SU1765784A1 - Converter of transient electric resistance of contacts into voltage - Google Patents

Abstract

Usage: in the measuring technique, in particular in the information-measuring systems. SUMMARY OF THE INVENTION: The device comprises a signal generator 1, a voltage transformer 3, an amplifier 8, clamps 6 for connecting a measured electrical resistance of the contacts, capacitors 2 of constant capacitance. One output of the signal generator 1 is connected to one of the terminals b for connecting the contacts. The other output of the signal generator 1 is connected via a load 7 to a second terminal 6. Parallel to the terminals 6, a resonant circuit, formed by capacitors 2 of constant capacity and primary winding 4 of transformer 3, is connected. The secondary winding 5 of the transformer 3 is voltage by one output connected to the common bus and the other to the input of the amplifier 8 having the output 9. The voltage transformer 3 is made on a ferrite core having a short-circuited winding 10. 2 Il.

Description

The invention relates to a measurement technique, in particular, to information and measurement systems, and can be used in measuring transient electrical resistance of contacts of contactors, switches of relays, etc.

A device for measuring and converting electrical resistance to voltage 1 is known.

Device 1 contains a voltage source (square-wave pulse generator), large-scale current transducer, synchronous detector, indicator, node

phase adjustments, a field effect transistor, a bandpass filter, and a control voltage source.

AC power with a constant amplitude through a large-scale converter is fed through one pair of terminals to a measured resistance, the voltage drop across which through another pair of terminals goes to the amplifier, the signal from which, corrected in phase by the phase control unit, goes to the synchronous detector controlled by signal of the source of rectangular pulses, and is fed to the indicator.

The presence of a phase adjustment unit in the device, a bandpass filter, allows measuring small active resistances with sufficient noise immunity, however, the accuracy of conversion of the resistance value to voltage strongly depends on the quality of the voltage source, the stability of the bandpass filter, the sensitivity of the synchronous detector, which together This complicates the measurement process; in addition, the conversion characteristic is unknown, which is a drawback of the device.

A device 2 is known comprising a voltage source, a key, a single-stage amplifier, a voltage amplifier and a memory block.

The conversion process is divided into two cycles. In the first cycle, the memory unit remembers the voltage corresponding to the additive error (method error). In the second cycle, the voltage on the measured resistor and the voltage corresponding to the method error are recorded. At the output of the converter, there is a voltage that does not contain voltage due to the additive error of the converter and corresponding to the voltage drop across the measured resistor.

The accuracy of the conversion in the device depends on the multiplicative (instrumental) error due to the parameters of the reference voltage source, the reference resistor, the nonlinearity of the links involved in the conversion process, which can be attributed to the lack of the device. In addition, the conversion process is rather complicated,

The closest in technical terms to the device claimed is device 3, a converter of impedance parameters to voltage, containing a voltage source, exemplary complex resistances, amplifiers, input terminals and an output terminal, a current transformer and a voltage transformer.

The output voltage of the converter consists of the favorable voltage of the main amplifier and the correction voltage generated by the correction amplifier from the conversion error made by the first amplifier.

The disadvantages of this device include the fact that the accuracy of transforming the impedance into voltage depends on the ratio of currents and magnetic fluxes in transformers, the stability of the transfer coefficients of amplifiers, the accuracy of preparation and the values of exemplary resistances. in the feedback circuit and the input resistances of the amplifiers, and all this is difficult to achieve with high accuracy.

In addition, the transformation characteristic is unknown, which is important for the subsequent processing of the output signal.

The purpose of the invention is to improve the conversion accuracy by obtaining a linear relationship and reducing hardware costs.

The goal is achieved in a known device comprising a voltage source, a voltage transformer, an amplifier, clamps for connecting the measured electrical contact resistance by connecting the primary winding of the transformer, parallel to the terminals for connecting the measured electrical contact resistance, one output of the secondary winding the voltage transformer is connected to the input of the amplifier, the second output of the secondary winding of the voltage transformer is connected to a common bus voltage transformer is further provided with short-circuited winding.

Namely, the connection in the known device through the capacitors of the primary winding of the voltage transformer parallel to the terminals for connecting the measured electrical resistance of the contacts, resulting in the LC circuit, the selection of the operating point of the device on the linear portion of the LC circuit, allows to obtain a high conversion accuracy contact resistance to voltage and linear relationship between the output voltage and the measured contact resistance, the lack of precision in the device Comparison elements drastically reduce hardware costs, making the device simple and convenient to use, connecting one output of the secondary winding of a voltage transformer to the input of an amplifier, the second output of which is connected to a common bus, makes it possible to capture even minor voltage changes occurring in the secondary winding, the presence in the voltage transformer of the short-circuited noise-reducing winding also improves the conversion accuracy and stability of the device, resulting in a tuned one The device significantly simplifies the process of measuring the transient electrical resistance of the contacts, since it reduces to connecting the measured resistance to the terminals available for this purpose.

Fig, 1 shows a block diagram of the device, which contains:

1- voltage source;

2- capacitors

3-voltage transformer;

A - the primary winding of the voltage transformer 3;

5- secondary winding of transformer 3;

6- clamps for connecting contacts;

7- load;

8-amplifier;

9- exit;

10- short-circuited voltage transformer winding 3.

FIG. 2 schematically shows a voltage transformer 3 which contains;

4- the primary winding of the voltage transformer 3;

5- secondary winding of voltage transformer 3;

10- short-circuited winding of voltage transformer 3;

11- ferromagnetic core. One output voltage source 1

connected to one of the clips 6 for connecting the test object. The other output of the voltage source 1 is connected via a load 7 to a second terminal 6 for connecting a test object.

In parallel with the terminals 6 for connecting the test object, the primary winding 4 of the voltage transformer 3 is connected via capacitors 2. The secondary winding 5 of the voltage transformer 3 is connected to the input of the amplifier 8 having output 9 and the other to the common busbar.

The voltage transformer 3 contains a ferromagnetic core 11, on which the primary 4 and secondary 5 windings are located, as well as the short-circuited winding 10.

The device for converting the transient electrical resistance of the contacts to the voltage operates as follows.

After switching on the voltage source 1, made on the basis of the known circuit 4, allowing adjustment of the frequency and amplitude and the output of which is connected to the load 7, through the capacitors 2 the primary winding 4 of the voltage transformer 3, the LC circuit organized by the primary winding 4 of the voltage transformer 3 and capacitors 2, is tuned to resonance at a certain frequency.

In this case, the tuning is performed in such a way that the working frequency corresponds to a point located not on the top of the resonance curve, but on the linear portion of one of its branches.

This operation is performed once during the setup process of the device.

Further operation of the device is carried out in this way.

Before the conversion of the transient electrical resistance of the contacts to the voltage

The initial resistance of the clamps (conductors for connecting the test object) is selected by adjusting the amplitude of the voltage source 1 so that the output 9 of the amplifier 8 or even

there was no voltage, or a value corresponding to the initial resistance. After that, the control object is connected to the terminals 6 and, depending on the magnitude of the transient resistance

contacts, the LC circuit is shunted to a greater or lesser extent (primary winding 4, capacitors 2).

It is known that the LC circuit tuned to resonance has active resistance.

Now, if such a circuit is bridged by resistance (transient electrical resistance of the contacts), then the system will redistribute the currents

It is also known that the current in one of two parallel branches, FIG. 4, is equal to the total current multiplied by the resistance of the other branch and divided by the sum of the resistances of both branches, i.e. when the LC circuit is bypassed by the control object, the current through the primary winding 4 of the voltage transformer 3 will be

45

Z + Zx

where I is the total (total) current;

And - the current flowing through the LC-circuit - Z-impedance LC-circuit;

Zx - complex resistance of the object of control.

This current will cause the secondary winding 5 of the voltage transformer 3 signal (voltage) corresponding to the magnitude of the contact resistance of the transformer, which is amplified by the amplifier 8, and from its output 9 is fed to the recording

a device (not shown in the diagram), and the scale of which can be calibrated in Omax, or directly measured, for example, with a B7-27 A / 1 5 voltmeter, and the resistance value determined from the conversion characteristic.

Since the operating point of the device is on one of the branches of the resonance curve, in its linear section, the conversion characteristic is linear. LC circuits have good quality, so the device is sensitive to very small values of the control object.

A load 7 is needed to optimally select the total current and limit this current consumed from the voltage source 1.

The short-circuited winding 10 provides for the suppression of random noise, the presence of which can seriously affect the accuracy and linearity of the conversion process.

The introduction of the short-circuited winding 10 allows to obtain an output signal to the measuring circuit with almost no distortion, which leads to a more accurate measurement and, consequently, to a more accurate process of converting the contact resistance to voltage. It happens as follows. In a short-circuited winding 10, a self-induction EMF is induced, which causes a current in it that creates its own electromagnetic field directed oppositely to the main one, which reduces the signal in the secondary winding 5. Thus, external influences as well as distortions of the output signal arising due to the heterogeneity of the core material 11 the transformer 3, the disturbing signal in the output winding is compensated by the field of the short-circuited winding 10.

The capacitors of the capacitors 2 may be different in their nominal value, however, for the identical connection of the LC circuit to the terminals 6, their value follows

choose the same, and such that the resonance at the received frequency is ensured. In addition, they perform the role of coupling capacitors, excluding the constant component, if the output

For some reason, the voltage of the voltage source 1 is not purely sinusoidal.

Thus, compared with prototype 3, the claimed technical solution

Claims (1)

allows to increase the accuracy of conversion of transient electrical resistance of contacts to voltage, ensures linearity of the conversion process, by eliminating precision comparison elements (exemplary measures) dramatically reduces hardware costs, greatly simplifies the measurement process. The invention transforms an electrical contact transistor into a voltage containing a voltage source, a voltage transformer, an amplifier, clamps for connecting the measured electrical resistance of the contacts, which is so that, in order to improve the accuracy of conversion by obtaining a linear relationship and reduce hardware costs, in it parallel to the terminals for connecting the measured electrical contact resistance through capacitors connected primary winding tr voltage transformer, one output of the secondary winding of the voltage transformer is connected to the input of the amplifier, The second terminal of the secondary winding of the voltage transformer is connected to the common bus, and the voltage transformer is additionally equipped with a short-circuited winding. 1 & FIG. 2