United States Patent
Haselwood et al.
us] 3,651,471  Mar. 21,1972
 DATA STORAGE AND TRANSMISSION SYSTEM
 Inventors: Donald E. Haselwood, Deerfield; Carl M. Solar, Glenview, both of III.
 Assignee: A. C. Nielsen Company, Chicago, III.
 Filed: Mar. 2, 1970
 Appl.No.: 15,696
 U.S.CI 340/172.5
 IntCI G06f9/18
 Field of Search 340/172.5
 References Cited
UNITED STATES PATENTS
3,266,018 8/1966 Higgins 340/172.5 X
3,289,170 11/1966 Curreyetal 340/172.5
3,323,1 12 5/1967 Haselwood et al 340/172.5
3,400,378 9/1968 Smith et al 340/172.5
3,405,393 10/1968 Haselwood 340/172.5
3,408,629 10/1968 Haselwood 340/172.5
Primary Examiner—Raulfe B. Zache
Attorney—Mason, Kolehmainen, Rathburn & Wyss
A system for economically monitoring via telephone a large number of remotely located television receivers or the like. Remotely located data handling systems check the status of receiver groups once every 30 seconds. Whenever a change in status is detected, the altered status is recorded as a "change line data set" in a continuously circulating memory which can store 40 such data sets. At periodic intervals a central unit contacts the remotely located data handling system via telephone. The data sets are then repeatedly transmitted to the central unit in the form of a frequency modulated audio tone. With the aid of a marker bit that reverses its sign each time the circulating memory fully circlates, the central unit is able to extract the 40 data sets from the modulated tone and is also able to check for transmission errors.
25 Claims, 2 Drawing Figures