RU2540941C2 - Universal dc sensor with uncoupling and low-voltage power supply - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: sensor comprises a measurement shunt, connected in series with a load, an operational amplifier (OA), a transformer, four interchanged switching links, an integrator, a control transistor of p-n-p type. The first output of the shunt is connected to the second output of the load. The second output of the shunt is connected to the switching contact of the second link. The first output of the load is connected to the switching contact of the first link. Normally open contacts of the first and fourth link are connected with a normally closed contact of the second link and a plus bus. The base of the transistor via the resistor is connected to the outlet of the OA and via the other resistor with the emitter of the transistor, and the emitter is connected to the plus output of the OA power supply and the plus bus. The minus output of the OA power supply is connected with the common bus. The collector of the transistor is connected to the inlet of the RC-filter, the outlet of which is connected to the buses of power supply of the introduced blocking generator, assembled with usage of the transistor, two resistors, a capacitor, a diode and two windings of the transformer. Two other windings with identical transformation ratios are connected to the introduced voltage multipliers. The outlet of the first multiplier is connected to the device outlet. The positive outlet of the second multiplier via the feedback resistor is connected to a non-inverting inlet of the OA, and the negative one - to an inverting inlet of the OA. The first divider is connected between the plus bus and the switching contact of the third link, and its outlet is connected to the inverting inlet of the OA. The second divider is connected between the switching contact of the fourth link and the common bus, and its outlet is connected to the non-inverting inlet of the OA. The balancing resistor with taps, which is connected to the balancing outputs of the OA. The fifth interchanged link is connected between the plus bus and one of the outlets of the balancing resistor.

EFFECT: simplification and increased reliability of a device.

1 dwg

Description

The invention relates to measuring equipment and can be used in various spacecraft systems.

A known direct current measuring transducer comprising a magnetic circuit, covering a current path with a measured current, the magnetic circuit having a narrow gap in which a Hall sensor and a power amplifier are located, wherein its input is connected to one of the output terminals of the Hall sensor, and the other output terminal of the latter is connected to ground bus, a negative feedback winding connected between the output of the power amplifier and the load, the other output of which is connected to the ground bus, the power amplifier contains a follower but the connected alternating voltage amplifier based on a differentiating operational amplifier, a storage device and a current amplifier, and the current terminals of the Hall sensor are connected to a sinusoidal current source, one of the current terminals being connected to the ground bus, and the other terminal connected to the voltage comparator and pulse shaper connected in series , the output of the latter is connected to the control input of the storage device (RF patent No. 2234706).

The known device has undoubted advantages, such as:

- the presence of galvanic isolation of the output of the device 12 from the current lead 2;

- it does not require a model resistor (shunt);

- current lead 2 can be connected to any bus in which it is necessary to measure the current - at least in positive, at least in negative.

However, this device is not reliable enough, since it has a large number of functional units (4, 6, 10, 11) and, therefore, elements, it requires a secondary power source (not shown in Fig. 1), which generally increases the number of elements in the device, increases its size and weight.

A known DC-DC converter containing the first and second magnetic circuits, the first of which is the first working winding, the second is the second, bias winding, compensation and measuring windings, a valve block with two input leads, are simultaneously located on both magnetic circuits, the first of which is connected to the first output terminal of the AC source, the first output terminal of the valve unit is connected to the second through a series-connected DC source and a winding with In addition, the first output of the compensation winding is connected to the first output of the measuring device, and the conclusions of the measuring winding are connected to input buses, a reference resistor, a DC amplifier and a shunt resistor, while the magnetic cores are placed in a magnetic screen, on top of which the measuring and compensation windings, the valve block are placed made with an additional two pairs of output terminals, each of which is connected to one of the working windings, the second input terminal of the valve block is connected to the second output a reference resistor is connected between the first and second terminals of the valve block, in addition, they are connected to the input of a DC amplifier, parallel to the terminals of which a shunt resistor is connected, the first terminal of which is connected to the second terminal of the compensation winding, and the second terminal is connected to the second the output of the measuring device (ed. testimonial. USSR No. 1291889).

However, this device for measuring current is not reliable enough and has large dimensions and weight due to the presence of a large number of elements necessary for its implementation (elements: in the AC source 9; valve units 10, 11; in the DC amplifier 13, for which it is necessary secondary power source - it is not shown in Fig. 1; 1-8, on which a magnetic amplifier is essentially made).

Closest to the proposed technical essence (prototype) is a device for measuring current, containing a DC amplifier with isolation (ed. Certificate of the USSR No. 1336200) with a measuring shunt connected to its input.

The disadvantages of the prototype are: insufficiently high reliability due to the presence of a large number of elements - to power the amplifier 1 requires an additional bipolar secondary power source, which increases the total number of elements and dimensions of the device at least twice; insufficiently high noise immunity due to the presence in the device of both positive and negative feedbacks.

The aim of the invention is to simplify the device, increase reliability, noise immunity, long-term accuracy, giving the device the ability to work from one source with a reduced supply voltage and versatility - the ability to work with a measuring resistor (shunt) included in any power bus (plus or minus).

This goal is achieved by the fact that in the current sensor containing a measuring shunt, which is connected in series with the load, an operational amplifier (OA), a transformer having four windings, four soldered switching jumpers are introduced; the first terminal of the measuring shunt is connected to the second terminal of the load, the normally open contact of the third jumper and the normally closed contact of the fourth jumper; the second terminal of the shunt is connected to the switching contact of the second jumper; a first load terminal is connected to a switching contact of the first jumper; normally closed contacts of the first and third jumpers are connected to a normally open contact of the second jumper and are connected to the common negative bus; normally open contacts of the first and fourth jumpers are connected to a normally closed contact of the second jumper and the plus bus; an integrator assembled on an operational amplifier and a capacitor introduced is introduced; a p-n-p type regulating transistor is introduced, the base of which is connected through a resistor to the op-amp output and through another resistor to the emitter of the same transistor, and the emitter is connected to the plus terminal of the op-amp power supply and plus bus; the negative terminal of the power supply of the OS is connected to a common bus; the collector of the control transistor is connected to the input of the introduced RC filter, the output of which is connected to the power buses of the input blocking generator, assembled using a transistor of two resistors, a capacitor, a diode and two transformer windings; two other windings with the same transformation coefficients are connected to the input voltage multipliers (for example, triplers), the outputs of which are connected to shunt resistors; the output of the first multiplier is connected to the output of the device; the positive output of the second multiplier through the feedback resistor is connected to the non-inverting input of the op-amp, and the negative is connected to the inverting input of the op-amp; two resistive dividers with the same division factors are introduced; the first divider is connected between the plus bus and the switching contact of the third jumper, and its output is connected to the inverting input of the op-amp; the second divider is connected between the switching contact of the fourth jumper and the common bus, and its output is connected to the non-inverting input of the op-amp; introduced a balancing resistor with taps, which is connected to the balancing conclusions of the op-amp; introduced the fifth soldered jumper, which is connected between the plus bus and one of the terminals of the balancing resistor.

The electrical circuit diagram of the device is shown in the figure (for clarity of the illustration, soldered wire jumpers 1-4 are shown as single-pole two-position switches and shown in the position when the shunt is connected to the plus bus, and jumper 44 is shown as a soldered single-pole multi-position switch, which is shown in the connection position to the middle terminal of the balancing resistor 43).

A direct current sensor with galvanic isolation of the device output from the power bus contains: four soldered switching jumpers 1-4; measuring shunt 5, the first terminal of which is connected to the second terminal of the load 6, the normally open contact of the jumper 3 and the normally closed contact of the jumper 4; the second terminal of the shunt 5 is connected to the switching contact of the jumper 2; the first output of the load 6 is connected to the switching contact of the jumper 1; normally closed contacts of jumpers 1 and 3 are connected to a normally open contact of jumper 2 and are connected to the common negative bus; normally open contacts of jumpers 1 and 4 are connected to a normally closed contact of jumper 2 and the plus bus; an integrator assembled on an operational amplifier 7 and a capacitor 8; a regulating transistor 9, the base of which is connected through the resistor 10 to the output of the op-amp 7 and through the resistor 11 to the emitter, and the emitter to the positive output of the op-amp and the plus bus; the negative output terminal of the op-amp power supply is connected to a common bus; the collector of the transistor 9 is connected to the input of the RC filter 12, 13; four-winding transformer 14 with windings 15-18; on elements 14-16, 19-23 a blocking generator is assembled, the power bus of which is connected to the output of the RC filter 12, 13; in the transformer 14, the windings 17 and 18 have the same transformation ratio; winding 18 through a voltage multiplier - a triplicator (elements 24-29) is connected to a shunt resistor 30, and the output of the device; winding 17 through a voltage multiplier - a triple (elements 32-37) is connected to a shunt resistor 37; the positive output of the multiplier (elements 31-36) through the feedback resistor 38 (it determines the upper point of the measuring range) is connected to the non-inverting input A of the op-amp 7, and the negative - to the inverting input B of the op-amp 7; a first resistive voltage divider, which is assembled on resistors 39, 40 and connected between the positive power bus and the switching contact of the jumper 3; the output of the first divider (connection point 39 and 40) is connected to the inverting input B of the OS 7; a second resistive divider, which is assembled on resistors 41, 42 and connected between the switching contact of the jumper 4 and the common bus; the output of the second divider (connection point 41 and 42) is connected to the non-inverting input A of the OS 7; the division factors of the dividers with high accuracy are equal to two, because assembled on four precision resistors of the same rating; balancing resistor 43 with additional taps, the extreme terminals of which are connected to the balancing terminals of the op-amp 7, and one of the taps, when the device is set to the minimum output voltage at zero measuring current, is connected by a soldered jumper 44 to the plus bus.

The device operates as follows. When power is applied, current begins to flow through shunt 5 and load 6; voltage drop appears on shunt 5:

, (1) $$U_w=R_w\cdot I_n$$

, (one)

where U _W - voltage drop on the shunt 5;

R _W - the resistance of the shunt 5;

I _W - load current 6.

With the same resistances 39-42, the division coefficients of the first and second dividers will be equal to two, so you can find the voltage between the non-inverting A and inverting B inputs of the OS 7:

(2) $$U_{A-B}=\frac{U_{P\mathrm{and}t}-U_w}{2}-\frac{U_{P\mathrm{and}t}}{2}=-0,5U_w$$

(2)

From the expression (2) it can be seen that U _AB is independent of the supply voltage U _pit .

Due to the negative feedback, the integrator on the op amp 7 and the cascade on the transistor 9 will supply such a supply voltage to the blocking generator so that the positive voltage coming from the output of the multiplier (elements 31-36) through the resistor 38 to point A compensates for the one present at the point A with respect to point B, the negative voltage (2) is negligible.

When the load current changes, the compensating voltage at the output of the multiplier (elements 31-36) and the voltage at the output of the multiplier (elements 24-29) will equally change, i.e. the conversion U = f (I) will be performed with galvanic isolation.

The proposed device is simpler because contains fewer elements and, therefore, its reliability is higher. The noise immunity of the device is increased due to the introduction of an integrator 7, 8 and an RC filter 12, 13. The supply voltage of the device was reduced by introducing voltage multipliers into it, thereby preserving the possibility of using standardized transformers. The long-term accuracy of the device is improved by introducing the balancing of the op-amp 7 by soldering the jumper 44 to one of the additional terminals of the balancing resistor 43, i.e. the unreliable movable contact of the tuning resistor is excluded (the recommended op-amp balancing circuit is shown in Fig. 7 on l.56 in AEYAP.431130.187-17TU). The device’s universality has been increased by simply soldering the four jumpers, the measuring shunt can be included in the plus or minus bus (this may be necessary for the developer of the design documentation when, at the time of its release, for some reason, it is not 100% known which bus to include the shunt in).

The prototype, when measuring current from 0 to 0.6 A with a shunt of 0.1 Ohms and an output voltage of 0 to 6 V under normal conditions, had a non-linearity of the output characteristic U = f (I) of not more than 1% at U _pit = 3.7 -5.5 V.

A prototype device was assembled: on a chip 140UD17A; transistors 2T313B and 2T3117A; transformer TIL2V; diode assembly 2DS627A; resistors C2-29V, C2-33H, resistive assembly B19K-1-1 (balancing resistor 44); capacitors K10-17, K53-65.

Of the patent information materials known to the applicant, no signs were found that are similar to the totality of the features of the claimed object.

Claims (1)

A universal DC sensor with isolation and low-voltage power supply, comprising a measuring shunt that is connected in series with the load, an operational amplifier (OA), a transformer having four windings, characterized in that four soldered switching jumpers are introduced; the first terminal of the measuring shunt is connected to the second terminal of the load, the normally open contact of the third jumper and the normally closed contact of the fourth jumper; the second terminal of the shunt is connected to the switching contact of the second jumper; a first load terminal is connected to a switching contact of the first jumper; normally closed contacts of the first and third jumpers are connected to a normally open contact of the second jumper and are connected to the common negative bus; normally open contacts of the first and fourth jumpers are connected to a normally closed contact of the second jumper and the plus bus; an integrator assembled on an operational amplifier and a capacitor introduced is introduced; a p-n-p type regulating transistor is introduced, the base of which is connected through a resistor to the op-amp output and through another resistor to the emitter of the same transistor, and the emitter is connected to the plus terminal of the op-amp power supply and plus bus; the negative terminal of the power supply of the OS is connected to a common bus; the collector of the regulating transistor is connected to the input of the introduced RC filter, the output of which is connected to the power buses of the introduced blocking generator, assembled using a transistor, two resistors, a capacitor, a diode, and two transformer windings; two other windings with the same transformation coefficients are connected to the input voltage multipliers, the outputs of which are connected to shunt resistors; the output of the first multiplier is connected to the output of the device; the positive output of the second multiplier through the feedback resistor is connected to the non-inverting input of the op-amp, and the negative is connected to the inverting input of the op-amp; two resistive dividers with the same division factors are introduced; the first divider is connected between the plus bus and the switching contact of the third jumper, and its output is connected to the inverting input of the op-amp; the second divider is connected between the switching contact of the fourth jumper and the common bus, and its output is connected to the non-inverting input of the op-amp; introduced a balancing resistor with taps, which is connected to the balancing conclusions of the op-amp; introduced the fifth soldered jumper, which is connected between the plus bus and one of the terminals of the balancing resistor.