SU1160321A1 - Device for measuring amplitude values of a.c.electric signals - Google Patents

Abstract

A DEVICE FOR MEASURING AMPLITUDE VALUES OF VARIABLE ELECTRIC SIGNALS, containing a controllable oscillating circuit, whose power supply circuit through a resistor is connected to the output of the reference voltage generator; an input resistor, one of the terminals of which is connected to the input of the device, and an indicator, characterized in that, for the purpose of precision, by eliminating the additive component of the error e - ti, an indicator of the tuning of the oscillator circuit, summation of the resistor, choke and key element are entered into it, the second output of the input resistor through a summing resistor connected to the control input of the oscillating circuit connected to one of the outputs of the controlled DC source, the second terminal of which is connected via a choke to the connection point of the input and summed-in resistors connected to the input of the key element (L the output of which is connected to the common bus of the device, the indicator is connected to It allelic the controlled constant current source, and the input setting Ind katsfa oscillation circuit connected to the output amplifiers in liters.

Description

The invention relates to a radio measuring technique and can be used in the development of devices for measuring the amplitude values of variable electrical signals. The aim of the invention is to improve accuracy by eliminating the additive error component. In FIG. 1 shows a block diagram of the device; in fig. 2 dependency graphs, which show how the device works. The device contains an input resistor 1, a generator 2 voltage reference frequency, a resistor 3, a controlled oscillatory circuit 4, an amplifier 5, an inductance 6, a varicap and 8 an oscillating circuit 4, a key element 9, a choke 10, a controlled source 11 constant the current indicator (voltmeter) 12, the output device 13, the source 14 of the reference voltage of the amplifier 15, the indicator 16 of the oscillating coil setting 4, the summing resistor 17. In FIG. t shows the boundary voltages 18 (UO and 19 (U) of the varicaps 7 and 8, at which resonance in the oscillatory circuit 4 occurs or disappears, the volt-capacitance characteristic 20 of the varicaps 7 and B, the coordinate axis 21 of the capacitance of the varicap 7 and 8, coordinate axis 22 of the reverse voltage on the varicap 7 and resonant curve 23 of the oscillating circuit 4, input voltages 24 and 25, shifted by the voltage of the controlled constant current source 11. The input of the device through the input resistor 1 and the summing resistor 17 is connected to the control input oscillatory circuit 4. Output oscillating circuit 4 is connected to the input of amplifier 5, the output of amplifier 5 is connected to the input of indicator 16 for oscillating coil 4. Generator 2 of the reference frequency is connected via resistor 3 to the input of oscillating circuit 4. Controllable direct current source 11 is connected to su11 through ) to the resistor 17. Indicator 12 is connected in parallel to the source 11. The device operates in three stages. At the first stage, the input signal is directly measured, as a result of which two voltage values are determined from the indicator 12. At the second stage, in the absence of an input signal, calibration is performed to determine the sensitivity threshold of the device. In the third step, the unknown amplitude of the input signal is determined numerically from the measurement results in the first two steps. The principle of operation of the proposed device at the first stage consists in fixing the moments of occurrence and disappearance of the resonance arising in the oscillatory circuit formed from inductance 6 and two varicaps 7 and 8, under the influence of the bias voltage and the signal under study, which change the capacitance of the varicaps 7 and 8 and, therefore, the resonant frequency of the circuit. The change in the magnitude of the bias voltage is carried out using a controlled DC source 11, and the magnitude of the magnitude of this voltage is measured by an indicator 12 (a DC voltmeter). The sensitivity of the device is determined by the choice of the boundary values of the voltages 18 (U) and 19 and (U) on the varicaps 7 and 8 (Fig. 2), at which resonance occurs at the point of maximum slope of the volt-capacitance characteristic 20. The point corresponds to the maximum voltage on the resonant curve 23 taken from the additional inductance 6 of the resonant circuit 4, fixed by the indicator 16. The difference of the voltmeter readings, recorded at the time of occurrence and disappearance of the resonance in the circuit, is a measure of the amplitude span s measured signal. The elimination of the systematic measurement error caused by the difference in the boundary values of voltages 18 and 19 is provided by a preliminary calibration, which is carried out at the second stage in the absence of a measured signal by changing the bias voltage to the side of the boundary values of voltage 18 and 19, which allows these values using a voltmeter 12 and take them into account when

processing the results in the third measurement step. Calibration is carried out with the contacts of the key element 9 closed.

Consider the process of measuring the amplitude of the input signal in more detail. In the absence of a measured signal on the input bus 6, set the key element 9 to a position in which the control 1 1y source 11 is connected to the common bus through the choke 10 (the position of the contacts of the key Element 9 in this case is not shown in Fig. 1). Increasing the voltage sources 11, achieve resonance in the circuit, which leads to a sharp increase in the voltage amplitude on the additional inductance 6, which after detecting the rectifiers 13 will exceed the reference voltage of the source 14 and will be fixed by the indicator 16. Voltmeter 12 reading this the moment is assumed to be equal U. A further increase in the bias voltage will lead to the disappearance of the resonance in the circuit and the indicator 16 will be restored to its original position. Voltmeter 12 at this moment fixes the value of voltage equal to and. After this, the bias voltages are reduced to zero, the contacts of the key element 9 open (the position of the contacts of the key element 9 in this case are shown in Fig. 1), and the input bus serves the measured signal

U UMS-ifiQt Uo (1) where Urti is the amplitude of the measured

alternating voltage; L / e - constant component of the measured voltage

Jt is the frequency of the measured voltage;

t time

1603214

Increasing the bias voltage with the help of a controlled source 11, a resonance is generated in the circuit 4, and at the same time S fixes the reading of the voltmeter 12 equal to U}. Since the emergence of the resonance in the circuit is determined by the boundary value of the voltage and (18), the following equality

  and 2)

With a further increase in the bias voltage, the resonance in the circuit and, therefore, the signal at the output of the amplifier 15 will be maintained until

 then, while the sum of the armature voltage, which is the result of the bias voltage and the input signal, does not exceed the limit value of the voltage U (19). Voltmeter 12 at the time of the disappearance

resonance in the circuit fixes a voltage value equal to J c. For this case, the equality

  u (3)

The minus sign in front of the sought amplitude shows that in the formula (3) the inverse of the half-wave amplitude of the measured signal is used. From formulas (2) and (3), it is possible to find the magnitude of the amplitude of the measured signal and the value of its constant component

u - (u-uVu2-u,)

(four)

one

Uo j (u -u-U -JJ2) (5)

it follows from formula (4) that the result of measuring the amplitude of a signal does not depend on the magnitude of its constant

component, otherwise, the presence of a constant component does not affect the accuracy of the signal amplitude measurement.

Since the measurement result is formed as the difference between the two measurements, the component error of the device is additive.

one

FIG. 2

Claims (1)

DEVICE FOR MEASURING amplitude value of the alternating electric signals, comprising controllable oscillation circuit, the feed circuit which via a resistor connected to the output voltage of the generator * · zheniya reference frequency, an amplifier having an input connected to an output-controlled oscillating circuit ¹ controls ^the constant current source, an input resistor , one of the conclusions of which is connected to the input of the device, and an indicator, characterized in that, in order to improve accuracy, by eliminating the additive component of the error, an oscillation circuit tuning indicator is introduced to it, summing the resistor, inductor and key element, and the second output of the input resistor through the summing resistor is connected to the control input of the oscillating circuit connected to one of the terminals of the controlled constant current source, the second output of which is connected via the inductor to the input connection point and summing resistors connected to the input of the key element, the output of which is connected to the common bus of the device, the indicator is connected in parallel controlled from a DC power source and the input oscillation circuit setup indicator coupled to the output amplifiers / A. izmrrTis ·>