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OPC Items are the backbone of a group. They get their values from PLCs and the values are then used by other items the group and/or to write to the database. They are directly subscribed to an OPC server at the rate of the group and are executed by the group so their alerts are evaluated when the group is executed. These items are executed even when the trigger isn't active.
OPC Item Properties
General:
| • | Name - The name of the OPC item in the group. There cannot be duplicate names within a group. |
| • | Datatype - The datatype used to read values from the PLC. |
Clicking on the Browse OPC... button in this section will allow you to select the tag you want and Ignition will fill out the following fields for you.
| • | OPC Server - The Selected OPC Server. This is a dropdown list showing all the OPC Servers added in the Ignition Gateway. |
| • | OPC Item Path - The OPC Item's address Including Device name or Channel if required. |
| • | Property - Which property of the OPC item you want to use. |
| 2) | Quality - Quality code from OPC Server (192 = GOOD_DATA) |
| 3) | Timestamp - The last time the item value changed |
| 4) | Name - The SQLBridge Item Name property of this Item. |
| • | Mode - Options for displaying values based on the Item value. |
| 1) | Direct Value - Item value |
| 2) | Hour Meter - Record the amount of time the Item value is non-zero. This accumulation will reset to zero when the item value goes to zero. The datatype should be set to integer or float when using an Hour Meter regardless of the OPC Item type. |
| • | On Zero - Use a zero value to accumulate time instead of a non-zero value |
| • | Retentive - Retain the Hour Meter value when it is not accumulating. |
| • | Units - The time units to display. |
| 3) | Event Meter - Record the number or times the Item value is non-zero. The datatype should be set to integer when using an Event Meter regardless of the OPC Item type. |
| • | On Zero - Use a zero value to accumulate events instead of a non-zero value |
| • | Mode - Changes the items directional read/write option. |
| 1) | Use group's mode - Inherit the Update Mode from the Item's Group. |
| 2) | OPC to DB - Only read from the OPC server and write to the database. |
| 3) | DB to OPC - Only read from the database and write to the OPC Server. |
| 4) | Bi-directional OPC wins - Read and Write to both the database and OPC Server. On group start, write OPC Server values to the database. |
| 5) | Bi-directional DB wins - Read and Write to both the database and OPC Server. On group start, write database values to the database. |
| • | Target Type - This is the selection for what the Item will write to when the group executes. |
| 1) | None, read-only item - Do not write this value to the database. |
| 2) | Database field - Write the Item value to the specified column in the database table. This list will populate with all the column names from the Group's target table after the first time the group is run. |
| • | Target Name - The name of the column in the database that this Item will write to when the group executes. The Target Name list will populate with all the column names from the Group's target table if the Target Type is Database field. |
Alerting:
Alerting settings for the OPC items. See SQLTags Alerting for a full explanation.
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