Abstract:
A power source monitor and method to monitor various operating line conditions of an electrical power outlet comprising measuring line voltage and frequency, analyzing wiring conditions, displaying the line conditions and generating an alarm when any of the line conditions are not within a corresponding predetermined range.

Description:
CROSS REFERENCE APPLICATION 
   This is a non-provisional patent application of provisional patent application Ser. No. 60/520,177 filed Nov. 14, 2003. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   A power source monitor and method to monitor operating line conditions of an electrical power outlet. 
   2. Description of the Prior Art 
   Various types of metering equipment are available to measure power line sources. The classic multimeter comprising two probes with selectable functions and ranges is cumbersome and awkward to use. The probes are placed into high voltage power receptacles, moved from hole to hole and require knowledge of systematic measurement techniques to analyze power source connections. Other testing devices simply plug into the receptacle to read the voltage and still other devices simply to test the wiring. Popular plug-in analog voltmeters are inexpensive but lack accuracy. They are average reading only for use only with sine wave sources. The small plug-in wire diagnostics testers are effective only for analyzing wiring combinations only. These products require that the user have both types used in sequence or to use two outlets. Most do not have back lighting, limiting use to days only. Some newer meters are multifunction with voltage, wiring diagnostics and sometimes frequency. They use LED displays that are difficult to read in direct sunlight and use average voltage measurement for sine wave sources. Meters require RMS or Root Mean Square technology to measure non-sine wave sources accurately. Such meters measure, not monitor. These meters lack audible alarms to indicate fault conditions, requiring periodic reading. 
   The original Digital Line Monitor Model 662 test device provided rectified average voltage measuring shown on an LED display along with wire diagnostics and surge protection. When introduced, Graphic Line Monitor Model 8040 included a color-coded bar graph display, wire diagnostics and surge protection. 
   Most meters on the market use rectified average voltage measurement and do not work on modified sine or square wave sources such as solid state generators, inverters and Uninterruptible Power Supplies (UPS) with useful accurately. The RMS voltage measurement technique is the only method for accurately measuring power sources. The RMS measurement value of a voltage source refers to power delivering capability or effective value. The RMS value is equal to the value of a DC source, which would deliver the same power if it were, replaced a time-varying AC source. For example if an rectified average measuring meter is used to measure a modified sine wave source at full duty cycle it will display a 29% error in its voltage reading. The cost of the RMS measuring equipment has been traditionally much more costly than average measuring devices, therefore only usually available in expensive digital multi-meters. 
   U.S. Pat. No. 5,144,232 discloses an example of testing devices typical of such instruments used to monitor various line conditions. 
   SUMMARY OF THE INVENTION 
   The present invention relates to a power source monitor for testing a standard 120 volt 15 amp outlet. The power source monitor may be temporarily plugged into an outlet or socket or may be attached or mounted on the outlet cover. The LCD display with back lighting allows the power source monitor to be used indoors and outdoors. This display technology provides a clear and readable display that can be seen in direct sunlight and at night. 
   The power source monitor uses a RMS voltage measurement technique. The RMS value of a source is determined by, first squaring the magnitude of the waveform at each instant. This makes the value of the magnitude a positive even when the original waveform has negative values. Then the average or mean value of the squared magnitudes is determined. Finally, the square root of this average is taken to get the result. The power source monitor further synchronizes the RMS measurement over a number of alternating current cycles to resolve errors due to the phase of the sampling. While the synchronized RMS measurement function is performed the power source frequency is measured. The synchronization qualification provides qualified edges for the alternating current zero crossings, that reduces interference that normally cause false frequency measurements. The zero crossing edges are qualified by repeated sampling and correlating the source voltage sequence to a reference voltage sequence. 
   The power source monitor will display the line voltage in RMS volts and then the line frequency. The LCD display will show an “F” in front of the number to denote frequency. The two readings are displayed alternately. The display modes can be changed by pressing the MODE button on the front panel of the power source monitor. The three modes VOLT/FREQ alt           VOLTAGE         FREQUENCY         back to VOLT/FREQ alt, cycle through as the “MODE” button or control is pressed.
   When the power source monitor detects a fault condition, an audible alert is generated and a fault indication is displayed. The wiring faults are Ground Fault (GF) and Polarity Fault (PF). The voltage faults are Low voltage (LO) and High voltage (HI) when the measured line voltage is less than or greater than a predetermined voltage respectively. The frequency faults are Low Frequency (LO) and High Frequency (HF) when the measured line frequency is less than or more than a predetermined frequency respectively. The fault LED illuminates when one of the predetermined fault thresholds is exceeded. The fault thresholds must be activate and sustained for three seconds to engage the audible alert. Fault reset thresholds must be obtained to re-enable the fault alarms. When a wiring fault (GF or PF) is displayed, the MODE button may be used to sequence the display to show the current voltage or frequency by successive button actuations. 
   The surge protection or transient suppression on the input source lines, protects other devices on the same circuit by absorbing surges up to a predetermined amount with a maximum withstanding surge current of a predetermined amount. 
   The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a fuller understanding of the nature and object of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings in which: 
       FIG. 1  is a schematic block diagram of the power source monitor of the present invention. 
       FIG. 2A  is a front view of the power source monitor of the present invention. 
       FIG. 2B  is a back view of the power source monitor of the present invention. 
       FIG. 3  is a schematic circuit diagram of the power source monitor of the present invention. 
   

   Similar reference characters refer to similar parts throughout the several views of the drawings. 
   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The present invention relates to a power source monitor for use with a power source outlet to monitor measure and analyze various line condition including voltage, frequency and wire conditions at the power source outlet. The power source monitor may comprise a portable enclosure with a three-prong plug that connects to power line, neutral and ground. The power source monitor contains a digital display and diagnostic fault indicator enunciator with an audible alarm. An input mode switch is provided to select the different operation modes of the power source monitor. The power source monitor includes digital and analog circuitry that provides operational power, voltage scaling, and processing of the power line signals to generate display and alert outputs. 
   As shown in  FIG. 1 , the power source monitor generally indicated as  10  comprises a output section including an enunciator  12 , a digital display  14  and an audible alarm  18  coupled to a microcontroller  20 . An AC power source including a power line  45 , neutral line  44  and a ground line  46  supplies the operating power and source signals for the power source monitor  10 . The power line  45  is coupled with a diode  30  to feed a rectified DC signal to a power supply  50 , the rectified power level is shifted through resistors  32  and  33  and feed to an analog to digital converter  26  in the microprocessor  20 . The neutral line  44  is coupled to a metal oxide veristor  48  that protects the power source monitor  10  from power surges and coupled to the level shifting resistor  33  and the power source  50  to complete the power supply circuit. The ground line  46  is coupled to the resistor  36  to provide a pull up function in an open ground condition and to a rectifier  31  to provide a rectified signal to level shifting resistors  35  and  34 . The resistor  34  is coupled to ground; while, the junction of the level shifting resistors  35  and  34  are coupled to the microprocessor  20  to provide the signal corresponding to the state of the ground line  46  with respect to the neutral line  44 . The microprocessor  20  includes the analog to digital converter  26  to receive signals from the level shifted line  45  and the ground line  46  and an oscillator  24  controlled by a crystal  22  to provide the timing for operation of the power source monitor  10 . A switch  16  is connected to the microcontroller  20  so that the operator can control the multi-mode operation of the power source monitor  10 . 
     FIG. 2A  shows the location or disposition of the enunciator  12 , the digital display  14  and the audible alarm  18  on the front panel  39  of the power source monitor housing  40  having a mounting lug  42  formed thereto to attach the power source monitor  10  to a power outlet plate (not shown). The input mode switch  16  is also disposed on the front panel  39 .  FIG. 2B  shows the plug terminals containing the power line  45 , the neutral line  44 , and the line ground  46 . 
     FIG. 3  is a schematic diagram of the power source monitor  10  electrically connected to the power line  45 , the neutral line  44  and the ground line  46 . The power line  45  supplies power with respect to the neutral line  44  with a the metal oxide veristor  48  electrically connected between the respective lines and the power line  45  further electrically connected to the diode  30  and the resistor  36 . The rectified signal from the diode  30  supplies the operating power for the power source monitor  10  along with the signal to measure the operating line voltage and frequency. The power source is coupled through the diode  30  to resistors  51  through  54  to reduce the voltage to an operative level for the electronic circuitry. The resistor  54  is, in turn, electrically coupled to a diode  55  that is coupled to a zener diode  56  to provide a maximum input voltage coupled to a capacitor  57  to filter of the rectified source power and coupled to an IC regulator  58 . 
   A VCC  60  such as 3 volts stabilized by a capacitor  59  is coupled to IC regulator  58 . The capacitor  59  is connected to VCC  60  and neutral line  44 , the ground terminal of regulator  58 , the negative terminal of filter capacitor  57  and the zener diode  56 . The rectified signal from the diode  30  coupled through a resistor  60  feeds through resistors  61 ,  62  and  63  coupled to LEDs  64  through  69  to provide the back lighting for the LED digital display  14  and the LED  69  coupled to the neutral line  44 . The ground line  46  is connected to resistor  36  that provides a pull up open ground detection also connected to the power line  45 . The ground terminal  46  is also connected to the diode  31  and the cathode of diode  31  to provide a rectified signal to resistor  34  coupled to the resistor  35  that references the neutral line  44 . The connection between the resistors  34  and  35  provides a level shifted voltage that connects to a capacitor  39 . The ground signal  27  is fed to the microprocessor  20  and the analog to digital converter  26 . The capacitor  39  filters the ground voltage signal with reference to the neutral line  44 . Rectified signals from the diode  30  are fed to resistor  32  coupled to resistor  36  through variable adjustable resistor  37  providing an adjustable shifted line voltage signal  28  coupled to the microprocessor  20  and the analog to digital converter  26 ; The level shifted line voltage signal  28  is also fed to capacitor  38  to provide filtering and the capacitor references the neutral line  44 . The microprocessor  20  timing is supplied by the crystal or ceramic resonator timing device  22 . The microprocessor  20  performs analog to digital conversion of the shifted line signal  28  and shifted the ground signal  27 . The microprocessor  20  determines wiring diagnostics from the shifted ground signal  27  compared to predetermined operational voltage thresholds. A reading in the shifted ground signal  27  from about one third to about two thirds of the line voltage signal  28  indicates an open ground fault. Alternatively, the lower shifted ground signal threshold may comprise a substantially constant value such as about 20 volts. A reading in the shifted ground signal  27  of greater than about two thirds of the line voltage signal  28  indicates reverse polarity. In addition, the microprocessor  20  computes the RMS voltage by taking multiple instantaneous samples using the analog to digital converter and squares the rating, then take the sum of the squares, then computes the square root of the average resulting in the RMS value of the power source line voltage  45  with respect to power source neutral  44 . 
   The microprocessor  20  further computes the power source frequency by counting the number of rectified pulses on the shifted line voltage  28  using the ceramic resonator  22  as the time base. Microprocessor  20  generates display messages on display  14  and enunciator  12  to show wiring diagnostics, RMS voltage and line frequency. Microprocessor  20  power source is filtered by capacitor  21  that is connected between VCC  60  and neutral  44 . The buzzer  18  is coupled to the microprocessor  20  to generate the audible alerts in the event of fault conditions for 5 seconds or until the mode switch  16  is pressed. The liquid crystal display module  14  directly connects to the microprocessor  20  through the display the results of the measurement readings along with the fault condition messages. The resistor  29  is used as a pull-up for the reset of the microprocessor  20 . The microprocessor  20  generates visual enunciator signal coupled to resistor  17  and the LED  12  and to VCC  60 . 
   The power source monitor  10  is plugged into a standard 120 volt 15 amp type outlet. The power source monitor  10  can be mounted by attaching the unit with the center screw of the outlet cover. The viewing angle of the LCD display is optimized for viewing at a 12:00 o&#39;clock viewing position. Looking directly down at the unit mounted in a low outlet gives the best viewing contrast. The LCD display with back lighting allows the power source monitor  10  power source monitor  10  used indoors and outdoors. This display technology provides a clear and readable display that can be seen in direct sunlight and at night. 
   The operation of the power source monitor  10  will display the line voltage in RMS volts and then the line frequency in Hertz. The LCD display will show a “F” in front of the number to denote frequency. The two readings will automatically alternate back and forth. The display modes may be changed by pressing the MODE button  16  on the front panel  41  of the power source monitor  10 . The three modes VOLT/FREQ alt           VOLTAGE         FREQURNCY         back to VOLT/FREQ alt cycle through as the “MODE” button  16  is pressed or depressed.
   When the power source monitor  10  detects a fault condition an audible alert sequence will be generated for a predetermined period such as 5 seconds and shows the cause for the fault on the display  14 . The wiring faults are Ground Fault (GF) and Polarity Fault (PF). A first predetermined range for the voltage faults extend between Low voltage (LO) when the line voltage is less than a predetermined voltage such as 102 Vac or lower and High voltage (HI) when the line voltage is greater than a predetermined voltage such as 135 Vac or higher. Once the audible fault alarm  18  is activated, the power source monitor  10  generates a second predetermined voltage fault range or fault reset threshold such as 108 Vac and 128 Vac. When the voltage measured by the source monitor  10  comes within the second predetermined range, the indicator is reset and re-enabled to allow for subsequent activation upon detection of a subsequent fault condition. 
   The frequency faults are Low Frequency (LF) when the line frequency is less than a predetermined frequency such as less than 58 Hz and High Frequency (HF) when the line frequency is greater than a predetermined frequency such as over 62 Hz. The fault LED illuminates upon any fault threshold is exceeded. When a fault threshold is exceeded for a predetermined period such as three seconds the audible fault alarm is generated. Fault reset thresholds must be obtained to re-enable the fault alarms. When a wiring fault (GF or PF) is displayed, the MODE button  16  is used to sequence the display  14  to show the line voltage or line frequency by successive button actuations. 
   The surge protection (or transient suppression) on the input source lines, protects other devices on the same circuit by absorbing surges up to 300 joules with a maximum withstanding surge current of 10,000 amps. 
   It will thus been seen that objects set forth above, among those made apparent from the proceeding description are efficiently obtained since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above description are shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. 
   Now that the invention has been described,