Full and partial cycle counting apparatus and method

Abstract

Apparatus for determining the number of cycles occurring in a frequency modulated signal during a sample period, including not only the number of full cycles but any portion of a cycle, by determining the number of whole cycles and adding to this a value obtained by counting the number of high frequency clock cycles occurring between the time of the last rising edge of a full cycle and the end of the sample period, and the number of high frequency clock cycles occurring from the last rising edge prior to the start of the sample period and the start of the sample period and the number of high frequency clock cycles in a whole cycle.

I claim: 
     
       1. Apparatus for determining the number of full cycles and any fraction of a cycle N t  in an output signal F 1  during a sample period, the signal F 1  consisting of a plurality of cycles and each cycle having a leading edge comprising: clock means producing a high frequency clock pulse; and   counting means operable to count the number LE, of leading edge occurrences during the sample period, to count the number of clock cycles N n-1 , occurring between the last leading edge occurrence prior to the start of the sample period and the start of the sample period, to count the number of clock cycles N n , occurring between the last leading edge occurrence prior to the end of sample period and the end of the sample period, .[.and.]. .Iadd.the counting means including means .Iaddend.to count .[.the.]. .Iadd.a first.Iaddend.number of clock cycles, .[.D.]. .Iadd.D n-1 , occurring in the period between two consecutive leading edges .Iadd.just prior to the start of the sample period and to count a second number of clock cycles, D n , occurring in the period just prior to the end of the sample period, .Iaddend.and producing an output indicative of N t  in accordance with the equation   N.sub.t =LE.[.-N.sub.n-1 /D+N.sub.n /D.]. .Iadd.+N.sub.n /D.sub.n -N.sub.n-1 /D.sub.n-1. .Iaddend. .[.2. Apparatus according to claim 1 wherein the counting means includes means to count a first D value, D.sub.n-1, just prior to the start of the sample period and a second D value, D.sub.n, just prior to the end of the sample period and the output indicative of N.sub.t is in accordance with the equation N.sub.t       
     
     
        =LE+N n  /D n  -N n-1  /D n-1 ..]. 3. Apparatus according to claim 1 wherein the counting means includes means to store the number LE n-1  of leading edge occurrences in F 1  at the start of the sample period and the number LE n  of leading edge occurrences in F 1  at the end of the sample period with LE being determined by 
     
     
        LE n  -LE n-1 . 4. Apparatus according to claim 1 further including means to generate a first pulse to mark the start of the sample period and 
     
     
        a second pulse to mark the end of the sample period. 5. Apparatus according to claim 1 wherein the signal F 1  is an output of a digital accelerometer having a sensing axis and N t  is indicative of the 
     
     
        incremental change in velocity along the sensing axis. 6. Apparatus according to claim 5 wherein the digital accelerometer has a second output F 2  and further including apparatus for determining the number of full cycles and any fraction of a cycle N' t  in F 2  during the sample period, the signal F 2  consisting of a plurality of cycles with each cycle having a leading edge and the counting means is operable to count the number LE', of leading edge occurrences during the sample period, to count the number of clock cycles N' n-1 , occurring between the last leading edge occurrence prior to the start of the sample period and the start of the sample period, to count the number of clock cycles N' n , occurring between the last leading edge occurrence prior to the end of sample period and the end of the sample period, counting the number of clock cycles D', between two consecutive leading edges and producing an output indicative of N' t  in accordance with the equation N' t   
     
     
        =LE'+N' n  /D'-N' n-1  /D'. 7. Apparatus according to claim 6 wherein the counting means includes means to count a first D' value D' n-1 , just prior to the start of the sample period and a second D' value D' n , just prior to the end of the sample period and the output indicative of N' t  is in accordance with the equation 
     
     
       N' t  =LE'+N' n  /D' n  -N' n-1  /D' n-1 . 8. Apparatus according to claim 6 wherein the counting means includes means to store the number LE' n-1  of leading edge occurrences in F 2  at the start of the sample period and the number LE' n  of leading edge occurrences in F 2  at the end of the sample period with LE' being determined by 
     
     
        LE' n  -LE' n-1 . 9. Apparatus according to claim 6 further including processor means connected to receive the outputs indicative of N t  and N' t  and operable to produce a resultant output indicative 
     
     
        of the incremental change in velocity along the sensing axis. 10. Apparatus according to claim 9, further including circuit means receiving an output signal F T  which varies in frequency with temperature and operable to produce a signal LE T  to the processor so as to modify the calculation of incremental velocity along the sensing 
     
     
        axis as a function of temperature. 11. Apparatus according to claim 10 wherein the signal F T  is a plurality of cycles and the circuit means includes counting means to count the number of cycles in F T  during 
     
     
        the sample period to produce LE T . 12. The method of determining the number of cycles and portions of a cycle N t  in a signal F 1  during a sample period with each cycle having a leading edge comprising the steps of: A) producing first and second strobe pulses to define a sample period;   B) producing a plurality of clock cycles during the sample period;   C) counting the number of leading edge occurrences LE in F 1  during the sample period;   D) counting the number of clock cycles N n-1  between the last leading edge in F 1  prior to the start of the sample period and the first strobe pulse;   E) counting the number of clock cycles N n  between the last leading edge in F 1  prior to the end of the sample period and the second strobe pulse;   F1) counting the number of clock cycles .[.D during two consecutive.]. .Iadd.D n-1  occurring between the last two .Iaddend.leading edges in F 1  .Iadd.prior to the start of the sample period;   F2) counting the number of clock cycles D n  occurring between the last two leading edges in F 1  prior to the end of the sample period.Iaddend., and   G) solving for N t  according to the equation   N.sub.t =LE+N.sub.n .[.D.]. .Iadd.D.sub.n -N.sub.n-1 /.[.D.]. .Iadd.D.sub.n-1 .Iaddend.. .[.13. The method of claim 12 wherein step F) includes the further steps of:       F1) counting the number of clock cycles D n-1  occurring between the last two leading edges in F 1  prior to the start of the sample period;   F2) counting the number of clock cycles D n  occurring between the last two leading edges in F 1  prior to the end of the sample period, and wherein step G) solves for N t  for F 1  according to the equation   
     
     
       N t  =LE+N n  /D n  -N n-1  /D n-1 ..]. 14. The method of claim 12, wherein step C includes the further step of: C1) storing the number LE n-1  of leading edge occurrences in F 1  at the start of the sample period,   C2) storing the number LE n  of leading edge occurrences in F 1  at the end of the sample period and   C3) producing LE in accordance with the equation   LE=LE.sub.n -LE.sub.n-1.