Browse Prior Art Database

Analog Output

IP.com Disclosure Number: IPCOM000093078D
Original Publication Date: 1967-May-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

Belet, JJ: AUTHOR [+3]

Abstract

During a failure of central processing unit CPU 10, which is exercising a process variable control function, associated equipment can be used to maintain valve 12 at its last position, as measured by transducer 14. The latter normally makes this measurement and supplies it on lines 16 to analog-to-digital converter ADC 18 associated with CPU 10. Digital-to-analog converter DAC 20, through normally closed switch 22, provides an input value to control circuitry 24. The latter, in response to that input, sets valve 12 in a particular position.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 90% of the total text.

Page 1 of 2

Analog Output

During a failure of central processing unit CPU 10, which is exercising a process variable control function, associated equipment can be used to maintain valve 12 at its last position, as measured by transducer 14. The latter normally makes this measurement and supplies it on lines 16 to analog-to-digital converter ADC 18 associated with CPU 10. Digital-to-analog converter DAC 20, through normally closed switch 22, provides an input value to control circuitry 24. The latter, in response to that input, sets valve 12 in a particular position.

During normal operation, signal conditioner 25 receives an indication of the valve 12 position from transducer 14. Switch 26 is normally in the position shown and error amplifier 28 generates, as its error signal D, a signal representing the offset voltage. Switch 30 is grounded at this time, so the offset voltage has no effect on circuitry 24. During this time, the measured value of the valve 12 position is stored on capacitor 32.

In fallback mode when CPU 10 fails, switch 30 is connected to terminal 31 and switch 26 opens. The input to amplifier 29 has a high impedance. Initially, it is the last measured value of the valve 12 position as stored on capacitor 32 and generated by conditioner 25. A signal representing that value appears at both terminals 34 and 36 of amplifier 28. Should the valve 12 position change, the input to terminal 34 differs from the input to terminal 36. An error signal is then generated o...