. 5  is a circuit level diagram of the miswire protection circuit  70 . Reversing switches  74   1  and  74   2  electronically flip the communication line, and full-wave bridge  76  flips the power lines. In one preferred four wire ordering scheme, the two RS-485 communication lines are on the outside, and the two power lines are on the inside. 
     Referring again to  FIG. 4 , when the system controller  28  attempts to communicate with an individual emitter module  24 , the first byte sent is the “address.” At this time, the microcontroller  44  in the emitter module  24  needs to retrieve the “address” from the emitter module address circuit. The “address” of the emitter module is set at the installation by adjustment of two rotary encoder switches  90  located on the emitter module  24 . The microcontroller  44  gets the address from the rotary encoder switches  90  and a serial shift register  92 . The rotary encoder switches  90  provide seven binary data lines to the serial shift register  92 . When needed, the microcontroller  44  shifts in the switch settings serially to determine the “address” and stores this within its memory. 
     The emitter module  24  includes an IR receive circuit  94  which includes an IR receiver  96 , an IR decoder  98 , and the two rotary encoder switches  90 . When an infrared signal is received, the IR receiver  96  strips the carrier frequency off and leaves only a serial data stream which is passed to the IR decoder  98 . The IR decoder  98  receives the data and compares the first five data bits with the five most significant data bits on the rotary encoder switches  90 . If these data bits match, the IR decoder  98  produces four parallel data lines and one valid transmission signal which are input into the microcontroller  44 . 
     The emitter module  24  also includes a watchdog timer  100  to reset the microcontroller  44  if it gets lost. 
     The emitter module  24  further includes a switching power supply  102  which receives between 20-28 VDC from the system controller  28  and creates +12 VDC, +5 VDC, −5 VDC, and ground. As discussed above, a switching power supply was selected because of the need to conserve power due to possible long wire runs which cause large voltage drops. 
       FIG. 9  is a self-explanatory flowchart of the software associated with the emitter module&#39;s microcontroller  44 . 
       FIG. 6  is a schematic block diagram of the system controller  28 . The system controller  28  performs at least three basic functions; communicate with the emitter modules  24 , communicate with an external monitoring computer (not shown), and display data. The system controller  28  communicates with the emitter modules  24  using RS-485 communications  104 , and can communicate with the monitoring computer using RS-232 communications  106 . The system controller  28  includes a microcontroller  110 , which can be a microprocessor. Inputs to the microcontroller  110  include five pushbutton switches  112  and a keyswitch  114 . The pushbutton switches  112  are used to scroll through an LCD display  116  and to select and change settings. The keyswitch  114  is used to set the system into a standby, run or setup mode. 
     The system controller  28  also includes memory  118  and a watchdog timer  120  for use with the microcontroller  110 . A portion of the memory  118  is an EEPROM which stores C REF  and B REF  for the emitter modules  24 , as well as other system configuration information, when power is turned off or is disrupted. The watchdog timer  120  detects if the system controller  28  goes dead, and initiates resetting of itself. 
     To address an individual emitter module  24 , the system controller  28  further includes two rotary encoder switches  122  and a serial shift register  124  which are similar in operation to the corresponding elements of the emitter module  24 . 
     During set up of the system  22 , each emitter module  24  is set to a unique number via its rotary encoder switches  90 . Next, the system controller  28  polls the emitter modules  24   1 - 24   n  to obtain their status-alarm values. In one polling embodiment, the system controller  28  checks the emitter modules  24  to determine if they are numbered in sequence, without any gaps. Through the display  116 , the system controller  28  displays its finding and prompts the operator for approval. If a gap is detected, the operator may either renumber the emitter modules  24  and redo the polling, or signal approval of the existing numbering. Once the operator signals approval of the numbering scheme, the system controller  28  stores the emitter module numbers for subsequent operation and control. In an alternative embodiment of the invention, the system controller  28  automatically assigns numbers to the emitter modules  24 , thereby avoiding the necessity to set switches at every emitter module  24 . 
     As discussed above, the remote control transmitter  30  may send commands directly to the emitter modules  24  or may send the commands through the system controller  28 . Accordingly, the system controller  28  includes an IR receiver  126  and an IR decoder  128  for this purpose. 
     The system controller  28  also includes synchronization links, sync in  130  and sync out  132 . These links allow a plurality of system controllers  28  to be daisy-chained together in a synchronized manner so that the firing rate and phase of emitter modules  24  associated with a plurality of system controllers  28  may be synchronized with each other. Since only a finite number of emitter modules  24  can be controlled by a single system controller  28 , this feature allows many more emitter modules  24  to operate in synchronized manner. In this scheme, one system controller  28  acts as the master, and the remaining system controllers  28  act as slave controllers. 
     The system controller  28  may optionally include relay indicators  134  for running alarms in a light tower or the like. In this manner, specific alarm conditions can be visually communicated to an operator who may be monitoring a stand-alone system controller  28  or a master system controller  28  having a plurality of slave controllers. 
     The system controller  28  houses three universal input AC switching power supplies (not shown). These power supplies produce an isolated 28 VDC from any line voltage between 90 and 240 VAC and 50-60 Hz. The 28 VDC (which can vary between 20-30 VDC) is distributed to the remote modules  24  for powering the modules. Also, an onboard switching power supply  136  in the system controller  28  receives the 28 VDC from the universal input AC switching power supply, and creates +12 VDC, +5 VDC, −5 VDC, and ground. A switching power supply is preferred to preserve power. 
       FIG. 10  is a self-explanatory flowchart of the software associated with the system controller&#39;s microcontroller  110 . 
       FIG. 7A  is a schematic block diagram of a balance control circuit  138  of an emitter module  24   1 . An ion balance sensor  140  (which includes an op-amp plus an A/D converter) outputs a balance measurement, B MEAS , taken relatively close to the emitters of the emitter module  24   1 . The balance reference value  142  stored in the microcontroller  44 , B REF1 , is compared to B MEAS  in comparator  144 . If the values are equal, no adjustment is made to the positive or negative high voltage power supplies  146 . If the values are not equal, appropriate adjustments are made to the power supplies  146  until the values become equal. This process occurs continuously and automatically during operation of the emitter module  24   1 . During calibration or initial setup, balance readings are taken from a charged plate monitor to obtain an actual balance reading, B ACTUAL , in the work space near the emitter module  24   1 . If the output of the comparator shows that B REF1  equals B MEAS , and if B ACTUAL  is zero, then the emitter module  24   1  is balanced and no further action is taken. However, if the output of the comparator shows that B REF1  equals B MEAS , and if B ACTUAL  is not zero, then the emitter module  24   1  is unbalanced. Accordingly, B REF1  is adjusted up or down by using either the remote control transmitter  30  or the system controller  28  until B ACTUAL  is brought back to zero. Due to manufacturing tolerances and system degradation over time, each emitter module  24  will thus likely have a different B REF  value. 
       FIG. 7B  is a scheme similar to  FIG. 7A  which is used for the ion current, as discussed above with respect to C REF  and C MEAS . In  FIG. 7B , C MEAS  is the actual ion output current, as directly measured using the circuit elements  56 ,  58  and  60  shown in  FIG. 4 . Comparator  152  compares C REF1  (which is stored in memory  150  in the microcontroller  44 ) with C MEAS . If the values are equal, no adjustment is made to the positive or negative high voltage power supplies  146 . If the values are not equal, appropriate adjustments are made to the power supplies  146  until the values become equal. This process occurs continuously and automatically during operation of the emitter module  24   1 . During calibration or initial setup, decay time readings are taken from a charged plate monitor  148  to obtain an indication of the actual ion output current, C MEAS , in the work space near the emitter module  24   1 . If the decay time is within a desired range, then no further action is taken. However, if the decay time is too slow or too fast, C REF1  is adjusted upward or downward by the operator. The comparator  152  will then show a difference between C MEAS  and C REF1 , and appropriate adjustments are automatically made to the power supplies  146  until these values become equal in the same manner as described above. 
     As discussed above, conventional automatic balancing systems have hardware-based feedback systems, and suffer from at least the following problems: 
     (1) Such systems cannot provide very fine balance control, since feedback control signals are fixed based upon hardware component values. 
     (2) The overall range of balance control is limited based upon the hardware component values. 
     (3) Quick and inexpensive modifications are difficult to make, since the individual components are dependent upon each other for proper operation. 
     Conventional ion current control circuitry suffers from the same problems. In contrast to conventional systems, the software-based balance and ion current control circuitry of the present invention do not suffer from any of these deficiencies. 
       FIG. 8  shows a perspective view of the hardware components of the system  22  of  FIG. 2 . 
     The microcontrollers  44  and  110  allow sophisticated features to be implemented, such as the following features: 
     (1) The microprocessor monitors the comparators used for comparing B REF  and B MEAS , and C REF  and C MEAS . If the differences are both less than a predetermined value, the emitter module  24  is presumed to be making necessary small adjustments associated with normal operation. However, if one or both of the differences are greater than a predetermined value at one or more instances of time, the emitter module  24  is presumed to be in need of servicing. In this instance, an alarm is sent to the system controller  28 . 
     (2) Automatic ion generation changes and balance changes for each individual emitter module  24  may be ramped up or ramped down to avoid sudden swings or potential overshoots. For example, when using the pulse DC mode, the pulse rate (i.e., frequency) may be gradually adjusted from a first value to the desired value to achieve the desired ramp up or down effect. When using either the pulse DC mode or the steady-state DC mode, the DC amplitude may be gradually adjusted from a first value to the desired value to achieve the desired ramp up or down effect. 
     The scope of the present invention is not limited to the particular implementations set forth above. For example, the communications need not necessarily be via RS-485 or RS-232 communication/power lines. In particular, the miswire protection circuitry may be used with any type of communication/power lines that can be flipped via switches in the manner described above. 
     It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.