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TMR Digital Input Modules

Each TMR digital input (DI) module has three isolated input channels which independently process all data input to the module. A microprocessor on each channel scans each input point, compiles data, and transmits it to the main processors upon demand. Then input data is voted at the main proces-
sors just prior to processing to ensure the highest integrity. All critical signal paths are 100 percent triplicated for guaranteed safety and maximum avail-ability. Each channel conditions signals independently and provides optical isolation between the field and the Tricon.

All TMR digital input modules sustain complete, ongoing diagnostics for each channel. Failure of any diagnostic on any channel activates the module Fault indicator which in turn activates the chassis alarm signal. The module Fault indicator points to a channel fault, not a module failure. The module is guaran-teed to operate properly in the presence of a single fault and may continue to operate properly with certain kinds of multiple faults. Models 3502E, 3503E, and 3505E can self-test to detect stuck-ON conditions where the circuitry cannot tell whether a point has gone to the OFF state. Since most safety systems are set up with a de-energize-to-trip capability, the ability to detect OFF points is an impor-tant feature. To test for stuck-ON inputs, a switch within the input circuitry is closed to allow a zero input (OFF) to be read by the optical isolation circuitry. The last data reading is frozen in the I/O communication processor while the test is running.

All TMR digital input modules support hot-spare capability, and require a sepa-rate external termination panel (ETP) with a cable interface to the Tricon backplane. Each module is mechani-cally keyed to prevent improper instal-lation in a configured chassis.