CH636485A5 - Signal generator for generating sinusoidal output signals with predetermined mutual phase angle, and use thereof as three-phase generator for calibrating electricity meters - Google Patents

Description

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PATENT CLAIMS

1. Signal generator for generating sinusoidal output signals with a predetermined mutual phase position, with a number generator controlled by a clock generator, a function generator and at least one digital / analog converter, the number generator emitting binary-coded phase step signals to the function generator, which the function generator codes in binary Instantaneous value signals and converted by the digital / analog converter into an analog signal, characterized in that the number generator (10 to 16) for the cyclical generation of each of the output signals (UR; IR; Us; Is; Uj! It) assigned phase step signals ( Ph) is set up such that each output signal (UR; IR; Us; Is; UT; IT) has a memory (19 to 24; 39 to 44) connected to the digital / analog converter (18) or to the function generator (17). is assigned and that a clock distributor (38) connected to the clock generator (37) is arranged for cyclically clocking the memories (19 to 24; 39 to 44).

2. Signal generator according to claim 1, characterized in that the memories (19 to 24) are sample and hold circuits and that the digital / analog converter (18) all output signals (UR; IR; Us; Is; UT; IT; ) is assigned together.

3. Signal generator according to claim 1, characterized in that the memories (39 to 44) are digital read-write memories and that each memory (39 to 44) is followed by a digital / analog converter (45 to 50).

4. Signal generator according to one of claims 1 to 3, characterized in that the number generator (10 to 16) consists of at least one angle input element (10; 11), an adder (14) and an accumulator (16), the angle input element (10 ; 11) is connected to a first (13) and the output of the accumulator (16) to a second input (15) of the adder (14) and the output of the adder (14) is connected to the input of the accumulator (16).

5. Signal generator according to claim 4, characterized in that two angle input elements (10; 11) via a clock (37) controlled switch (12) to the first input (13) of the adder (14) are connected.

6. Signal generator according to claim 2, characterized in that a reference voltage input (39) of the digital / analog converter (18) via a multiple switch controlled by the clock distributor (38) can be connected to at least two adjustable reference voltage sources.

7. Signal generator according to one of claims 1 to 6, characterized by three via a low-pass filter (25; 27; 29) to one of the memories (19; 21; 23) or one of the digital / analog converters (45; 47; 49 ) connected voltage amplifier (31; 33; 35) for generating a voltage triangle and through three via a low pass filter (26; 28; 30) to one of the memories (20; 22; 24) or one of the digital / analog converters (46; 48; 50) connected current amplifier (32; 34; 36) for generating a current triangle.

8. Signal generator according to claims 6 and 7, characterized in that the voltage amplifiers (31; 33; 35) and the current amplifiers (32; 34; 36) are connected to an effective value measuring device, the output signal of which controls the reference voltage sources.

9. Signal generator according to claim 7, characterized in that in each case a voltage amplifier (31; 33; 35) and a current amplifier (32; 34; 36) are connected to a phase angle measuring device, the output signal of which controls the angle input element (10).

10.'Use of the signal generator according to one of claims 1 to 7 as a three-phase voltage and three-phase current generator for the calibration of electricity meters.

A signal generator of the type mentioned in the preamble of claim 1 is known (IEEE Transactions on Audio and Electroacoustics, March 1971, pp. 48-57), which generates two output signals phase-shifted by 90 ° with respect to one another. A computer with a ROM memory serves as the function generator and an accumulator serves as the number generator. For each phase step marked by the number generator, the associated sine value and cosine value are simultaneously calculated in the computer and output to a digital / analog converter. This solution requires a complex function generator.

The object of the invention specified in claim 1 is to provide a signal generator which is characterized by a simpler circuit structure.

With the signal generator according to the invention, a simpler structure of the function generator is achieved. The technical effort is relatively low, in particular, if a larger number of output signals are to be generated.

Two exemplary embodiments of the invention are explained in more detail below with reference to the drawing. Show it:

1 is a schematic diagram of a signal generator,

Fig. 2 is a diagram and

Fig. 3 is a schematic diagram of another signal generator.

The signal generator shown in FIG. 1 generates three alternating voltages UR, each phase-shifted by 120 ° with respect to one another; Us and UT as well as three alternating currents IR, Is and Ix, each phase-shifted by 120 °. The current triangle IR, Is, Ij is shifted from the voltage triangle UR, Us, UT by the phase angle <p, which can be preselected at an angle input element 10 and is output by it in binary-coded form. In the example shown, a second angle input element 11 outputs an angle value of 121 ° in a likewise binary-coded form. Depending on the position of a switch 12, which is shown symbolically in the drawing and can consist of several gates corresponding to the number of bits of the binary coded angle values, either the angle input element 10 or the angle input element 11 is connected to a first input 13 of an adder 14, the second Input 15 is connected to the output of an accumulator 16 and its output is connected on the one hand to the input of the accumulator 16 and on the other hand to the input of a function generator 17. A digital / analog converter 18 is connected downstream of the function generator 17 and is connected on the output side to the memory inputs of six sample and hold circuits 19 to 24. A low-pass filter 25 to 30 is connected to each of the sample-and-hold circuits 19 to 24, followed by an amplifier 31 to 26 in each case. The amplifiers 31, 33 and 35 are voltage amplifiers and emit the output voltage UR or Us or UT. The amplifiers 32, 34 and 36 working as current amplifiers deliver the output current IR or Is or IT.

A clock generator 37 generates clock pulses with the frequency fo. These arrive at a clock distributor 38 which on the one hand clocks the accumulator 16 with clock pulses of the frequency fs = fo / 2 and controls the switch 12 and on the other hand clock signals fi to f «with the frequency fo / 6 to the clock inputs of the sample-and-hold circuits 19 outputs up to 24, whereby these are cycled.

The accumulator 16 and the adder 14 together with the angle input members 10 and 11 and the switch 12 form a number generator which outputs binary-coded phase step signals Ph to the function generator 17, which are transmitted from the function generator 17 into binary-coded instantaneous value signals and from the digital / analog converter 18 are converted into an analog signal. As will be explained in more detail below, the number generator generates for each of the output signals UR,

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Us * Is, Ut and IT in cyclical order phase step signals Ph, which are converted by the function generator 17 into binary-coded instantaneous value signals and from the digital / analog converter 18 into a corresponding analog signal proportional to a reference voltage Urer and converted into the assigned sample-hold Circuits 19 to 24 are stored in analog form until the next cycle. The function generator 17 therefore outputs only an instantaneous value within each phase step and can accordingly be of simple construction. A ROM memory is preferably suitable as function generator 17, in which the associated instantaneous value of the sine function is stored for each phase step signal that occurs. Since only the sine function of the 1st quadrant has to be written into the ROM memory and the sine values of the three other quadrants can be obtained by mirroring the 1st quadrant, a relatively small storage capacity is sufficient.

The mode of operation of the signal generator described is explained in detail below with reference to the diagram in FIG. 2. 2, the numbers 0 to 7 denote individual phase steps. The various clock signals are again designated fo, fs and fi to fó. The position of the switch 12 in the individual phase steps can be seen from the line labeled S. The respective value of the phase step signal Ph at the output of the adder 14 is entered in the line Ph and the value stored in the accumulator 15 is entered in the line A.

For easier understanding, let us assume for the time being that the switch 12 is permanently in the 121 ° position. With a clock pulse of the clock signal fs at phase step 1, the phase step signal Ph assumes the value 0 °, this value is stored in the accumulator 16, the function generator 17 forms the associated sine value in binary-coded form and the digital / analog converter 18 in analog form , A clock pulse of the clock signal fi appears at the clock input of the sample and hold memory 19 and the analog value assigned to the output voltage UR is stored in the sample and hold circuit 19. At the next clock pulse of the clock signal fs, i.e. in phase step 3, the value 121 ° of the angle input element 11 is added to the old value 0 ° of the accumulator 16 in the adder 15, the new value 121 ° is adopted in the accumulator 16 and the corresponding sine value assigned to the output voltage Us is entered in the sample and hold -Circuits 21 stored. In phase step 5, the sine value of 242 ° assigned to the output voltage UT is stored in the sample and hold circuit 23, in phase step 7 the sine value of 363 ° = 3 ° assigned to the output voltage UR is stored in the sample and hold circuits 19, etc.

If one considers the formation of the output voltage UR on its own, for example, it would appear that the number generator would do nothing other than increase the value of the phase step signal Ph by 3 ° for every sixth phase step. For each output voltage UR, Us and UT, the number generator works as a separate triangle number generator. At the output of the sample-and-hold circuits 19, 21 and 23, step-shaped output voltages appear that approximate a sine curve and are phase-shifted from one another by exactly 120 °. The low-pass filters 25, 27 and 29 smooth the step-shaped output voltages and amplify them to the required value with the voltage amplifiers 31, 33 and 35.

The sine values assigned to the output currents IR, Is, and IT are each formed in the next phase step after the calculation of the sine value of the output voltage UR, Us or UT of the corresponding phase, that is to say in the phase steps 0, 2,4, 6 ... in the example shown the switch 12 changes in phase step 2 to the position <p that

Adding element 12 carries out the addition 0 ° + (p, the phase step signal Ph thus assumes the value <p, the function generator 17 outputs the associated sine value, at the clock input of the sample-and-hold circuit 20 a clock pulse of the clock signal fi and the am appears Analog value assigned to output current IR is stored in the sample and hold circuit 20. No clock pulse of the clock signal fs appears at the clock input of the accumulator 16 in phase step 2, so that the value cp is not stored in the accumulator 16. In phase step 4, how It can be seen from the drawing that the sine value of 121 ° + <p assigned to the output current Is in the sample and hold circuit 22, in phase step 6 the sine value of 242 ° + <p assigned to the output current IT in the sample and hold circuit 24 stored etc. The resulting stepped output voltages of the sample-and-hold circuits 20, 22 and 24 are smoothed with the low-pass filters 26, 28 and 30 and with the current amplifiers 32, 34 and 36 formed into appropriate streams of the required strength.

The signal generator described thus forms a voltage triangle UR, Us, UT and a current triangle IR, Is, Ij, which rotate counterclockwise and are rotated relative to one another by the angle cp. Although the number generator executes steps of 121 ° and not of 120 °, the triangles are exactly equilateral because the corresponding sine value is scanned accordingly later. As a result of the delayed sampling of the sine values of the output currents IR, Is and IT compared to the sine values of the assigned output voltages UR, Us and UT, the current triangle is not by the angle (p) compared to the voltage triangle, but by the angle <p-0.5 in the example described ° This must be taken into account when preselecting the angle (p in the angle input element 10.

The said angle value of 121 ° of the angle input member 11 is to be understood only as an example and depends on the desired fineness of the staircase curve of the analog signals at the output of the sample and hold circuits 19 to 24. Of course, the angle value of the angle input member 11 can also be less than 120 ° so that the voltage and current triangles turn clockwise. In an 8-bit binary system, this angle value is preferably represented by the binary number 01010101, which corresponds to an angle of 360 ° -85 / 256 «119.5 °.

In the example shown, the digital / analog converter 18 has a reference voltage input 39 which is connected to a reference voltage source Uref. The analog signal at the output of the digital / analog converter 18 is proportional to the reference voltage, so that the amplitude values of all output voltages and output currents can be influenced together by changing the reference voltage. If the reference voltage input 39 can be connected to several adjustable reference voltage sources via a multiple changeover switch controlled by the clock distributor 38, the amplitude values of the output voltages UR, Us and UT and those of the output currents IR, Is and Ij can be set independently of one another by changing the reference voltages. An automatic readjustment of the output signals based on their effective values is possible if the voltage amplifiers 31, 33 and 35 and the current amplifiers 32, 34 and 36 are connected to an effective value measuring device, the output signal of which controls the reference voltage sources. Automatic readjustment of the phase angle is also possible by connecting a voltage amplifier 31, 33, 35 and a current amplifier 32, 34, 36 of the same phase to a phase angle measuring device, the output signal of which controls the angle input element 10.

3 have the same reference numerals as in the

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Fig. 1 on the same parts. Instead of the sample-and-hold circuits 19 to 24 (FIG. 1), the signal generator according to FIG. 3 has digital read-write memories (RAM) 39 to 44, the memory inputs of which to the function generator 17 and the clock inputs to the Clock distributors 38 are connected. Each of the read-write memories 39 to 44 is followed by a digital / analog converter 45 to 50, the output of which leads to one of the low-pass filters 25 to 30.

The signal generator according to FIG. 3 is somewhat more complex in comparison to that according to FIG. 1, but is distinguished by the advantage that the working speed of the digital / analog converter must be 45 to 50 less than that of the digital / analog -Converters 18

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The digital / analog converters 45 to 50 advantageously have reference voltage inputs for connecting a reference voltage with which the amplitude values of the output voltages and output currents are set or regulated

5 can. Furthermore, it is advantageous to connect an additional element upstream of the function generator 17, which allows an angle signal to be added to the phase step signal Ph, so as to additionally influence or readjust the phase angle of the output voltages and output currents.

10 The signal generators described are advantageously used as three-phase voltage and three-phase current generators for calibrating electricity meters.

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2 sheets of drawings