SU359606A1 - METHOD OF MEASURING SMALL DIFFERENCES OF TWO SIGNALS FREQUENCIES - Google Patents

Description

The invention relates to the field of electrical measuring equipment and can be used to improve the accuracy, noise immunity and simplify the process of measuring small frequency differences.

The known method of measuring small frequency differences of two signals, based on determining the increment of the phase difference of these signals, not exceeding in the measurement cycle, and changing the initial phase of one of the signals, is characterized by reduced accuracy, noise immunity and complicated measurement process.

The described method differs from the known one in that the initial phase difference is set smaller by changing the phase difference of the input signals to exceed the initial phase of the first signal, while passing the pulses of the first signal generated at the moments of its transition through the zero level in two directions the pulses of the second signal, generated at the moments of its transition through the zero level in one direction, are measured, and the difference between the total durations of two alternately formed groups of pulses of the difference f s signals, the number of pulses in which the same.

intersections of the instantaneous values of the first and second signals through a given level, and changing, if necessary, the initial phase of one of the signals at the beginning of the measuring cycle.

The duration of the next t-ro pulse formed from the measured signals

t /, f / .slnH-f P ,,),

f /, 7, Sln (u) + Au)) + cp, J,

when D «) С 1 is equal to

. 2 Ds.

, Wo-Wo1

M, i

sh "

where Ui, Uz - amplitudes of signals;

(O is the fundamental frequency of the signals; Aso is the difference between the frequencies of the signals;

t is the current time from the beginning of the measurement; Fo1 and fo2 - the initial phases of the signals;

t / i, f / 2 are the instantaneous values of the signals. The difference of the successive sums of the duration of an equal number of pulses

2 D (c. Woa - Wo1

§ (

N

j

is an estimate of the frequency difference

N-i

Ash: -

27СЛ

Pulse sequence fill factor

K. i +

3 -Ui /, -

(g 1,2,3 ... 2l)

27С

ABOUT)

due to a change in the initial phase by not reaching a single value in the measurement cycle.

The method allows to increase the accuracy, noise immunity and simplify the measurement process.

The drawing shows a block diagram of an apparatus for carrying out the described method in one of the embodiments.

The device consists of drivers 1 and 2 pulses, block 3 select the initial phases, trigger 4, inverter 5, counter 6 pulses, keys 7 and 5, the integrating amplifier 9, resistors 10 11 and capacitor 12.

Shaper 1 and 2 convert the measured signals in a sequence of pulses corresponding to the moments of the transition of signals through the zero level. Block 3 selection of the initial phase provides the output of the initial phase difference signals less. In this case, pulses are used corresponding to the moments of transition of the first signal through the zero level in two directions, and pulses corresponding to the points of transition of the second signal through the zero level in one direction. The pulses of the first signal arrive at the counting input of the trigger, set at the beginning of the cycle, to the initial state only after the second signal passes through the zero level, so that at the output

The trigger produces a square-shaped signal, the phase of which matches whether it is different from the phase of the input signal.

The trigger 4 generates latitude-modulated pulses, the duration of which corresponds to the phase difference of the signals. Inverter 5 changes the polarity of the pulses. Counter 6 opens in turn the keys 7 and S to pass two groups of pulses equal in number but with different polarity to the input of the integrating amplifier 9. The duration of the measurement cycle is determined by the counter 6. At the end of the measurement cycle, the output voltage of amplifier 9 is proportional to the difference frequencies.

Subject invention

Method for measuring small frequency differences

two signals, based on determining the increment of the phase difference of these signals, not exceeding in the measurement cycle, and changing the initial phase of one of the signals by, characterized in that, in order to increase

accuracy, noise immunity and simplification of the measurement process, establish the initial phase difference is less, changing when the phase difference of the input signals exceeds the initial phase of the first signal by,

This passage of the pulses of the first signal, generated at the moments of its transition through the zero level in two directions, is controlled by the pulses of the second signal, formed at the moments of its transition through the zero

level in one direction, and measure the difference of the total durations of two alternately formed groups of pulses of the phase difference of the signals, the number of pulses in which is the same.