Patent GB-1322113-A (GB)
Title: Method and apparatus for measuring speed-error in a pulse train
IPC: H04L25/04
Filed: 1971-06-09
Abstract: 1322113 Electric selective signalling SUSQUEHANNA CORP 19625/71 Heading G4H [Also in Division H4] Transmission speed error is measured and indicated in order that such errors can be distinguished from distortion. Space/mark transitions received on line 10 are differentiated at 12, and mark/space transitions after inversion at 16 are differentiated at 14. For measurement of pulse distortion, outputs of 12, 14 pass through OR gate 18 and gate 20 to activate a one shot multivibrator 24 for say 15 Á.sec. during which time gate 26 is open to pass current through a meter 28. If a transition occurs at other than the correct time the pointer of meter 28 will be deflected which by circuitry (not shown) may be held at its highest value. As start-stop telegraph signals are transmitted as distinct characters, a binary counter 30 acts as a timer which is adjustable to correspond with the code number, e.g. five unit, eight unit &c. The start pulse mark/space transition is applied through gate 32 to line 34 to reset flipflop in the counter 36 hence decoder block 38 removes a clamp on line 40. Block 38 is set according to the code number and controls the count between start and stop pulses. The start transition is also applied to multivibrator 44 hence disabling AND gate 20 to prevent passage of a start transition so that this is not measured for distortion; the start transition also resets a binary up/down counter 46 directionally controlled by a flip-flop 48 and driven by a variable frequency oscillator at 100 times Baud rate of telegraph signals. With correct speed, counter 46 counts up and down each half period equally. Flip-flop 48 is controlled by decoder circuits 56, 58 connected selected outputs of counter 46. When coact = 50, all inputs to AND 56 become true, output from which sets flip-flop 48 to "down" hence count progresses towards zero, when reversal upwards takes place. Counter 46 also controls a conventional analogue ladder 52 giving an ascending and descending "staircase" output produced by a system of weighted resistors. If a transition occurs at other than the expected point, a current dependent on the discrepancy will flow through gate 26, while open, to instrument 28. The invention resides in the provision, to gate 20, of a third input switchable for speed error measurements, to a flip-flop 60 set by line 34 signals and reset by an AND gate 64 connected to ABCD outputs of counter 36. When count = 6 flip-flop 60 is reset to disable AND gate 20. This arrangement provides for up to five transitions each character. At the same time a switch 66 is reversed disabling differentiator 12 hence only space-mark transitions are used. These are processed by the arrangement described above but the speed error scale will be appropriate and indicate such error. An additional flip-flop 70 toggled by the output of AND 20 and responsive to flip-flop 48 activates one of lamps 72, 74. In a modification, Fig. 2 (not shown), only one selected transition in each character is used and flip-flop 60 is set by ABCD input lines to AND gate 80.