DIAGNOSTICS FOR A PROGRAMMABLE LOGIC CONTROLLER

摘要

To reduce the cost and/or space occupied by diagnostic circuitry (34) in a module of a programmable logic controller (24) with multiple outputs (28), a multiplexer (26) connects the same diagnostic circuitry (34) to the different outputs (28). The outputs (28) are sequentially tested with the same circuitry (34). To limit stress on an output driver (36), an overload (30) condition may be tested while the driver is off. A different source (32) of power is applied to the output (28), and the results of the application are measured (56) for shorting to ground.