DE4119376C1 - - Google Patents

Description

The present invention relates to a further development of the German telemetry period measurement method Patent 40 36 107 (main patent)

In general, the invention relates to a telemetry Measuring method for a telemetry system, among others the period of a signal generated by a sensor determined and transmitted to a telemetry receiver.

It is already a period measurement method for a telemetry System known, using a microprocessor thereby measuring a period of a signal to be measured is that between two flanks of the same direction of the signals to be measured a counter by means of a clock signal is counted up. The counter reading, that of the period is then transmitted. Likewise, it is known in such a system in the case of relative count the clocks for high-frequency signals to be measured, the during a fixed number of periods of the measured Signals are fed to the counter. The number of The measured period of the signal to be measured is at this system so determined that during the number of Measuring periods at the lowest frequency to be measured maximum counter reading of the counter is just reached. With the measuring time increases with increasing frequency of the signal to be measured from, so that necessarily the achievable resolution decreases with increasing frequency.

With period measuring devices or frequency measuring devices for the laboratory area is known to have an automatic frequency measuring range setting of the microprocessor-controlled measuring device by causing this to be the period measurement initially based on a number of measurement periods,  which correspond to the measuring signal with the lowest measurable frequency, carries out. If a meter overflow occurs here, becomes the number of measuring periods by a factor of 1000 decreased, whereupon a new counting up of the counter takes place. Should an overflow occur again, again a reduction in the number of measuring periods by Factor 1000 made until finally a very high frequency Signal without counter overflow with respect to its Period duration can be measured.

It is also known in such multiple measuring devices in the event of a meter overflow from a period measurement to switch to a frequency measurement of the signal to be measured. However, such a measuring method requires a basic setting time for the measuring device, which depends on what frequency the signal to be measured has. There inside a telemetry measurement method only a certain, unchangeable time window for measurement and transmission measurement data is available for one sensor at a time, comes the just described, with multiple measuring devices in Laboratory measuring methods used in the field of telemetry Measurement technology out of the question.

Based on the above-mentioned prior art, the Subject of the German patent 40 36 107 depends on a telemetry period measurement method of type mentioned in such a way that without increasing the circuitry outlay for the telemetry measuring system, with which the measuring method can be carried out, an increased Measurement resolution is reached. This is the subject of the main patent mentioned by a telemetry period Measuring method achieved the following process steps has: Counting clock pulses over at least half a period a measurement signal by means of a counter for determination one indicating the approximate period of the measurement signal Period duration counter reading, reading one Period duration range in which the period duration counter reading falls, assigned number of measuring periods from a table  by means of the period duration counter reading, the number of measuring periods is chosen so that the counting of the clock pulses by means of the counter even for the longest period Period range just not for a counter overflow leads, counting the clock pulses over the number of measuring periods of periods of the measurement signal, and transmission of the Counter reading and a number representing the measuring period Information about a telemetry receiver.

The subject of the main patent takes place for the investigation the number of measuring periods before accessing the table initially counting the clock pulses over a period instead of. If the measurement signal is a high-frequency If the measurement signal is active, the counter reaches the measurement over a single period only a low meter reading, which is therefore only an inaccurate reproduction of the measurement period is. Is initially determined on the basis of this Meter reading now on the table for reading out the number of measuring periods accessed, it can lead to a readout of a Number of measuring periods come, which only applies to measuring signals which are in a different period. Around to prevent invalid measurement caused by this the assignment of initial period duration readings to the different numbers of measuring periods in the table are sufficient Scope to prevent invalid measurements take into account, however, thereby ensuring the best possible utilization the counter capacity and thus to the maximum possible Measuring accuracy is dispensed with.

A frequency measuring method is known from DE 38 11 735 A1, in which a program control first measures a frequency after a first sub-procedure the clock pulse of the signal are counted during a period, whereupon the clock pulses depending on the measurement result counted over several periods of the signal or pulses of the signal to be measured during a specified gate time be counted.  

From US 41 07 600 a measuring method is known in which the clock rate of a clock signal as a function of frequency of the measurement signal is selected by first half Period of the measurement signal counted at a fixed clock rate will and depending on the measurement result the new Clock rate is set.

From US 47 60 536 is a frequency and period measuring device known in which successive periods of Signals to be measured each from clock pulses with step by step divided clock frequency can be counted.

From US 45 17 684 it is known for a frequency measuring device to use a memory that has a suitable Memory addressing the numerical values for the frequency and linked the period. This is the purpose of the mission a computer to link these variables can be avoided.

The invention according to the present additional application hence the task of determining the telemetry period Measuring method according to German patent 40 36 107 to develop so that a better measurement accuracy is achieved becomes.  

This task is accomplished by a telemetry period measurement method solved according to claim 1.

The telemetry period measurement method according to the invention stipulates that after reading the first table of the period duration counter value determined, for example, for a period duration it is checked whether the from the first Table readout number of measuring periods exceeds a limit. If this is not the case, the method according to the invention runs Procedure with counting the clock pulses over the Number of measuring periods continues, whereupon the meter reading determined in this way is transmitted to the telemetry receiver. If so the result of the test is positive and thus the measurement signal is classified as high frequency, after reading the first table a counting of clock pulses over a Carried out a plurality of period durations of the measurement signal, before using it to determine a plurality of periods Count value on a second table for reading out the now the exact number of measuring periods is accessed. After this The counter with the clock pulses is read from the second table about the number of measuring periods read from this second table counted up before the count to the telemetry Recipient is transmitted.

A preferred embodiment of the telemetry according to the invention Period duration measuring method is specified in a subclaim.

The following will refer to the accompanying Drawings a preferred embodiment of the invention Telemetry period measurement method explained in more detail. It shows:

The only figure a flow diagram of a preferred embodiment of the  Telemetry period measurement method according to the invention.

A first process step 1 forms the start of the measuring process. A program operating according to the method can be a subroutine for controlling a microprocessor of a telemetry measuring system which, in a cyclically repeating manner with a cycle duration of 80 ms, for example, with a plurality of subroutines in a time-multiplexed manner, the output signals from a plurality of telemetry systems. Processed sensors and transmitted them to a telemetry receiver.

In this case, the first method step 1 is the program step with the execution of which the microprocessor of the telemetry measuring system begins when the time window for processing and transmitting the output variable of a sensor with a frequency output signal has been reached, this output variable being detected by means of the period duration measuring method shall be.

In a second method step 2 , a counter is loaded with a start value. In the preferred embodiment, the starting value is 7800 H. This starting value of the counter is selected such that when the counter is incremented with a clock signal which is derived from a CPU clock over a period of a measuring signal with the lowest frequency to be detected, there is just none Counter overflow takes place.

In step 3 , the counter is started, whereupon the start value is incremented with each clock pulse.

In method step 4 it is checked whether a counter overflow has occurred. If this is the case, the measurement signal to be tested can already be classified as too low-frequency for evaluation by means of the measurement method, so that the measurement can be defined as unfavorable. In this case, the program goes to step 6 to be explained later.

In the subsequent method step 5 it is checked whether a signal edge indicating the end of a period of the measurement signal has occurred. In the preferred embodiment, the microprocessor responds to falling edges of the signal to be measured and generates an interrupt when a falling edge occurs. As long as no signal edge occurs, the microprocessor remains in a waiting loop, in which it returns to program section 4 .

In the event of the counter overflow, which is detected in the test according to method step 4 , the counter status is set to zero in a 6th method step 6 , whereupon the program jumps to method step 19 to be explained later, which transfers the counter status and the coded number of periods ldn serves. In this case, the measuring cycle ends with the subsequent method step 20 .

Steps 4 and 5 serve, on the one hand, to wait for the next falling edge for the purpose of synchronizing the start of the period measurement, and on the other hand, for signals that are too low-frequency, an error message indicating this fact, for example in the information cnt = 0, may exist to which the receiver of the telemetry system can be transmitted.

If the signal frequency is too low, the time available for a measuring cycle can be exceeded already in the synchronization to the start of measurement in method steps 4 and 5 . The starting value of the counter, which is selected in method step 3 already explained and method step 9 still to be explained, is dimensioned such that the time until the counter overflow just allows the measurement of the longest possible period of the measurement signal.

In the configuration according to the embodiment is the start value 7800 H, so that until the counter overflows, which corresponds to the counter reading FFFFH after 0000 H, the Time of 8800 H - meter readings pass. This matches with a duration of 40.8 ms and thus a lowest Measuring frequency of 24.5 Hz.

The same time limit applies during the measurement of the first period to be explained with reference to the method steps from the 9th method step. In this case too, the counter must be set to the explained start value in a 9th method step 9 .

In the worst case, which corresponds to the start of measurement immediately after the occurrence of a falling edge, 40.8 ms have to be waited for the first falling edge. The subsequent measurement of a period takes the same time. The resulting maximum time for the period measurement is 81.6 ms. If a signal with a longer period is present, this leads to a counter overflow either when waiting for the first edge already explained with reference to steps 4 and 5 or when waiting for the second edge to be explained, which leads to a termination of the measuring program jumps to step 19 .

Method step 6 thus has the effect that in the event of a counter overflow, which is detected in test step 4 , the occurrence of the next signal edge is not waited for, since otherwise the permissible measurement time could be exceeded.

As mentioned, in step 9, the counter is pre-assigned with a start value, which in the preferred exemplary embodiment has the value 7800 H.

Method steps 10 and 11 correspond identically to method steps 4 and 5 , with the detection of the overflow in method 10 leading to a jump to method 6 .

After detecting the signal edge in 11th step 11 due to the interrupt event occurring here, the counter is stopped in a 12th step 12 . Stopping the counter in this method step enables the manipulation of a 16-bit counter with 8-bit instructions, as explained below, to be carried out in processors from the 8051 family. If one were to carry out manipulations with 8-bit commands while a 16-bit counter was running, a carry could take place between the manipulation of a low-order bit group of the counter and the manipulation of a high-value bit group of the counter, which would lead to an error. This problem is eliminated in the method according to the invention in that the manipulation of the 16-bit counter is stopped before each of the manipulations explained below, as is also the case with the 12th method step 12 .

In the subsequent 13th process step, the counter reading reduced by the start value and as an input counter reading cnt1 saved. As mentioned, this storage takes place in that with the counter stopped one after the other the least significant byte and then the most significant byte below the address cnt1 can be saved.

In the 14th method step 14 , the counter is set to a further start value (start value *), which has the value 15 here. This default setting of the counter with a starting value of 15 counter values instead of resetting the counter to the value zero has the following background. The time that has elapsed during the interruption of the counter must be taken into account. In the exemplary embodiment shown, this takes place in that the start value *, which is stored in the 14th method step 14 , the interruption during the 12th and 13th method step with 9 counter readings and an interruption to be explained later in a 22nd and 23rd method step with 6 counter readings.

In the subsequent method step 15 , the counter is started again starting from the start value mentioned.

The counter reading cnt1 stored in the 13th method step 13 is used to access a first table during a 16th method step 16 . The determined counter reading cnt1 represents a first approximation of the period of the signal to be measured and is used as an input variable for reading out the first table, in which a predetermined number of measuring periods n and a specific coding ldn are assigned to each predetermined counter reading range. The number of measuring periods n is chosen so that the counting of the clock pulses by means of the counter does not lead to a counter overflow even with the longest period of a signal belonging to the period of this value n. The measurement period numbers n are stored in such a graduation with the associated coding ldn in the first table for the respective counter readings cnt1, which is associated with a specific counter reading cnt1 and thus with a certain, already approximated period of the measurement signal, such a number of measurement periods n that this the next smaller value that can be represented by a power of two is below the value that results from the counter reading and thus the approximate period duration already determined divided by the period duration of the clock pulses and divided by the maximum permissible counter reading. In a preferred, practical embodiment, the number of measuring periods n is assigned the coding as a logarithm dualis ldn.

In other words, the measurement period numbers are n Powers of two fixed with the exponent ldn. Possible  Values of the number of measuring periods n are therefore 1, 2, 4, 8, 16, 32, 64,. . .

This staggered assignment of the measurement period numbers to the approximate period duration previously classified by steps 1 to 15 makes it possible, using the clock signal, to count the counter up to a relatively high value regardless of the period duration of the signal to be measured, before the next occurring interrupt Signal after the last period stops the counter. The high counter reading enables, as will be explained below, a period duration measurement for each signal regardless of its period duration with a high resolution.

A particularly important aspect of the telemetry period duration measuring method can now be seen in the fact that the counter in the 15th method step 15 is started before the method step 16 of reading out the first table and thus runs for the duration of the table reading out. In other words, in this aspect, in contrast to the configuration after the main patent application, the counter is not stopped for the table access, but runs during the period of the table access, whereby at least the time for measuring a period of the measurement signal is gained. Since the measuring time is limited, this leads to an increase in measuring accuracy, especially when measuring in the range of low frequencies.

After accessing the table in the 16th step, the number of measuring periods n is checked in the 17th step to determine whether it is equal to 1. If this is the case, the input counter status cnt1 stored in the 13th method step is adopted as counter status cnt, whereupon the method ends the measuring cycle with the method steps 19 and 20 already explained.

If the test in the 17th method step is negative, it is checked in a 21st method step 21 whether the number of measuring periods n is less than or equal to 32 . If this is not the case, the counter is stopped at a 22nd method step 22 and then the counter reading is increased by an overflow counter reading cntov read from the first table during the 16th step. As explained above, this addition also takes place with two successive 8-bit additions of a higher-order bit group of the overflow counter reading and a lower-order bit group of the overflow reading cntov to the current counter reading cnt, whereupon the counter is started again in the 24th method step 24 . This overflow counter reading cntov is dimensioned in such a way that the counter overflows shortly before the maximum permissible measurement time is reached and the measurement is ended at the latest. This measure is necessary in the case of rapidly falling measurement signal frequencies. If one were not to add up the overflow counter cntov, the value of which depends on the period, to the current value of the counter, the measurement over the number of measuring periods n, which is obtained by reading the first table in the 16th step 16 , could result in the measuring time being exceeded cause, because during the measuring period after reading the table at the 16th step 16 the current period of the measuring signal has increased and no longer corresponds to the prior protection. In a 25th method step 25 , a loop counter b is pre-assigned with the number of periods n reduced by 1. In the subsequent method step 26 , the counter overflow is checked. If this occurs, the program jumps to 19th step 19 .

Otherwise, the occurrence of a signal edge of the measurement signal is checked in the subsequent method step 27 . If no signal edge occurs, the program returns to 26th step 26 . If this is the case, however, the loop counter is decremented in method step 28 . In the subsequent method step 29 , it is checked whether the loop counter b has reached the value zero. If this is not the case, the program returns to the 26th method step 26 . Otherwise, in the subsequent method step 30, the counter is finally stopped, whereupon in the 31st method step 31, the counter reading cnt is again reduced by the overflow counter reading cntov by means of two 8-bit subtractions in order to obtain the true measured value. In this case, the measuring cycle is completed with a jump to the 19th method step.

If the test in the 21st method step 21 is positive, the program continues with a further test step 33 , in which it is checked whether the measurement period number n is greater than or equal to 512. If this is not the case, the measurement signal is classified as a signal of a medium frequency range. In this case, in a 34th method step 34, the number of measuring periods n is divided by a loop counter value of an inner loop counter to be explained, which is 32 in the example case. In the subsequent method step 35 , the counter is checked for overflow. If an overflow occurs, the program goes to 19th step 19 . Otherwise, it is checked in the following method step 36 whether a signal edge occurs. If this is not the case, the program returns to step 35 . If a signal edge occurs, the counter status is set to zero in the next method step 37 . The method steps 38 to 44 explained below form an inner loop counter.

First, in a 38th method step 38, the loop counter status is set to zero, whereupon in the subsequent method step 39 it is checked whether a counter overflow takes place. If this is the case, the program goes to 19th step 19 . Otherwise it is checked whether a measurement signal edge has occurred. After this check in method step 40 , the program returns to method step 39 if no signal edge has occurred. If a measuring signal edge occurs, the loop counter status is incremented in the subsequent method step 41 .

In the subsequent step 42 , it is checked whether the current loop counter reading has reached the end value 32 . If this is not the case, the program returns to the 39th step. Otherwise, the measuring period counter is decremented in a 43rd method step. In the subsequent method step it is checked whether the number of measuring periods n has reached the value zero. If this is not the case, the program returns to the 38th method step 38 . Otherwise, the counter is stopped in the subsequent method step 45 and the counter content is stored as counter reading cnt, whereupon the program continues with the 19th method step 19 .

As already mentioned, it is checked in the 33rd method step 33 whether the number of measurement periods n is greater than or equal to 512. If this check leads to a positive result, the program continues with the 47th method step 47 , in which the counter is checked for overflow. If an overflow occurs, the program jumps to step 19 .

Otherwise, it is checked in the subsequent method step 48 whether a signal edge of the measurement signal occurs. If this is not the case, the program returns to the 47th method step 47 . Otherwise, in the subsequent method step 49 the counter reading is set to zero, whereupon in step 50 a loop counter reading is set to zero. The program routine explained below with the method steps 49 to 57 serves to achieve a higher accuracy in determining the number of measuring periods for high frequencies of the measuring signal. In other words, the initial measurement of a single period to determine the number of measuring periods is fraught with uncertainties due to the low meter readings at high frequencies, which can only be countered in an initial measurement over a single period by taking the table values for the number of measuring periods into account the measurement inaccuracy. However, this would lead to a loss in the achievable accuracy. Therefore, in the program routine explained below, the period of the measurement signal is estimated over several periods.

For this purpose, the loop counter reading is set to zero in the 50th method step 50 , whereupon the counter is checked for overflow in the 51st method step 51 . If an overflow occurs, the program jumps to step 19 . Otherwise, it is checked whether a signal edge of the measurement signal has occurred. If this check at step 52 is negative, the program returns to step 51. Otherwise, a loop counter reading is incremented in the subsequent method step 53 . In the subsequent method step 54 , it is checked whether the loop counter reading has reached a number of periods for the initial check of 20 periods. If this is not the case, the program routine returns to the 51st step. Otherwise, the counter is stopped in the subsequent 55th method step 55 and its value is stored in the following method step 56 as counter reading cnt1. In a 57th method step 57, this is used to access a second table from which the number of measurement periods, their coding ldn and the overflow counter reading cntov are read out for the high frequency range present here.

In the subsequent method step 58 , it is checked whether the coding ldn is greater than or equal to 14. If this is not the case, the measured signal is assigned to the upper range of medium frequencies, so that the program carries out the period duration measurement by jumping to the 34th program step 34 .

If the test at step 58 is positive, this means that the measurement signal is classified as the highest-frequency measurement signal. In this case, the method does not perform a period measurement, but rather a frequency measurement in the subsequent method steps 59 to 67 to be explained.

The upper limit frequency of the period measurement is through specified the speed of the processor used. One interrupt must be processed for each edge of the measurement signal will. The period may be that for the processing of a Interrupts must not be less than the processing time required otherwise individual edges cannot be registered. This would severely limit the upper cutoff frequency so not all in a telemetry measurement process occurring frequencies could be covered.

However, when using the 8051 microcontroller Possibility to count pulses in terms of hardware. Here lies the cut-off frequency at a 24th of the processor clock frequency, because the measurement signal with a 12th of the processor clock frequency is scanned.

In the preferred embodiment, that has been realized is the cutoff frequency of the period measurement 106 kHz, while that of frequency measurement at 426 kHz lies.

The combination of both methods enables the measurement of frequencies between 25 Hz and 426 kHz, with the maximum permissible measurement time of 80 ms is exceeded. The resolution of the frequency measurement is 13 bits at frequencies around 100 kHz and rises to 15 Bit at the upper limit frequency.

With a method adapted to the maximum measuring time of 160 ms is a period measurement between 13 Hz and 106  kHz with a resolution between 15 and 16 bit possible. The Frequency measurement achieves a resolution of 14 to 16 Bit at signal frequencies between 106 kHz and 418 kHz.

To carry out the frequency measurement, the measurement signal on Input T0 (timer 0) of the processor (not shown). Each falling edge then increases the count of the Timers 0. A signal must be used as the time base for frequency measurement with a fixed frequency at input INT1 (interrupt 1). The timer 0 can be counted by the bit TRO (Timer Run 0) can be controlled. For frequency measurement counting with this bit for a specific given one Time allows. This time is called the corresponding number counted by edges at input INT1.

In the realized embodiment, the comparison frequency a frequency of 1.25 kHz at input INT1, which corresponds to the period of 800 µs. The measurement will carried out over 98 such periods, so that results in a measuring time of 78.4 ms. This is together with the the maximum measurement time of 80 already explained ms observed.

If, as explained in the 58th program step, the presence of high-frequency measurement signals is determined, a comparison frequency pulse counter with the number of measurement periods n is loaded in the subsequent method step 59 . A check is then carried out in step 60 to determine whether there is an edge of the comparison frequency at input INT1. If so, the program goes back to step 60. Otherwise, the counter, which now serves as a signal edge counter, is set to zero in the subsequent step 61 . If the occurrence of a signal edge is detected in the subsequent method step 62 , the counter is incremented in the 63rd method step 63 . Otherwise, the program goes directly to the subsequent method step 64 , in which it is checked whether there is an edge of the comparison frequency.

If this is the case, the comparison frequency pulse counter b is decremented in the 65th method step 65 . Otherwise this program step is skipped, whereupon the program checks at the 66th program step 66 whether the comparison frequency pulse counter b has meanwhile reached the count value zero. If not, the process goes back to the 62nd step. Otherwise, the current counter reading is stored as counter reading "cnt" in the subsequent program step 67 , whereupon the transmission of the counter reading "cnt" and the coded number of periods "ldn" takes place in the 19th process step before the process is ended in the 20th process step.

In the preferred embodiment, the following data between the telemetry transmitter and the telemetry receiver transfer:

On the one hand counter reading cnt as a 16-bit word and on the other hand the coding of the period number ldn as a 4-bit word.

The processor clock frequency fcpu of 10.24 MHz is known.

On the part of the telemetry receiver must for the calculation the signal frequency two cases can be distinguished:

On the one hand, the case of the period measurement, which is present in the preferred embodiment when the coding ldn is in the value range between 0 and 13. Since the two logarithm of the number of periods is transmitted with ldn, the number of periods is determined as follows: n = 2 ^ldn .

In this case, the frequency f is calculated as follows:

If the coding ldn has the value 14 or 15, it says so that a frequency measurement has been carried out. The Period number n in this case is 98 with a value of ldn = 14 or 196 with a value of ldn = 15. The frequency is then calculated as follows:

An invalid measurement is coded as cnt = 0. The shortfall the lower limit frequency is coded as ldn = 0.

It is obvious to a person skilled in the art that the specified Numerical values only to explain a case distinction serve and thus depend on the application.

Claims (3)

1. Telemetry period measurement method with the following process steps:

• 1.1 counting ( 15 ) clock pulses over at least half a period of a measurement signal by means of a counter to determine a period duration counter reading indicating the approximate period of the measurement signal, (cnt1)
• 1.2 Reading out ( 16 ) a number of measuring periods (n) assigned to a period duration range in which the period duration counter reading (cnt1) falls, from a first table by means of the period duration counter reading (cnt1), the measuring period number (n) being selected such that the Counting the clock pulses by means of the counter does not lead to a counter overflow even with the longest period of this period,
• 1.3 counting the clock pulses over the number of measuring periods (n) of periods of the measuring signal, and
• 1.4 transmission of the counter reading (cnt) and information (ldn) representing the number of measuring periods (n) to a telemetry receiver, according to patent 40 36 107,

characterized by the following process steps between process step 1.2 of reading ( 16 ) the first table and process step 1.3 of counting the clock pulses:

• 1.5 Check ( 33 ) whether the number of measurement periods (n) obtained in method step 1.2 exceeds a counter value (512);
• 1.51 if the result of the test ( 33 ) after method step 1.5 is negative,
• 1.6 Continue with process steps 1.3 and 1.4
• 1.52 if the result of the test ( 33 ) after method step 1.5 is positive,
• 1.7 renewed counting ( 47 to 54 ) of clock pulses over a counting time comprising a plurality ( 20 ) of period durations of the measurement signal, which is longer than that of method step 1.1, by means of a counter for the renewed determination of a period duration counter reading indicating the approximate period duration of the measurement signal ( cnt1);
• 1.8 rereading a number of measuring periods (n) assigned to a period duration range in which the period duration counter falls, from a second table by means of the period duration counter reading, the number of measuring periods being chosen so that the counting of the clock pulses by means of the counter even with the longest period duration this period does not lead to a counter overflow, and
• 1.9 Continue with the steps of counting the clock pulses over the number of measuring periods determined in this way and transmitting ( 19 ) the count (cnt) and the information representing the number of measuring periods (n) to the telemetry receiver.

2. Telemetry period measurement method according to claim 1, characterized in that method step 1.7 comprises the following steps:

• 1.71 Reset and restart ( 49 ) the counter (cnt: = 0);
• 1.72 resetting ( 50 ) a loop counter;
• 1.73 incrementing ( 53 ) the loop counter on each edge of the measurement signal; and
• 1.74 stop ( 55 ) of the counter as soon as the count of the loop counter corresponds to the plurality ( 20 ) of period durations.