RU2335776C1 - Resistance strain gauge signal converter - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: resistance strain gauge signal converter contains operational amplifier, and power supply connected to one terminal and global bus of the converter, output of the operational amplifier is connected to the second terminal, complemented input is connected to the third terminal. Additionally the converter includes voltage source and commutator switch contact of which is connected to uncomplemented input of the operational amplifier, other two contacts of the commutator are connected respectively to one terminal of voltage source and global bus of the converter connected to other terminal of voltage source.

EFFECT: improved performance of the converter.

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Description

The invention relates to electrical engineering, in particular to electrotensometry, and is intended for use as a signal converter of four-wire bridge and single strain gauge sensors of multi-point measuring systems for analysis of the stress-strain state of structures.

The crucial stage in the modern industrial production of machinery, apparatus and structures is the determination of deformations, stresses, displacements and forces caused by power loads. The solution to this problem is provided by measuring devices capable of measuring signals from strain gauge sensors, which are both a strain gauge bridge and single strain gauges (see, for example, L. Daychik, N. I. Prigorovsky, G. Kh. Khurshudov. Methods and tools full-scale tensometry: Reference. Fundamentals of machine design. - M.: Mechanical engineering, 1989. Fig. 6 - p. 51; Fig. 7 - p. 53; p. 89; Fig. 3 - p. 120; Fig. 7 - p. .121). An important element of such measuring devices is a signal converter of strain gauge sensors to electrical voltage.

A known 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 (O. Horna. Strain gages. M.-L.: Gosenergoizdat, 1962, Fig. 1 - p. 13). However, the resistance of the connecting wires and their variations introduce significant errors in the conversion result. For example, when conducting field (full-scale) experiments, the length of the connecting measuring lines connecting the sensors to the measuring equipment reaches 200 m or more (Glagovsky B.A., Piven I.D. Resistance electrotensometers. L .: Energia, 1972, p. 59 ) In addition, multi-point measuring systems for switching sensors have switches at the input, which, according to the transition resistance, introduce additional conversion errors.

The closest in technical essence and the achieved effect to the proposed one is a signal converter of bridge resistor sensors, containing a current source connected to one vertex of the supply diagonal of the bridge, and an operational amplifier whose output is connected to another vertex of the supply diagonal of the bridge; the non-inverse input of the operational amplifier is connected to the common bus of the device, the inverse input is connected to one vertex of the output diagonal of the bridge, and the output signal is taken from the second top of the output diagonal of the bridge by two (current and potential) wires (see, for example, Gutnikov BC Integrated electronics in measuring devices. Leningrad: Energy, 1980, Fig. 5-14a - p. 128). Such a construction of the converter significantly reduces errors from the influence of the resistances of the connecting wires, the switching elements of the input switches and their variations. Moreover, the fact that the bridge power source is connected to the device’s common bus and the converter output signal is removed relative to the device’s common bus positively affects (from the point of view of aggregation) the construction of all measuring equipment. However, such a converter requires five wires to connect the bridge sensor to the converter, which accordingly must have five connection terminals. In addition, such a converter does not allow (except for bridge sensor signals) to convert sensor signals in the form of a single strain gauge.

The aim of the invention is to expand the functionality of the Converter, namely the possibility of converting signals from both bridge and single strain gauge sensors.

To this end, in the signal transducer of the strain gauge sensors containing the operational amplifier, and the current source connected to one connecting terminal and the common bus of the converter, the output of the operational amplifier is connected to the second connecting terminal, the inverse input is connected to the third connecting terminal, the voltage source and switch are introduced, the switching contact of which is connected to the non-inverse input of the operational amplifier, the other two contacts of the switch are connected respectively to one glue mm voltage source and a common converter bus connected to another voltage source terminal

Conducted patent research did not reveal identical and similar technical solutions. The proposed Converter can be manufactured on an industrial scale and is suitable for use in industry and construction.

The inventive device has been successfully tested. The set of essential features of the claimed device does not follow explicitly from the studied prior art, has significant differences from the considered analogues. Therefore, the claimed device meets the criterion of "novelty" and has an inventive step.

The invention is illustrated by drawings, which show a diagram of the proposed device and shows examples of its use. Figure 1 shows the connection to the strain gauge bridge, figure 2 - connection of the proposed Converter to a single strain gauge. Since the strain gauge bridge and a single strain gauge are not elements of the proposed device, they are shown in dotted diagrams.

The converter contains a current source 1, a voltage source 2, an operational amplifier 3, a switch 4, connecting terminals 5, 6, 7. The position 8 indicates the common bus of the device, the position 9 is the pick-up point of the converter output signal relative to the common bus 8, and the position 10 is a switching contact switch 4, positions 11 and 12 are the other contacts of switch 4. The indices R and R1 ÷ R4 denote a single strain gauge and a strain gauge bridge, respectively.

The current source 1 is connected to one connecting terminal 5 and the converter common bus 8, the output of the operational amplifier 3 is connected to the connecting terminal 6, and its inverse input is connected to the connecting terminal 7, switching contact 10 of switch 4 is connected to a non-inverse input of operational amplifier 3, contact 11 switch 4 is connected to one terminal of the voltage source 2, the other terminal of which and terminal 12 of switch 4 are connected to the common bus 8 of the Converter

The Converter is connected to a strain gauge bridge (R1 ÷ R4) (Figure 1) or to a single strain gauge R (Figure 2), as shown in the figures.

The position of the switch 4, in which the non-inverse input of the operational amplifier 3 is connected to a common bus 8 (Figure 1), corresponds to the operating mode of the converter with a strain gauge bridge (R1-R4), and the position of the switch 4, in which the non-inverse input of the operational amplifier 3 is connected to the source 2 voltage corresponds to the mode of operation of the Converter with a single strain gauge R (Figure 2).

The operational amplifier 3 is covered by deep negative feedback, so the potential at its inverting input is almost equal to the potential at its non-inverting input. The current of the current source 1 flows through terminal 5, the strain gauge R or the strain gage bridge R1 ÷ R4, terminal 6 to the output of the operational amplifier 3. The inverse input of the operational amplifier 3 is connected to the sensor through terminal 7, through which current does not flow, so the potentials at both ends of this device sections are equal, regardless of its length and resistance of the connecting wire.

If the Converter is connected to the strain gage bridge (Figure 1), the current from the current source 1 flows along one diagonal of the bridge (R1 ÷ R4), a useful signal is generated on the other diagonal of the bridge, one vertex of which (as well as the non-inverse and inverse inputs of the operating amplifier 3) is under the potential of the common bus (0 V), and the output signal U of the converter is removed from the other vertex, the value of which (up to the sign) is:

или U=IΔR,

or U = IΔR,

with R1 = R3 = R0 + ΔR and R2 = R4 = R0-ΔR,

where ΔR is the increment of the resistance of the strain gages of the bridge (R1-R4);

(see, e.g., Karandeev KB Special methods of electrical measurements. M. - L .: Gosenergoizdat, 1963, p.100).

When the Converter is operating with a single strain gauge (Figure 2), the potential of one of the terminals of the strain gauge R will always be almost equal to the voltage E of the voltage source 2. The output signal U of the converter here is equal to the difference between the voltage E and the voltage drop across the strain gauge R:

U = E-IR

or U = E-I (R0 + ΔR) = (E-IR0) -IΔR,

where R0 is the nominal (initial) resistance of the strain gauge,

ΔR is the increment of the resistance of the strain gauge.

With E = IR0, the output voltage of the converter is proportional to the increment of the resistance of the strain gauge:

U = -IΔR.

The characteristic of the converter as a function of the increment of the resistance ΔR here can be asymmetric (if required) by the appropriate choice of the ratio of the voltage value E of the voltage source 2 and the current value I of the current source 1.

The useful characteristics of the proposed technical solution include the simplicity of automation of the switching of converter operation modes by making switch 4 based on electronic CMOS circuits with a control input.

This converter has a number of positive properties: the ability to work with remote sensors with four-wire connection, the ability to electronically switch sensors with four-channel microcircuits, the small number of elements used, their uniformity in both modes (which provides greater stability, reliability), is easy to maintain.

The implementation of the proposal in multi-point measuring systems for the analysis of the stress-strain state of structures in mechanical engineering and other industries will significantly simplify the receipt of test results, reduce the cost of manufacturing and maintenance of measuring equipment, increase the reliability of its work, and therefore the reliability of recommendations issued by the industry to improve tested designs.

Claims (1)

A strain gauge signal converter comprising an operational amplifier and a current source connected to one connection terminal and a common converter bus, an output of the operational amplifier is connected to a second connection terminal, an inverse input is connected to a third connection terminal, characterized in that a voltage source and a switch are inserted therein whose switching contact is connected to the non-inverse input of the operational amplifier, the other two contacts of the switch are connected respectively but to one terminal of the voltage source and the common bus of the converter connected to the other terminal of the voltage source.

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