US20130158920A1 - Pulse width modulated voltage measuring circuit and method - Google Patents
Pulse width modulated voltage measuring circuit and method Download PDFInfo
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- US20130158920A1 US20130158920A1 US13/588,061 US201213588061A US2013158920A1 US 20130158920 A1 US20130158920 A1 US 20130158920A1 US 201213588061 A US201213588061 A US 201213588061A US 2013158920 A1 US2013158920 A1 US 2013158920A1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R23/00—Arrangements for measuring frequencies; Arrangements for analysing frequency spectra
- G01R23/02—Arrangements for measuring frequency, e.g. pulse repetition rate; Arrangements for measuring period of current or voltage
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/165—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values
- G01R19/16566—Circuits and arrangements for comparing voltage or current with one or several thresholds and for indicating the result not covered by subgroups G01R19/16504, G01R19/16528, G01R19/16533
- G01R19/16576—Circuits and arrangements for comparing voltage or current with one or several thresholds and for indicating the result not covered by subgroups G01R19/16504, G01R19/16528, G01R19/16533 comparing DC or AC voltage with one threshold
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/003—Measuring mean values of current or voltage during a given time interval
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/02—Measuring effective values, i.e. root-mean-square values
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/04—Measuring peak values or amplitude or envelope of ac or of pulses
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/165—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values
- G01R19/16528—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values using digital techniques or performing arithmetic operations
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F17/00—Digital computing or data processing equipment or methods, specially adapted for specific functions
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
- H02H3/08—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to excess current
- H02H3/087—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to excess current for dc applications
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
- H02J7/0068—Battery or charger load switching, e.g. concurrent charging and load supply
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16H—GEARING
- F16H59/00—Control inputs to control units of change-speed-, or reversing-gearings for conveying rotary motion
- F16H59/02—Selector apparatus
- F16H59/08—Range selector apparatus
- F16H59/10—Range selector apparatus comprising levers
- F16H59/105—Range selector apparatus comprising levers consisting of electrical switches or sensors
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
- G01B7/003—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring position, not involving coordinate determination
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
- G01B7/14—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring distance or clearance between spaced objects or spaced apertures
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/12—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means
- G01D5/244—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing characteristics of pulses or pulse trains; generating pulses or pulse trains
- G01D5/245—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing characteristics of pulses or pulse trains; generating pulses or pulse trains using a variable number of pulses in a train
- G01D5/2454—Encoders incorporating incremental and absolute signals
- G01D5/2455—Encoders incorporating incremental and absolute signals with incremental and absolute tracks on the same encoder
- G01D5/2457—Incremental encoders having reference marks
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
- H02H3/02—Details
- H02H3/06—Details with automatic reconnection
Definitions
- the present invention relates generally to electronic measurement, and more particularly to voltage measuring circuits, suitable for measuring root-mean square voltages and other metrics of a time varying voltages.
- UPS universal power supplies
- alarm systems often monitor AC mains to sense power outages.
- Typical techniques require the AC voltage signal to be sampled continuously. From the sampling, the zero crossing of the assessed may be assessed and a root-mean-square (RMS) voltage value may be calculated as the square root of the arithmetic mean of the squares of the sampled values.
- RMS root-mean-square
- the peak value of the signal may be assessed, and an RMS voltage may be calculated—for example for a perfectly sinusoidal signal, the RMS voltage may be calculated as the peak voltage divided by the square root of two ( ⁇ 2).
- RMS root-mean-square
- Typical measuring circuits include a voltage divider used to sample the AC voltage signal of interesting.
- isolating the measuring circuit from the remainder of the circuit proves to be costly, and is usually accomplished using an isolation transformer, or an analog to digital converter, powered by an isolated power source.
- a voltage measuring circuit includes a rectifier to receive an alternating current (AC) voltage to be measured and to provide a rectified output; a comparator for comparing the rectified output and producing therefrom a square wave having a pulse width indicative of the rectified output exceeding a threshold; a calculation circuit for converting a measurement of the pulse width into a measurement of the voltage and optionally an opto-isolator interconnecting the comparator to the calculation circuit.
- the rectifier may provide operating power to the comparator and an input side of the opto-isolator, from the AC voltage signal being measured.
- the remainder of the measuring circuit may powered by a source isolated from the voltage to be measured.
- the method comprises: rectifying the AC voltage signal to provide a rectified output; comparing the rectified output and producing therefrom a square wave having a pulse width indicative of the rectified output exceeding a threshold; converting a measurement of the pulse width into a measurement of the magnitude of the AC voltage signal.
- FIG. 1 is a graph of a sinusoidal wave form corresponding to an input voltage
- FIG. 2 is a block diagram of a voltage measuring circuit, exemplary of an embodiment of the present invention.
- FIGS. 3A and 3B are block diagrams of possible calculation circuits used in the voltage measuring circuit of FIG. 2 ;
- FIGS. 4A , 4 B and 4 C are graphs of waveforms formed by the measuring circuit of FIG. 2 ;
- FIG. 5 is a schematic diagram of a voltage measuring circuit, exemplary of an embodiment of the present invention.
- FIG. 2 illustrates an exemplary voltage measuring circuit 10 , capable of measuring the magnitude of an alternating current (AC) voltage source 12 that provides a sinusoidal voltage V IN , as for example depicted in FIG. 1 .
- source 12 provides a voltage V IN that is sinusoidal having an amplitude V pk , at a frequency of 1/T f (where T f is the period of the sinusoid).
- voltage measuring circuit 10 includes a full wave bridge rectifier 18 that receives V IN from source 12 and provides a full-wave rectified output V RECT , as depicted in FIG. 4A .
- the output of rectifier 18 is provided to a voltage divider 20 and the output of rectifier 18 is further used to power downstream components, as detailed below.
- Voltage divider 20 includes resistor R 3 30 and resistor R 6 32 that provide fractional voltage
- V RECT to the input of a comparator 22 .
- Comparator 22 may be formed using a conventional operational amplifier 24 whose inverting input is driven by a reference source 36 , that provides a reference DC voltage V i .
- the non-inverting input of operational amplifier 24 acts as the input to comparator 22 that receives the divided voltage
- the output of amplifier 24 acts as a comparator output that drives opto-isolator 28 .
- the output of comparator 22 will be high any time V COMP
- the resulting output of comparator 22 drives opto-isolator 28 .
- the output of opto-isolator 28 will be a pulse-width modulated (PWM) square wave, of period T f , as depicted in FIG. 4C .
- PWM pulse-width modulated
- the output of opto-isolator 28 may be provided to a calculation circuit 16 that may translate the width of the PWM square wave to a signal representative of the magnitude of AC voltage source 12 , measured for example as a peak or RMS voltage, and optionally the frequency of V IN .
- a calculation circuit 16 may translate the width of the PWM square wave to a signal representative of the magnitude of AC voltage source 12 , measured for example as a peak or RMS voltage, and optionally the frequency of V IN .
- the absence of a square wave output voltage at opto-isolator 28 may be interpreted as low or no output voltage fault or condition.
- the output of operational amplifier 24 drives opto-isolator 28 through resistor 26 .
- V RMS the RMS voltage
- the input to comparator 22 may be expressed as:
- t o represents the time of intersection of V IN and V i .
- V pk may be determined:
- V p ⁇ ⁇ k K ⁇ V i ⁇ sin ⁇ ( 2 ⁇ ⁇ ⁇ 1 T f ⁇ t 0 ) ⁇ ( 2 )
- u may be interrelated to the period of V IN , T f , as:
- V p ⁇ ⁇ k K ⁇ V i ⁇ sin ⁇ ( ⁇ ⁇ u 2 ⁇ ( u + w ) ) ⁇ ( 5 )
- the RMS voltage may be calculated from V pk by observing
- the output of opto-isolator 28 may feed an input to a processing/calculation circuit 16 .
- calculation circuit 16 may take the form of a processor 42 , in the form of a controller, microprocessor, digital signal processor (DSP) or the like, under program control, as depicted in FIG. 3A .
- Processor 42 may sample the output of opto-isolator 28 to determine values of w and u.
- the processor 16 may sample the output of opto-isolator 28 to calculate w and u.
- processor 16 may calculate the magnitude of the voltage V pk as
- an average V RMS value is of interest.
- the average may be determined as the sum of RMS values during n cycles divided by n.
- the average RMS voltage may be determined as:
- Circuit 14 may perform the calculation above.
- V i may be arbitrarily chosen based on the operating voltage of amplifier 24 .
- V i is typically chosen as less than the operating voltage.
- V i may be chosen as 1.24V, which is a typical reference voltage.
- the calculation may be simplified to reduce the number of multiplications and divisions performed. This may, for example, be done by choosing a specific number of samples (n), based on the chosen values of V i and K, and adjusting K as required. That is, for any particular chosen V i , n may be chosen as an integer approximation of K/ ⁇ 2. This simplification helps when calculating the RMS averaging. If a proper n and K are chosen, the averaging operation may be reduced to a summing operation instead of summing and division. However, this is only to decreases the required computational power.
- n determines how many samples must be added together to produce an average value of the input RMS voltage
- n the number of samples, n must be an integer.
- choice of K and n may be made such that the ration of K/ ⁇ (2 ⁇ n) equals one (1) or some other integer.
- R 3 and R 6 may be chosen as
- Continuous sampling over multiple cycles may be averaged to determine the average RMS voltage.
- processing/calculation circuit 16 may further determine AC frequency, and/or a fault condition.
- processing/calculation circuit 16 may monitor the output of opto-isolator 28 for each cycle to assess a fault. For example, if the output remains in high impedance (or logic high, if biased) for half of an AC cycle (i.e. no square wave output), a fault may be sensed, and optionally signalled. Likewise the AC frequency of V IN may be sensed as
- frequ . 1 2 ⁇ ( u + w ) .
- Processor 42 may provide separate digital outputs V out , FREQU_OUT, FAULT_OUT, indicative of measured voltage, frequency or generate a fault flag.
- Rectifier 18 may further provide the operating current/voltage to comparator 22 , and opto-isolator 28 .
- circuit 10 components on the input side of opto-isolator 28 do not need to share a power supply with processing/calculation circuit 16 .
- Circuit 14 may be formed using discrete or integrated components, or possibly using one or more microcontrollers, digital signal processors (DSPs), or a combination thereof.
- DSPs digital signal processors
- FIG. 5 illustrates an example circuit 14 formed using four diodes arranged as bridge rectifier 18 .
- Voltage divider 20 is formed from resistors R 3 and R 6 .
- Comparator 22 (including a reference source) may be formed using from two resistors R 4 , R 5 and a controllable Zener diode U 2 .
- a depletion mode MOSFET Q 1 , the resistor R 1 , the capacitor C 1 and fixed value zener diode D 2 bias the comparator 22 and opto-isolator 28 .
- Opto-isolator 28 may be a standard opto-coupler such as 4N31 or 4N32 six pin packaged opto-coupler.
- Q 1 and R 1 form a constant current source that charges C 1 which supplies energy around the input voltage zero crossing, when diodes of rectifier 18 do not provide supply current.
- D 2 limits the bias voltage across the comparator, U 2 (the controllable zener diode U 2 is used as comparator).
- the resistor R 4 is used to bias U 2 and R 5 to limit the current through the LED of opto-coupler 28 .
- the circuit of FIG. 5 uses relatively few components and may be produced at a low cost. It further provides for isolation between the power supply used to provide power to controller 16 , and the voltage being measured. Moreover, the output of circuit 14 may easily feed controller 16 or another DSP or processor, using, for example a general purpose I/O (GPIO) pin.
- GPIO general purpose I/O
- processing/calculation circuit 16 may take the form of an integrator as depicted in FIG. 3B .
- the ratio u/(u+w) represents the duty cycle of the output signal of opto-isolator 28 , with a fixed frequency 1/(u+w).
- the output of opto-isolator 28 may be integrated to form a signal proportional to the AC input voltage.
- a suitable integrator may be formed using a conventional operational amplifier 38 , a capacitor 34 and a resistor 32 .
- a further resistor 31 may bias the output of opto-isolator 28 .
- the integrator may integrate the waveform of FIG. 4C over multiple cycles, and thereby present an average analog voltage signal proportional to u. Proper choice of values for capacitor 34 and resistor 32 allow amplifier 38 to output a bounded voltage proportional to V pk and V RMS
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Abstract
A voltage measuring circuit includes a rectifier to receive an alternating current (AC) voltage to be measured and to provide a rectified output; a comparator for comparing the rectified output and producing therefrom a square wave having a pulse width indicative of the rectified output exceeding a threshold; a calculation circuit for converting a measurement of the pulse width into a measurement of the voltage and optionally an opto-isolator interconnecting the comparator to the calculation circuit. The rectifier may provide operating power to the comparator and an input side of the opto-isolator, from the AC voltage signal being measured. The remainder of the measuring circuit may powered by a source isolated from the voltage to be measured.
Description
- The present application claims priority from U.S. Provisional Patent Application No. 61/577,303, filed Dec. 19, 2011 the contents of which are hereby incorporated by reference.
- The present invention relates generally to electronic measurement, and more particularly to voltage measuring circuits, suitable for measuring root-mean square voltages and other metrics of a time varying voltages.
- Many practical applications require measuring the magnitude of an AC voltage signal.
- For example, universal power supplies (UPS) often measure source voltages with great precision. Likewise alarm systems often monitor AC mains to sense power outages.
- Typical techniques require the AC voltage signal to be sampled continuously. From the sampling, the zero crossing of the assessed may be assessed and a root-mean-square (RMS) voltage value may be calculated as the square root of the arithmetic mean of the squares of the sampled values. Alternatively, for known periodic waveforms, the peak value of the signal may be assessed, and an RMS voltage may be calculated—for example for a perfectly sinusoidal signal, the RMS voltage may be calculated as the peak voltage divided by the square root of two (√2). Yet other techniques involve rectifying the AC voltage signal and filtering the resulting rectified signal as a proxy for the amplitude of the AC voltage signal.
- Typical measuring circuits include a voltage divider used to sample the AC voltage signal of interesting. However, isolating the measuring circuit from the remainder of the circuit proves to be costly, and is usually accomplished using an isolation transformer, or an analog to digital converter, powered by an isolated power source.
- Accordingly, there is a need for a new AC voltage measurement circuit that may be more inexpensively isolated, and method.
- Exemplary of an embodiment of the invention, a voltage measuring circuit includes a rectifier to receive an alternating current (AC) voltage to be measured and to provide a rectified output; a comparator for comparing the rectified output and producing therefrom a square wave having a pulse width indicative of the rectified output exceeding a threshold; a calculation circuit for converting a measurement of the pulse width into a measurement of the voltage and optionally an opto-isolator interconnecting the comparator to the calculation circuit. The rectifier may provide operating power to the comparator and an input side of the opto-isolator, from the AC voltage signal being measured. The remainder of the measuring circuit may powered by a source isolated from the voltage to be measured.
- In accordance with an aspect of the present invention, there is provided method of measuring the magnitude of an AC voltage signal. The method comprises: rectifying the AC voltage signal to provide a rectified output; comparing the rectified output and producing therefrom a square wave having a pulse width indicative of the rectified output exceeding a threshold; converting a measurement of the pulse width into a measurement of the magnitude of the AC voltage signal.
- Other aspects and features of the present invention will become apparent to those of ordinary skill in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.
- In the figures which illustrate by way of example only, embodiments of the present invention,
-
FIG. 1 is a graph of a sinusoidal wave form corresponding to an input voltage; -
FIG. 2 is a block diagram of a voltage measuring circuit, exemplary of an embodiment of the present invention; -
FIGS. 3A and 3B are block diagrams of possible calculation circuits used in the voltage measuring circuit ofFIG. 2 ; -
FIGS. 4A , 4B and 4C are graphs of waveforms formed by the measuring circuit ofFIG. 2 ; and -
FIG. 5 is a schematic diagram of a voltage measuring circuit, exemplary of an embodiment of the present invention. -
FIG. 2 illustrates an exemplaryvoltage measuring circuit 10, capable of measuring the magnitude of an alternating current (AC)voltage source 12 that provides a sinusoidal voltage VIN, as for example depicted inFIG. 1 . As illustrated inFIG. 1 ,source 12 provides a voltage VIN that is sinusoidal having an amplitude Vpk, at a frequency of 1/Tf (where Tf is the period of the sinusoid). - As illustrated in
FIG. 2 ,voltage measuring circuit 10 includes a fullwave bridge rectifier 18 that receives VIN fromsource 12 and provides a full-wave rectified output VRECT, as depicted inFIG. 4A . - The output of
rectifier 18 is provided to avoltage divider 20 and the output ofrectifier 18 is further used to power downstream components, as detailed below. -
Voltage divider 20 includesresistor R 3 30 andresistor R 6 32 that provide fractional voltage -
- VRECT to the input of a
comparator 22. -
Comparator 22 may be formed using a conventionaloperational amplifier 24 whose inverting input is driven by a reference source 36, that provides a reference DC voltage Vi. The non-inverting input ofoperational amplifier 24 acts as the input tocomparator 22 that receives the divided voltage -
- as depicted in
FIG. 4B - As will be appreciated, the output of
amplifier 24 acts as a comparator output that drives opto-isolator 28. The output ofcomparator 22 will be high any time VCOMP -
- equals or exceeds V1, and low otherwise, as depicted in
FIG. 4B . The resulting output ofcomparator 22 drives opto-isolator 28. The output of opto-isolator 28 will be a pulse-width modulated (PWM) square wave, of period Tf, as depicted inFIG. 4C . The width u of the square wave (i.e. the time the output ofcomparator 22 is high) is dependent on the frequency and amplitude of VIN. - As such, the output of opto-
isolator 28 may be provided to acalculation circuit 16 that may translate the width of the PWM square wave to a signal representative of the magnitude ofAC voltage source 12, measured for example as a peak or RMS voltage, and optionally the frequency of VIN. As well, the absence of a square wave output voltage at opto-isolator 28 may be interpreted as low or no output voltage fault or condition. - Specifically, the output of
operational amplifier 24 drives opto-isolator 28 throughresistor 26. Now, by measuring the width u of the square wave, it is possible to determine Vpk and/or the RMS voltage (VRMS) ofsource 12, and/or the frequency of VIN. - In particular, as illustrated in
FIG. 4B , the input tocomparator 22 may be expressed as: -
- where to represents the time of intersection of VIN and Vi.
- From this, Vpk may be determined:
-
- Expressed in terms of u, the width of the PWM square wave (i.e. the time it is on) depicted in
FIG. 4C , -
- Noting that u may be interrelated to the period of VIN, Tf, as:
-
T f=2·(u+w) (4) - where w represents the time the PWM square wave is off.
- Substituting equation (4) into equation (3), yields:
-
- For a sine wave, the RMS voltage may be calculated from Vpk by observing,
-
- The output of opto-
isolator 28 may feed an input to a processing/calculation circuit 16. In one embodiment,calculation circuit 16 may take the form of aprocessor 42, in the form of a controller, microprocessor, digital signal processor (DSP) or the like, under program control, as depicted inFIG. 3A . -
Processor 42 may sample the output of opto-isolator 28 to determine values of w and u. For example, theprocessor 16 may sample the output of opto-isolator 28 to calculate w and u. For example,processor 16 may calculate the magnitude of the voltage Vpk as -
- or the RMS voltage VRMS as
-
- Typically, an average VRMS value is of interest. The average may be determined as the sum of RMS values during n cycles divided by n.
- That is, the average RMS voltage may be determined as:
-
-
Circuit 14 may perform the calculation above. For convenience, Vi may be arbitrarily chosen based on the operating voltage ofamplifier 24. Vi is typically chosen as less than the operating voltage. In the depicted embodiment, Vi may be chosen as 1.24V, which is a typical reference voltage. Now, K will need to be chosen based on the minimum voltage to be measured. That is, KVi should be chosen to be less than or equal to the minimum voltage to be measured. If, for example, the lowest VRMS to be measured VRMS— min=57 V (corresponding to a lowest contemplated VRMS of 57 V), K may be chosen as VRMS— min/Vi=57/1.24=45.9677. - Additionally or alternatively, the calculation may be simplified to reduce the number of multiplications and divisions performed. This may, for example, be done by choosing a specific number of samples (n), based on the chosen values of Vi and K, and adjusting K as required. That is, for any particular chosen Vi, n may be chosen as an integer approximation of K/√2. This simplification helps when calculating the RMS averaging. If a proper n and K are chosen, the averaging operation may be reduced to a summing operation instead of summing and division. However, this is only to decreases the required computational power.
- That is, for the example minimum detection of VRMS of 57V, and Vi chosen as 1.24 V, and K=45.9677, a choice of n around 32.5 would reduce multiplication/division. This choice of n and K eliminates the need to multiply and divide. The number of samples (represented by the integer value of “n”) determines how many samples must be added together to produce an average value of the input RMS voltage
- However, as n represents the number of samples, n must be an integer. Thus n may be chosen as n=32 (related to averaging of 32 samples). K may in turn be adjusted/chosen to be K=√{square root over (2)}·32=45.2548. Put another way, to simplify division and multiplication, choice of K and n may be made such that the ration of K/√(2·n) equals one (1) or some other integer.
- In turn, R3 and R6 may be chosen as
-
- using standard available resistor values.
- Continuous sampling over multiple cycles may be averaged to determine the average RMS voltage.
- Conveniently, processing/
calculation circuit 16 may further determine AC frequency, and/or a fault condition. For example, processing/calculation circuit 16 may monitor the output of opto-isolator 28 for each cycle to assess a fault. For example, if the output remains in high impedance (or logic high, if biased) for half of an AC cycle (i.e. no square wave output), a fault may be sensed, and optionally signalled. Likewise the AC frequency of VIN may be sensed as -
-
Processor 42 may provide separate digital outputs Vout, FREQU_OUT, FAULT_OUT, indicative of measured voltage, frequency or generate a fault flag. - Rectifier 18 (
FIG. 2 ) may further provide the operating current/voltage tocomparator 22, and opto-isolator 28. As such, in the depictedembodiment circuit 10 components on the input side of opto-isolator 28 do not need to share a power supply with processing/calculation circuit 16. -
Circuit 14 may be formed using discrete or integrated components, or possibly using one or more microcontrollers, digital signal processors (DSPs), or a combination thereof. -
FIG. 5 illustrates anexample circuit 14 formed using four diodes arranged asbridge rectifier 18.Voltage divider 20 is formed from resistors R3 and R6. Comparator 22 (including a reference source) may be formed using from two resistors R4, R5 and a controllable Zener diode U2. A depletion mode MOSFET Q1, the resistor R1, the capacitor C1 and fixed value zener diode D2, bias thecomparator 22 and opto-isolator 28. Opto-isolator 28 may be a standard opto-coupler such as 4N31 or 4N32 six pin packaged opto-coupler. Q1 and R1 form a constant current source that charges C1 which supplies energy around the input voltage zero crossing, when diodes ofrectifier 18 do not provide supply current. D2 limits the bias voltage across the comparator, U2 (the controllable zener diode U2 is used as comparator). The resistor R4 is used to bias U2 and R5 to limit the current through the LED of opto-coupler 28. - Conveniently, the circuit of
FIG. 5 uses relatively few components and may be produced at a low cost. It further provides for isolation between the power supply used to provide power tocontroller 16, and the voltage being measured. Moreover, the output ofcircuit 14 may easily feedcontroller 16 or another DSP or processor, using, for example a general purpose I/O (GPIO) pin. - In an alternative embodiment, processing/
calculation circuit 16 may take the form of an integrator as depicted inFIG. 3B . In particular, the ratio u/(u+w) represents the duty cycle of the output signal of opto-isolator 28, with a fixed frequency 1/(u+w). As such, the output of opto-isolator 28 may be integrated to form a signal proportional to the AC input voltage. A suitable integrator may be formed using a conventionaloperational amplifier 38, acapacitor 34 and aresistor 32. Afurther resistor 31 may bias the output of opto-isolator 28. The integrator may integrate the waveform ofFIG. 4C over multiple cycles, and thereby present an average analog voltage signal proportional to u. Proper choice of values forcapacitor 34 andresistor 32 allowamplifier 38 to output a bounded voltage proportional to Vpk and VRMS - Of course, the above described embodiments are intended to be illustrative only and in no way limiting. The described embodiments of carrying out the invention are susceptible to many modifications of form, arrangement of parts, details and order of operation. The invention, rather, is intended to encompass all such modification within its scope, as defined by the claims.
Claims (19)
1. A voltage measuring circuit, comprising:
a rectifier to receive an alternating current (AC) voltage to be measured and to provide a rectified output;
a comparator for comparing said rectified output and producing therefrom a square wave having a pulse width indicative of said rectified output exceeding a threshold;
a calculation circuit for converting a measurement of said pulse width into a measurement of said voltage.
2. The circuit of claim 1 , further comprising an opto-isolator interconnecting said comparator to said calculation circuit.
3. The circuit of claim 1 , wherein said calculation circuit comprises an integrator.
4. The circuit of claim 1 , wherein said calculation circuit comprises a processor for sampling said square wave to determine at least one of said pulse width, and frequency of said square wave.
5. The circuit of claim 4 , wherein said processor is operable to calculate a frequency of said AC voltage from at least one of said pulse width and said frequency of said square wave.
6. The circuit of claim 4 , wherein u is the time said square wave is high, and w is the time said square wave is low in a period, and wherein said processor calculates said frequency as
7. The circuit of claim 4 , wherein said threshold equals K·Vi and wherein u is the time said square wave is high, and w is the time said square wave is low in a period, and wherein said processor calculates said measurement of said voltage as
8. The circuit of claim 4 , wherein said threshold equals KVi and wherein u is the time said square wave is high, and w is the time said square wave is low in a period, and wherein said processor calculates said measurement of said voltage as
9. The circuit of claim 4 , wherein said threshold equals KVi and wherein u[i] is the time said square wave is low, and w[i] is the time said square wave is high in a period, and wherein said processor calculates said measurement of said voltage as
10. The circuit of claim 9 , wherein K and n are chosen so that the ratio K/√2·n) approximates an integer.
11. The circuit of claim 1 , wherein said processor signals a fault when no square wave is output by said comparator.
12. The circuit of claim 2 , wherein said rectifier provides operating power to said comparator and an input side of said opto-isolator, from said AC voltage being measured.
13. A method of measuring the magnitude of an AC voltage signal, said method comprising:
rectifying said AC voltage signal to provide a rectified output;
comparing said rectified output and producing therefrom a square wave having a pulse width indicative of said rectified output exceeding a threshold;
converting a measurement of said pulse width into a measurement of said magnitude of said AC voltage signal.
14. The method of claim 13 , wherein said converting comprises integrating said square wave.
15. The method of claim 13 , wherein said converting comprises sampling said square wave to determine a time that said square wave is on and a time that said square wave is off.
16. The method of claim 15 , wherein said threshold equals K·Vi and wherein u is the time said square wave is high, and w is the time said square wave is low in a period, and wherein said measurement said voltage is calculated as
17. The method of claim 16 , wherein said threshold equals K·Vi and wherein u is the time said square wave is high, and w is the time said square wave is low in a period, and wherein said voltage is calculated as
18. The method of claim 15 , wherein said threshold equals K·Vi and wherein u[i] is the time said square wave is low, and w[i] is the time said square wave is high in a period of said AC voltage, and wherein said measurement of said voltage is calculated over n periods as
19. The method of claim 18 , wherein K and n are chosen so that K/(√2·n) approximates an integer.
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SE1251405A SE1251405A1 (en) | 2011-12-19 | 2012-12-11 | Pulse width modulated voltage measuring circuit and method |
CO12227012A CO6690120A1 (en) | 2011-12-19 | 2012-12-14 | Circuit and method for measuring pulse width modulated voltage |
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US13/588,061 Abandoned US20130158920A1 (en) | 2011-12-19 | 2012-08-17 | Pulse width modulated voltage measuring circuit and method |
US13/625,999 Active 2033-08-08 US9110107B2 (en) | 2011-12-19 | 2012-09-25 | Battery test circuit with energy recovery |
US13/630,986 Active 2032-12-03 US9488683B2 (en) | 2011-12-19 | 2012-09-28 | Digital circuit and method for measuring AC voltage values |
US13/648,242 Active 2033-05-15 US9134354B2 (en) | 2011-12-19 | 2012-10-09 | System and method for ground fault detection and fault type evaluation |
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US13/472,003 Abandoned US20130154834A1 (en) | 2011-12-19 | 2012-05-15 | Cabinet with tamper detection system and method |
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US13/648,242 Active 2033-05-15 US9134354B2 (en) | 2011-12-19 | 2012-10-09 | System and method for ground fault detection and fault type evaluation |
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US20020163820A1 (en) * | 2001-05-07 | 2002-11-07 | Norihito Nakamura | Power converter apparatus using power device |
US7813885B2 (en) * | 2006-01-20 | 2010-10-12 | Carrier Corporation | Method and apparatus for measurement of AC voltages in an HVAC system |
US20080301476A1 (en) * | 2006-02-27 | 2008-12-04 | Fujitsu Limited | Power supply and method of controlling same |
US20120209547A1 (en) * | 2009-10-23 | 2012-08-16 | Alexander Katsoulis | Method and appliance for the detection of current discontinuity in switched electrical point of an alternating network |
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US20110227632A1 (en) * | 2008-11-24 | 2011-09-22 | Lotto Christian | Charge pulse detecting circuit |
US8760147B2 (en) * | 2008-11-24 | 2014-06-24 | Csem Centre Suisse D'electronique Et De Microtechnique Sa—Recherche Et Developpement | Charge pulse detecting circuit |
US20150219711A1 (en) * | 2014-02-03 | 2015-08-06 | Denso Wave Incorporated | Apparatus for determining deterioration of photocoupler |
US10365319B2 (en) * | 2014-02-03 | 2019-07-30 | Denso Wave Incorporated | Apparatus for determining deterioration of photocoupler |
CN107931783A (en) * | 2017-11-24 | 2018-04-20 | 上海沪工焊接集团股份有限公司 | Rectangular wave amplitude modulation current potential sorting circuit and method |
CN115407118A (en) * | 2022-09-03 | 2022-11-29 | 迈思普电子股份有限公司 | AC zero-crossing detection circuit for isolated output square wave |
CN117478140A (en) * | 2023-12-26 | 2024-01-30 | 四川莱福德科技有限公司 | High-precision full-voltage alternating current-direct current sampling circuit and method for LED power supply |
Also Published As
Publication number | Publication date |
---|---|
CA2792785A1 (en) | 2013-06-19 |
US20130154597A1 (en) | 2013-06-20 |
US20130154660A1 (en) | 2013-06-20 |
US9134354B2 (en) | 2015-09-15 |
CO6690120A1 (en) | 2013-06-17 |
US9488683B2 (en) | 2016-11-08 |
SE1251405A1 (en) | 2013-06-20 |
US9046555B2 (en) | 2015-06-02 |
US20130158924A1 (en) | 2013-06-20 |
US20130154834A1 (en) | 2013-06-20 |
US20130154620A1 (en) | 2013-06-20 |
US9360507B2 (en) | 2016-06-07 |
US20130154654A1 (en) | 2013-06-20 |
US9110107B2 (en) | 2015-08-18 |
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