SU444116A1 - Device for measuring weak electrical signals - Google Patents

Description

The invention relates to electrical measuring equipment, in particular, to devices for measuring weak electrical signals using a modulation measuring method.

A device for measuring weak electrical signals is known, comprising a modulator and an input amplifier, a detector, and a low-frequency amplifier connected in series.

The exponentially weighted accumulation of a weak signal in the integrating circuits of a synchronous detector limits the sensitivity of this device. In addition, the circuit requires calibration of the noise level of the generator and bridge circuit before each measurement. This eliminates the possibility of automating measurements and affects their accuracy.

Therefore, the known device cannot be used to measure the weakness of the electromagnetic field in the field, when the destabilizing mechanical and climatic factors have a particularly significant effect on the calibration accuracy, automating the measurement process, and the weight and dimensions of the device.

The aim of the invention is to increase the sensitivity of measurements.

To achieve this goal, a key in series is included in it, the analog converter is a cathode, a reversible counter and a digital indicator, a trigger, a time interval circuit, the input is connected to a modulator, a switch converter

analogue-cathode, trigger, and output-with a key and a reversible counter, and the trigger output is also connected to the reversing counter.

Measurement sensitivity increase

it is provided by periodic switching of the signal at the input of the input amplifier by the switch of the signal, conversion of the voltage at the output of the amplifier to the binary code by the analog-to-code converter (PAK), accumulation

for a fixed time determined by the time interval generating unit and the key, the difference of the samples is noise and signal + noise, formed in the reversible counter using a control trigger, which sends the samples corresponding to the closed switch (signal + noise) to the direct reverse input the counter, and the counts corresponding to the open switch (“noise”) to the reversing input of the counter. The result of the accumulation is recorded by a digital indicator.

The drawing shows a block diagram of the device. It consists of a signal switch 1,

input amplifier 2, detector 3, UPCH 4, key o, analogue converter - code (PAK) 6, reversible counter 7, digital indicator 8, trigger of uiravleii 9, time interval 10 generation circuit, modulator 11. The device works as follows. The input signal is fed to the input of amplifier 2 through controlled switch 1, periodically closing and opening the signal supply circuit. At the output of the amplifier, a sequence is formed, the half-period of which is an additive mixture of the signal and the amplifier's own sound, half a period is only sound. Detector 3 highlights the envelope of this 15 periodic sequence, the amplitude of which is determined by the signal strength (since detection is assumed to be quadratic). The up / down counter forms sample differences “signal + sound and“ noise, 20 converted PAK 6 to binary code. Consider the process of accumulating differences in a reversible counter that combines the functions of subtraction and accumulation. It is known from statistical radio, 25 that the dispersion and the average value of the process at the output of a quadratic detector with an integrating load are equal to: where W is the spectral density of the process; 2D - the spectrum band of the process; a is the integrator time constant. At the output of the detector, therefore, the periodic sequence will have; for readings "shchum for readings" signal -} - crack (G-f) D. 2 (ITc-f) A Hos.sh. - - The counts corresponding to the half-period signal — + - are fed to the forward input of the reversible counter 7, and the counts 50 to the reversing input, which is provided by control trigger 9 operating synchronously with the input switch 1. This corresponds to the subtract operation. In addition, the reversible counter will accumulate 55 results of the subtraction as the number of periods of the modulating meander of the modulator 11 increases. The result that accumulates in the reversible counter by the end of the accumulation cycle is proportional to the signal power. After the end of the cycle, this result is highlighted on the slit of the electron-optical indicator 8. After the readings are taken, the reversible counter returns to the zero state by switching 65 5 10 30 40 45 toggle switches off and measuring. The device is ready for the next measurement. The magnitude of the maximum signal that can be measured by a device is determined by the number of bits of the converter's analogue - code 6. The voltage range of this converter must cover the maximum possible signal. The capacity of the reversible counter is not particularly important here, because with a large signal, an attenuator can be installed that reduces the accumulation time in the block of the time interval 10. The maximum sensitivity of the device is determined by many factors: the discrete value of the ACM 6, the accumulation time, the degree of approximation of the characteristic detector to quadratic, etc. There is a limit, after which no increase in the accumulation time can increase the sensitivity. This limit is due to the magnitude of the weak signal at One transformation (detection) and corresponds to the ratio of the signal to the noise at the input of the device is 0.01-0.02. This is quite sufficient for most practical purposes. Before measurement and during the measurement process, no calibrations and adjustments are required. The whole measurement process is reduced to switching the toggle switch off and measuring and setting the attenuator that determines the duration of the accumulation cycle to the desired position in the block of time intervals 10; the use of subtraction of samples "signal-щ noise and" noise makes it possible to measure regardless of the level of the input amplifier without additional calibrations using linear accumulation (without weight function) difference of samples increases the sensitivity of the device compared to the accumulation in a synchronous detector with an exponential weight function; The accuracy of the readings is determined by the spread of readings due to the spread of the standard deviation in the accumulation of differences and the degree of stabilization of the discrete value of PAK 6. The low-current power source of PAK 6 can be made in dimensions acceptable for small-sized equipment with a sufficient degree of stabilization (fraction of a percent). The scatter of readings due to the expansion of the standard deviation can be reduced to any given minimum value by averaging a small number of measurements. Subject of the Invention A device for measuring weak electrical signals, comprising a modulator and a series-connected input amplifier, a detector, a low-frequency amplifier, characterized in that, in order to increase the sensitivity, a series-connected key, analog-to-code converter, reversible counter and digital indicator, trigger, time interval circuit, input connected to modulator,

a switch, an analog converter - a code, a trigger, and an output with a key and a reversible counter, and the trigger output is also connected to a reversible counter.