Purpose
The Digital Alarm (DA) block sends and receives digital data (1 or 0) from an I/O driver or OPC server to provide alarm control. Using this block, you can suspend alarms and define an alarm condition and an alarm priority. The block can also wait a specified time interval before issuing an alarm, close a contact when an alarm occurs, and automatically reissue and acknowledge alarms.
Features
The Digital Alarm block:
- Is a primary block.
- Can be used as a stand-alone block.
- Generates alarms when values are outside of defined limits.
- Sends and receives values from an I/O driver or OPC server when placed in Automatic mode.
- Receives values from operator input in the iFIX WorkSpace, from scripts, from Program blocks, or from Easy Database Access programs when operating in Manual mode.
- Can be used in a chain with exception-based or time-based processing.
- Can be configured using Continuous Output that allows blocks to attempt to write the contacts with every scan, even if the value being written in unchanged. Without Continuous Output, the block only attempts to write to the defined contact tag when a value has changed and it needs to be written to the PLC. (In this case, the write is a one-time attempt, so if it fails, the write will not be retried until the block needs to write a new value.)
- Can be configured using the Suppress COMM Alarm option, which allows you to separate the original alarm condition from the COMM alarm, and return the DA block to the same state as it was prior to a COMM alarm. If you disable the Suppress COMM Alarm option, DA blocks handle one alarm at a time. (As a result, it is possible that acknowledgement of a COMM alarm could cause the ACK bit in the PLC to be written, and the original alarm condition, if already acknowledged, could re-alarm.)
- Can be configured to enable the Event messaging (Suspend mode), which applies suppression behavior to disable alarm processing but shows an alarm message. When the tag is in suspend mode, the Alarm state is set to OK. Since the Alarm is an alarm message only, it does not appear in the alarm summary. Alarm processing continues with each alarm state transition recorded in the alarm loggers; however, this does not display in the alarm summary. The alarm state contact (tag) is not processed.
NOTE: Because the contact mode of “Never” does not reset the contact, the Continuous Output option is not supported for this contact mode.
