Inversion Masks: Take Care of Troubleshooting

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Contact inputs on GE Speedtronic DS200DTBA boards send +63/-63 DCV to the switched device in the field. If the switch in the device is closed, current flows through the field device and the DTBA card will then annunciate logic 1 for the point, e.g. L33CB1O.

During factory set up many of these Contact Inputs can be set with an inversion mask, that is, when a current is flowing through the field device a logic 0 is shown for the point and visa versa. This is to give a fail-safe condition for critical switches should a disconnect occur in the field.

To observe which points are inverted, the point should be checked by first identifying its channel slot in the IO.ASG file then checking whether that slot is inverted in the IO Configurator.

The scale used for the point CIM_1 or CIM as shown in the IO.ASG file cannot be trusted to truly reflect whether the point is inverted.

Many of these points are inverted during commissioning to suit different NO/NC switches in the field, so care must be taken to ensure a system will always fail safe in case of a disconnect.

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