SU1278750A1 - Device for automatic control of disctrimination threshold in acoustical logging of wells - Google Patents

Abstract

This invention relates to well logging by acoustic methods and can be used in acoustic logging equipment. The aim of the invention is to increase the noise immunity and speed of the device for adjusting the discrimination threshold. In a device with large signal-to-noise ratios, the discrimination threshold is determined by the amplitude of the signal and is set so that it provides a low probability of missing the phase to be separated. When reducing the ratio of the signal. - noise up to a certain value, the discrimination threshold begins to be determined by the noise level and is set so that the probability of response from it does not exceed a predetermined value. The device combines the positive qualities of adjustments of the noise and signal level discrimination threshold. This is achieved by introducing into the device containing a comparator, a noise measurement window generator and a series-connected reversible counter and code converter — analogue, coincidence circuit, adder, and to increase the speed of the speed dial and speed reset blocks. The accelerated dialing unit consists of a sequentially connected counter and a code converter - an analog. The accelerated reset unit i consists of two counters, a multiplexer and a coincidence circuit. (L Block of the speed dial allows C to make the number of pulses issued by the discriminator not only proportional to the number of noise emissions entering the measurement window, but also the difference between their amplitude and the discrimination horn, so that the contents of the reversible counter will increase at an accelerated rate. The Nl intervals of the arrival of noise emissions and, depending on this, regulates the frequency of the pulses at the subtractive input of the reversible counter. be CAG .rotazhnogo material quality due to enhanced noise immunity separation lane. Vågå entry signal to background noise ACUNS cally. ZP 2 f-ly. 2 yl.

Description

The invention relates to well logging by acoustic methods. The purpose of the invention is to increase the resistance and speed of the device to regulate the threshold of dis- crimination. Figure 1 shows the functional diagram of the device; Fig. 2 shows the voltage plots at the output of the main units. The device comprises an adder 1, a comparator 2, a coincidence circuit 3, a reversible counter 4, a converter 5, an analogue code generator, a noise measurement window 6, a speed dial 7, an accelerated reset block 8 , counters 9-11, converter 12, code analog, multiplexer 13, and circuit 14 match. The device works as follows. Adder 1 is supplied with a voltage proportional to the amplitude of the signal from the dynamic characteristics meter, which is part of the ground equipment. This voltage, with a certain weight ratio, is applied to one of the inputs of comparator 2 and determines the discrimination threshold. The weighting factor is chosen so that the i-like probability of the comparator tripping for the subsequent phases is not the same, in which the quality of the logging material is considered excellent. If the amplitude of the signal falls only on us, that the discrimination threshold becomes commensurate with the noise emissions, the summing input of the reversible counter 4 through the coincidence circuit 3 receives impulses that increase its content. At the same time, a reset signal is sent to its subtracting input at a certain rate. If the number of pulses arriving at the summing input refracts the number of reset pulses, the voltage at the output of the transducer is 5 code - and the tax increases, thereby causing an increase in the discrimination threshold. This in turn leads to a decrease in the number of triggers from noise. This process continues until the average frequencies of the pulses at both inputs of the reversible counter 4 are matched and the specified probability of a correct response is restored. As the signal-to-noise ratio increases, the voltage at the output of the converter 5 code-analogue decreases and becomes equal to zero. From this point on, the discrimination threshold is determined only by the amplitude of the signal. The frequency of the pulses arriving at the subtracting input of the reversible counter, and the weight transfer ratio of the signal adder 1 are chosen so that the probability of the comparator firing from noise is not higher than the permissible one. Thus, in this device, at large signal-to-noise ratios, the discrimination threshold is determined by the amplitude of the signal and is set so that it provides a low probability of missing the transmitted phase. When reducing the signal-to-noise ratio to a certain value, the discrimination threshold is determined by the noise level and is set so that the probability of response from it does not exceed a predetermined value. Those. This device combines the positive quality of the noise and signal level discrimination threshold adjustments. The time interval at which the number of noise triggers is measured is set by a pulse (Fig. 2, plot 15) produced by the measurement window generator 6. This period of time in the practice of low-quality acoustic logging can not be made large enough. The most suitable time for this purpose is the time interval between the sync pulse and the signal (Fig. 2, plot 16). There is a so-called dead zone in which only the tails of the signal emitted in the previous cycle can fall. This time interval is small, so the number of comparator actuations caught in it is very small, and the frequency of their arrival is extremely uneven. Therefore, to obtain a sufficiently objective assessment of the average frequency of noise failures, it is necessary to make measurements. in a sufficiently large number of clock cycles, for which a large capacity reversible counter is required. However, an increase in these values leads to a decrease in the speed of the autoregulation system, as a result of which it cannot operatively monitor

beyond the level of interference, which leads to a reduction in noise immunity.

In order to improve the speed, a speed dialing unit 7 and an accelerated reset unit 8 are entered into the device.

The accelerated dialing unit 7 consists of a binary counter 9 of small capacity and a converter 12 code — analogue, the voltage from the output of which goes to the adder 1. In the normal state - :. The scientific research institute counter 9 is reset, and its operation is prohibited by the voltage from the output of the imaging unit 6 of the noise measurement window. As soon as the interval at which noise emissions are measured starts, counter 9-15 is unlocked. The first pulse from the output of circuit 3 of coincidence records a unit in the counter 9. In this case, a voltage step appears at the output of converter 12 of the analogue code, the discrimination threshold again becomes greater than the input signal, and the comparator is turned off (Fig. 2, plots 16-19). If the noise emission voltage continues to increase, it reaches a new discrimination threshold, the comparator triggers again and gives another short impulse. These processes continue until the noise emission passes through the extremum (Fig. 2, plot 16). Thus, the number of pulses taken by the discriminator is proportional not only to the number of noise emissions that entered the measurement window, but also. the difference between their amplitude and the discrimination threshold, as a result of which the content of the reversible counter 4 rises at an accelerated rate. At the end of the noise measurement window, the counter 9 and the voltage at the output of the converter 12 code-analogue are reset to zero, and by the time the first entry signal arrives, the discrimination threshold will be incremented only by changing the content of the reversing counter 4 (Figure 2, plot 20) the accelerated reset of indications with an increase in the signal-to-noise ratio serves as an accelerated reset unit 8 consisting of two counters 10 and 11, a multiplexer 13 and a coincidence circuit 14. Pulses transmitted to the summing input of the reversible counter 4 cause resetting of the counters 10 and 11.

At the same time, the multiplexer 13 is set in such a position that pulses are transmitted to the output from the highest bit of the counter 10, to the counting input of which the clock signals are triggered, triggering the entire apparatus (Figure 2, plot 21). If there are few measurement cycles between two adjacent signals at the summing input of the reversible counter 4 (in the illustrated version of the accelerated reset unit 8), the counters 10 and 11 are constantly zeroed and nothing arrives at the subtracting input of the reversible counter 4. This in turn contributes to an accelerated increase in the discrimination threshold. If the intervals between the two neighboring operations of the comparator (Fig. 2, plot 22) from noise increase, counter 10 has time to count to eight, the potential that appears at the output of the multiplexer 13 appears at its highest bit and causes a decrease in the content in the reversing counter 4 per unit. At the same time, this pulse through a normally open circuit 14 of coincidence arrives at the counting input of counter 11 and causes a unit to be written to it. In addition, in multiplexer 13, the next lower bit of counter 10 is connected to the gain, the potential on which appears after 4 clock cycles. If, during this time, the counters 10 and 11 are not reset, the next lower order bit is connected to the output of the multiplexer 13, recalculating the input clock pulses into two. And finally, the next switching of the counter 11 causes the input to the input of the multiplexer 13 of all input signals, i.e. reversible counter 4 begins to reset its readings by one for each: time (figure 2, plot 23). Simultaneously with the connection of clock pulses to the output of the multiplexer, the potential at the highest discharge of counter T1 closes the coincidence circuit 11, prohibiting further passage of pulses to its counting input. Thus, the accelerated reset unit 8 provides an analysis of the noise emission arrival intervals, and, depending on this, adjusts the frequency of the pulses on the subtractive input of the reversible counter (Fig. 2, plots 21-23).

With a rapid decrease in the number of triggers from noise, the frequency of the reset pulses rapidly increases, which leads to a rapid decrease in the contents of the reversible counter 4 and a decrease in the discrimination threshold, and therefore a decrease in the probability of missing the signal phase of the signal by the amplitude discriminator

The use of the proposed device will improve the quality of logging material by increasing the noise immunity of the selection of the first entry of the sital against the background of acoustic noise.

Claims (3)

1. A device for automatically adjusting a discrimination threshold in acoustic logging of wells, comprising a comparator, the first input of which is the analog input of the device as a whole, the noise measurement window generator, the input of which is connected to the trigger input of the device, and the series-connected reversing counter and converter code - An analogue, characterized in that, in order to increase the noise immunity and speed, a coincidence circuit, an adder, an accelerated reset unit and an accelerated unit are introduced into the device Abor, npii4eM in the coincidence circuit one of the inputs is connected with the output of the comparator and the device as a whole, and the other with the output of the shaper measurement window, the adder of the first A input is connected to the output of the signal amplitude meter, the second - with the converter output with the output of the dialing acceleration unit, and the output with the second input of the comparator, for the accelerated dialing unit, the counting input is connected to the output of the coincidence circuit, and the main input - to the output of the noise measurement window generator, for the accelerated reset unit, the counting input is connected to Odom noise shaper measuring window, zeroed yuschy input - yield matching circuits, and the output with the subtracting input of the reversible counter. 2. The device according to claim 1, wherein the accelerated dialing unit consists of a series-connected counter and a code converter, the counterpart, the counter clock input is counting and the R input is the outgoing inputs of the block as a whole, and the output of the converter the analogue code is its output. 3. The device according to claim 1, of which is that the accelerated reset unit consists of two counters, 25 of the multiplexer and the same match, while the first counter has a synchronous input connected to the counting input of the unit as a whole and one of the information inputs of the multiplexer, the other informational inputs of which are connected to the output buses of the first counter, the R input combined with the R input The second counter and with the zero input of the unit as a whole, the second counter has a synchronous input connected to the output of the coincidence circuit, and the output buses are connected to the control inputs of the multiplexer, for the coincidence circuit the first input is connected to the output of the multiplexer 40 and with the output of the unit as a whole, and the second input - with the highest bit of the second counter.