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US 9,239,575 B2Granted
Diagnostics for a programmable logic controller
AssigneeSiemens Aktiengesellschaft
InventorsRobert Alan Weddle, James F. Archer
Life of this patent
Estimating the term…
Abstract
To reduce the cost and/or space occupied by diagnostic circuitry in a module of a programmable logic controller with multiple outputs, a multiplexer connects the same diagnostic circuitry to the different outputs. The outputs are sequentially tested with the same circuitry. To limit stress on an output driver, an overload condition may be tested while the driver is off. A different source of power is applied to the output, and the results of the application are measured for shorting to ground.
Claims14
A system for diagnostics for a programmable logic controller, the system comprising:
- a plurality of outputs of the programmable logic controller connectable with respective loads;
- an output driver connected with the plurality of outputs;
- a current source;
- a diagnostic detection circuit;
- a multiplexer configured to connect the current source and the diagnostic detection circuit to the plurality of outputs in sequence;
- and
- a central processing unit,
- wherein the plurality of outputs comprise outputs of an expansion bus connected with the central processing unit of the programmable logic controller,
- wherein the output driver provides driver current for operating the respective loads, the central processing unit operating the output driver,
- wherein the current source is configured to provide a diagnostic current operable to avoid operating the respective loads,
- wherein the multiplexer comprises a plurality of switches, each of the switches connecting one of the plurality of outputs to the current source and the diagnostic detection circuit, the multiplexer operable to select a single output of the plurality of outputs at a given time by closing the respective switch, the current source and the diagnostic detection circuit are connected at a same node to the single output,
- wherein multiplexing for a first sequence comprises:
- selecting a first output and not a second output of the plurality of outputs of the programmable logic controller;
- and
- connecting, with a first switch of the plurality of switches, the first output to the diagnostic detection circuit, the connecting being in response to the selecting of the first output, the connecting being while a second switch is open, the second switch disconnecting the second output from the diagnostic detection circuit;
- wherein measuring for the first sequence comprises:
- applying power to the first output through the first switch with the first switch connecting the first output to the diagnostic detection circuit;
- and
- measuring, responsive to the applying of the power to the first output, a first diagnostic for the first output with the diagnostic detection circuit;
- wherein multiplexing for a second sequence comprises:
- selecting the second output after measuring for the first output;
- and
- connecting, with the second switch, the second output to the diagnostic circuit, the connecting being in response to the selecting of the second output, the connecting being while the first switch is open, the open second switch disconnecting the second output from the diagnostic detection circuit;
- and
- wherein measuring for the second sequence comprises:
- applying power to the second output through the second switch with the second switch connecting the second output to the diagnostic circuit;
- and
- measuring, responsive to the applying of the power to the second output, a second diagnostic for the second output with the diagnostic detection circuit.
25 more elements
A method for diagnostics for a programmable logic controller, the method comprising:
- multiplexing a diagnostic circuit to outputs of the programmable logic controller;
- measuring a diagnostic of the outputs with the same diagnostic circuit, the measuring being performed sequentially for the outputs based on the multiplexing,
- wherein multiplexing comprises connecting the diagnostic circuit and a current source to different ones of the outputs at different times,
- wherein multiplexing for a first sequence comprises:
- selecting a first output and not a second output of the outputs of the programmable logic controller;
- and
- connecting, with a first switch, the first output to the diagnostic circuit, the connecting being in response to the selecting of the first output, the connecting being while a second switch is open, the open second switch disconnecting the second output from the diagnostic circuit;
- wherein measuring for the first sequence comprises:
- applying power to the first output through the first switch with the first switch connecting the first output to the diagnostic circuit;
- and
- measuring, responsive to the applying of the power to the first output, a first diagnostic for the first output with the diagnostic circuit;
- wherein multiplexing for a second sequence comprises:
- selecting the second output after measuring for the first output;
- and
- connecting, with the second switch, the second output to the diagnostic circuit, the connecting being in response to the selecting of the second output, the connecting being while the first switch is open, the open second switch disconnecting the second output from the diagnostic circuit;
- and
- wherein measuring for the second sequence comprises:
- applying power to the second output through the second switch with the second switch connecting the second output to the diagnostic circuit;
- and
- measuring, responsive to the applying of the power to the second output, a second diagnostic for the second output with the diagnostic circuit.
17 more elements
A system for diagnostics for a programmable logic controller, the system comprising:
- a plurality of outputs of the programmable logic controller;
- a power source connected with the plurality of outputs;
- a diagnostic detection circuit configured to compare a voltage at one of the plurality of outputs to a threshold while the one output is in an off state with the power source connected, the comparison testing for a short-to-ground;
- a multiplexer configured to connect and disconnect the power source and the diagnostic detection circuit to the one output and configured to connect and disconnect the power source and the diagnostic detection circuit to other outputs of the plurality of outputs of the programmable logic controller in sequence;
- an output driver of the programmable logic controller, the output driver configured to be output zero volts in the off state, and
- a processor configured to
- detect the short-to-ground when the voltage is below a reference voltage, and
- react to a detection of the short-to-ground by causing the programmable logic controller to send a notification to a panel or supervisory computer,
- wherein the multiplexer comprises a plurality of switches, each of the switches connecting one of the outputs to the power source and the diagnostic detection circuit, the multiplexer operable to select a single output of the outputs at a given time by closing the respective switch, the power source and the diagnostic detection circuit connected at a same node to the single output,
- wherein multiplexing for a first sequence comprises:
- selecting a first output and not a second output of the plurality of outputs of the programmable logic controller;
- and
- connecting, with a first switch of the plurality of switches, the first output to the diagnostic detection circuit, the connecting being in response to the selecting of the first output, the connecting being while a second switch is open, the second switch disconnecting the second output from the diagnostic detection circuit;
- wherein measuring for the first sequence comprises:
- applying power to the first output through the first switch with the first switch connecting the first output to the diagnostic detection circuit;
- and
- measuring, responsive to the applying of the power to the first output, a first diagnostic for the first output with the diagnostic detection circuit;
- wherein multiplexing for a second sequence comprises:
- selecting the second output after measuring for the first output;
- and
- connecting, with the second switch, the second output to the diagnostic circuit, the connecting being in response to the selecting of the second output, the connecting being while the first switch is open, the open second switch disconnecting the second output from the diagnostic detection circuit;
- and
- wherein measuring for the second sequence comprises:
- applying power to the second output through the second switch with the second switch connecting the second output to the diagnostic circuit;
- and
- measuring, responsive to the applying of the power to the second output, a second diagnostic for the second output with the diagnostic detection circuit.
23 more elements
Dependencies are inferred from the claim text.