Device alerts and PV Bad Alarm indications could mean that devices are dropping off the segment. This can be due to low voltage or noise on the segment. Noise can be caused by inadequate termination, the device itself, shielding, or grounding. The Fieldbus Segment Checkout Procedure provides some help in isolating voltage and noise problems. Devices dropping off the segment can also be caused by scheduling problems involving the module execution rate and/or the macrocycle causing intermittent block errors.