MD1011Z - Method for transmission of three signals through the four-wire communication line - Google Patents

Abstract

The invention relates to methods of transmitting three signals and can be used in communication interfaces when transmitting information, in measuring the values of three thermo- or tenor resistors. The essence of the invention is that the values of currents at the input and output of the communication line, which correspond to the characteristic values of the conductances, they form two projective coordinate systems. For this purpose, the traveling currents with the required values are used. The projective coordinates of the points relative to their coordinate system are equal to each other. By measuring the currents at the input, the projective coordinates of the point are restored and the values of the informational or signal conductances are calculated.

Description

The invention relates to methods of transmitting three signals and can be used in communication interfaces for transmitting information, for measuring the values of three thermo- or strain gauges. Other devices can also be connected to the four-conductor communication line.

A method of transmitting signals from a transmitter to a receiver, connected to the communication line with two conductors with equal conductances and with a voltage source on the receiver side, is known, which includes transmitting the signal by the transmitter by varying its conductance, reading the current values in each conductor by the receiver and calculating the transmitted signal by integrating the measured currents [1].

The disadvantage of this method is the limited scope of use due to the high material consumption and the cost of the corresponding device. This disadvantage is related to the fact that the two-conductor communication line must be a separate communication line. Therefore, for the transmission of three signals, three separate communication lines or six conductors must be used. The final value of the leakage conductance (resistance) between the conductors of the communication line leads to the interaction of the signals and does not allow the use of the common conductor for the transition from the six-conductor switching line to the more economical four-conductor line.

The closest solution is a method of transmitting two signals from a transmitter to a receiver, located on the three-conductor communication line, which includes transmitting the signal from the transmitter by varying its conductance in two conductors of the communication line in relation to the third conductor, the last being a common conductor, consecutively connecting the conductances of two sets, each consisting of four conductances, reading by the receiver the values of the corresponding currents at the input and calculating the transmitted signals. In each set, two conductances are established with maximum and minimum values, the third conductance is a reference and ensures the zero value of the current and voltage for the fourth informational conductance of the other set.

The peculiarity of the procedure is that the values of the currents at the input and output of the communication line, which correspond to the conductance sets, form two projective coordinate systems. From projective geometry it is known that the coordinates of the points are equal to each other with respect to their coordinate systems. By measuring the input currents of the communication line, the projective coordinates of the output point can be restored.

For this, the complex ratio of the four conductances, as an inhomogeneous projective coordinate in each set, is assumed for each transmitted signal, and the informational conductance is calculated from this complex ratio. The homogeneous projective coordinates are calculated according to the two corresponding input current sets, after which the aforementioned inhomogeneous projective coordinates or the transmitted signals are calculated. In this procedure, manipulations or switchings are used only at the output of the line, i.e. from the transmitter side, which is convenient in practice [2].

The disadvantage of this method is the limited scope of use due to the increased consumption of materials and the cost of the corresponding device. This disadvantage is related to the fact that in the case of transmitting three signals through the four-conductor communication line, three sets of four conductances must be used. In the general case of such a communication line, the reference conductance of one set does not ensure the zero value of the current and voltage simultaneously for the informational conductances of other conductance sets. Therefore, it is not possible to introduce two projective coordinate systems, calculate homogeneous projective coordinates according to the input currents and restore the transmitted signals, and increasing the number of conductors of the communication line leads to an increase in the price of the corresponding device.

The problem that the invention solves consists in expanding the field of use, reducing the consumption of materials and the cost of the corresponding device.

The method, according to the invention, eliminates the above-mentioned disadvantages by including the calculation of the values of the displacement currents of two displacement current sources, connected to two conductors at the output of the communication line, and of the values of the reference conductances of three sets, each formed by four conductances: two of which have the minimum and maximum values, the third conductance being reference, and the fourth - informational, at the same time each of the reference conductances in each set ensures the zero value of the current and voltage simultaneously for the informational conductances in the other sets, the transmission of the signal from a transmitter to a receiver, located respectively at the input and output of the communication line, by varying the conductance of the transmitter in each of the three conductors of the communication line in relation to the fourth common conductor with the consecutive connection of the conductances in the sets, in each set the complex ratio of the four conductances, as a non-homogeneous projective coordinate, represents each transmitted signal, and the informational conductance is calculated from this complex ratio, the reading by the receiver of the values of the corresponding input currents and the calculation of the homogeneous projective coordinates and the mentioned inhomogeneous projective coordinates or the values of the transmitted signals, according to the respective sets of currents at the input of the communication line.

The essence of the procedure lies in the fact that the sources of displacement currents of the required value, together with the reference conductances, allow the use of projective coordinate systems for the currents at the input and output of the communication line and the calculation of the transmitted signals, according to the currents at the input of the initial four-conductor communication line.

The invention is explained by the drawings in Fig. 1-4, which represent:

- Fig. 1, functional diagram of the device with which the process is carried out;

- Fig. 2, equivalent diagram of the outgoing communication line;

- Fig. 3, equivalent diagram of the communication line with the displacement current sources;

- Fig. 4, equivalent diagram of the communication line with the reference conductance of the second load;

- Fig. 5, projective coordinate systems at the entrance and exit of the communication line.

The device in Fig. 1 contains the receiver 1 of the signals transmitted at the input of the four-conductor communication line 2, with loss conductances, and the transmitter 3 of the transmitted signals, located at the output of this communication line 2.

In turn, the receiver 1 contains a voltage source 4, which through the input current transducers 5 is connected to the input of the communication line 2.

The transmitter 3 contains 6 output current transducers, which are connected to the measuring inputs of the block 7 for calculating the parameters of the communication line 2, while the measuring inputs of the block 7 are connected to the output of the communication line 2. The outputs of the block 7 are connected to the inputs of two sources 8-1, 8-2 of displacement currents and three shapers 9-1, 9-2, 9-3 of the reference conductances for each set. The outputs of the multi-channel control pulse generator 10 are connected to the control input of the block 7 and to the control inputs of the signal switches 11,12, 13. The combined inputs of the switching contacts of the switches 11, 12, 13 through the current transducers 6 are connected to the corresponding outputs of the communication line 2, the outputs of the switching contacts 11-2, 12-2, 13-2 of the switches 11, 12, 13 are connected to the conductances with maximum value (short-circuit mode), and the outputs of the switching contacts 11-6, 12-6, 13-6 are connected to the conductances with minimum value (idle mode).

The outputs of the switching contacts 11-1, 11-3, 11-4 are connected to the output of the informational conductance shaper 14, the outputs of the switching contacts 12-1, 12-3, 12-5 are connected to the output of the informational conductance shaper 15, and the outputs of the switching contacts 13-1, 13-4, 13-5 are connected to the output of the informational conductance shaper 16.

The outputs of the switching contacts 11-5, 12-4, 13-3 are connected to the corresponding shapers 9-1, 9-2, 9-3 of the reference conductances , , .

The formers 14, 15, 16, in the case of information transmission, represent the outputs of the "voltage-resistance" converters, some of the inputs of which are connected to the sources 17, 18, 19 of the transmitted signals, and other inputs are connected to the respective formers 9-1, 9-2, 9-3 of the reference conductances. The formers 14, 15, 16 can represent thermo- or strain-resistors.

The outputs of the input current transducers 5 are connected to the block 20 for calculating the transmitted signals.

The procedure is carried out as follows.

In the first stage, the parameters - of the communication line 2 are determined and the values of the displacement currents and the reference conductances , , are calculated.

For the calculation of the parameters - , from the receiver 1 side, from the voltage source 4 through the input current transducers 5, the voltage is applied to the communication line 2. In the initial state, the formers 8-1, 8-2 generate the displacement currents , equal to zero. The communication line 2, from the output side, is represented as an active multipole (see fig. 2) and is described in the parameters - by the following system of equations:

,\tab(1)

where , , are the short-circuit currents in all loads simultaneously. In this case, the switching contacts 11-2, 12-2, 13-2 are closed by applying control pulses from the generator 10 to the control inputs of the switches 11, 12, 13.

Next, the parameters are determined - by the method known from the theory of electrical circuits - the method of the no-load mode and the short-circuit mode. For this purpose, the necessary switching is performed by the control pulses of the generator 10. For example, for the mode of the first conductor of line 2 and for the second and third conductors, we obtain:

, ;

, , .

These quantities (values) are applied to the measurement inputs of the parameter calculation block 7. Therefore, from the system of equations (1) we obtain the following equations:

,

,

.

According to these equations, the values are calculated in block 7. The other parameters - are calculated in the same way.

To calculate the values of the displacement currents of the sources 8-1, 8-2 and of the reference conductances , , we analyze the equivalent circuit in Fig. 3. Taking into account the directions of the currents, we obtain:

, , .

In this case, system (1) will have the following form:

.\tab(2)

Let the conductance of the second load be equal to the reference value, so . Then the current and voltage of this load correspond to , . According to the requirements of applying the projective coordinate system, we consider that ; .

The obtained correlations determine the scheme in Fig. 4. Therefore, from the system of equations (2) we obtain the following equations:

(3)

Let the conductance of the first load be equal to the reference value, i.e. . Then the current and voltage of this load correspond to , . According to the requirements of applying the projective coordinate system, we consider that ; .

In this case, from the system of equations (2) we obtain the following equations:

(4)

From here we get:

,\tab(5)

.\tab(6)

We substitute (6) into (3). Then:

,\tab(7)

,

,\tab(8)

.\tab(9)

We substitute (9) and (5) into (4). Then:

,

.\tab(10)

Let the conductance of the third load be equal to the reference conductance, i.e. . Then the current and voltage of this load will correspond to , . According to the requirements of applying the projective coordinate system, we consider that , .

Therefore, from the system of equations (2) we obtain the following equations:

(11)

From here we get:

.\tab(12)

We substitute (12) and (6) into (11). Then:

,

.\tab(13)

Using the correlations (6) and (9) and the correlations (8), (10) and (13), the control block 7 generates the necessary signals for the displacement current formers 8-1, 8-2 and for the reference conductance formers 9-1, 9-2, 9-3.

In the second stage, the direct transmission of signals is carried out.

The control pulses from the generator 10 are applied to the control inputs of the switches 11, 12, 13 of the transmitter 3. The switching contacts of all the switches 11, 12, 13 synchronously and consecutively connect the respective conductances from three sets to the communication line 2. In this way, a set of six triplets of conductances is obtained at the output of the communication line 2. These conductances 2 correspond to a set of six triplets of currents at the input and output of the communication line 2.

The marking of the currents and their correspondence to the conductances are presented in table 1. To simplify what is written, we consider that , , .

Table 1

Contacts Conductance sets Output currents Input currents 1 2 3 4 5 6

In Fig. 5 for clarity the geometric interpretation of the obtained sets of conductances and currents is presented. The point in space with coordinates corresponds to the point with coordinates . The characteristic values of the currents at the input and output of the communication line 2, which correspond to the reference conductances, the minimum and maximum values of the conductances, form two projective coordinate systems in the form of coordinate tetrahedra (see Fig. 5). The coordinate tetrahedron , the unit (scale) point corresponds to the tetrahedron , the point . For convenience, the correspondence of the characteristic values of the currents is presented in Table 2.

Table 2

Output characteristic points Output currents Input characteristic points Input currents

From projective geometry it is known that the projective coordinates of the points , with respect to the coordinates of the proper coordinate tetrahedra are equal to each other. Then, the current value of the conductance can be represented as a complex ratio between four values, or the inhomogeneous coordinate:

.\tab(14)

The extreme values or base values correspond to the minimum conductance value and the reference value. The point with the maximum conductance value is the unity point.

For the conductances , , similarly we obtain:

, .\tab(15)

We consider these coordinates (complex relations) as the transmitted signals, so, , , . Then, by the trainers 14, 15, 16, the informational conductances , , , are calculated using the signals transmitted from the sources 17, 18, 19 and the values of the reference conductances:

, , .\tab(16)

In turn, homogeneous projective coordinates express inhomogeneous coordinates in the following way:

, , \tab(17)

where is the proportionality coefficient.

The homogeneous coordinates are determined by the ratio of the distances of the point and the distances of the point to the respective planes of the coordinate tetrahedron. Then, the distances , correspond to the plane , therefore, , .

Similarly, , correspond to the plane , , . It is also obtained that , correspond to the plane , , , and the distances , correspond to the plane .

So, we get:

, , , .\tab(18)

Similarly, the same homogeneous coordinates are determined by the ratio of the distances of the points to the planes of the coordinate tetrahedron:

,

,\tab(19)

,

,

where the determinants of the matrices of the characteristic values of the currents have the following form:

, , , ,

, , , ,

, , , ,

, , , .

Then the homogeneous projective coordinates (19) present the inhomogeneous coordinates or transmitted signals according to (17), as follows:

,

,\tab(20)

.

In this case, three signals can be calculated only from the currents measured at the input of the communication line. For this purpose, the input currents measured by the transducers 5 are transmitted to the calculation block 20.

The additional advantages of the method are determined by the fact that the measurement errors of the input currents in expression (20) are mutually reduced.

1. US 8446977 B2 2013.05.21

2. MD 543 Y 2012.08.31

Claims (1)

Method of transmitting three signals through a four-conductor communication line, which includes calculating the values of the displacement currents of two displacement current sources, connected to two conductors at the output of the communication line, and the values of the reference conductances of three sets, each formed by four conductances: two of which have the minimum and maximum values, the third conductance being reference, and the fourth - informational, at the same time each of the reference conductances in each set ensures the zero value of the current and voltage simultaneously for the informational conductances in the other sets; transmitting the signal from a transmitter to a receiver, located respectively at the input and output of the communication line, by varying the transmitter conductance in each of the three conductors of the communication line in relation to the fourth common conductor with the consecutive connection of the conductances in the sets, in each set the complex ratio of the four conductances, as an inhomogeneous projective coordinate, represents each transmitted signal, and the informational conductance is calculated from this complex ratio; reading by the receiver of the values of the corresponding currents at the input and calculating the homogeneous projective coordinates and the mentioned inhomogeneous projective coordinates or the values of the transmitted signals, according to the respective sets of currents at the input of the communication line.