Diagnostic circuit for programmable logic safety control systems

Claim 2

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.

Claim 3

The method of operating a programmable controller based logic system as recited in claim 1 further comprising the step of: monitoring said input modules continuously to assure that said input modules which monitor said output modules on which said solid state switches reside are electrically connected to said programmable controller and that power is available to said input modules from said alternating current voltage source.

Claim 4

The method of operating a programmable controller based logic system as recited in claim 1: wherein said step of monitoring intermittently said second image register and the integrity of said second solid state switch includes initiating a start signal; generating a pulse of approximately one-half second duration; switching said first of two series solid state switches to the on-state for the duration of said pulse; detecting the presence or absence of voltage at the output of said second of two series solid state switches for the duration of the pulse; and latching in a permissive to start upon the detection of absence of voltage at the output of said second of two series solid state switches.

Claim 5

The method of operating a programmable controller based logic system as recited in claim 1, 2, or 3: wherein said step of monitoring said first image register and the integrity of said first solid state switch includes monitoring said first image register and the integrity of said first solid state switch while the burner associated field device logic is not in the startup stage.

Claim 6

The method of operating a programmable controller based logic system as recited in claim 4: wherein said step of monitoring said first image register and the integrity of said first solid state switch includes monitoring said first image register and the integrity of said first solid state switch while the burner associated field device logic is not in the operation stage.

Claim 7

The method of operating a programmable controller based logic system as recited in claim 1, 2, or 3: wherein said step of monitoring said first image register, said second image register and the integrity of the series combination of said first and second solid state switches includes monitoring said first image register, said second image register and the integrity of the series combination of said first and second solid state switches while the field device logic is not in the startup stage.

Claim 8

The method of operating a programmable controller based logic system as recited in claim 6: wherein said step of monitoring said first image register, said second image register and the integrity of the series combination of said first and second solid state switches includes monitoring said first image register, said second image register and the series combination of said first and second solid state switches while the field device logic is not in the operation stage.

Claim 9

The method of operating a programmable controller based logic system as recited in claim 2: wherein said step of monitoring said input modules continuously to assure that said input modules which monitor said output modules on which said solid state switches reside are electrically connected to said programmable controller and that power is available to said input modules includes controlling normally when said input modules are electrically connected to said programmable controller.

Claim 10

The method of operating a programmable controller based logic system as recited in claim 2: wherein said step of monitoring said input modules continuously to assure that said input modules which monitor said output modules on which said solid state switches reside are electrically connected to said programmable controller and that power is available to said input modules includes alarming the condition of at least one of said input modules being electrically disconnected from said programmable controller.

Claim 11

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: 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.

Claim 12

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: 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.

Claim 13

The method of operating a programmable controller based burner management system as recited in claim 10 further comprising the step of: monitoring said input modules continuously to assure that said input modules which monitor said output modules on which said solid state switches reside are electrically connected to said programmable controller and that power is available to said input modules from said alternating current voltage source.

Claim 14

The method of operating a programmable controller based burner management system as recited in claim 10: wherein said step of monitoring intermittently said second image register and the integrity of said second solid state switch includes initiating a burner start signal; generating a pulse of approximately one-half second duration; switching said first of two series solid state switches to the on-state for the duration of said pulse; detecting the presence or absence of voltage at the output of said second of two series solid state switches for the duration of the pulse; and latching in a permissive to start upon the detection of absence of voltage at the output of said second of two series solid state switches.

Claim 15

The method of operating a programmable controller based burner management system as recited in claim 10, 11, or 12: wherein said step of monitoring said first image register and the integrity of said first solid state switch includes monitoring said first image register and the integrity of said first solid state switch while the burner associated field device logic is not in the startup stage.

Claim 16

The method of operating a programmable controller based burner management system as recited in claim 13: wherein said step of monitoring said first image register and the integrity of said first solid state switch includes monitoring said first image register and the integrity of said first solid state switch while the burner associated field device logic is not in the operation stage.

Claim 17

The method of operating a programmable controller based burner management system as recited in claim 10, 11, or 12: wherein said step of monitoring said first image register, said second image register and the integrity of the series combination of said first and second solid state switches includes monitoring said first image register, said second image register and the integrity of the series combination of said first and second solid state switches while the burner associated field device logic is not in the startup stage.

Claim 18

The method of operating a programmable controller based burner management system as recited in claim 15: wherein said step of monitoring said first image register, said second image register and the integrity of the series combination of said first and second solid state switches includes monitoring said first image register, said second image register and the series combination of said first and second solid state switches while the burner associated field device logic is not in the operating stage.

Claim 19

The method of operating a programmable controller based burner management system as recited in claim 11: wherein said step of monitoring said input modules continuously to assure that said input modules which monitor said output modules on which said solid state switches reside are electrically connected to said programmable controller and that power is available to said input modules includes controlling normally when said input modules are electrically connected to said programmable controller.

Claim 20

The method of operating a programmable controller based burner management system as recited in claim 11: wherein said step of monitoring said input modules continuously to assure that said input modules which monitor said output modules on which said solid state switches reside are electrically connected to said programmable controller and that power is available to said input modules includes alarming the condition of at least one of said input modules being electrically disconnected from said programmable controller.