Method and apparatus for determining line frequency and detecting variable frequency light sources
US5394217A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Sep 27, 1993 |
| Grant date | Feb 28, 1995 |
| Priority date | — |
| Expiry date | Sep 27, 2013 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG03B7/093
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
A line frequency is determined by interleaved sampling of ambient light to obtain analog voltage samples at predetermined sampling rates associated with two or more line frequencies. Where there are two line frequencies, one method separates the first samples by a time period at least equal to an analog-to-digital conversion time, and less than the earliest time when a sample associated with one line frequency would coincide with a sample from the other. There are n samples per flicker frequency period and Q samples for each line frequency are taken. In a second method, a first common sample is taken for all line frequencies, and a condition characterized by simultaneous samples for different line frequency sample groups triggers a common sample for all line frequencies. For both methods, digital sample values one through Q-1 for each group are operated on to obtain a result, and then two through Q are similarly operated on to obtain a second result. The result for samples one through Q-1 for a given line frequency is compared to the result for samples two through Q. If the results for a given line frequency are within a predetermined limit, the presence of that line frequency is i…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.