Diagnostic circuit for programmable logic safety control systems
First Claim
1. In a programmable controller based logic system having an alarm system for alarming malfunctions, an alternating current voltage source, first and second image registers, electronic input and output modules, said output modules containing solid state switches capable of switching the output module load power, and first and second output module solid state switches connected in series to energize and deenergize an energize-to-start, deenergize-to-stop field device, a method of operating a programmable controller based logic system comprising:
- a. monitoring said first image register, said second image register and the integrity of the series combintion of said first and second solid state switches;
b. independently of and simultaneously with step (a), monitoring said first image register and the integrity of said first solid state switch;
c. independently of steps (a) and (b), monitoring intermittently said second image register and the integrity of said second solid state switch; and
d. alarming an unsafe condition whenever said monitoring indicates the failure of said first image register. and second image register, said first solid state switch, said second solid state switch or the series combination of said first solid state switch and said second solid state switch.
1 Assignment
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Accused Products
Abstract
A programmable controller (41) based logic system places two electronic output converters (14,18) in series for redundant protection against the inadvertent energization, due to the failure of an image register (66,68) or due to the shorted failure of a triac (10,12) on the output converters (14,18), of an energize-to-start, deenergize-to-stop field device (28). A control and monitor circuit monitors the image registers (66,68) and the output converter (14,18) triacs (10,12) that switch power on and off to the field device (28) to assure that the triacs (10,12) have not failed in an unsafe mode or that the image registers (66,68) have not failed. The monitor circuit continuously monitors both image registers (66,68), the first triac (10) and the series combination of the two triacs (10,12). The monitor circuit intermittently monitors the second image register (66) and the second triac (12). A failure of either or both triacs (10,12) or either or both image registers (66,68) energizes an alarm.
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Citations
18 Claims
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1. In a programmable controller based logic system having an alarm system for alarming malfunctions, an alternating current voltage source, first and second image registers, electronic input and output modules, said output modules containing solid state switches capable of switching the output module load power, and first and second output module solid state switches connected in series to energize and deenergize an energize-to-start, deenergize-to-stop field device, a method of operating a programmable controller based logic system comprising:
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a. monitoring said first image register, said second image register and the integrity of the series combintion of said first and second solid state switches; b. independently of and simultaneously with step (a), monitoring said first image register and the integrity of said first solid state switch; c. independently of steps (a) and (b), monitoring intermittently said second image register and the integrity of said second solid state switch; and d. alarming an unsafe condition whenever said monitoring indicates the failure of said first image register. and second image register, said first solid state switch, said second solid state switch or the series combination of said first solid state switch and said second solid state switch. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. In a programmable controller based burner management system having an alarm system for alarming malfunctions, an alternating current voltage source, first and second image registers, electronic input and output modules, said output modules containing solid state switches capable of switching the output module load power, and first and second output module solid state switches connected in series to energize and deenergize an energize-to-start, deenergize-to-stop burner associated field device, a method of operating a programmable controller based burner management system comprising:
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a. monitoring said first image register, said second image register and the integrity of the series combination of said first and second solid state switches; b. independently of and simultaneously with step (a), monitoring said first image register and the integrity of said first solid state switch; c. independently of step (a) and (b), monitoring intermittently said second image register and the integrity of said second solid state switch; and d. alarming an unsafe condition whenever said monitoring indicates the failure of said first image register, said second image register, said first solid state switch, said second solid state switch or the series combination of said first solid state switch and said second solid state switch. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18)
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Specification