Electrical apparatus for recognizing missing pulses in an otherwise regular pulse sequence of varying frequency

Omission of a pulse in an otherwise regular pulse sequence, such as may be produced by omission of a tooth of a rotating gear that is used to generate a pulse sequence through a pick-up, is utilized after the manner of a special framing pulse, saving the complications of providing a framing pulse, especially in gasoline engine ignition timing. A counter is started with the beginning of every pulse of the sequence and is operated at a multiple of the sequence frequency. If the frequency varies, the count status when the next pulse arrives will vary slightly and this variation may be caused to change the initial condition for the beginning of each count cycle to keep the repetitive counting generally in step with the varying frequency. When a pulse of the sequence is skipped, however, the repetitive counter goes into a range of content states well beyond those produced by frequency variation and a decoding stage with an appropriate threshold value stored therein gives an indication that a pulse has been missed, which prepares a response to the next pulse which will produce a timing reference signal instead of a correction to the circuits following the frequency of the observed pulse sequence. The latter and also an engine load sensor address an ROM to provide the timing angle signal.

This invention relates to electric circuit apparatus for recognizing the 
absence of a missing pulse in an otherwise regular sequence of pulses 
either to prevent malfunction of an apparatus when the absence of a pulse 
is purposely left out of an otherwise regular pulse sequence as a kind of 
framing signal or the like. 
The recognition of a missing pulse in an otherwise regular pulse sequence 
is of particular importance in the most varied regions of measurement 
technology, as well as in the control and regulation of machines and 
electrical systems. 
The omission of a pulse in an otherwise regular pulse sequence can, on the 
one hand, be utilized as an intended control signal, as in the case of 
numerically controlled machine tools, or for the control of internal 
combustion engines with pulse transmitters operating in proportion to 
engine speed, in which case, for example, a trigger pulse is generated for 
determining the ignition moment compared to a reference position of the 
crankshaft, where the reference position can be regularly indicated by the 
skipping of a pulse of an otherwise regular pulse sequence. On the other 
hand, the failure of a pulse to appear in a regular sequence can also be 
regarded as an alarm signal in an otherwise continuous process, for 
example in the case of packaging or wrapping machinery operation in which 
the supply of wrapping material fails or the article is not presented in 
its place on the transmission, belt in either of which situations, no 
wrapping process can be carried out. Apparatus for recognition of the 
omission of a pulse in a sequence, finally, can also be of consequence for 
physiological measurements, as for example in monitoring the heartbeat of 
a patient. In the latter case, the skipping of a heart action can be 
recognized as an asystoly and indicated by an alarm. 
Known apparatus for recognizing the omission of a pulse in an otherwise 
regular pulse sequence consists of a timing circuit that is set off with 
every new pulse of the sequence and thus forced into its switched-over 
condition. If a pulse of the sequence is omitted, the timing circuit flops 
over into another switching condition and triggers an output signal. It is 
furthermore also known to operate a counter at a frequency higher than the 
repetition rate of the pulse sequence and to stop and reset the counter at 
the occurrence of each pulse of the sequence in question and to compare 
the content of the counter with a predetermined value every time. 
In German Pat. No. 1,917,389, a method and apparatus for generating trigger 
pulse is disclosed in which an extinction pulse generator produces a 
trigger pulse whenever a predetermined time spacing between two pulses is 
exceeded. The predetermined time is, however, fixedly set and requires 
switching over in the case of pulse repetition frequencies that vary 
strongly. 
These circuits and devices have the disadvantage of being able to operate 
only on pulse sequences of at least approximately constant frequency. In 
many fields of applicability, it is required, however, to recognize pulse 
omissions even in pulse sequences of frequencies that vary with time. For 
such cases, it was necessary in the known equipment to make frequent 
switching between ranges of frequencies, a feature which is inconvenient 
either where there are closely succeeding frequency changes or where there 
is operation over long periods. 
It is an object of the present invention, accordingly, to provide apparatus 
for detection of the omission of a pulse of an otherwise regular pulse 
sequence which is useable for pulse sequences that vary considerably in 
repetition rate with time. 
SUMMARY OF THE INVENTION 
Briefly, a second pulse sequence of a frequency that is a multiple of the 
pulse sequence to be followed is used to step a counter that is reset to a 
predetermined count upon the arrival of each new pulse of the sequence to 
be observed. A decoding circuit produces an output signal whenever the 
counter reaches a predetermined count condition that is not reached in the 
regular interpulse interval of the sequence even with the greatest 
expected frequency change rate. Preferably the value of count to which the 
counter is set at the beginning of each counting operation is the value of 
the frequency multiplication factor by which the frequency of the pulse 
sequence to be observed is multiplied to obtain the counting frequency. In 
that case, a down counter is used and the decoding stage is set to produce 
an output signal when a predetermined negative count content is reached. 
Preferably, the frequency multiplication by a digital multi-operated from a 
reversible counter of which the content is representative of the pulse 
frequency as last measured. The stored count of the reversible counter is 
subject to variation in dependence upon the content of the first mentioned 
counter at the beginning of a new pulse of the pulse sequence to be 
observed. Preferably when the first mentioned counter at that moment has a 
positive count content, the reversible counter counts forward by one unit 
and when at that moment the count content of the first mentioned counter 
is negative, the reversible counter is set back by one unit. 
The apparatus according to the invention has the advantage that it can set 
itself to recognize the omission of a pulse at the particular 
instantaneous frequency of the pulse sequence in question. In consequence, 
the recognition function can also be effective when the pulse sequence 
being observed varies strongly. Long period applications are likewise made 
possible without range switching from time to time or resetting of 
apparatus adjustments. 
In a preferred form of the invention, the pulse sequence at the multiple 
frequency is controlled in phase by a digital phase regulation loop as is 
for example described in German published patent application (OS) No. 2 
347 839. 
A logical AND connection is provided in one embodiment to produce a pulse 
upon the appearance of a pulse of the observed sequence that follows the 
omission of a pulse, so that the omission of a pulse can be used as the 
start signal for further operations. Such provisions can considerably 
extend the field of application of the apparatus of the present invention. 
The pulse sequence to be observed can in a preferred manner be a 
periodically moved reference body that generates pulses in a mechanical or 
electric pick-up device of a frequency proportional to the periodicity of 
the movement of the reference body. For example, the reference body can be 
a toothed wheel mounted on a rotating shaft and the pick-up can be 
magnetic or inductive. Toothed racks can be similarly used to produce 
pulses. A further possibility consists in the detection of pulses, for 
example photoelectrically, from the movement of articles piece by piece to 
or in wrapping or packing machinery. If the reference body is formed as a 
rotating toothed wheel that is driven by the crankshaft of an internal 
combustion engine, the teeth of the toothed wheel can be provided, in a 
further embodiment of the invention, as plug-in studs or pegs, so that the 
position of the missing tooth and hence of the missing pulse in the pulse 
cycle can be varied. This can be of advantage when the missing pulse is 
used to provide a start signal and it is desired to be able to vary its 
position relative to a reference point or reference position in or of the 
machinery. 
The arrangement of an engine driven toothed wheel causing the generation of 
a series of pulses can be utilized for triggering ignition timing pulses 
at a preselected ignition moment in an engine. When the apparatus 
according to the invention detects the omission of a pulse, the magnitude 
of the signal corresponding to the ignition angle can be generated in a 
digital calculation circuit in dependence on various parameters and the 
signal in question can then trigger the ignition event under defined time 
relation to the omitted pulse. 
In a particular form of the invention, an additional down counter is 
utilized having a counting rate that is the output frequency of the 
digital multiplier stage used with the reversible counter. In such cases, 
it is convenient to provide a switching stage that is responsive to the 
null condition of the additional down counter. The predetermined value 
from which the additional down counter starts a counting operation can be 
provided by a read-only memory at the beginning of the counting operation. 
The read-only memory can conveniently contain complete characteristic 
curve information, such as a table of corresponding values and the value 
to be read out may be determined utilizing both the content of the 
reversible counter and the content of still another counter as the ROM 
address. The other counter just mentioned is conveniently operated only 
during a fixed period determined by a timing circuit that is triggered by 
a switching stage responsive to the null of the reversible counter so as 
to measure the frequency oscillation modulated by an engine-load sensor.

FIG. 1 shows the basic circuit diagram of an embodiment of the present 
invention. The signals of a pulse sequence 2 that is approximately uniform 
except for certain missing pulses, proceed from the input terminal 1 to 
the input of a pulse-shaping stage 3 that has a control input 4. The 
output of the pulse-shaping stage 3 is connected with the input of a 
frequency multiplier, the output of which is in turn connected to the 
input of a counter 8. The output of the counter 8 is connected to a 
decoder stage 9 that delivers the output signal to the output terminal 10. 
The output of the pulse-shaping stage 5 is further connected with the 
start input of the counter 8. Finally, a fixed number store 11 is provided 
that is likewise connected with the counter 8. 
The signals of the pulse sequence 2 proceed over the input terminal 1 to 
the input of the pulse-shaping stage 3, where they are standardized so 
that at the output of the pulse-shaping stage 3 a pulse sequence 5 is 
provided, all the pulses of which have a definite duration (width) and 
flank steepness. The circuit may, for example, consists of a gate opened 
by the beginning of each pulse of sequence 2 at input 1 for a duration 
equal to the period of standard width and steepness pulses continuously 
supplied from input 4 to another input of the gate so that a selected one 
of the latter pulses becomes a member of the output sequence 5. The pulse 
sequence 5 is multiplied in frequency by the frequency multiplier 6, so 
that a pulse sequence 7 of higher frequency is generated that is counted 
in a counter 8. Upon the arrival of a pulse of the pulse sequence 5 at the 
input of the frequency multiplier 6, a pulse is provided to the counter 8 
to cause a prescribed count start magnitude to be set into the counter 8 
after being read out of the fixed value store 11. The counter 8 now starts 
counting from the prescribed beginning magnitude that was set in by the 
fixed value store 11, changing the count by one unit with the arrival of 
each pulse of the pulse sequence 7. The content of the counter 8 is 
continually transferred to the decoder stage 9. Whenever a pulse in the 
otherwise regular pulse sequence 2 is missing, the counter 8 is not set at 
or near the usual time, because no shape pulse appears at the output of 
the circuit 3 to do it. The counter 8 then counts further and can pass 
beyond a positive or negative limit value determined by the content of the 
fixed value store 11 and provided as a reference value set in the decoder 
stage 9. In this case, when a pulse of the sequence being observed is 
missing, a relaxation circuit (flipflop) is operated and an output signal 
is furnished to the output terminal 10. 
In FIG. 2, a further developed embodiment of the apparatus of the invention 
is represented. The frequency multiplier 6 is in this case constituted by 
a reversible counter 12 and a digital multiplier stage 13. The digital 
multiplier stage 13 operates here as a count-to-frequency converter, so 
that the content at any time of the reversible counter 12 appears as a 
frequency at the output of the digital multiplier stage 13. The apparatus 
of FIG. 2 differs from that of FIG. 1 in that the counter 8 is coupled 
back to the input of the reversible counter. Furthermore, between the 
decoder stage 9 and the output terminal 10, a logic gate 14, which in this 
case has the function of an AND gate, is provided. The second input of the 
AND gate is connected to the output of the pulse-shaping stage 3. The 
output 15 of the logic gate 14 goes to the output terminal 10. 
The manner of operation of the basic circuit can now be illustrated by an 
example. Let the fixed value store 11 contain the multiplication factor of 
the frequency multiplier 6 and let it be assumed that the counter 8 is 
constituted as a backwards counter, which is to say a down counter. The 
information feedback from the counter 8 to the reversible counter 12 
determines the direction in which the reversible counter 12 will step. 
When the operation is in step, which is to say when the pulse sequence 5 
is entirely regular, the frequency of the pulse sequence at the output of 
the digital multiplier stage 13 steps the counter 8 down exactly to zero 
in every cycle, since during a counting cycle n pulses reach the counter 8 
from the digital multiplier stage 13, because each pulse of the pulse 
sequence 5 produces a counting cycle and there are n times as many pulses 
in the pulse sequence 7 as in the pulse sequence 5 if n is the frequency 
multiplication factor of the frequency multiplier 6. Since at the 
beginning of the counting cycle the content of the counter 8, which is in 
this case a down counter, is set to the value n, at the end of the 
counting cycle the counter 8 has counted down to zero. If however the 
frequency of the pulse sequence 5, following that of the pulse sequence 2 
at the input terminal 1 varies, a positive or negative remainder content 
will be found in the counter 8 when the next pulse of the pulse sequence 5 
arrives and this next pulse from the pulse-shaping stage 3 causes this 
remainder to be read into the reversible counter 12 through the feedback 
connection from the counter 8 to the reversible counter 12. Whether the 
remainder content in the counter 8 is positive or negative, when the next 
shaped pulse from the circuit 3 opens the reversible counter 12 to read in 
the remainder, determines whether the frequency of the observed pulse 
sequence has risen or has fallen. If one pulse of the sequence being 
observed at the input terminal 1 is missing, the counter 8 continues 
counting far into the negative count region. A particular negative 
threshold value is provided in the decoder stage 9 that is more negative 
than would be produced by a mere change in frequency of the sequence and 
must therefore correspond to a missing pulse situation, so that when this 
particular value of negative count is reached, an output pulse will be 
provided to one input of the logic gate 14. The logic gate 14 will not 
provide a signal at its output 15 for the output terminal 10 until the 
next shaped pulse from the pulse-shaping stage 3 has arrived. This 
arrangement assures that the indication of a missing pulse is given only 
when another pulse of the observed sequence has been detected, in other 
words when it is clear that the pulse sequence, except for the missing 
pulse, is inherently regular. The output signal can be suppressed in the 
event that the next pulse is missing also if the duration of the output 
signal of the decoder circuit 9 is appropriately limited. 
FIG. 3 shows another illustrative embodiment of the apparatus according to 
the invention. A pick-up device 17 associated with a rotating toothed disk 
16 provides output signals corresponding to each teeth of the disk to the 
pulse-shaping stage 3. The processing of the output signals delivered by 
the pulse-shaping stage 3 proceeds in the same way as described for the 
apparatus of FIG. 2. There is provided in addition, however, a load sensor 
22 that provides a control signal to a frequency modulated oscillator 21 
that may be referred to as the load-frequency converter. The latter 
delivers a signal, of which the frequency is significant, for the counter 
20 which in turn is connected with the read-only memory (read-out store) 
19. A second input of the read-only memory 19 is connected with the output 
of the reversible counter 12. The output of the read-only memory 19 is 
supplied to a second down counter 18, that has other inputs connected to 
the output of the digital multiplier stage 13 and with the output 15 of 
the logic gate 14 respectively. The output of the second down counter 18 
is provided to a switching stage 24 the output of which is connected to 
the output terminal 25 of the circuit. The output of the switching stage 
24 is also connected to a counting stage 23 that provides an output to a 
second input of the counter 20. 
Let it be assumed, for instance, that the rotating disk 16 is driven by the 
crankshaft of a gasoline engine. There are then generated in the pick-up 
17 signals having a frequency proportional to the speed of revolution 
(r.p.m) of the crankshaft of the engine. It is useful to mark the rotary 
position of the disk 16 by omitting a tooth from the regular sequence of 
teeth around its periphery, so that the pulse sequence that is provided to 
the pulse-shaping circuit 3 periodically skips a pulse. This marking or 
framing of the pulse sequence can be utilized, for example, to indicate 
the upper dead-point of the piston movement in a reference cylinder of the 
engine, which is a common type of reference position of an engine 
crankshaft in engine valve and ignition timing measurements. In a 
preferred embodiment of the apparatus of the invention, all of the teeth 
of the toothed disk are constituted as insertable and removable pegs or 
studs, so that the marking or framing of the resulting pulse sequence can 
be provided at a large number of possible positions of the disk 
circumference. The pulse cycles provided by the pick-up device 17 to the 
pulse-shaping circuit 3 are therefore regular except for the pulses that 
are missing because of the missing tooth or teeth utilized for marking. In 
other words, the missing pulse operates in the same way as a framing pulse 
is used in some recurrent pulse systems. 
If the speed of the engine varies, the phase regulation above described 
provided by the frequency multiplying stage 6 will produce a corresponding 
correction. At the output of the reversible counter 12, there will then be 
a count content that is proportional to the speed of the engine. This 
value is then supplied to one input of a read-out store 19 (for example a 
read-only memory, a widely available device known by the acronym ROM), in 
which a so-called ignition characteristic field is stored. Such an 
ignition characteristic field makes possible the determination of the 
optimum ignition angle (degrees of crankshaft rotation) of an internal 
combustion engine for the particular combination of the parameters "speed" 
and "load". In other words, the speed and the load provide an address for 
the read-only memory which contains a table of all the answers for every 
possible combination of speed and load, each answer being an ignition 
timing angle, and in response to the proper address combination, the 
appropriate answer is furnished. For this purpose, the read-only memory, 
in addition to having an address input for speed which is furnished by the 
reversible counter 12, has a second address input for a signal 
proportional to load, which is produced in response to the load sensor 22 
by the frequency modulated oscillator 21 in the form of a frequency 
proportional to the load that is furnished to a counter 20, which counts 
this frequency during a particular period of time determined by a timing 
circuit 23. With the provision of the signals proportional to speed and 
proportional to load, the place where the appropriate ignition angle is 
stored in the read-only memory can be addressed and the desired ignition 
angle can then be read out in response. The value thus read out in read 
into the second down counter 18 as an initial value for a counting cycle. 
The second down counter 18 is then caused to count down in step with the 
frequency multiplied pulse sequence provided at the output of the digital 
multiplier stage 13. The start pulse for the second down counter 18 is 
provided by the output 15 of the logic gate 14. If the down counter 18 
counts down to zero from its initially set value, the switching stage 24 
is put into operation and provides a signal at the output terminal 5 for 
triggering an ignition spark. At the same time, the timing circuit 23 is 
triggered that now enables the counter 20 to count the output frequency of 
the load sensitivity oscillator 21 for a predetermined period of time. 
Although the invention has been most particularly described with reference 
to its application to the timing of gasoline engine ignition, it will be 
understood that a variety of applications of apparatus for detecting the 
omission of a pulse in an otherwise regular pulse sequence of varying 
frequency and it will also be recognized that although the invention has 
been described with reference to particular illustrative examples, 
variations and modifications are possible within the inventive concept.