RU2194998C1 - Device measuring direct current - Google Patents

Abstract

FIELD: instrumentation. SUBSTANCE: device measuring direct current includes D C conductor passed through magnetic circuit with winding which start is connected to one lead of first capacitor, another lead of first capacitor being connected to ground. Finish of winding of magnetic circuit is connected through second capacitor to ground and to output of inverter which input is connected to start of winding of magnetic circuit and to threshold unit through matching element. Output of threshold unit is linked through pulse storage circuit and former of discrete level connected in series to output of device. EFFECT: enhanced noise immunity in process of measurement of direct current. 1 cl, 3 dwg

Description

 The invention relates to instrumentation, and in particular to electrical engineering, and can be used for testing the windings of electrical and electromechanical products for integrity, as well as for monitoring the integrity of cable communication lines.

 A known device selected as an analogue "Method for measuring direct current and a device for its implementation" described in US patent 5814983, CL. G 01 R 33/00, contains a generator, single vibrators, a sampling and storage circuit, an R-S flip-flop and a magnetically saturating sensor with three windings, the first of which is designed for measured direct current, the second for bias current and the third for generating pulse current. When the measured direct current flows through the first conductor, the magnetic circuit passes from an unsaturated state to a saturated one. In this case, the bias current is subtracted from the current of the third winding shown in the first winding. The result of the difference is the value of the measured current.

The disadvantage of analogue should include:
- lack of protection against interference induced in the first winding of the device;
- the complexity of the circuitry of the device.

 The closest in technical essence and the achieved positive effect to the claimed device is selected as a prototype "Device for measuring direct current" described in Japanese patent 2816175, cl. G 01 R 19/00.

 A device for measuring direct current contains a direct current conductor passing through a magnetic circuit with a winding, the beginning of which is connected to one of the terminals of the first capacitor, and the second terminal of the capacitor through a resistor from which the useful signal is removed, is connected to the input of the generator.

 When direct current flows through the conductor, the magnetic circuit of the device enters saturation, as a result of which the inductance of the winding changes and, as a result, the frequency of the generator changes. By changing the time shift of the working signal taken from the resistor, relative to the reference signal, the value of the flowing direct current is judged.

 When testing the windings of electrical products, in particular the windings of electrovalves or pyromedics of rocket and space technology (RCT) products, they use integrity with a weak safe current of 5-20 mA. In addition, the process of testing the integrity of automation elements is carried out during the time when other more powerful energy consumers are tested, which create an unfavorable noise situation on the RCT product. If you use the prototype for these purposes, then it will take the interference from other consumers as a useful signal. As a result, the reliability of his work is reduced.

 The disadvantage of the prototype is the lack of noise immunity when measuring direct current.

 The technical result of the invention is the provision of noise immunity of the device when measuring direct current.

 The technical result is achieved due to the fact that in a device for measuring direct current containing a direct current conductor passing through a magnetic circuit with a winding, the beginning of which is connected to one of the terminals of the first capacitor, unlike the prototype, the other terminal of the first capacitor is connected to ground, and the end of the winding of the magnetic circuit is connected through the second capacitor to the ground and to the output of the inverter, the input of which is connected to the beginning of the winding of the magnetic circuit and through the matching element is connected to a threshold device, the output One of which, through series-connected pulse storage and a discrete level driver, is connected to the output of the device.

 The invention is as follows. When testing a powerful consumer on an RCT product in the control circuit of an electrovalve or pyromedicine in which a device for measuring direct current is installed, interference induced from this consumer may occur. This short-duration interference, introducing the magnetic circuit of the device into saturation, will form a short series of pulses at the input of the pulse storage device. A short series of pulses at the output of the pulse accumulator will generate a pulse accumulation voltage, the value of which will be insufficient to switch the discrete level driver. It follows that the false signal induced in the DC current measurement circuit by the claimed device will not be generated.

 Thus, a set of features characterizing the connection of the threshold device and the shaper of the discrete level through the pulse storage device, which blocks the interference signal, provides noise immunity of the claimed device.

 Figure 1 presents a functional diagram of a device for measuring direct current.

 In FIG. 2 is an electrical schematic diagram of an example of a specific embodiment of the device according to FIG.

 In FIG. 3 shows timing diagrams of the operation of the device of FIG. 2.

 Presented in figure 1, a functional diagram of a direct current measuring device comprises a direct current conductor 1 passing through a magnetic circuit 2 with a winding 3, which is connected between the input and output of the inverter 4, translating it into active mode of operation. Moreover, the input and output of the inverter 4 through the capacitors 5, 6 are respectively connected to ground. The input of the inverter through the matching 7 element is connected to the input of the threshold 8 of the device, the output of which through a serially connected drive 9 of the pulses and the shaper 10 of the discrete level is connected to the output 11 of the device.

 The magnetic circuit 2 with a winding 3, an inverter 4 and capacitors 5, 6 are intended for the formation of an oscillator with a DC-controlled inductance. The matching element 7 is designed to coordinate the load of the above-mentioned oscillator and threshold 8 of the device, which is designed to measure the value of direct current. The drive 9 pulses is designed to convert a sequence of pulses into a linearly increasing voltage accumulation of pulses. The discrete level driver 10 is designed to block the measured interference current.

 The device operates as follows.

 When the supply voltage is applied, the oscillator starts. Moreover, the capacitors 5 and 6 work in antiphase, ensuring the passage of the pulsed current through the winding 3, which is included in the feedback of the inverter 4. In this case, the winding 3 and the capacitors 5 and 6 are timing elements of the indicated oscillator. The pulse or AC component of the voltage from the beginning of the winding 3 through the matching 7 element is fed to the input of the threshold 8 device. The threshold of the threshold device 8 is configured so that the voltage supplied from the winding 3 with the unsaturated core 2 does not switch the threshold device 8. And vice versa, the voltage coming from the winding 3 with a saturated core 2 switches the device 8, which explains the measurement of direct current in the conductor 1. For example, as a direct current conductor 1, in which it is necessary to measure its value, we consider the control circuit of an electrovalve or pyro means. The safety requirements for the work carried out with automation elements during their integrity test prescribe the use of safe currents of the order of 5-20 mA. When a direct current flows through a conductor 1, for example 5 mA, the magnetic circuit 2 enters into saturation, which contributes to a significant decrease in the inductance of its winding 3. As a result, the frequency and amplitude of the voltage in the winding 3 increase. The voltage increased in amplitude through the matching 7 element is input threshold 8 of the device and switches it, forming a sequence of pulses at its output. The pulse train length is determined by the DC pulse length. As the pulses arrive at the input of the drive 9 pulses from its output, a pulse accumulation voltage will increase linearly to a certain steady state, which, when the trigger level of the discrete level generator 10 is exceeded, will form a discrete signal on the device output 11. This signal will mean that the direct current in the conductor 1 is measured, its value is at least 5 mA, which corresponds to the integrity of the winding of the tested automation element. However, the conductor 1 can have a large length (up to 50 m), which is an essential electrical circuit for inducing in it, in particular, longitudinal interference. This interference, introducing the magnetic circuit 2 into saturation, will form a short sequence of pulses from the output of the threshold device 8. The pulse train will generate a linearly increasing pulse storage voltage at the output of the drive 9 pulses, the level of which will be insufficient to switch the shaper 10 of the discrete level. Thus, a set of features characterizing the inclusion of the drive 9 pulses between the threshold 8 device that measures direct current, and a shaper 10 of a discrete level that blocks interference, provides noise immunity of the device.

 Presented in FIG. 2 is an electrical schematic diagram of an example of a specific embodiment of the device according to FIG. 1 includes a direct current conductor 1 passing through a magnetic circuit 2 with a winding 3, an inverter 4, capacitors 5 and 6, a matching element 7 made in the form of a capacitor, a threshold 8 device, a 9 pulse drive and discrete level driver 10. As a core, an MN saturation magnetic circuit with a rectangular static hysteresis loop was used (material 84KXSR KVShU 684450.001 TU). The threshold device 8 is made in the form of a resistive voltage divider 12 and 13, the midpoint of which is the input of the threshold device 8, through the back-connected diode 14 connected to the ground and to the base of the transistor 15. The collector of the transistor 15 is connected to the resistor 16 and the inverter 17, the output of which is the output of the threshold 8 device. The drive 9 pulses made in the form of series-connected diode 18 and resistor 19, and the output of the resistor 19, which is the output of the drive 9 pulses, through a parallel connected capacitor 20 and the resistor 21 is connected to ground. An inverter is used as a shaper 10 of a discrete level.

Presented in figure 3 diagrams of the operation of the device according to figure 2 include:
a - diagram of the measured direct current;
b - voltage diagrams at the beginning and at the end of winding 3, moreover, the voltage diagrams A, B correspond to the unsaturated state of the magnetic circuit 2, and the voltage diagrams B, D to the saturated state. The diagram shows the level U of _the threshold of operation of the threshold device 8;
c is a pulse sequence diagram formed by a threshold device 8;
g is a diagram of the formation of the voltage accumulation of pulses in the drive 9 pulses. The diagram shows the level U _crab operation of the shaper 10 of the discrete level.

где
τ₁ = R₁₉•C₂₀
Напряжение разряда для первой скважности определяется как

где
τ₂ = R₂₁•C₂₀.
Таким образом, если допустить, что длительность и скважность импульсов одинаковы, то функцию накопления импульсов можно реализовать при условии τ₁≤τ₂. Причем динамика увеличения напряжения накопления импульсов с выхода накопителя 9 импульсов определяется также соотношением τ₁, τ₂.
Итак, число импульсов, определяемое в конкретном случае длительностью сигнала помехи, будет недостаточно, чтобы напряжение накопления импульсов достигло величины уровня срабатывания U_cpa6 формирователя 10 дискретного уровня. Следовательно, формирователь 10 дискретного уровня не сработает и сигнал помехи им будет заблокирован, чем и будет обеспечена помехозащищенность.When applying a supply voltage to the device at the beginning and at the end of the winding 3, voltages are generated respectively of form B and A according to figure 3 of diagram (b). Waveform B through a matching capacitor 7 to the input 8 of the device threshold, _then threshold U which is determined by the resistive divider 12 and 13. The U _thresh threshold is set so that the amplitude of the voltage form B is insufficient for controlling the transistor 15. Hovering interference in conductor 1, diagram (a) according to FIG. 3, the magnetic core 2 goes into a saturation state. As a result, the inductance of the winding 3 drops, which contributes to an increase in the frequency and amplitude at the beginning and at the end of the winding 3 — voltage of form G and B, respectively, according to FIG. 3 diagrams (b). The voltage of the form G supplied through the matching element 7 to the input of the threshold device 8 will be sufficient to open the transistor 15. Thus, the positive half-wave voltage (negative cut off by the diode 14) from the output of the threshold device 8 will generate pulses according to figure 3 of the diagram (in ) The sequence of pulses supplied to the input of the drive 9 pulses through the diode 18 and the resistor 19 will charge the capacitor 20. Moreover, the capacitor 20 is charged for the duration of the pulse duration, and during the duty cycle between pulses, the capacitor 20 is discharged through the resistor 21 according to figure 3 diagram (g) . The charge voltage of the capacitor 20 for the first pulse is defined as

Where
τ ₁ = R ₁₉ • C ₂₀
The discharge voltage for the first duty cycle is defined as

Where
τ ₂ = R ₂₁ • C ₂₀ .
Thus, if we assume that the duration and duty cycle of the pulses are the same, then the function of the accumulation of pulses can be implemented under the condition τ ₁ ≤ τ ₂ . Moreover, the dynamics of increasing the voltage of the accumulation of pulses from the output of the drive 9 pulses is also determined by the ratio of τ ₁ , τ ₂ .
So, the number of pulses, determined in a specific case by the duration of the interference signal, will not be enough for the pulse accumulation voltage to reach the value of the triggering level U _cpa6 of the discrete level _driver 10. Therefore, the discrete level driver 10 will not work and the interference signal will be blocked by them, which will provide noise immunity.

 The duration of the DC signal in the conductor 1 when monitoring the integrity of the automation element is significantly longer than the duration of the interference signal. Therefore, the voltage accumulation of the pulses will reach the value of the level of operation of the shaper 10 of the discrete level. As a result, the latter will work and set a discrete level characterizing the integrity of the tested automation element.

Used Books
1. Japan patent 2816175, cl. G 01 R 19/00, 04/28/89.

 2. US patent 5814983, cl. G 01 R 33/00, 09/29/98.

 3. Japan patent 2835093, cl. G 01 R 19/00.

 4. Magnetic cores like MP, MD, MN and KL. Specifications KVShU 684459.001 TU. 1998 year

Claims (1)

 A device for measuring direct current, containing a direct current conductor passing through a magnetic circuit with a winding, the beginning of which is connected to one of the terminals of the first capacitor, characterized in that the other terminal of the first capacitor is connected to the ground, and the end of the winding of the magnetic circuit is connected through the second capacitor to the ground and with the output of the inverter, the input of which is connected to the beginning of the winding of the magnetic circuit and through the matching element is connected to a threshold device, the output of which through series connected accumulate l and pulse shaper discrete level connected to the output device.

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