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Browse Prior Art Database

Analog Output with Fallback and Storage

IP.com Disclosure Number: IPCOM000093125D
Original Publication Date: 1967-May-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 48K

Publishing Venue

IBM

Related People

Leon, AF: AUTHOR [+2]

Abstract

Central processing unit CPU 10 governs the status of process variable 12 by analog signals on line 14. If there is a failure of CPU 10, variable 12 can be maintained at either its last measured value, as indicated by a signal on line 16, or at about some preset value.

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Analog Output with Fallback and Storage

Central processing unit CPU 10 governs the status of process variable 12 by analog signals on line 14. If there is a failure of CPU 10, variable 12 can be maintained at either its last measured value, as indicated by a signal on line 16, or at about some preset value.

During normal direct digital control operation, CPU 10 generates a desired value for variable 12. That value is converted to an analog signal by digital-to- analog converter DAC 18 and stored on capacitor 20 through closed relay 22. CPU 10, through connection 23, energizes signal source 24. The latter, in turn, renders transistor 26 conductive and thus renders field effect transistors FET's 28 and 30 conductive. Current from source 32, coupled with signals on lines 34 and 36, render der amplifier 38 operative. The analog signal generated by DAC 18 is amplified and applied to variable 12 so as to set such variable at a desired value. Feedback on line 39 to FET 30 assures linearity of control. The measured value of variable 12 is, at the same time, fed back along line 16, through relay 40 and onto capacitor 42 for storage.

Should CPU 10 experience a failure, source 24 is so energized as to render transistor 26 nonconductive and to supply a signal along line 44 so as to render transistor 46 conductive. At the same time, FET's 48 and 50 are rendered conductive, thus governing the output of amplifier 38. The input to FET 48 is an analog signal representing the last measured value...