RU2577549C2 - Method of measuring parameters of sinusoidal voltage and meter therefor (versions) - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: invention relates to electric radio measurements and can be used in designing digital devices for measuring mean-square values of sinusoidal signals. Method and its versions is determining parameter of sinusoidal voltage by measuring only its instantaneous value selected strictly at certain moment, which depends on analysed voltage frequency and measured parameter. Measuring device includes analogue comparator, analog-to-digital converter, time interval former and averaging unit.

EFFECT: technical result achieved when using present group of inventions is enabling implementation of relatively simple digital devices.

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Description

The invention relates to the field of electro-radio measurements and can be used in the construction of digital meters RMS, RMS and amplitude values of sinusoidal signals.

.A known method that is widely used in modern digital meters [Metrology and electro-radio measurements in telecommunication systems / Edited by B.N. Tikhonova - M .: Hot line - Telecom, 2007, p. 160-161, fig. 7.10], according to which the studied alternating voltage of the sinusoidal shape is converted to direct, as a rule, by its half-wave rectification, after which the obtained average straightened value is converted to digital form, and the final result is presented after the digital code of the average straightened voltage is multiplied by a constant coefficient, depending on which parameter (rms or amplitude) should be measured, for example, to obtain the rms rms multiplied by

.

The disadvantages of the method are the need to perform the analog operation of converting AC voltage to DC, the accuracy of which determines the final result, as well as the need to perform arithmetic operations of multiplication by constant coefficients. Of course, the analog operation of converting AC voltage to DC can be abandoned by directly converting AC voltage to a digital code and thus implementing in an digital basis an algorithm that directly follows from the definitions of the mean-rectified and / or rms values, see for example [Pat. RU 2298194. Publ. 04/27/2007. Bull. No. 12]. However, this approach requires even more arithmetic operations, for example, to obtain the mean square value, you will need to perform the operations of squaring, summing, division and extraction of the square root.

As a prototype, a method for measuring sinusoidal voltage parameters was selected, according to which, to determine the amplitude value, the time interval between two half-wave points having equal values is measured, and then the amplitude or root mean square value is calculated from the known functional relationship between the measured time interval and the required parameter [Pat. RU 2229138. Publ. 05/20/2004. Bull. No. 14]. The method allows to obtain information about the values of the investigated voltage by measuring only in the time domain, thus excluding the operation of the amplitude-digital voltage conversion. At the same time, its drawback limiting the application is the need to perform a relatively complex arithmetic operation to calculate the value of a trigonometric function that relates the measured time interval to the estimated voltage. In addition, the sensitivity of the method depends on the choice of the level at which the time interval between the same points is measured, which in practice, at a fixed level, limits the real measurement range.

The structure of the prototype device that implements the known method includes two analog comparators, a synchronizer, a time interval meter and a functional converter. The first inputs of the analog comparators are combined and make up the input of the device, the second input of the first analog comparator is a threshold level input, the second input of the second analog comparator is connected to the zero potential bus, the output of the first analog comparator is connected to the synchronizer input, the output of which is connected to the control input of the time interval meter, the information input of which is connected to the output of the second analog comparator, the outputs of the time interval meter are connected to the inputs of the functional Converter, the output of which is the output of the device [Pat. RU 2229138. Publ. 05/20/2004. Bull. No. 14]. The disadvantages of the device are due to the disadvantages of the method, first of all, the need to use a functional converter, which serves to calculate the values of trigonometric functions, that is, the relative complexity of the implementation and a limited measurement range.

The technical result achieved using the present invention consists mainly in simplifying the implementation of the method and expanding the measurement range.

The technical result is achieved by the fact that in the method of measuring the parameters of a sinusoidal voltage having a period Τ (option 1), according to the invention, at the time of the zero voltage transition, a predetermined time interval is started, at the moment of its completion, the instantaneous voltage value is sampled, the absolute value obtained The instantaneous voltage value is an estimate of the measured parameter of the sinusoidal voltage.

The technical result is also achieved by the fact that in order to implement the method according to embodiment 1, an analog-to-digital converter and a time interval shaper, an input, are introduced into the rms meter of the sinusoidal voltage, containing an analog comparator, the first input of which is the input of the meter of the rms value of the sinusoidal voltage which is connected to the output of an analog comparator, the second input of which is connected by a bus of zero potential, the output is formed For time intervals, it is connected to the clock input of the analog-to-digital converter, the information input of which is connected to the input of the rms value of the sinusoidal voltage, the output of which is the output of the analog-to-digital converter.

The technical result is also achieved by the fact that in the method for measuring the parameters of a sinusoidal voltage having a period Τ (option 2), according to the invention, at the time of the zero voltage transition, a predetermined time interval is started, at the moment of its completion, the instantaneous voltage value is selected, the specified procedure repeat n times for n periods with storing the obtained absolute values of the instantaneous voltage values, to obtain an estimate of the measured parameter of the sinusoidal voltage I average n absolute instantaneous values.

The technical result is also achieved by the fact that in order to implement the method according to embodiment 2, an analog-to-digital converter, a time interval shaper, and a block are introduced into the rms meter of the sinusoidal voltage, containing an analog comparator, the first input of which is the input of the meter of the rms value of the sinusoidal voltage averaging, the input of which is connected to the output of the analog-to-digital converter, the second input of the analog comparator is connected to a zero potential time slots meter output connected to the clock input of the analog-digital converter, an information input of which is connected to the input of measuring the rms value of the sinusoidal voltage, the output of which is the output of the averaging unit.

The technical result is also achieved by the fact that in the method for measuring the parameters of the sinusoidal voltage (option 3), according to the invention, the period Τ of the sinusoidal voltage is determined, then at the time of the zero voltage transition, the countdown of the predetermined time interval associated with the period T is started, at the time of its completion sampling the instantaneous voltage value, the obtained absolute value of the instantaneous voltage value is an estimate of the measured parameter of the sinusoidal voltage.

The technical result is also achieved by the fact that in the method for measuring the parameters of the sinusoidal voltage (option 4), according to the invention, the period Τ of the sinusoidal voltage is determined, then at the time of the zero voltage transition, the countdown of the predetermined time interval associated with the period T is started, at the time of its completion sampling of the instantaneous voltage value, this procedure is repeated n times for η periods with storing the obtained absolute values of the instantaneous voltage values, for Nia evaluation sinusoidal voltage measured parameter n averaged absolute values of instantaneous.

The invention is illustrated graphic material. In FIG. 1 is a timing chart explaining a measurement principle. In FIG. 2 presents a generalized functional diagram of the meter. In FIG. 3 shows a functional diagram of one of the possible embodiments of a meter operating with a constant frequency voltage, including a functional diagram of a time interval shaper, and in FIG. 4 is a functional diagram of a voltage meter of arbitrary frequency, including a functional diagram of a shaper of time intervals, designed to work with signals of arbitrary frequency. In FIG. Figure 5 shows timing diagrams explaining the principle of operation of a voltage meter of arbitrary frequency.

Timing diagrams (Fig. 1) contain an input a (t) sinusoidal signal with a constant period Τ and a varying amplitude A, time intervals u (t) of duration T / 8 and T / 4, as well as short sampling pulses C at the output of the time interval shaper .

The functional diagram of FIG. 2 contains an analog comparator 1, analog-to-digital converter (ADC) 2, a shaper 3 of time intervals and an averaging unit 4, the output of which is the output of the meter, the input a (t) of which is the positive (non-inverting) input of the comparator 1, negative (inverting) input which is connected to the bus of zero potential, the output of the comparator 1 is connected to the input of the shaper 3 time intervals, the output of which is connected to the clock input C of the ADC 2, the information input DI of which is combined with the positive input of the comparator one.

The functional diagram of FIG. 3 contains an analog comparator 5, ADC 6, a clock generator 7, a trigger 8, a logic element AND 9, a counter 10, a digital comparator 11, registers 12 and 13 with a high-impedance output state, the output resolution inputs OE of which are RMS measurement mode selection inputs and MAX, respectively, whose positive input is the input a (t) of the meter, the output of which is the ADC 6 output, the information input DI of which is combined with the positive input of the analog comparator 5, the output of which is connected to the clock input C of trigger 8, D-input is a logical input “1”, and the resetting input R is combined with the resetting input R of the counter 10 and connected to the output of the digital comparator 11, the first information input of which is connected to the output of the counter 10, the counting input CU of which is connected to the output of element 2I 9, the first input which is connected to the output of the clock generator, and the second input to the output of the trigger 8, the second information input of the digital comparator 11 is connected to the outputs of the registers 12, 13, and the clock input of the ADC 6 is connected to the output of the comparator 11. Elements 7-13 form the world-leader of time intervals.

The functional diagram of FIG. 4 contains an analog comparator 14, ADC 15, triggers 16, 17, logic elements 2I 18 and 3I 19, as well as a reverse counter 20, the output of the countdown transfer PD of which is connected to the clock input C of the ADC 15, the information input DI of which is combined with the analog input a comparator 14, the output of which is connected to the combined clock inputs C of the triggers 16, 17, the direct outputs of which are connected to the first inputs of the elements 2I 18 and 3I 19, respectively, the second inputs of which are the inputs of the clock pulses CLK1 and CLK2, respectively, the third input of the element 3I 19 soy is dined with the inverse output of trigger 16, the output of element 2I 18 is connected to the input of direct counting CU (summing input) of counter 20, and the output of element 3I 19 is connected to the input of counting down CD (subtracting input) of counter 20, the input of zeroing of trigger 17 is connected to the transfer output PD counter 20, and the D-input of the trigger 17 is the input of a logical unit.

Timing diagrams (Fig. 5) contain an input a (t) sinusoidal signal with period G and RMS value A _RMS , pulses S at the output of comparator 14, pulses Q1 at the output of trigger 16, counting pulses CU at the input of direct counting of the counter 20, pulses Q2 at the output of the trigger 17, packets of counting pulses CD at the input of the countdown of the reversible counter 20 and pulses C (PD) at the output of the transfer of the counter 20.

The idea of the claimed method for measuring the parameters of the sinusoidal voltage, which include the root mean square value, the average rectified and the amplitude, is that the desired value can be expressed through the phase of the sinusoid, which remains unchanged when the amplitude A changes. Therefore, the countdown from the beginning of any half-wave of the time interval, corresponding to a given phase, in fact, determines the moment the sinusoid reaches the instantaneous value a (t) equal to the desired parameter Ax. The above is illustrated by the graphs of FIG. 1, which shows time intervals of duration T / 8 and T / 4 (see FIG. 1, b and c) and their corresponding instantaneous values in FIG. 1, a. The desired value of A _x when counting the time interval with a discrete Δt and duration nΔt (n is an integer) is determined by the formula

Where

- временной сдвиг, характеризующий конкретную полуволну с номером k;

- time shift characterizing a specific half-wave with number k;

k = 0, 2, 4, 6, ... - for positive half-waves;

k = 1, 3, 5, 7, ... - for negative half-waves;

Δt _x is the error in the binding of the time interval nΔt to the beginning of the half-wave.

, следовательно указанное значение синусоидального напряжения будет соответствовать фазе φ = arcsin (2/π), что после вычислений и выражения в долях периода T дает значение, равное T/9,1 (arcsin (2/π)≈ 0,69), то есть nΔt = T/9,1For measuring the rms value of A _RMS sinusoidal voltage, the interval nΔt is set to T / 8 (see Fig. 1, b), for measuring amplitude A, it is set to T / 4 (see Fig. 1, c). When measuring the average straightened value A _{| AVG |} should be based on a relationship

therefore, the indicated value of the sinusoidal voltage will correspond to the phase φ = arcsin (2 / π), which, after calculating and expressing in fractions of the period T, gives a value equal to T / 9.1 (arcsin (2 / π) ≈ 0.69), then there is nΔt = T / 9.1

At the end of the formation of the specified time intervals, a short pulse C is generated (see Fig. 1d), the leading edge of which determines the instant of sampling the instantaneous voltage value a (t), the absolute value of which at the moment of time corresponding to the phase chosen by the above method is an estimate of the measured sinusoidal voltage parameter. The specified impulse in the circuit implementation of the method is necessary for clocking the ADC.

It is easy to understand that under real measurement conditions there are disturbances leading to errors in determining the desired phase (position of sample pulse C). In this case, assuming that the errors are distributed according to the normal law or another with a symmetrical shape, it is advisable from the point of view of reducing errors to average the results of measuring instantaneous values over a series of half-waves, and it is possible to average the measurements not only in each successive period, but also in each half-wave, thus increasing, by 2 times, the number of samples obtained.

The principle of operation of the meter shown in figure 2, is as follows. The input sinusoidal signal a (t), which is the measured alternating voltage, is fed simultaneously to the input of the analog comparator 1 and ADC 2, however, the ADC 2 is clocked strictly at time points corresponding to the achievement of a (t) of the set value, according to the measurement method under consideration, i.e. at times t _φ

Where

nΔt = T / 4 - when measuring the amplitude value;

nΔt = T / 8 - when measuring the root mean square value;

nΔt = T / 9.1 - when measuring the average straightened value. The instants of time t _{φ are} counted under the assumption that the signal a (t) is zero at the origin. If we count from the beginning of the half-wave, regardless of whether it is positive or negative, then the sampling times are determined by the end of the time interval nΔt, which is measured by the former 3 from the beginning of the half-wave action. At the end of the interval count nΔt, the shaper 3 generates a sampling pulse supplied to the clock input of the ADC 2, as a result, the latter digitizes and remembers the voltage count a (t _φ ) until the next pulse arrives at input C. The samples obtained in this way enter the averaging unit 4, which serves to obtain an estimate of the desired parameter as a result of averaging individual measurements.

Changing the duration of the generated time interval allows you to switch the meter in the measurement mode of one of the possible parameters of the sinusoidal voltage A _rms , A _{| AVG |} , A. As an example, figure 3 shows a diagram of a meter with an open shaper time intervals, which provides the ability to control these intervals. The shaper of the time intervals is started on the leading edge of the pulse at the output of the comparator 5, in connection with which the trigger 8 switches to the logical “1” state at the output, and through the logic element 2I 9, the clock (counting) pulses started to arrive at the counting input of the counter 10 generator 7. The current code at the output of the counter 10 is compared using a comparator 11 with one of the codes stored in the registers 12, 13. In the first of them is stored a code of magnitude T / 8, in the second - magnitude T / 4. Depending on which of the parameters A _RMS or A should be measured, the code T / 8 (register 12) or T / 4 (register 13) is sent to the right input of the comparator 11 according to the scheme. Switching is carried out by applying to one of the RMS or MAX inputs a permission level OE (Output Enable), which is necessary to enable the output of the selected register, leaving the output of the other in a high impedance state. At the moment of equality of codes - current and stored in one of the registers 12, 13 - a voltage surge appears at the output of comparator 11, which returns trigger 8 to its original state and resets counter 10, after which the signal level at the output of comparator And returns to the previous one. Thus, a short pulse of sample C is generated, which is fed to the input of the ADC 6.

It should be noted that the error in the formation of time intervals can be quite simply reduced by choosing the period of the counting pulses Δt, a multiple of the generated time interval. A significant contribution to the measurement error in the time domain is provided by Δt _x - instability of the moment of linking the beginning of the time interval to the moment the sinusoid passes through zero, which on the one hand is caused by the instability of the response times of the input analog comparator 5 (1), and on the other hand, by the random nature of the time relationship the moment the sinusoid passes through zero and the position of the front of the nearest counting pulse at the output of the generator 7. In the particular case, the error in determining the rms value A _x caused by I by a random error Δt _{x of the} beginning of the formation of a time interval of duration T / 8, will be determined from the expression

and relative error

A decrease in the error ΔA is achieved either by synchronizing the clock pulses of the shaper of the time intervals with the moment the sinusoid passes through zero, that is, by tightly linking the phase of the clock pulses to zero values of the voltage under study, or by reducing the period Δt of the repetition of clock pulses to a value leading to permissible errors ΔA. In the latter case, one should proceed from the fact that the maximum deviation of the beginning of the generated time interval from the required position will be determined by the discrete Δt, on the assumption that the delay of operation of the start circuits of the shaper of the time intervals is negligible compared to Δt.

To the noted regarding measurement errors, it should be added that since the method, in the form presented above, is designed to work with a sinusoidal voltage of known and constant frequency, the deviation of the frequency from the set will certainly lead to measurement errors. At the same time, when applying the method, in particular, to control the mains voltage of 50 Hz with a rms value of 220 V, the maximum frequency deviation of 0.4 Hz allowed by the existing GOST will lead to a relative error in determining the rms value of not more than 1%.

From the above descriptions of the method and functional diagrams of the meters (see Fig. 1-3), both the algorithmic and structural simplicity of the claimed solutions, the ease of obtaining an estimate of the selected parameter, and, as a result, the possibility of creating a simple, reliable and inexpensive digital meter are visible. The only arithmetic operation necessary for averaging the results is the summation of the samples in the accumulating adder, but the averaging of the results can easily be done without division operations by accumulating the results, the number of which is a multiple of 10. As for the measurement range, it is determined only by the bit depth of the applied ADC.

To apply the above approach in situations where the frequency of the sinusoidal voltage is not known, its preliminary measurement and accounting of the received information in the shaper of time intervals is required. A functional diagram of such a meter is shown in FIG. 4 (without averaging block). A feature of the meter is a time interval generator, which allows you to set time intervals depending on the frequency of the clipped sinusoidal voltage a (t) supplied to its input (see Fig. 5). Clipping is carried out in an analog comparator 14, which in this scheme is advisable to implement with a hysteresis loop, and the choice of the lower threshold of operation as close to zero as possible. This is necessary for a single operation of the comparator 14 when the sine wave approaches zero in real conditions of interference.

. При измерении среднеквадратического значения N=8, амплитудного N=4 и средневыпрямленного N=9,1. По окончании обратного счета, фактически отсчета требуемого временного интервала, на выходе переноса PD счетчика 20 появляется перепад напряжений, который обнуляет триггер 17, в связи с чем прекращается подача тактовых импульсов CLK2 на вход CD счетчика 20, на выходе переноса завершается формирование короткого импульса, отстоящего от начала полуволны на время, равное T/8 (см. фиг. 5), и служащего импульсом выборки C(PD) для АЦП 15.The operation of the shaper consists of two stages, the first measures the period T, the second measures the time interval, in the particular case equal to T / 8 (to simplify the presentation of the material, we assume that the meter in Fig. 4 serves only for measuring the rms voltage ) In the comparator 14, as shown in the time diagram (see Fig. 5), the input voltage is clipped with the allocation of pulses S (Signum), the leading edges of which determine the moments when the sinusoid passes through zero. These pulses are fed to the input of the counting trigger 16 (T-flip-flop), which operates in the division mode by two, thus emitting pulses (output Q1) with a duration equal to the period of the input pulses. The duration of the indicated pulses, period T, is measured by discretely counting the clock pulses CLK1 from the output of element 2I 18 to the input of the direct count CU of the reverse counter 20. The counting ends at the negative edge of the pulse at the direct output (Q1) of trigger 16, which (front) coincides with the moment the sinusoid passes through zero when the polarity changes from negative to positive, and the high logic level that appeared at the inverse output of trigger 16 allows the passage of clock pulses CLK2 to the CD countdown input of the reversible counter 20. In this case, the trigger 17 is in a state of high logic level at the output (output Q2), since it was translated into this state by the positive edge of the pulse S. Thus, the process of counting the required time interval T / 8 is started, the value of which is set both by the value of T and the ratio of the periods of the clock pulses CLK1 Δt ₁ and CLK2 Δt ₂ , to obtain a time interval N times smaller than the period T, the condition must be fulfilled:

. When measuring the rms value of N = 8, the amplitude of N = 4 and the average straightened N = 9.1. At the end of the countdown, in fact, the countdown of the required time interval, a voltage drop appears on the transfer output of the PD counter 20, which resets the trigger 17, and therefore the supply of CLK2 clock pulses to the input of the CD counter 20 is stopped, the formation of a short pulse is stopped at the transfer output from the beginning of the half-wave for a time equal to T / 8 (see Fig. 5), and serving as the sampling pulse C (PD) for the ADC 15.

From the description of the principle of operation of the time slot driver shown in FIG. 4, it is easy to understand that to switch the measurement modes, the ratio of the periods of N clock pulses should be changed. In particular, this can be done by using one reference clock generator, the frequency of which, depending on the measurement mode, is reduced by 8 or 4 times. In this case, the reference frequency is used as the clock frequency of the CLK2 sequence, being the frequency determining the discrete and, accordingly, the accuracy of the formation of the time interval, and the frequency of the CLK1 sequence, reduced by N times, is used to count the period of the studied sinusoidal voltage.

Claims (11)

1. The method of measuring the rms value of a sinusoidal voltage having a period T, characterized in that at the time of the transition of the zero mark voltage, the time interval equal to T / 8 is started, at the moment of its completion, the instantaneous voltage value is sampled, the absolute value of the instantaneous voltage value is obtained evaluation of the measured parameter of the sinusoidal voltage. 2. A rms sine wave voltage meter comprising an analog comparator, the first input of which is an input of a rms sine wave meter, characterized in that an analog-to-digital converter and a time interval shaper are introduced, the input of which is connected to the output of the analog comparator, the second input of which connected to the zero potential bus, the output of the time interval former is connected to the clock input of the analog-to-digital converter a generator, the information input of which is connected to the input of the rms sine voltage meter, the output of which is the output of an analog-to-digital converter. 3. The rms value of the sinusoidal voltage according to claim 2, characterized in that the time interval shaper included in its composition is a device at the output of which, upon completion of the time interval equal to T / 8, a counting pulse appears. 4. A method for measuring the rms value of a sinusoidal voltage having a period T, characterized in that at the time of the zero-voltage transition, the time interval equal to T / 8 is started, at the moment of its completion, the instantaneous voltage value is sampled, this procedure is repeated n times for n periods with storing the obtained absolute values of the instantaneous voltage values, to obtain an estimate of the measured parameter of the sinusoidal voltage average n absolute instantaneous values. 5. The method according to p. 4, characterized in that the countdown of the time interval equal to T / 8, is carried out during the action of the positive half-wave. 6. The method according to p. 4, characterized in that the countdown of the time interval equal to T / 8 is carried out during the action of the negative half-wave. 7. The method according to p. 4, characterized in that the countdown of the time interval equal to T / 8 is carried out during the action of both positive and negative half-waves. 8. A rms sine wave voltage meter comprising an analog comparator, the first input of which is an input of a rms sine wave meter, characterized in that an analog-to-digital converter, a time interval shaper, and an averaging unit, the input of which is connected to the output of the analog-digital converter, the second input of the analog comparator is connected to the zero potential bus, the output of the time interval meter is connected to ovym input of the analog-digital converter, an information input of which is connected to the input of measuring the rms value of the sinusoidal voltage, the output of which is the output of the averaging unit. 9. The measuring instrument of the rms value of the sinusoidal voltage according to claim 8, characterized in that the time interval shaper included in its structure is a device at the output of which, upon completion of the time interval equal to T / 8, a counting pulse appears. 10. The method of measuring the rms value of the sinusoidal voltage, characterized in that the period T of the sinusoidal voltage is determined, then at the time of the zero voltage transition, the time interval T / 8 begins to be counted, at the moment of its completion, the instantaneous voltage value is sampled, the absolute value of the instantaneous voltage value is obtained is an estimate of the measured parameter of the sinusoidal voltage. 11. A method of measuring the rms value of the sinusoidal voltage, characterized in that the period T of the sinusoidal voltage is determined, then at the time of the zero voltage transition, the time interval T / 8 begins to be counted, at the moment of its completion, the instantaneous voltage value is sampled, this procedure is repeated n times for n periods with storing the obtained absolute values of the instantaneous voltage values, to obtain an estimate of the measured parameter of the sinusoidal voltage average n absolute true instantaneous values.

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