RU2046360C1 - Device for measuring phase shift between two signals - Google Patents

Abstract

FIELD: measuring devices. SUBSTANCE: device has memory unit, first and second amplitude detectors, pulse generator, first and second adders, trigonometric conversion unit, first and second input buses, output bus and corresponding connections. EFFECT: increased functional capabilities. 2 cl, 4 dwg

Description

The invention relates to measuring equipment, in particular to devices for measuring the phase shift of two harmonic signals, and can be used in phase meters of the infra-low frequency range, when calibrating the measuring channels. The device is required to ensure high accuracy of measuring the phase difference F _o lying in the first quadrant (O <F _o <π / 2) for signals that allow amplitudes to change in a wide dynamic range in the presence of constant components in the signals.

 A simple device for determining the phase shift [1] containing a multiplier of these studied signals and a device that emits a constant component obtained from the multiplication of signals is known. The voltage value of this constant component is proportional to the absolute value of the phase shift.

 The device is characterized by insignificant accuracy of determination, especially in the infra-low-frequency region, because of the need to isolate the constant component with high accuracy obtained from the multiplication of signals, the error increases significantly if there is a constant component, at least in one of the signals.

 More sophisticated devices can improve accuracy. So, in [2], a device for measuring the phase shift between two voltages was considered, containing two key detectors and a common auxiliary sine heterodyne generator with a frequency close to that of a factor many times the frequency of the measured oscillations, as well as sinus to spike pulses converters, low-pass filters with associated links.

 Instead of the required value of the phase difference, the device measures other values of the phase difference, and also measures the frequency ratio, therefore the accuracy of such a device is low, especially if there is a constant component in one or both signals.

 In [3], a device was proposed for measuring the phase shift of two sinusoidal signals, comprising a modulator, a carrier frequency generator, a low-pass filter, a registrar, a demodulator, a multiplier device, which has an advantage over [2] but it is low in accuracy, since it uses a lot of intermediate actions modulation, demodulation, multiplication. The measurement accuracy decreases significantly with a decrease in the amplitude of the studied signals and in the presence of a constant component in the studied signals.

signU₂₁[arccosU₂₂/

Как видно из этого выражения, устройство содержит блоки деления, функциональные преобразователи, содержащие сумматоры, квадраторы, блоки извлечения квадратного корня, тригонометрические преобразователи, сумматоры с блоками управления знаком (управляемыми усилителями).The closest technical solution to the claimed one for a larger number of similar technical features is a device [4] containing filtering devices that separate sinusoidal signals from a constant component, phase-shifting units that shift both signals by an angle π / 2 in the advance direction, and an analog storage unit with devices sample-storage, which measures and remembers four instantaneous signals at the same time (two after the filter and two after the phase-shifting units), and the phase difference is determined using managed registration unit according to the formula F _o signU ₁₁ [arccosU ₁₂ /

signU ₂₁ [arccosU ₂₂ /

As can be seen from this expression, the device contains division blocks, functional converters containing adders, quadrants, square root extraction blocks, trigonometric converters, adders with sign control units (controlled by amplifiers).

As a result, the error in the measurement of the phase shift will be large especially in the region of infra-low frequencies due to the presence of four component errors from the measurements of four instantaneous values. With a decrease in the values of the studied signals, the error increases due to the value of the residual constant component at the output of each of the filters and phase-shifting units. These constant components can be taken into account in each of the four measuring channels, however, there will be a very cumbersome circuit for correcting the values of the constant components even for measuring F _o in one quadrant.

 The aim of the invention is to improve the accuracy of measurement in the presence of dc signals.

 The purpose of the device for measuring the phase shift of two signals, containing a sample-storage unit, the information input of which is connected to the first input of the device, a trigonometric converter and two adders, is achieved by the fact that it additionally contains a pulse shaper and two amplitude detectors, the inputs of which are connected to the first the input of the device, the outputs of the first and second amplitude detectors are connected to the first and second inputs of the first adder, respectively, the first output of which is connected to the first input of the trigo a measuring transducer, the second input of which is connected to the output of the second adder, the first and second inputs of which are connected to the second output of the first adder and the output of the sample-storage unit, respectively, the input of the pulse former is connected to the second input of the device, and the output to the control input of the sample-storage unit , the output of the trigonometric transducer is the output of the device; the first adder contains a summing unit and a subtraction unit, the corresponding inputs of which are paired together and connected to the first and second inputs of the first adder, respectively, the outputs of the summing unit and the subtraction unit are connected to the first and second outputs of the first adder, respectively.

When dividing two sinusoidal (filtered from the constant component) signals x (t), y (t) of the same frequency, the signal-to-frequency f (t) x (t) / y (t) is a function of time:
f (t) [Asin (ω t + F ₁ )] / [Bsin (ω t + F ₂ )] (1) where Bsin (ω t + F ₂ ) ≠ 0; F ₁ and F _{2 the} initial phases of the two studied signals; A and B are the amplitudes of the studied vibrations.

 The function f (t) will be a periodic discontinuous function and in appearance will resemble the functions of tangents or cotangents.

In the case of F ₁ > F ₂ , F ₂ 0, expression (1) can be written as follows for K> 0, 0 ≅ F _o ≅ π / 2:
f (t) K [cosF _o + sinF _o ctg (2 π t / T)] (2) where T 2 π / ω; F _o the phase difference between the studied vibrations.

In the middle of the half-period of the divider signal under consideration, the second terms vanish, therefore, for (2) we obtain an expression for determining the phase shift values F _{o of the} two signals filtered from the constant component, replacing f (t) and K by the ratio of signals at time instants t ₁ and t ₂ :
F _o arccos [U _xph (t ₁ ) / U _xph (t ₂ )] (3) where U _hf is the signal filtered from the constant component;
t ₁ moment of time when the voltage reference signal Uy (t) reaches its extremum;
t _{2 the} point in time when the measuring voltage signal Ux (t) reaches its extremum.

 Figure 1 presents the functional diagram of the device.

 A device for measuring the phase shift of two signals contains a sampling-storage unit 1, first and second amplitude detectors 2 and 3, a pulse shaper 4, a first adder 5, a second adder 6, a trigonometric transducer 7.

 The blocks in the device are interconnected as follows. The first input of the device is connected to the inputs of the first and second amplitude detectors 2 and 3, as well as to the first input of the sampling unit 1, storage. The second input of the device is connected to the input of the pulse shaper 4, the output of which is connected to the second (control) input of the sampling-storage unit 1. The outputs of the first amplitude detector 2 and the second amplitude detector 3 are connected, respectively, to the first and second inputs of the first adder 5. The first and second outputs of the first adder 5 are connected to the first input of the trigonometric transducer 7 and the first input of the second adder 6, respectively. The output of the sample-storage unit 1 is connected to the second input of the second adder 6, the output of which is connected to the second input of the trigonometric transducer 7.

 In FIG. 2 is a structural diagram of a first adder 5. The first adder 5 comprises a summing unit 8 and a subtraction unit 9. The corresponding inputs of the summing unit 8 and the subtraction unit 9 are paired together and connected to the first and second inputs of the first adder 5, respectively. The outputs of the summing unit 8 and the subtracting unit 9 are connected to the first and second outputs of the first adder 5, respectively.

The device operates as follows. One of the studied harmonic signals (see Fig. 3a), for example, U _x (t), is a measuring one, and the signal U _y (t) is a reference. Then the input signal Ux (t) can be represented as U _x (t) A _o sin (ω t + F _x ) + U _c , where A _{o is the} amplitude; ω circular frequency; F _x initial phase; U _{c is the} constant component of the input voltage U _x (t). This voltage U _x (t) from the first input of the device is supplied simultaneously to the inputs of the first amplitude detector 2, the second amplitude detector 3 and the first input of the sample-storage unit 1. The input voltage reference signal U _y (t) B _o sin (ω t + F _y ) + U _o from the second input of the device is supplied to the input of the pulse shaper 4. The desired phase shift F _o is equal to F _o F _x F _y .

The first amplitude detector 2 extracts the amplitude of the positive half-wave, and the second amplitude detector 3 extracts the amplitude of the negative half-wave of the measuring voltage signal Ux (t). Therefore, at the output of the first amplitude detector 2 receive voltage U ₂ A _o + + U _c ; and at the output of the second amplitude detector 3, a voltage U ₃ A _o U _{c is} obtained, where U _{c is the} constant component of the signal Ux (t). Voltages U ₂ and U _3, respectively, are applied to the first and second inputs of the first adder 5, namely, to the corresponding inputs of the summing and subtracting units 8, having transmission factors K ₂ K ₃ 0.5. When summing and subtracting the voltages U ₂ and U ₃ at the output of the first adder 5, respectively, the voltages U _{5 - 1} (U ₂ + U ₃ ) / 2U _x (t ₂ ) -U _c = A _o and U _{5 - 2} ( U ₂ U ₃ ) / 2 U _c .

The voltage U _{5 - 2} U _{c is} supplied to the first input of the second adder 6, the second input of which receives the voltage U1 from the output of block 1 of the sample-storage.

Shaper 4 pulses generates logical signals of voltage U ₄ , which are control signals for block 1 sample-storage. They arrive at the second (control) input of the block 1 sample-storage. The formation of these output pulses U _{4 is} illustrated by the diagram figb. the logical unit of voltage U ₄ is the “storage” signal and appears at time t ₁ when the voltage U _y (t) of the divider signal reaches its extreme value, therefore its constant component U _o does not affect the formation of the “Storage” signal. Logical "0" is the signal "sample" for block 1 sample-storage. On figv-g shows how the output pulses are formed in the time interval corresponding to the "Storage" mode, starting from time t ₁ and tending to time t ₃ .

Thus, the corresponding inputs of the trigonometric transducer 7 in the period of time "Storage", corresponding to the time interval from t ₁ to t ₃ , the voltage U _{5 - 1} from the first output of the first adder 5 U _{5 - 1} U _x (t ₂ ) U _c equal to the amplitude A _{o of the} signal U _x (t), and the voltage U ₆ from the output of the second adder 6, equal to U ₆ U _x (t ₁ ) U _c at time t ₁ , when the reference voltage U _y (t) reaches its extremum (figa).

Converter 7 performs trigonometric function arkkosinusnogo converter outputs a U ₇ a voltage proportional to the value arccos [U ₆ / U _{5 - 1]} where voltage U ₆ and U _{5- 1} are the voltages on the first and second inputs, respectively. Therefore, the voltage U ₇ will be equal to U ₇ arccos {[U _x (t ₁ ) -U _c ] / [U _x (t ₂ ) -U _c ] arccos {U _хф (t ₁ ) / U _хф (t ₂ )]
The trigonometric transducer 7 can be constructed in different ways, by first performing the division operation, for example, using a series-connected division unit and a trigonometric converter, the output of which receives a DC voltage proportional to the voltage at the output of the division unit. Or using a trigonometric pulse converter with a reference generator, pulses are obtained at the output of such a converter, the duration of which is proportional to the quotient of the division of voltage signals U ₆ and U _{5 - 1} .

In the second case, the amplitude of the signals of the reference generator is set equal to the voltage of the amplitude A _{o of the} signal U _x (t), this voltage is supplied to one input of the comparison unit of the trigonometric transducer 7, the threshold voltage U _x (t ₁ ) -U _{c is} supplied to the second input, as a result at the output of the trigonometric converter 7, a sequence of voltage pulses U _{7 is formed} , the duration of which is proportional to the value of arccos {[U _x (t ₁ ) -U _c ] / [U _x (t ₂ ) -U _c ]
The device scheme will not change if the arcsin value is used to determine the phase shift {[U _x (t ₃ ) -U _c ] / U _x (t ₂ ) -U _c ]
If it is necessary to determine the sign and extend the interval of measured phase shifts, a unit for determining the phase ratio and a controlled adder should be added to the device.

A device for measuring the phases of two signals is built using standard elements. Sampling-storage unit 1 is constructed, as in [5], peak detectors similar to [5] can be used as amplitude detectors 2 and 3; Pulse generator 4 consists of a high-pass filter and a sign comparator connected in series, as presented in [5] Adders 5 and 6 can be performed similarly to that given in [5] As a trigonometric transducer 7, for example, you can use the arccosine transducer, as in [6]
The advantage of the proposed device is the preservation of high accuracy of measurements at infralow frequencies in the presence of constant components in the signals under conditions when the signal amplitudes vary in a large dynamic range.

 An analysis of the error of the links and blocks used in the device shows that the total error is about 0.1%, which is a higher indicator compared to the errors of modern digital devices for measuring phase shifts. The advantage of the proposed device is also the ability to use it to produce small-sized, economical, but precision measuring equipment.

Claims (2)

 1. DEVICE FOR MEASURING PHASE SHIFT OF TWO SIGNALS, containing a sampling-storage unit, the information input of which is connected to the first input of the device, a trigonometric converter, first and second adders, characterized in that a pulse shaper, first and second amplitude detectors, inputs are introduced into it which are connected to the first input of the device, the outputs to the first and second inputs of the first adder, respectively, the first output of which is connected to the first input of the trigonometric converter, the second input is it is connected to the output of the second adder, the first and second inputs of which are connected to the second output of the first adder and the output of the sample-storage unit, respectively, the input of the pulse shaper is connected to the second input of the device, and the output to the control input of the sample-storage unit, the output of the trigonometric converter is an output devices.  2. The device according to claim 1, characterized in that the first adder comprises a summing unit and a subtraction unit, the corresponding inputs of which are paired together and connected to the first and second inputs of the first adder, respectively, the outputs of the summing unit and the subtraction unit are connected to the first and second the outputs of the first adder, respectively.

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