RU2238570C1 - Bridge transformer - Google Patents

Abstract

FIELD: electric engineering.

SUBSTANCE: device has bridge sensors power source, connected to one output of power main for bridge sensors, and operational amplifier, output of which is connected to another output of bridge sensors power main, and inverse input - to one output of bridge sensors output line, while between resistor of another output of bridge sensors output line and non-inverse input of operational amplifier a voltage separator is switched in, which is made in form of two serially connected resistors. As output of voltage separator is loaded for a very high input resistance of operational amplifier, the very voltage separator may always by made with use of high-ohm resistors, to allow practically non-loaded bridge sensors output line and allow to evade effect from resistor of output line of bridge sensors as a result of transformation.

EFFECT: higher sensitivity of device, higher value of output signal of device.

2 cl, 2 dwg

Description

The invention relates to electrical engineering, in particular to strain measurement, and can be used as a signal converter of bridge strain gauge sensors.

A bridge converter with a power source connected to the supply diagonal of the bridge and an output signal taken from the output diagonal of the bridge is widely known (O. Khorna. Strain gages. M.-L.: Gosenergoizdat, 1962, Fig. 1). However, the resistance of the connecting wires and their variations introduce significant errors in the conversion result.

The closest in technical essence and the achieved effect is the bridge converter shown in figure 1, containing the power supply of the I / E bridge (current generator or voltage generator) connected to one output of the power diagonal of the bridge R1 / R2 / R3 / R4, and operating amplifier U, the output of which is connected to the other output of the bridge’s supply diagonal, and the inverse input is connected to one output of the bridge’s output diagonal, non-inverse with the device’s common bus (Gutnikov BC Integrated electronics in measuring devices. L .: Energy, 1980, Fig. 5-1 2c, p. 124 and fig. 5-14a, p. 128). In such a bridge converter, errors from the influence of the resistances of the connecting wires and their variations are significantly reduced, the bridge power supply is connected to the device common bus, the converter output signal is removed relative to the device common bus.

When the bridge power supply, which is a voltage source E, the output signal U of the bridge converter is equal to:

(see ibid., formula 5-13).

For the working imbalance of the bridge:

R1 = R + ΔR; R2 = R-ΔR; R3 = R + ΔR; R4 = R-ΔR,

the output signal has the form:

.

.

When the bridge power supply, which is a current source I, the output signal U of the bridge converter is equal to:

For the working imbalance of the bridge, here the output signal has the form:

U = IΔR.

However, the output signal U of such a bridge converter is small, which, as is known, is not enough for most tasks, and it is necessary to introduce additional amplification devices that inevitably introduce additional errors (in particular, for example, increase the noise component of the useful signal and its corresponding drift) .

An object of the present invention is to increase the sensitivity of a bridge converter.

The technical result of the invention is a significant, for example 10-fold, increase in the output signal of the bridge converter.

The technical result is achieved by the fact that in a bridge converter containing a bridge power supply connected to one output of the bridge’s supply diagonal, and an operational amplifier, the output of which is connected to the other output of the bridge’s supply diagonal, and an inverse input with one output of the bridge’s output diagonal, between the other terminal the output diagonal of the bridge and the non-inverse input of the operational amplifier include a voltage divider, while the voltage divider is made in the form of two resistors connected in series.

Figure 1 is a diagram of a prototype; figure 2 - diagram of the proposed bridge Converter.

The bridge converter comprises a bridge R1 / R2 / R3 / R4, an operational amplifier U, an I / E bridge power supply and a voltage divider D, consisting, for example, of resistors r1 and r2 (Fig. 2).

The bridge converter operates as follows.

The bridge R1 / R2 / R3 / R4 through its diagonal of power is powered jointly by the I / E power source and the operational amplifier U. As a result of the useful imbalance, there is a useful bridge output signal equal to the potential difference on its output diagonal φ _d -φ _b . The potentials at the non-inverse and inverse inputs of the operational amplifier U are almost equal (due to its large gain), i.e. φ _b = φ _d . Therefore, the input to the non-inverse input of the operational amplifier of the bridge potential part φ _d , i.e. potential φ _d , increases the potential φ _b and, of course, in turn increases the potential φ _d , which is the output signal of the bridge converter U.

With a bridge power supply, which is a voltage source E, we have, as a first approximation, the following system of equations:

Here i1, i2, i3, i4 are the currents through the corresponding bridge resistances R1, R2, R3, R4; φ _a , φ _b , φ _c , φ _d are the corresponding potentials of the bridge vertices; n is the division factor of the divider; r1, r2 - resistors of the divider; φ _d is the potential at the output of the divider, E is the voltage of the power source, U is the output voltage of the bridge converter.

We carry out the corresponding transformations:

φ _c = φ _b -R2i2 = U-R3i3;

U-R3i3 = φ _b -R2i2;

UR1R4-ER1R3 + UR1R3 = nUR1R4-ER2R4 + nUR2R4;

U (R1R4 + R1R3-nR1R4-nR2R4) = E (R1R3-R2R4);

For the working imbalance of the bridge:

- коэффициент усиления полезного сигнала.Where

- gain of the useful signal.

With a bridge power supply, which is a current source I, we have, to a first approximation, the following system of equations:

We carry out the corresponding transformations:

R1i1 + φ _b = R4 (I-i1) + U;

R1i1 + φ _b = R4I-R4i1 + U;

φ _b -R2i1 = U-R3 (I-i1);

U-φ _b = R3I- (R3 + R2) i1;

(U-φ _b ) (R1 + R4) -R3I (R1 + R4) + R4I (R2 + R3) + (U-φ _b ) (R2 + R3) = 0;

(U-φ _b ) (R1 + R2 + R3 + R4) = I [R3 (R1 + R4) -R4 (R2 + R3)];

For the working imbalance of the bridge:

U = KIΔR.

That is, as in the previous case, the useful signal is amplified by a factor of K. For example, with a divisor dividing factor of n = 0.9, the useful signal of the proposed bridge converter is 10 times larger than that of the prototype, without any additional amplifying elements that could introduce additional errors due to their noise and drift components.

It should be noted that the voltage divider can be performed according to any known scheme, for example, potentiometric with adjustment of the division coefficient using variable resistors. Because the output of the divider is loaded with a very high input resistance of the operational amplifier, the divider itself can always be made using high-resistance resistors, which will practically not load the output diagonal of the bridge and avoid the influence of the resistance of the output wire of the bridge on the conversion result.

According to this proposal, the institute carried out the corresponding theoretical and experimental studies on the creation of specific converters, which confirm the possibility of implementing the considered bridge converters and the possibility of obtaining the claimed technical result.

The implementation of the proposal in the IMS for strength studies of aircraft structures will significantly increase the reliability of the test results, and therefore, the reliability of recommendations issued by the industry on improving the design of aircraft.

Claims (2)

1. A signal converter of bridge sensors, comprising a bridge power source connected to one output of the bridge’s power diagonal, and an operational amplifier, the output of which is connected to the other bridge’s power supply diagonal, and an inverse input with one output of the bridge’s output diagonal, characterized in that between the resistance of the other output of the output diagonal of the bridge and the non-inverse input of the operational amplifier includes a voltage divider. 2. The bridge converter according to claim 1, characterized in that the voltage divider is made in the form of two series-connected resistors.

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