DE2332037A1 - Frequency measuring device - measures duration of a specified number of periods of the frequency - Google Patents

Abstract

The frequency is derived as the reciprocal of the measured period. The device has an adjustable frequency divider whose ratio is set with teh duration of the specified number of periods, and its signal input is connected to the output of a pulse generator delivering a fixed repetition frequency f1. The frequency divider output has a frequency fT, characteristic for the measured frequency fx. The frequency f1 is such that the above output frequency fT is greater than fx. A frequency meter has a counter whose counting input is connected to the frequency divider output through a gate opened during a specified period.

Description

2332D37

Applicant: Stuttgart, 15 Msd 1973

Spectrospin AG .P 2672 Rü / Sc

Industriestrasse 26
CH-8117 Zurich-Fällanden
Switzerland

Arrangement for measuring frequencies

The invention relates to an arrangement for measuring frequencies which determine the duration t of a certain Number η of periods of the frequency to be measured fx determined and based on the relationship "frequency = 1 / period" a characteristic of the frequency fx Value returns'.

4 0 9 3 8 1/0268

The direct frequency measurement in which the number of Periods of the frequency to be measured is counted within a certain measuring time and from this the Frequency is determined only provides sufficiently accurate results if they are within the measurement time counted number of periods is sufficiently large. Is the frequency to be measured so low that one is sufficient long measurement time cannot be provided, or a frequency to be measured is not available for the duration the required measurement time before, it is known that in this case the unknown frequency is thereby increased measure, - that the duration t of η whole periods of this frequency is measured, η can also be the value to have. To determine the frequency from this time measurement, it is then necessary to perform a division Determination of the value n / t to be carried out. An analog or a digital computer can be used for this purpose However, this increases the cost of the measuring arrangement. The invention has the task based on creating an arrangement of the type mentioned, which avoids this great effort.

The invention consists in that an adjustable frequency divider is provided, its division factor is set as a function of the duration t and its signal input with the output of a pulse generator is connected, which supplies pulses with a known, fixed repetition frequency f1 and its output signal has a frequency fm which is fχ for the frequency to be measured is characteristic.

One advantage of the invention is that if the frequency to be measured fx is so low that the measurement time required for the direct frequency measurement cannot be made available, the

409881/0268

_ 3 -

Output of the e jib divisor appearing, for the frequency to be measured fx characteristic frequency f _m , as done in one embodiment of the invention, can be selected so that it lies in a frequency range that is easier to measure by conventional frequency meters than the frequency to be measured fx, namely in a higher frequency range; a frequency transformation can therefore be carried out. The arrangement can be made, for example, so that the frequency f ^, is one or more powers of ten greater than fx, then the calibration of a normally switched frequency meter can be carried out in a simple manner, z _% .B. by moving the decimal point.

Another advantage of the invention is that even if a frequency fx, which is so large that it can be measured using the method of direct frequency measurement, but is not available during the required measurement time, the arrangement can be made in such a way that that the frequency fm is, for example, exactly as large as the frequency fx, but is still available at the output of the adjustable frequency divider when the frequency fx is no longer present. This can be achieved in that the division ratio that corresponds to the short-term frequency fx is maintained for a longer time than the frequency fx is present, namely for the duration of the required measuring time. The frequency f _m is then generated for the duration of the required measuring time, so that this frequency can then be measured by a conventional frequency meter connected downstream; here

409SS1 / 0268

the frequency fx to be measured is thus to a certain extent stored. The number η of the periods used for the time measurement can be taken into account in any way, for example when setting the divider, when selecting the frequency f1 or when evaluating the frequency f _T

The adjustable frequency divider is preferably set in such a way that it divides by a number A which is proportional to the period. _{Then the frequency f T} occurring at the output of the divider is proportional to the frequency fx to be measured. However, it is also possible in certain applications not to provide a linear dependency between the determined time and the division factor A, but rather a non-linear dependency, for example on the logarithm of the frequency fx to be measured.

In one embodiment of the invention -is at the output the frequency divider is connected to a frequency meter which has a counter whose counting input is via a gate, that is open for a predetermined period of time, with xlern Output of the frequency divider is connected. The advantage here is that, if necessary, a reduction in the Frequency display errors can be achieved by increasing the length of time during which the door is open

409881/0268

can, and that by choosing the opening time dea Torah of the frequency measure can be easily calibrated can.

In one embodiment it is provided that the timer has a pulse generator that delivers a pulse train with the repetition frequency f2, and that the output dea impulse transmission via a gate circuit which is switched on during a predetermined number of periods of the frequency fx to be measured A further counter is connected to the counter input, the counting status of which influences the dividing ratio of the adjustable frequency divider · Here the advantage is that by choosing the ratio f / f2 «m for a certain frequency fx to be measured, a desired frequency f ^ can be set at the output dea Frequency divider can be obtained. In one embodiment, it is ensured that the frequency f2 is less than the frequency f1. This offers the advantage, which is important for the measurement of low frequencies, that the frequency f _T at the output of the adjustable frequency divider is greater by a factor of m than the frequency fx to be measured, so that in many cases it is easier to measure.

In one embodiment of the invention it is provided that the ratio f1 / f2 = m can be set to different values. This offers the advantage that, as a function of the frequency fx to be measured, the value m ao can be selected so that the error of the entire arrangement is as small as possible. The factor m in the relationship f _T = m * fx can be selected here.

409881/0268

In one embodiment of the invention it is provided that the pulse generator is provided by a further, Frequency divider adjustable to the division ratio 1 / m is formed, the signal input of which with is connected to the output of the pulse generator, and at the output of which the pulse train f2 appears. The advantage here is that the frequency ratio can be changed between f1 and f2 in a particularly simple way; besides, only one will Pulse generator required.

In one embodiment of the invention, a third divider is provided, its signal input is connected to the output of the pulse generator and its output to the control input of the Gate of the frequency meter is connected. The pre. part of this is that it deals with this Arrange the opening times of the gate to be controlled particularly easily without a separate timer.

The arrangement can be made so that the pulse generator is started at the beginning of each time measurement; here one obtains the same measurement result every time at any constant frequency fx. Easier it is, however, to let the pulse generator run unaffected by the timer; this possibility has the advantage that errors in the time measurement last for periods that are not an integer Multiple of the time interval between two pulses of the counter of the timer

409881/0268

supplied pulse train can be eliminated; such mistakes are caused by that when measuring time by counting pulses, no times that are shorter can be detected as the time interval between two consecutive impulses,

In one embodiment of the invention, in which the frequency meter, as explained above, * has a counter which is connected to the output of the adjustable frequency divider via a gate and which adds up the pulses supplied to it (an integration element could also be used as a counter here are), and in which the timer also has a counter in the manner described above, it is therefore provided that the timer measures the respective duration t of immediately successive periods or groups of η periods of the frequency to be measured fx with the pulse generator passing through and after each Measurement sets the adjustable frequency divider, and that the opening time of the gate of the frequency meter is dimensioned so that the counter of the frequency meter without resetting successively based on several settings of the adjustable divider output frequencies f _{T are} fed, so that after the gate is locked, the counter reading of the counter a ma For the mean value of the output frequency f _T and therefore for the mean value of the frequency to be measured fx within the measuring time, the advantage is that the period of the frequency to be measured fx is not only determined once within a certain available measuring time but can be determined as often as the available measuring time allows, so that the influence of measuring inaccuracies in the time measurement can be reduced.

"409881/0268

Further details and configurations of the invention emerge from the following description of an exemplary embodiment of the invention, which is shown in the drawing is shown. In other embodiments of the invention, the features that can be taken from the description and the drawing can be used individually or in groups can be used in any combination. The drawing shows details essential to the invention. Show it

Fig. 1 is a block diagram of a first embodiment of the invention,

Figure 2 is a detail of a block diagram of a

second embodiment of the invention,

3 shows a representation of the relative errors of the frequency measurement in exemplary embodiments of the invention.

In FIG. 1, the pulse sequence to be measured with the frequency fx is fed to the measuring input 2 of a timer 3 for measuring the period time tx = 1 / fy; the result of the measurement appears as number T from output 4- of the timer 3 and is stored in a memory 5 so that the timer is immediately ready for the next time measurement. An adjustable frequency divider is set to a division ratio of 1 / T by the number T stored in memory 5; a pulse train with a repetition frequency f1 is fed to this frequency divider at its signal input 8} at the output 9 of the adjustable divider 6 the pulse frequency f _T = f1 / T is therefore available. It is not imperative that the generator emit 7 pulses, but rather

409881/0268

BATH ORIGINAL

instead, a sine wave generator, for example, can also be provided, which supplies a frequency f1, if the adjustable frequency divider and the downstream frequency meter for processing sinusoidal oscillations are suitable.

The output 9 of the adjustable divider 6 is connected to the signal input 10 of a frequency meter 11. At the output of the frequency meter 11, a display device 12 is arranged, on which the measurement result of the entire arrangement appears. The frequency meter 11 has a gate 15 whose signal input is connected to the input 10 of the frequency meter 11 and whose signal output is connected to the counting input of a counter 14. The gate 15 is controlled to be conductive by a control unit for a predetermined time t_ _{Ä __.} The number F, which the counter 14 has reached when the gate is locked, is fed to the display device 12 and converted there into a frequency display of the frequency fx to be measured.

The timer 5 has a gate circuit 16, the signal input 17 of which is a pulse train with the repetition frequency f2 »f1 / m is supplied. The signal output of the gate circuit 16 is connected to the counting input of another Counter 18 connected. The gate circuit 16 is through a controller 19 controlled so that they respectively for the time of a period tx «i / fx of the to be measured Frequency fx is controlled conductive. After locking the

18 gate circuit 16 gives the counter the count T reached to the memory 5, which, as already mentioned, sets the adjustable frequency divider 6.

409881/0268

The input 17 of the gate circuit 16 supplied Pulse train with the frequency f2 is obtained in that the pulse train supplied by the pulse generator 7 divided down by a second adjustable frequency divider 20, the division ratio of which can be changed to 1 / m will. In addition, a third frequency divider is provided, the signal input of which is also that of the pulse generator 7 supplied pulse train is supplied and divides this pulse train down by a factor of 1 / k and to the control unit 15 of the frequency meter 11.

The adjustable frequency parts 6 and 20 can be designed, for example, as down counters, their highest counting position, from which they count downwards, can be set electrically and freely selectable, and then, when they have reached the count zero, the next pulse supplied to them will generate that from the pulse generator 7 delivered pulse sequence with the emission of an output pulse, switched back to its highest count will. The third frequency divider 21 can also be constructed using a counter, but it does need to not to be adjustable.

The arrangement shown in FIG. 1 works as follows: During a period tx »1 / fx of the frequency fx to be measured, 20 pulses with the repetition frequency f2 are fed to ^{the further counter ^ s from the second frequency divider via the gate circuit 16.} After the gate circuit 16 has been disabled, the count T of the further counter ^ g, since the frequency f2 is known, is a measure of the period tx. It applies

T - tx. f2 -.

409 88 1/0268 ./.

This results for the at the output of the adjustable Frequency divider 6 appearing pulse train a frequency

% - - fs - ^a * ^f3C

The final reading F of the counter 14- results accordingly to

Since both the number T and the number F have an uncertainty of a maximum of one counting step in their last digit, the specified relationships are not strictly accurate, but only approximate.

The control unit 15 is controlled by the third frequency divider 21 delivered pulse sequence is controlled so that it conducts gate 13 during a period k / f1 controls. This results in the following relationship for counter reading F of counter 14:

F «fχ. α · j

The count F of the counter 14- is therefore the one to be measured Frequency fx proportional; a direct decimal display of the frequency fx by the display device 12 is then possible if, through a suitable choice of the values m, k and f1, it is ensured that the product m. ^ r has a value which is any power of ten, for example 1000 or 10000; then you can get the correct frequency display obtained by the display device 12 by placing the comma in the appropriate position in the display device is set.

A09881 / 0268

The measurement error of the arrangement shown in Fig. 1 is essentially determined by two sources of error, namely, the number T does not exactly correspond to the period time Vfx, and the number F does not exactly correspond 'of the frequency fi / T. Since the further counter 18 does not have Difference between a whole and a fraction of a whole period is this counter display either the value rounded down to the nearest whole number or rounded up, i.e., es there is an uncertainty of the last digit of the number T of at most the value 1. The relative error of this display is therefore

t * / mm
I.

T " ^A tx * f1.

Since also with the counting of the pulse train delivered by the adjustable divider with the repetition frequency fi / T through the counter 14 has an uncertainty of one counting step occurs, the resulting relative error is fc ™ given by

Iv - 1 / F «3 r

The total relative error ^fc 4- _O 4. is composed as follows:

_ m. f χ. a

This result applies to the case that a period time tx is measured only once during the measuring time t g, and this measured value defines the division ratio 1 / T of the adjustable divider 6 during the entire measuring time.

A09881 / 0268

When the product ia · fχ becomes large, the first »summand of the total error becomes £ + . large, if this product becomes very small, the second summand becomes large. Therefore, in the arrangement shown in Fig. 1, provision is made for the second frequency divider 20 to be adjustable in terms of its division ratio Λ / m in order to obtain the smallest possible error in the entire measurement depending on the value of the frequency fx to be measured. It is provided that the second frequency divider can be set to values m «10} 100 and 1000. This setting can be done mechanically, for example with the aid of a rotary switch, which is set by the operating personnel depending on which frequency fx is expected, or after an orienting measurement; the setting

can; but also done by electrical signals will. So that the display device 12 directly displays the frequency fx correctly, it is provided that the Position of the comma in the display device 12 depending on the setting of the adjustable second frequency divider 20 is shifted accordingly by means of a control line A.

Assuming that the pulse generator 7 has a pulse repetition frequency f1 «10 MHz, and that the measuring time of the frequency meter 11 is one second, and that the further counters count up to at least 10

e ^ g

3, the curve A shows the course of the relative error £ ^ _ot · As curve A shows, a value m «1000 is provided for frequencies fx from 1 to 10 Hz, for 10 to 100 Hz a value Value m = 100 is provided, and for values from 100 to 1000 Hz a value m = 10 is provided; the frequency to be measured fx is higher

409881/0268

ils 1 kHz, the direct frequency measurement delivers
by the frequency meter 11 bypassing the timer J a smaller error than when initially
the period time tx is determined and from this only the
Frequency is determined.

It is also possible to connect the signal input 2 of the timer 3 \

To precede the arrangement shown in FIG. 1 with a divider which causes the timer 3 to measure the duration
several consecutive periods of the "to be measured".

Detects frequency fx; the timer determines 3 in. in the manner described, for example, the duration
of η periods of the frequency to be measured fx, then yields

the display device 12 shows a display which by the factor η '

too small is. In order to get the correct result, this display must first be multiplied by the value η
will. It is possible, with a suitable setting of the

second variable frequency divider 20 by die'ge- ■ \

if the time measurement of several periods described a lesser one;

Error than with measuring only one period to j

obtain. |

Another embodiment of the invention, which is described in the fol- constricting \, allows also, in the '. Fig. 3 shown by the curve A to error limits
fall below. This embodiment corresponds in,

essential to the arrangement shown in Fig. 1, they
however, instead of the timer 3, it has a different one
built timepiece 30 on. As with the one in Fig. 1
The arrangement shown is the pulse sequence supplied by the second adjustable frequency divider 20

409881/026 8

the frequency f2 is fed to the signal input of a gate circuit $ 1. In this embodiment of the invention, the timer $ 0 is designed so that it can measure the duration of immediately successive periods or groups of η periods of the frequency fx to be measured are provided, the counting inputs of which are alternately connected to the signal input of the gate circuit by the gate circuit 31 designed as a changeover switch. Switching takes place at the end of a time to be measured, and the counter that counted before the switchover transmits its count after the switchover a logic circuit 35 to the memory 5 ^a b and is then reset to Kuli The switching of the gate circuit is controlled by a control device 36 to which, as in the embodiment of the invention shown in FIG new count of the counter 33 and 3 ^ leads to a ne uen setting of the adjustable divider 6; If the frequency to be measured fx is constant, the counters 33 and 3 ^ nevertheless do not always deliver the same counting result T if the period of the frequency to be measured is not an integral multiple of the time interval between two pulses of the frequency fi fed to the input of the gate circuit 31 / xa is. In this case, with several successive timing processes, two different counter readings are eruit; -ΐβ lty which differ exactly by the V / ert 1, and the number of measurements with the slightly larger count and the lessons with the slightly lower count, if enough Measurements are present in such a relationship to one another that the mean value of this measurement is the true one

409881/0268 * ^{/ #}

BATH ORIGINAL

measuring Zei ^ results. With each new existing count T for the time measurement, the adjustable frequency divider 6 is reset and supplies a corresponding frequency f ^ via the gate 13 to the counter 14 of the frequency meter 11. The opening time of the gate 13 _> ie the letting time of the frequency meter 11 is so dimensioned that in the counter 14 pulses of output frequencies f ^ are summed up, which are based on several settings of the adjustable wedge 6. For example, the opening time can be dimensioned such that the pulse trains of the frequency f ^, which are based on ten different settings of the adjustable divider 6, are summed up in the counter 14. _{The frequencies f m} based on the various settings differ when, as explained above, the counter readings T of the counters 14 and 34 differ slightly, also slightly. If, after the gate 13 is blocked, the count of the counter 14 is divided by the number of settings of the adjustable divider 6 taken into account, which can be done, for example, by shifting the decimal point, this results in the average frequency supplied by the adjustable divider 6. This mean frequency corresponds to that frequency that would be obtained from averaging the times determined in the timer and then calculating the frequency from this mean value of the time.

BATH ORIGINAL

A09881 / 0268

The averaging described leads to the fact that the inaccuracy in the measurement of the period time has an effect is reduced to the accuracy of the final result. The mean value determined in the frequency meter 11 Frequency has a relative error £ φ which is smaller by the factor t / t. The total relative Error is thus

or in another notation

* me8B ^{f1 m} * * ΒΘ88 *

The course of ^. the arrangement 13t shown in FIG. 2 is shown in FIG. 3 as curve «B. A frequency f1 of 10 MHz and a measuring time t of 1 second are again assumed here. Here, too, the second adjustable frequency divider 20 must be set differently depending on the frequencies fx to be measured in order to obtain the smallest possible total error. For frequencies between 1 Hz and 100 Hz, m = 1,000 is set, for frequencies from 100 Hz to 10 kHz is set to m = 100, and for frequencies between 10 kHz and 1 MHz, m = 10;. For frequencies above 1 MHz, in turn, the direct frequency measurement results in a smaller error than a frequency determination from the period time. Curve B shows that the frequency measuring range of the second embodiment is larger than the application shown in FIG. 1, and that the measuring error is also smaller, with the exception of the lowest measurable frequency.

409881/0268

For comparison, curve G of FIG. 5 shows which one Error arises when the time of the timer 3 is about 1 second and from this (if necessary after Determination of the mean value of the period time) the frequency is determined by a high-precision computer.

The exemplary embodiments explained represent, without the frequency meter 11, a multiplier arrangement which supplies a frequency L »ι · fχ at the output of the adjustable frequency divider 6; this frequency f ^ follows the frequency fx very quickly, since only one setting of the adjustable frequency divider 6 has to be carried out and no control processes are required. _v The multiplication arrangement can be used quite generally, ie also detached from the task of frequency measurement. If necessary, as in the case of the frequency measurement, the arrangement can be set so that the frequency fm is just as large or smaller than the frequency fx.

The arrangement according to the invention can also be designed in such a way that it can be used for any additional value calculations that are carried out with a frequency measurement that need not have anything to do can be used.

409881/0268

Claims (9)

Claims 1. Arrangement for measuring frequencies, which determines the duration t of a predetermined number η of periods of the frequency to be measured fx and based on the relationship "frequency» l / period duration "supplies a value characteristic of the frequency fx, characterized in that an adjustable Frequency divider (6) is provided, whose division factor is set as a function of the time period t and whose signal input (8) with the. The output of a pulse generator (7) is connected, which supplies pulses with a known, fixed repetition frequency f1 and whose output signal has a frequency f _T which is characteristic of the frequency fx to be measured. 2. Arrangement according to claim 1, characterized in that the frequency f1 of the pulse train and the setting of the adjustable frequency divider (6) are chosen so that the output frequency f _{T of} the adjustable frequency divider (6) is greater than the frequency to be measured fx. 3. Arrangement according to claim 1 or 2, characterized in that at the output of the adjustable frequency divider (6) a frequency meter (11) is connected which has a counter (14) whose counting input is via a gate (13), which is open for a predetermined time, is connected to the output of the adjustable frequency divider (6) is. 409881/02 4. Arrangement according to one of the preceding claims, characterized in that the timer (5)
has a pulse generator which delivers a pulse train with the repetition frequency f2, and that the
The output of the pulse generator is connected via a gate circuit (16) which is conductively controlled for a predetermined number of periods of the frequency to be measured fx, to the counting input of a further counter 08) whose count (T) is the division ratio of the adjustable frequency divider (6) influenced · .5 · Arrangement according to claim 4, characterized in that the frequency f2 is less than the frequency f1. 6. Arrangement according to claim 4 or 5 »characterized in that that the ratio fi / f2 = m to different Fourth is adjustable. 7. Arrangement according to claim 6, characterized in that the pulse generator is formed by a further divider (20) adjustable to the division ratio l / m, the signal input of which is connected to the output of the pulse generator (7)
is connected and at the output of which the pulse train f2 appears. 8. Arrangement according to one of the preceding claims, characterized in that a third frequency divider (21) is provided, its signal input 409881/0268 - 21 - 2332D37 connected to the output of the pulse generator (7) is, and its output with the tax input of the gate (15) of the frequency meter (11) connected is. 9. Arrangement according to claim 3 and 4, characterized in that the timer (30) the respective Duration t of consecutive periods or groups of η periods of the to measuring frequency fx with a continuous pulse generator and after each measurement the adjustable Frequency divider (6) sets, and that the opening time of the gate (13) of the frequency meter (11) is so dimensioned that the counter (14) of the frequency meter without resetting one after the other output frequencies frp based on several settings of the adjustable divider (6) are supplied so that after locking the gate (13) the counter reading of the counter (14) a measure for the mean value of the output frequency fm and therefore for the mean value of the frequency to be measured fx is within the measuring time. 409881/0268