WO2009077230A1 - Method for measuring an alternating voltage and corresponding measuring circuit - Google Patents

Abstract

The invention relates to a method for measuring or detecting an alternating voltage, having a first half-cycle and a second half-cycle - per period - alternating by a reference level. The invention provides that for the measuring/detecting of the two half-cycles (58, 59) occurring within one and the same measuring/detecting region (67) at least one of them is displaced by means of an auxiliary voltage (99) acting in the associated half-period (51, 52).

Description

 description

Title Method for measuring an alternating voltage and corresponding measuring circuit

The invention relates to a method for measuring an alternating voltage, which - per period - by a reference level changing, a first half-wave and a second half-wave has.

State of the art

In modern electrical appliances or power tools electronics is usually used to implement a control, an increase in performance, a protective function and / or an additional function. In this case, microcontrollers are often used, with the help of these additional functions can be performed. For the implementation of these additional functions, it is often necessary to detect certain electrical variables as input variables for the electronics. For example, the speed control in an electrical appliance requires a closed loop, which requires an actual value detection of the speed. If the mentioned electrical appliance has, for example, a series-wound motor, the mains, armature and / or power component voltage can be detected for the closed control loop in order to determine the rotational speed therefrom. It is known to spread such quantities in analog fashion and then digitize them in order to supply them to the electronics, in particular the microcontroller.

The examples mentioned above require at least one AC voltage detection, which, according to the known embodiments, entail a corresponding expense and require a not inconsiderable number of components for the most accurate measurement result or detection result. In the course of this application, "measuring" means that an actual voltage value is determined. "Detecting" means that a determined voltage value is not directly read or made available in its size, but rather is prepared, for example, for one supply advanced processing stage. In both cases, it is necessary to be able to reproduce it with the greatest possible accuracy, so that the measurement and / or the subsequent further processing can be carried out substantially error-free and without deviations. In this respect, the term "measuring range" always means the term "detection range" and vice versa.

Disclosure of the invention

Due to the method according to the invention, in which it is provided for measuring or detecting the alternating voltage that at least one of them is displaced by means of an auxiliary voltage acting in the associated half-cycle for the measurement / detection of the two half-waves within one measuring range within the same measuring window, it is possible to shift realize a relatively accurate measurement or detection result with little effort. Due to the half-wave shift, the full measuring range or detection range can be used for each of the two half-waves, which enables a correspondingly high resolution and therefore leads to an accurate result. It is possible to position the measurement window or acquisition window in such a way that one of the two half waves without displacement substantially fills the measurement window with respect to the amplitude and the other of the two half waves is then shifted in such a way that it also substantially fills the measurement window with respect to the amplitude. Alternatively, it is of course also possible for both half-waves of the alternating voltage to be shifted by means of auxiliary voltages of different magnitude and different or equal auxiliary voltages in such a way that in turn the available measurement or detection range can be optimally utilized, so that a high resolution exists, which in turn allows an accurate measurement or detection. According to a development of the invention it is provided that the first half-wave is acted upon by a first DC voltage level of the auxiliary voltage and the second half-wave with a second DC voltage level of the auxiliary voltage for the respective displacement. So here are different DC voltage levels in the auxiliary voltage with respect to the respective half-wave before, in addition, the polarity of the respective auxiliary voltage is taken into account.

It is advantageous if an auxiliary AC voltage, in particular a square-wave voltage and / or a trapezoidal voltage, is used as the auxiliary voltage. In this case, the auxiliary AC voltage preferably has the same frequency as the AC voltage to be measured. In addition, it can be noted that the auxiliary AC voltage is in phase or 180 ° out of phase with the AC voltage. As a result of the above measures, the DC voltage level of the auxiliary voltage changes in the rhythm of the half periods of the AC voltage, so that the respective half-cycle of the AC voltage is always shifted in amplitude such that the most accurate possible measurement or detection within the measuring range or detection range is available.

It is advantageous if at least one of the two half-waves is scaled by amplification or attenuation within the measurement or detection range. In this case, therefore, the alternating voltage is amplified or attenuated with respect to its original course, but in each case such that a more accurate measurement or detection in the measuring window becomes possible.

In the case of the method according to the invention, it is also important that the half-wave extends through the scaling over the entire measuring range or for the most part over the measuring range. The larger the half-wave within the measuring or detection range, the better details can be detected and the more accurate the result can be determined. It may be important here for the measuring range to have an upper and a lower measuring range limit, to which an alternating voltage-free safety zone is connected in each case. Accordingly, the voltage to be measured or detected should be in the measuring range and should not extend into the safety zones. Since the safety zones relate to an upper and a lower peak value of the alternating voltage, an upper and a lower safety zone result in the measuring window, which images a non-half-wave shifted period. If the half-waves are shifted in their reference level, only one peak is present in the associated half-cycle, which means that the number of safety zones can be reduced to one. This results in a further improvement in the utilization of the measurement or detection range.

For measuring the AC voltage is preferably one with a

Resolution digitization planned. The AC voltage is therefore sampled at the resolution for digitization. In particular, a constant resolution is provided.

By means of the procedure according to the invention, a measurement or detection of the alternating voltage can preferably take place in order to determine the rotational speed of an electric motor or of a generator, in particular of a tachogenerator.

Finally, the invention relates to a measuring circuit or detection circuit for measuring or detecting an alternating voltage, in which case the method mentioned above is used.

The drawings illustrate the invention with reference to an embodiment, in which:

Brief description of the drawings 1 shows a circuit diagram of a measuring circuit for measuring / detecting a

AC voltage,

FIG. 2 shows an AC voltage to be measured / detected;

FIG. 3 shows a measured / detected alternating voltage in a measuring window,

FIG. 4 shows an exemplary embodiment of the measuring circuit shown in FIG. 1 by means of a microcontroller.

Embodiment (s) of the invention

FIG. 1 shows an electrical circuit 1 which serves to detect and / or measure an alternating voltage 2. The AC voltage 2 is provided by an AC voltage source 96. The circuit 1 has an AC voltage measuring device 21, with which the AC voltage 2 having a relatively high potential is directly displayed in the voltage value. Furthermore, the circuit 1 has a measured data acquisition 26, at which the alternating voltage 2 is made available at a reduced, lower potential in order to connect there, for example, a further processing. In particular, the arrangement according to the invention is suitable for providing a low-potential image of the AC voltage 2 at the measurement data acquisition 26 in a highly accurate manner in order to provide this image, for example, with electronics for further processing. By way of example, the said electronics are rotational speed detection devices, that is, the alternating voltage 2 lying at a higher electrical potential (for example 220 V or 380 V) is reduced from its relatively high electrical potential to the aforementioned low-level image by means of the electrical circuit according to the invention reduced electrical potential, but this reduction is highly accurate, that is, at the measurement data acquisition 26 is a voltage signal available, which is due to the high accuracy, for example, suitable in a connected control circuit of an electrical appliance to serve as further processed size. This may be, for example, a control loop of a speed control of a power tool, wherein for the realization of the mentioned, closed loop an actual value detection is necessary and for this actual value detection, the AC voltage 2 is not directly, but by means of the electrical circuit - to a lower potential - attenuated at the measured data acquisition 26 is provided.

According to Figure 1, the AC voltage source 96 via a line 3 - a neutral conductor 97 - connected to a node 5, which leads via an electrical line 8 to a node 9. The node 9 is connected via an electrical line 10 to a positive pole 11 of a power supply 12, for example a battery, in connection. The AC voltage source 96 is further connected via a line 4 - a phase 98 - to a node 6. A resistor 23 is connected to the node 6 and to a node 24 to which a further electrical resistor 33 is further connected, which leads to a switching tongue 35 of a changeover relay 46. A cooperating with the switching tongue 35 switching contact 36 leads via a line 37 to the node 9. The node 24 is connected via an electrical line 25 to a terminal 27 of the measured data acquisition 26 in connection. A connection 28 of the measurement data acquisition 26 is connected via a line 29 to a node 30. This is connected via a line 31 with a negative terminal 32 of the

Power supply 12 in conjunction. A line 39 leads from node 30 to a switching contact 38 of the changeover relay 46. An electromagnet 40 of the changeover relay 46 has a coil which leads via lines 41 and 42 to a node 18 and to a terminal 44 of a clock 43. The clock has a terminal 45 which is connected to a node 16, wherein the two nodes 16 and 18 are connected via a line 17. The node 18 is connected to ground 19. From the node 16, a line 15 leads to a node 14, which is connected via a line 13 to the node 5. Parallel to the nodes 5 and 6 is the

For this purpose, the node 6 is connected via a line 20 to a terminal 100 and the node 14 via a line 22 to a terminal 101 of the AC voltage measuring device 21. FIG. 2 illustrates the time course of a period 7 of the AC voltage 2. FIG. 2 shows a Cartesian coordinate system 47 with an abscissa 48 which represents the course of the time t and an ordinate 49, 5 of which a voltage U is assigned. A division of the period 7 into a first half period 51 and a second half period 52 is characterized by two vertical boundary lines 78 and 79. In the coordinate system 47, a constant reference level 50 is shown. The reference level 50 is indicated by circular symbols 53. The circular symbols 53 in the first half period 51 appear as fully filled circular symbols 54; the circular symbols 53 in the second half-period 52 appear as circular symbols 55. About the reference level 50 runs the AC voltage 2 of the AC voltage source 96 (Figure 1). The AC voltage 2 is sinusoidal and has a first half-wave

15 58 in the first half period 51 and a second half wave 59 in the second half period 52 on. The course of the alternating voltage 2 is characterized by square symbols 60, which, analogously to the marking of the reference level 50, in the first half-wave 58 as filled square symbols 61 and in the second half-wave 59 as unfilled square symbols 62

20 are executed.

The AC voltage 2 starts at the ordinate 49 at the reference level 50, is sinusoidal below the reference level 50 with an amplitude 63, and intersects the reference level 50 at the end of the first half-period 51 at a point of intersection 64 at the boundary line 78. In the second, continuously adjacent one Half-cycle 52, the AC voltage 2 sinusoidally above the reference level 50 with an amplitude 65. At the end of the second half-period 52, the AC voltage 2 intersects the reference level 50 at the boundary line 79th

30

FIG. 3 shows an alternating voltage 70, as present at the measured data acquisition 26, when the alternating voltage 2 from FIG. 2 is measured / detected by means of the measuring circuit 1. The AC voltage 70 is shown in a Cartesian coordinate system 110 with the abscissa 48, which represents the course of time t 35 and an ordinate 66, which is associated with a voltage U shown. she consists of a first half-wave 72 and a second half-wave 73, which run within a measuring window 103. The measuring window 103 has a limited measuring range 67, which has an upper measuring range limit 68 and a lower measuring range limit 69. A division of the period 7 into a first half period 74 and a second half period 75 is by two vertical

Boundary lines 78 and 79 marked. The first half-wave 72 extends sinusoidally in the first half period 74 with an amplitude 80 below a reference level 71, which lies in the upper measuring range limit 68. At the boundary line 78, the reference level 71 jumps to the lower measuring range limit 69. The alternating voltage 70 then runs sinusoidally in the second half-period 75 with an amplitude 81 above the lower measuring range limit 69. The reference level 71 and the alternating voltage 70 are analogous to FIG. 2 with circular symbols 77 and marked with square symbols 76.

The amplitudes 63 and 65 of the alternating voltage 2 to be measured / detected may be greater or smaller than the measuring range 67 in terms of magnitude. In order to be able to use this optimally, the amplitudes 63 and 65 must be brought to an optimum display size by amplification or attenuation. In the example of use from FIG. 1, the resistor 23 assumes the function of a voltage divider, as a result of which the amplitudes 63 and 65 are attenuated to the smaller amplitudes 80 and 81.

In order to be able to apply the reference level 50 half-wave into the upper measuring range limit 68 and into the lower measuring range limit 69, the already weakened AC voltage 2 is subjected to an auxiliary voltage 99 of the voltage source 12 as a function of its phase position about the reference level 50. For this purpose, the changeover relay 46 is connected in the first half-period 51 such that the switching tongue 35 is connected to the switching contact 36 and thus the AC voltage 2 is acted upon by a positive DC voltage level of the auxiliary voltage 99 from the positive pole 11 of the power supply 12. This results in a shift of the reference level 50 and thus the first half-wave 58 in the positive direction with respect to the ordinate 49. In the second half-cycle 52, the changeover relay 46 is connected such that the switching tongue 35 with the Switching contact 38 is connected and thus the AC voltage 2 with a negative DC voltage level of the auxiliary voltage 99 from the negative terminal 32 of the power supply 12 is applied. This results in a negative shift of the reference level 50 and thus the second half-wave 59 with respect to the ordinate 49. In order to realize the alternately positive or negative auxiliary voltage by means of the changeover relay 46, the changeover relay 46 is controlled by a clock 43. The clock generator 43 provides a square-wave voltage 104, the edges of which run synchronously with reference level passages of the alternating voltage 2. In this way, an auxiliary AC voltage is generated by the changeover relay 46, which is 180 ° out of phase with the AC voltage 2. This makes it possible to shift the AC voltage 2 as a function of its phase position in the measurement window 103. The amount of displacement about the original reference level 50 is determined by means of the resistor 33.

In order to prevent erroneous measurements due to fluctuations in the amplitudes 80 and 81, an upper safety zone 85 and a lower safety zone 84 are provided. The security zones 84 and 85 appear as AC-free regions 105 and 106. They are located between two peak values 82 and 83 of the half-waves 72 and 73 and the corresponding measurement range limits 68 and 69.

In summary, this procedure makes it possible to evaluate the AC voltage 2 of the AC voltage source 96 in the measurement data acquisition 26, which provides a limited measurement range 67 and at the same time allows each half wave 72 and 73 to be evaluated over the entire measurement range 67 with a correspondingly high measurement resolution and, if necessary, digitized. This leads to highly accurate measurement results.

Moreover, this measurement makes it possible to dispense with a further safety zone which would result if the period of the AC voltage 2 were represented at a constant reference level in the measuring area 67, since both a lower safety zone 84 and an upper safety zone 85 were used simultaneously and not half-periodically would have to be considered. 4 shows an exemplary implementation of the method according to the invention with a microcontroller 86. The AC voltage source 96 is connected on one side by means of the electrical line 3 - the neutral conductor 97 - to the node 5. The node 5 is also connected to the positive pole 11 of the power supply 12 in connection. Starting from the node 5, a further line 87, which connects the microcontroller 86 to the positive pole 11 of the power supply 12 and thereby supplies the microcontroller 86 with working voltage. The power supply 12 also has the negative terminal 32, which is connected to a node 88 and thus to the ground 19. The microcontroller 86 is also connected via a line 89 to the node 88 and thus to the ground 19 in connection, so that a power supply circuit from the power supply 12 to the microcontroller 86 is ensured.

The second line 4 - the phase 98 - of the AC voltage source 96 is connected to the node 6. Starting from the node 6, an electrical line 107 runs through a resistor 90 into a digital synchronization input 91. On the basis of the signals received at the digital synchronization input 91, the microcontroller 86 generates the auxiliary voltage 99 at a digital leveling output 92, which is reduced at a resistor 93. Starting from the node 6, the AC voltage 2 of the AC voltage source 96 passes through a resistor 94, which scales the amplitudes 63 and 65 of the AC voltage 2. At the node 95, the scaled AC voltage 2 from the resistor 94 is applied to the reduced auxiliary voltage 99 from the resistor 93 and passed via a line 108 in an analog voltage measurement input 109 to be evaluated there.

The method is particularly suitable for measuring circuits which are galvanically connected to one pole of the voltage to be measured. In addition, components can be saved compared with conventional measuring methods, as a result of which the power consumption of the measuring circuit can be greatly reduced. This results in the possibility to carry out the process with a simple and economical power supply.

Claims

claims 1. A method for measuring or detecting an AC voltage, the - ever Period - to a reference level alternating, a first half-wave and a second half-wave, characterized in that, for the within one and the same measuring / detection area (67) taking place measuring / detecting the two half-waves (58,59), at least one of them by means of a, in the associated half-period (51, 52) acting, Auxiliary voltage (99) is shifted. 2. The method according to claim 1, characterized in that the first half-wave (51) with a first DC voltage level of the auxiliary voltage (99) and the second half-wave (52) with a second DC voltage level of the auxiliary voltage (99) is applied to the respective displacement. 3. The method according to any one of the preceding claims, characterized in that as auxiliary voltage (99) an auxiliary AC voltage, in particular a square wave voltage and / or a trapezoidal voltage is used. 4. The method according to any one of the preceding claims, characterized in that an auxiliary AC voltage is used which has the same frequency as the AC voltage to be measured (2). 5. The method according to any one of the preceding claims, characterized in that the auxiliary AC voltage is in phase or 180 ° out of phase with the AC voltage (99). 6. The method according to any one of the preceding claims, characterized in that at least one of the two half-waves (51, 52) is scaled by gain or attenuation within the measurement / detection range (67). 7. The method according to any one of the preceding claims, characterized in that extending by scaling the half-wave (51, 52) over the entire measuring / detection area (67) or largely over the measuring / detection area (67). 8. The method according to any one of the preceding claims, characterized in that the measuring / detection area (67) has an upper and a lower measuring / detection area boundary (68,69), which is followed by an AC-free safety zone (84,85) , 9. The method according to any one of the preceding claims, characterized in that for measuring / detecting the AC voltage (2) it is scanned with a measurement / detection resolution for digitizing. 10.Verfahren according to any one of the preceding claims, characterized in that for digitization, a constant measurement / detection resolution is used. 11.Verfahren according to any one of the preceding claims, characterized in that by means of measurement / detection of the AC voltage (2) a speed of an electric motor or a generator, in particular tachometer generator, is determined. 12. measuring circuit (1) or detection circuit for measuring or detecting an AC voltage (2) according to the method according to one or more of the preceding claims.