GB1603956A - Measuring apparatus for determining the cycle duration of an ac waveform - Google Patents

Description

(54) MEASURING APPARATUS FOR DETERMINING THE CYCLE DURATION OF AN A.C. WAVEFORM (71) We, ROBERT BOSCH GMBH., a German company of Postfach 50, 7000 Stuttgart 1, Germany., do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a measuring apparatus for determining the cycle duration of an A.C. waveform in which the durations of the positive and negative wave components of a cycle of the A.C. waveform are respectively determined separately as measured sub-values.

Such a measuring apparatus is known from German OS 25 53 806. In that specification, two successively ascertained measured values are each compared with the other and if there is a deviation, a correction value is obtained for the electronic correction of the measured value deviation. On the occurrence of a correction value, the clock frequency being counted so as to provide an indication of the duration of each wave component is varied upwards or downwards. The frequency is then ascertained from the digital measured value by forming the reciprocal.

With the previously proposed measuring apparatus, a usable measured value becomes available after each wave component However, this is not the case when, for some reason, the opposite polarity wave components do not have a duty ratio of 1:1. This dissimilarity in the wave components occurs, for example, with measured value generators for determining the speed of vehicle wheels as are used, for example, in anti-lock braking systems. On the other hand, it is with just such systems that it is important to detect changes in speed as quickly as possible, especially with low wheel speeds.

The present invention provides measuring apparatus for determining the cycle duration of an A.C. waveform, comprising a timing means responsive to each change of polarity of the waveform to provide successive indications of the durations of successive opposite polarity components of the waveform, a store arranged to store each said indication for the duration of the timing by the timing means of the next component of the waveform and to replace the stored indication with the next indication provided by the timing means upon change of polarity of the waveform, and a summing means responsive to the timing means and store to provide an output indicative of the sum of the stored indication of the duration of the preceding component of the waveform provided by the store with the indication of the duration of the present component of the waveform provided by the timing means, thereby to provide a measure of the cycle duration of the waveform which is updated each time the waveform changes polarity.

The preferred embodiment of the invention delivers updated measured values after each wave component, but is of a simpler construction than the known apparatus; moreover, successive measured partial cycles are influenced by changes in the cycle duration of the waveform, and hence the apparatus has a faster response to such changes. The timing of each wave component is preferably achieved by a counter arranged to count clock pulses.

In a further embodiment, a pulse generator provides a clock frequency which is not constant; it is established by suitable means whether the clock frequency is in a particular predetermined relationship to the input frequency of the waveform. If this is not the case, the clock frequency is re-set by means of a correcting value produced from a comparison and dependent on the extent of the deviation. In this instance, the digital output value controlled by the clock frequency and proportional thereto, is a measure of the frequency to be measured. With this method, a store is provided in which a digital value including the deviation is stored at the end of each wave component of the A.C. wave form, and an adding member is provided which3 from the last stored digital value and the digital value produced during the next wave component, respectively forms a digital total signal which is used for correcting the digital output signal determining the clock frequency, which output signal is a measure of the frequency of the A.C. waveform.

Embodiments of measuring apparatus in accordance with the invention will now be described in more detail, with the aid of the accompanying drawings, in which: Figure 1 shows a block circuit diagram of a first embodiment of the invention; Figure 2 is a waveform timing diagram for explaining the method of operation of the arrangement of Figure 1; and Figure 3 is another embodiment of the invention.

In Figure 1, the rotor of a measured value generator for ascertaining the rotary speed is referenced 1, the teeth of which generate an A.C. voltage in the stator 2 during rotation of the rotor. The A.C. voltage is converted into square wave signals in the converter 3. Neither the measured value generator 1, 2 nor the converter 3 need, in this instance, be so constructed that the durations of the opposite polarity wave components of one cycle are exactly the same length. The voltage generated by the measured value generator 1, 2 is illustrated in Figure 2a with respect to time; successive wave components are clearly illustrated as being of different lengths. The converter 3 generates the square wave voltage illustrated in Figure 2b from the said A.C. voltage. The block 4 serves for recognising the forward and rear edges of the square wave voltage of Figure 2b.

Figure 2c shows its output pulses which serve as reset signals. Each of the output pulses from the block 4 is delivered to a counting device 5, to an intermediate store 6 and to a summing store 8. Each pulse acts in the counting device 5 so that the counter is re-set to zero and so that clock pulses (not shown) at a high frequency with respect to the frequency of the voltage of Figure 2a are counted by the counter. The numerical condition of the counter, which can be released as a digital value on the occurrence of the next reset pulse, is a measure of the duration of the just measured wave component. The numerical condition is illustrated in a simplified manner in Figure 2d; it should strictly be shown as a staircase curve. In the intermediate store 6, each reset pulse from the clock 4 acts so that the digital value of the counter 5 just reached on the occurrence of the pulse is stored in the intermediate store.

Figure 2e shows the successive stored values.

The first storage can take place for the first time at Ti. The total of the digital value stored in the intermediate store 6 and the digital value accumulated in the counter 5 is formed in the adder 7. It is implied in Figure 2g that this addition takes place continuously. It can be appreciated from Figure 2g that, between To and T1, the total value is determined by the condition of the counter 5 alone, that between T1 and T2, the total value is formed by the stored digital value produced between To and T1 and the accumulated digital value of the counter 5 and that at the instants T2, T, etc., a constant measured value is available whereby a constant speed is indicated. The pulses from the block 4 also delivered to the store 8 cause the storage of the total values therein at the instants T2, T, etc.; in the illustrated case, a constant measured value is produced as Figure 2f shows. This digital measured value can be used for producing a value proportional to the speed by forming -. Thus, with T the measuring apparatus in accordance with the invention, an updated measured value is available with each zero passage of the voltage of Figure 2a.

Another embodiment of the invention will be described by way of example with the aid of Figure 3. The parts 1 to 4 corresponds to the parts 1 to 4 in Figure 1. A counter 15 is influenced by clock pulses from a generator 21. At the instants of the pulses of Figure 2c, thus on the occurrence of zero passages of the voltage to be measured as to frequency, the counter is brought to an initial value, for example zero. It counts the pulses from the generator 21 up to the next reset pulse from block 4. At the next reset pulse, the numerical value is transferred to a store 16 and the counter is re-set to zero.

Then, the stored value and the new numerical value are added up in an adder 17 and are transferred into a store 18 at the next reset pulse (as shown in Figure 2c). A control device 19 compares this value stored in the store 18 with a predetermined desired value which is equal to the factor by which the frequency of the clock generator must lie above the frequency of the input voltage. If the value stored in store 18 deviates from the said desired value, then a correction signal for the digital value stored in the store 20 is produced from the deviation, which digital value has determined the clock frequency of the generator 21 used during measuring.

Therewith, another clock frequency is used during the following measurement. The signal provided in the store 20 is also a measure of the frequency of the waveform being measured; with a variation in the frequency being measured, the value in the store 20 and with it the clock frequency of the generator determined thereby, is correspondingly varied by the control circuit consisting of the counter 15, the store 16, the adder 17, the store 18, and the control device 19. The prin ciple in accordance with the invention of undertaking the measurement after each partial cycle to determine from the ascertained values of successive partial cycles a total value from which the sought-after frequency is then derived, is also produced hereby.

By means of the pulses from the block 4, the counter 15 can also be set to a respective value which corresponds to a mul tiple of the clock frequency with respect to the frequency to be measured and the deviation of the clock frequency from the desired frequency is then provided as a value to be stored in the store 16 and be added in the adder 17, by which the digital value in the store 20 and with it the clock frequency is then corrected correspondingly. The ap plication of the method in accordance with the invention also applies in this case.

WHAT WE CLAIM IS:- 1. Measuring apparatus for determining the cycle duration of an A.C. waveform, comprising a timing means responsive to each change of polarity of the waveform to provide successive indications of the durations of successive opposite polarity components of the waveform, a store arranged to store each said indication for the duration of the timing by the timing means of the next component of the waveform and to replace the stored indication with the next indication provided by the timing means upon change of polarity of the waveform, and a summing means responsive to the timing means and store to provide an output indicative of the sum of the stored indication of the duration of the preceding component of the waveform provided by the store with the indication of the duration of the present component of the waveform provided by the timing means, thereby to provide a measure of the cycle duration of the waveform which is updated each time the waveform changes polarity.

2. Measuring apparatus according to claim 1 further including means providing a reset signal in response to the waveform changing polarity, said timing means, store and summing means being responsive to said reset signal.

3. Measuring apparatus according to claim 2 wherein said timing means comprises a counter arranged to count pulses and being resettable by said reset signal.

4. Measuring apparatus according to claim 3 further including a pulse generator providing pulses at a fixed frequency to said counter.

5. Measuring apparatus according to claim 3 further including a controlled pulse generator providing pulses to said counter at a frequency which varies in accordance with the output of the summing means.

6. Measuring apparatus according to claim 5 further including a control device arranged to compare the output of the summing means with a predetermined desired value which is representative of a factor by which the frequency of said pulse generator should be greater than the frequency of said A.C. waveform, said control device providing a correction signal to control the frequency of said pulse generator.

7. Measuring apparatus according to any one of claims 3 to 6 wherein said summing means comprises an adder continuously adding the count output of said counter with the stored count output of the store, and a further store arranged to store the output of the adder in response to the reset signal.

8. Measuring apparatus for determining the cycle duration of an A.C. waveform, substantially as herein described with reference to Figure 1 or 3 and when constructed to operate as shown in Figure 2 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. ciple in accordance with the invention of undertaking the measurement after each partial cycle to determine from the ascertained values of successive partial cycles a total value from which the sought-after frequency is then derived, is also produced hereby. By means of the pulses from the block 4, the counter 15 can also be set to a respective value which corresponds to a mul tiple of the clock frequency with respect to the frequency to be measured and the deviation of the clock frequency from the desired frequency is then provided as a value to be stored in the store 16 and be added in the adder 17, by which the digital value in the store 20 and with it the clock frequency is then corrected correspondingly. The ap plication of the method in accordance with the invention also applies in this case. WHAT WE CLAIM IS:-

1. Measuring apparatus for determining the cycle duration of an A.C. waveform, comprising a timing means responsive to each change of polarity of the waveform to provide successive indications of the durations of successive opposite polarity components of the waveform, a store arranged to store each said indication for the duration of the timing by the timing means of the next component of the waveform and to replace the stored indication with the next indication provided by the timing means upon change of polarity of the waveform, and a summing means responsive to the timing means and store to provide an output indicative of the sum of the stored indication of the duration of the preceding component of the waveform provided by the store with the indication of the duration of the present component of the waveform provided by the timing means, thereby to provide a measure of the cycle duration of the waveform which is updated each time the waveform changes polarity.

2. Measuring apparatus according to claim 1 further including means providing a reset signal in response to the waveform changing polarity, said timing means, store and summing means being responsive to said reset signal.

3. Measuring apparatus according to claim 2 wherein said timing means comprises a counter arranged to count pulses and being resettable by said reset signal.

4. Measuring apparatus according to claim 3 further including a pulse generator providing pulses at a fixed frequency to said counter.

5. Measuring apparatus according to claim 3 further including a controlled pulse generator providing pulses to said counter at a frequency which varies in accordance with the output of the summing means.

6. Measuring apparatus according to claim 5 further including a control device arranged to compare the output of the summing means with a predetermined desired value which is representative of a factor by which the frequency of said pulse generator should be greater than the frequency of said A.C. waveform, said control device providing a correction signal to control the frequency of said pulse generator.

7. Measuring apparatus according to any one of claims 3 to 6 wherein said summing means comprises an adder continuously adding the count output of said counter with the stored count output of the store, and a further store arranged to store the output of the adder in response to the reset signal.

8. Measuring apparatus for determining the cycle duration of an A.C. waveform, substantially as herein described with reference to Figure 1 or 3 and when constructed to operate as shown in Figure 2 of the accompanying drawings.