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Electronic Fringe Counter

IP.com Disclosure Number: IPCOM000094267D
Original Publication Date: 1966-Aug-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 3 page(s) / 45K

Publishing Venue

IBM

Related People

Courselle, DF: AUTHOR

Abstract

Accurate bidirectional counting is accomplished by logic circuitry. The latter prevents trigger circuit recovery time from causing a false count to be sensed when the counter direction is reversed. The arrangement is useful for bidirectional light fringe counting in interferometric precision measurements.

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Electronic Fringe Counter

Accurate bidirectional counting is accomplished by logic circuitry. The latter prevents trigger circuit recovery time from causing a false count to be sensed when the counter direction is reversed. The arrangement is useful for bidirectional light fringe counting in interferometric precision measurements.

Interferometric light fringes are sensed by detectors 10 and 11. The light arrives at detector 10 in a 90 degree lagging relation with respect to light arriving at 11. The rise of an output from Schmitt trigger 12 causes shaper 44 to produce one output pulse of a fixed duration. The output of Schmitt trigger 13 in response to 11 causes shaper 45 to produce an output pulse of a time duration substantially the same as the output of 13.

Assume movement for a countdown direction causes 12 to produce an output pulse that precedes that of 13 with Vie pulse output of 13 preceding 12 for a countup direction. If movement being measured is to be counted in an up direction, the output from 13 provides one condition for And 15. The other input to 15 is subsequently conditioned by 12 because of the 90 degree phase difference between the 10 and 11 inputs. The presence of 13 output through Invert 20 deconditions And 19 in the interim as the output from 44 rises and falls before the fall of the output from 45. Therefore flip-flop 16 is set and line 17 is raised to indicate an up count condition to bidirectional counter 18. The rise of the 12 output causes 43 to produce a short pulse. This is the actual pulse counted by 18 after passing through delay 24 and normally conditioned And 41. Thus 18 is incremented by the 41 output if 17 is up.

For opposite movement which causes a down count, the 12 and 20 outputs initially complete the conditioning of 19 since 13 is producing the lagging input in this direction. This resets 16 so that line 22 is raised to effect decrementing the count in 18 for each pulse received from 24.

Since the pulses actually counted originate from 12, if the movement being measured reverses direction before 12 recovers, an extra up count might be recorded by 18 and the corresponding down count might fail to decrement 18 if 12 has not recovered. The fringe intensity represented by inputs to 12 and 13 from 10 and 11 is shown with 13 being gated into conduction at 25 while 12 begins to produce an output pulse at 26 and require...