Table Of Contents

Readback Diagnostics

    Last Modified: May 15, 2018

    • Internal readback diagnostics are available on both Single output and Dual output configurations. When you select one of these configurations, DOn.ReadbackFault will populate the Faults table.
    • Internal readback monitors the output signal and compares it to the configured output value in the User Program. If the output does not match the configured value, the User Program will return a fault on DOn.Readbackfault.
    • External readback diagnostics are available for single outputs. Select the Single output with external readback in the configuration column.
    • External readback monitors digital output signals for expected values. You can configure the readback delay to accommodate the time it takes for the signal to propagate. If the output signal does not match the expected value, the User Program will return a fault on DOn.Readbackfault.
      • You can set a maximum time for output values to propagate to the input channel.
      • A readback fault occurs when the propagation exceeds the defined maximum time limit.
      • To turn off readback delay, set value to 0.
      • Toggling outputs faster than the readback diagnostic response time will result in loss of the readback diagnostic.
      • If you set a digital output signal to Flash, you must configure the flash period larger than two times the readback diagnostic response time. Flash period = 2 × Readback diagnostic response time
    • You can monitor external readback diagnostics anywhere on the output circuit, before or after the actuator.

    You can use readback faults in two ways:

    • You can check the Module failsafe box for DOn.ReadbackFault. If a readback fault occurs, the module will go into Fail-safe Mode.
    • You can use DOn.ReadbackFault in the transition condition on the State Machine Diagram. If a readback fault occurs, the User Program will transition to a user-configured state.

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