RU2754963C1 - Null detector - Google Patents

Abstract

FIELD: measuring.SUBSTANCE: invention relates to the field of automation, robotic and measuring technology, and is intended for detection of the moment of transition (from negative to positive half-wave) of the input bipolar harmonic signal voltage over the zero level, can be used in apparatuses for measuring time intervals, in particular. The null detector is comprised of a first and second operational amplifiers, a first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, tenth, eleventh, twelfth and thirteenth resistors, a capacitor, a current limiter unit, an output signal regulator, a diode, and a Schmitt trigger.EFFECT: increased reliability, accuracy of detection of the zero input signal level and output signal quality and interference immunity.1 cl, 4 dwg

Description

The invention relates to the field of automation, robotic and measuring technology and is intended for detecting the moment of transition (from negative half-wave to positive) voltage of the input bipolar harmonic signal through the zero level, in particular, can be used in devices for measuring time intervals.

Known null-organ (Ac No. 881652 priority dated 06/03/1978, "Null-organ", authors: Gonchar A.V., Reshetnik A.I., Rumyantsev V.P., Sakharin V.G., IPC G05B 1 / 01, published 15.11.1981, bul. No. 42), containing the first and second limiting elements, a threshold element, a one-shot, an operational amplifier and a switch. Resistors are used as the first and second limiting elements, and a transistor is used as a switch. The inverting input of the operational amplifier is connected, respectively, through the switch and the first limiting element to the output of the operational amplifier and the input of the null-organ. The non-inverting input of the operational amplifier is connected to the ground rail. The control input of the key is connected to the first output of the second limiting element. The input of the null-organ through a series-connected threshold element and a one-shot is connected to the second output of the second limiting element.

The disadvantages of the well-known null organ are:

- low reliability: due to the absence of circuits for attenuation of input signals with a large voltage amplitude; due to the lack of protection from external influencing factors (WWF); due to the presence of redundant active elements (threshold element, one-shot, key), which are the main functional nodes of the null-organ;

- the absence of circuits for eliminating the zero offset of the input bipolar signal;

- no suppression of common-mode noise of the input signal;

- the minimum allowable and, most importantly, stable phase shift between the input sinusoidal and output rectangular pulse signals is not ensured due to a very large (and unstable during the exposure to VVF) gain of the operational amplifier at a time close to the moment when the input signal crosses zero;

- lack of interface elements with digital integrated microcircuits of an external device for processing output pulses of a null-organ;

- lack of protection from external factors. Known null-organ (RF patent No. 2712768 priority from 07/05/2019.

"Zero organ", authors: Arbuzov V.N., Fatin V.N., Babnev S.E., Gutnikov A.I., IPC: G05B 1/01, published on 31.01.2020, bul. 4), containing a high-pass filter (HPF), an input signal normalizer, an operational amplifier, a current limiter unit, an output signal normalizer, a Schmitt trigger, the first, second, third and fourth resistors. The HPF input is the input of a null organ. The output of the HPF through the input signal normalizer is connected to the first terminals of the first and second resistors and to the inverting input of the operational amplifier. The output of the operational amplifier is connected to the second terminal of the second resistor, to the first terminal of the third resistor and to the input of the output signal normalizer. The output of the output signal normalizer is connected to the input of the Schmitt trigger, the output of which is the output of the null organ. The power inputs of the null-organ are the inputs of the current limiter unit, the outputs of which are connected to the power inputs of the operational amplifier, the non-inverting input of which is connected to the second terminal of the third resistor and through the fourth resistor to the second terminal of the first resistor and to a common bus. This null organ is chosen as the closest analogue.

The disadvantages of the closest analogue are:

- no suppression of common-mode noise of the input signal;

- stretched trailing edge at the output of the output signal normalizer, which increases the phase shift between the input sinusoidal and output pulse signals;

- insufficiently high reliability.

The technical problem to be solved by the invention is to create a null-organ with the following characteristics:

- providing effective suppression of common-mode noise of the input signal (depending on the phase position, amplitude and frequency of the common-mode noise, the accuracy of detecting the zero level of the input signal can be significantly reduced);

- providing a minimum and highly stable phase shift between the detected zero voltage level of the input sinusoidal and the front of the output pulse signal, which is the result of detection;

- providing protection against through currents during exposure to external factors;

- maintaining operability with specified electrical characteristics under conditions of exposure to VVF with high values of exposure characteristics.

The technical results to be achieved by the invention are to increase the reliability, to increase the accuracy of detecting the zero level of the input signal and the quality of the output signal, to increase the noise immunity, and to ensure a high degree of immunity to VVF.

These technical results are achieved by the fact that in a null organ containing the first operational amplifier, the inverting input of which is connected to the first terminal of the first resistor and through the second resistor with a common bus and to the first terminal of the third resistor, the second terminal of which is connected to the non-inverting input of the first operational amplifier and through the fourth resistor with the second terminal of the first resistor and with the output of the first operational amplifier, the Schmitt trigger, the input of which is connected to the output of the output signal normalizer, and the output is the output of the null-organ, a block of current limiters, the inputs of which are the power inputs of the null-organ, and the first and second outputs are connected, respectively, to the power inputs of the first operational amplifier, new is that the fifth, sixth, seventh, eighth, ninth, tenth, eleventh, twelfth, thirteenth resistors, a capacitor, a diode, a second operational amplifier, the non-inverting input of which connected through the fifth a resistor with a common bus and with the first pin of the sixth resistor,

the second terminal of which is the first input of the null-organ, the inverting input of the second operational amplifier is connected to the first terminals of the seventh and eighth resistors, the second terminal of the first of which is the second input of the null-organ, the first and second inputs of the second operational amplifier are connected to the first terminal of the ninth resistor, the second terminal of which is connected through the tenth resistor to the third input of the second operational amplifier, to the first power input of the second operational amplifier and the third output of the current limiter unit, the fourth output of which is connected to the second power input of the second operational amplifier, the output of which is connected to the second terminal of the eighth resistor and through a capacitor and an eleventh resistor connected in series with the inverting input of the first operational amplifier, the output of which is connected through the twelfth resistor to the cathode of the diode and the input of the output signal normalizer, the output of which is connected to the anode of the diode and through the thirteenth resistor with a common bus.

Increased reliability is provided by:

- a divider formed by the fifth and sixth resistors, which halves the voltage amplitude of the input signal, thus protecting the zero-organ from input signals with an increased (relative to the maximum permissible) voltage amplitude;

- a divider formed by the eleventh and second resistors, which limits the voltage amplitude of the signal coming from the output of the second operational amplifier, preventing overloading at the input of the first operational amplifier, and, thus, additionally protecting the null-organ from signals with increased (relative to the maximum permissible) voltage amplitude;

- the use of a twelfth resistor limiting the currents flowing through the output signal normalizer and the first operational amplifier;

- the use of a block of current limiters, which protects the operational amplifiers from breakdown during exposure to VVF.

The accuracy of detecting the zero level of the input signal and the quality of the output signal are increased due to:

- effective suppression of common-mode noise of the input signal due to the use of a buffer differential stage on the second operational amplifier (OA);

- elimination of zero offset at the output of the second operational amplifier under normal climatic conditions and the absence of external factors due to the use of the ninth and tenth resistors;

- suppression of the constant component arising from the zero offset at the output of the second operational amplifier under the influence of VVF due to the use of a capacitor;

- ensuring a high steepness of the trailing edge of the pulse at the output of the output signal normalizer and a significant decrease in its delay due to the use of a diode.

The use of a buffer differential stage on the second operational amplifier provides suppression of common-mode noise of the input signal, thereby increasing the noise immunity of the null-organ and the accuracy of its detection. When the gain of the second op-amp is equal to one, the maximum attenuation of the input common-mode noise and the minimum signal delay at the output of the second op-amp are achieved.

The first and second inputs of the second operational amplifier are connected, completing an internal frequency equalization circuit to prevent self-excitation of the second operational amplifier at the high frequencies of its bandwidth.

FIG. 1 shows a functional diagram of a null organ. FIG. 2 shows the diagrams of the input and output signals of the null-organ. FIG. 3 and FIG. 4 shows the diagrams of the input sinusoidal signal and pulse at the output of the normalizer 18 in the absence and in the presence of diode 19, respectively.

The null organ (Fig. 1) contains the first 1 and the second 2 operational amplifiers, the first 3, the second 4, the third 5, the fourth 6, the fifth 7, the sixth 8, the seventh 9, the eighth 10, the ninth 11, the tenth 12, the eleventh 13, twelfth 14 and thirteenth 15 resistors, capacitor 16, current limiter unit 17, output signal normalizer 18, diode 19, Schmitt trigger 20.

The inverting input of the first op-amp 1 is connected to the first terminal of the first resistor 3 and through the second resistor 4 to a common bus and to the first terminal of the third resistor 5. The second terminal of the third resistor 5 is connected to the non-inverting input of the first op-amp 1 and through the fourth resistor 6 to the second terminal of the first resistor 3 and with the output of the first op-amp 1. The output of the Schmitt trigger 20 is the output of the null organ. The inputs of the block 17 of the current limiters are the power inputs of the zero-organ, and the first and second outputs are connected, respectively, to the power inputs of the first op-amp 1. The non-inverting input of the second op-amp 2 is connected through the fifth resistor 7 to the common bus and to the first terminal of the sixth resistor 8. The second terminal of the sixth resistor 8 is the first input (+ U _inx ) zero-organ. The inverting input of the second op-amp 2 is connected to the first terminals of the seventh 9 and eighth 10 resistors. The second terminal of the seventh resistor 9 is the second input (-U _inx ) of the zero-organ. The first "FC" and the second "NC1" inputs of the second op-amp 2 are connected to the first terminal of the ninth resistor 11, the second terminal of which is connected through the tenth resistor 12 to the third input "NC2" of the second op-amp 2, to the first power input of the second op-amp 2 and the third output of the block 17 current limiters. The fourth output of the current limiter unit 17 is connected to the second power input of the second op-amp 2. The output of the second op-amp 2 is connected to the second terminal of the eighth resistor 10 and through a series-connected capacitor 16 and the eleventh resistor 13 with the inverting input of the first op-amp 1. The output of the first op-amp 1 is connected through the twelfth resistor 14 with the anode of the diode 19 and the input of the output signal normalizer 18, the output of which is connected to the anode of the diode 19 and through the thirteenth 15 resistor with a common bus.

OA 2 together with resistors 7-12 forms a differential amplifier designed to suppress common-mode noise of the input signal. OA 2 must be fast. To maximize the attenuation of the input common-mode noise and ensure the minimum signal delay at the output of OA 2 relative to its input, the values of resistors 7, 8, 9 and 10 must be the same and precise. At the same time, their ratings should be as low as possible, provided that the resistance of the input signal source is repeatedly exceeded. The values of the resistors 11 and 12 are selected to reduce to zero the bias at the output of the second operational amplifier under normal climatic conditions and in the absence of external factors.

Capacitor 16 is designed to suppress the constant component of the output signal of OA 2, which arises due to a zero offset at its output under the influence of VVF.

The operational amplifier 1 together with the first 3, the second 4, the third 5, the fourth 6 and the eleventh 13 resistors forms a threshold device (PU) designed to form a bipolar pulse, the trailing edge of which is formed at the moment of transition (from negative half-wave to positive) of the input signal through zero. OA 1 must be fast. To ensure a high steepness of the fronts at its output, its gain (Ku) must be high enough (about 100). Ku OA 1 is determined by the ratio of resistors 3 and 13. Resistor 4 is designed to prevent overloading at the input of the first OA 1. The ratio of resistors 5 and 6 sets the hysteresis of the threshold device.

The normalizer 18 of the output signal is designed to convert bipolar pulses coming from the output of the control unit into unipolar positive ones. The normalizer 18 of the output signal can be implemented on three high-speed (to minimize the phase delay of the signal coming from the output of the PU) pulse diodes.

Diode 19 is designed to provide a high steepness of the trailing edge (which is a carrier of useful information) of the pulse formed at the output of the output signal normalizer 18, thereby further reducing its delay. FIG. 3 shows the diagrams of the input sinusoidal signal and the pulse at the output of the output signal normalizer 18 in the absence of diode 19, and FIG. 4 - in the presence of diode 19.

Resistor 14 limits the currents flowing through the output signal regulator 18 and op-amp 1.

Resistor 15, which together with resistor 14 forms a voltage divider, sets the amplitude of the pulses arriving at the input of the Schmitt trigger 20.

The high-speed Schmidt trigger 20 additionally increases the slope of the edges and stabilizes the phase of the output pulses "Uout" of the null-organ and ensures their coordination with a digital external device.

The block 17 of the current limiters is implemented on low-resistance resistors and is designed to prevent the breakdown of operational amplifiers 1 and 2 during exposure to VVF.

The null organ works as follows.

At the input of op-amp 2 through resistors 8 and 9, an input bipolar sinusoidal signal is supplied (see Fig. 2). Equal resistors 7, 8, 9, and 10 ensure maximum rejection of input common-mode noise by op-amp 2 and minimum input delay. The connected inputs "FC" and "NC1" close the internal frequency correction circuit of OA 2, preventing self-excitation at the high frequencies of its bandwidth. Resistors 11 and 12 eliminate the zero offset at the output of op-amp 2 under normal climatic conditions and in the absence of external factors. From the output of the op-amp 2, the signal through the capacitor 16 is fed to the inverting input of the op-amp 1. The capacitor 16 suppresses the constant component of the output signal of the op-amp 2, which arises due to a zero offset at its output under the influence of VVF. The gain of op-amp 1 is set by the ratio of the resistors 3 and 13, and must be high enough (about 100) to ensure a high steepness of the edges at its output. Resistor 4, together with resistor 13, forming a voltage divider, prevents overloading at the input of the first op-amp 1. Resistors 5 and 6 form a positive feedback circuit, providing a hysteresis of the threshold device to prevent "bounce" of the signal at its output in the presence of low-level high-frequency noise at its input ... The magnitude of the hysteresis is set by the ratio of the resistors 5 and 6. At the output of the threshold device, a bipolar pulse is formed, the trailing edge of which is formed at the moment of transition (from negative half-wave to positive) of the input signal through zero.

Further, the bipolar pulse generated by the threshold device is converted by the output signal normalizer 18 into a unipolar positive one. Diode 19 provides a high slope of the trailing edge of the converted pulse, reducing its delay. Resistor 14 limits the currents flowing through the output signal regulator 18 and op-amp 1.

Next, a unipolar positive pulse enters resistor 15, together with resistor 14 forming a voltage divider that sets the required pulse amplitude at the input of the Schmitt trigger 20. Then, an amplitude-limited unipolar positive pulse enters the input of the Schmitt trigger 20, at the output of which a positive rectangular output pulse with steep edge and the required amplitude level (see Fig. 2).

Block 17 current limiters limits the sharp increase in the amplitude of the currents flowing in the operational amplifiers 1 and 2, during exposure to VVF.

Claims (1)

Zero organ containing the first operational amplifier, the inverting input of which is connected to the first terminal of the first resistor and through the second resistor with a common bus and to the first terminal of the third resistor, the second terminal of which is connected to the non-inverting input of the first operational amplifier and through the fourth resistor to the second terminal of the first resistor and with the output of the first operational amplifier, a Schmitt trigger, the input of which is connected to the output of the output signal normalizer, and the output is the output of a null-organ, a block of current limiters, the inputs of which are the inputs of the power supply of the null-organ, and the first and second outputs are connected respectively to the inputs power supply of the first operational amplifier, characterized in that the fifth, sixth, seventh, eighth, ninth, tenth, eleventh, twelfth, thirteenth resistors, a capacitor, a diode, a second operational amplifier, the non-inverting input of which is connected through the fifth resistor with a common bus and with the first pin of the sixth resist ora, the second terminal of which is the first input of the zero-organ, the inverting input of the second operational amplifier is connected to the first terminals of the seventh and eighth resistors, the second terminal of the first of which is the second input of the null-organ, the first and second inputs of the second operational amplifier are connected to the first terminal of the ninth resistor, the second terminal of which is connected through the tenth resistor to the third input of the second operational amplifier, to the first power input of the second operational amplifier and the third output of the current limiter unit, the fourth output of which is connected to the second power input of the second operational amplifier, the output of which is connected to the second terminal of the eighth resistor and through a series-connected capacitor and an eleventh resistor with an inverting input of the first operational amplifier, the output of which is connected through a twelfth resistor to the cathode of the diode and the input of the output signal normalizer, the output of which is connected to the anode of the diode and through the thirteenth thread side with a common bus.

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