Edit a catalog unit

To edit an engineering catalog unit

1. In the Operations Control Management Console, expand a server group and then expand a server.

2. Expand Configuration Editor, expand System Configuration, and then expand Tag Configuration.

3. Select Engineering Units Catalog.

4. In the details pane, double-click the engineering unit catalog you want to edit. The Properties dialog displays.

   Note: Modifying a system-defined catalog is not recommended. If you select a system-defined catalog, a warning message displays. Click Yes to continue to the Properties dialog.

   

5. For the unit's Symbol, enter Formal and Basic values.

   If the Basic value is blank, it is automatically populated with the Formal value.

   The Basic value is displayed as the unit's symbol by default.

   Note: Unit symbols are case-sensitive and unique.
   
   In many cases, the formal and basic symbols are identical. In some cases, such as when extended characters are part of the symbol, it is appropriate to use the formal field for those values.

   

6. Enter a Name to describe the unit.

7. Selecting Visible allows this unit to be used as a canonical unit when creating an engineering unit. See Add an engineering unit for more information.

8. Select the Dimension and unit System this unit is associated with. See Manage dimensions, unit systems, and catalog unit visibility for more information.

9. If the selected dimension does not already have a base unit defined for the selected unit system, select Base to define this new unit as the base unit. If the dimension already has a base unit defined, this box is disabled.

10. The remaining fields are used to define the relationship between this unit and the other units in this dimension.

    Select a Reference Unit from the list. The list contains all visible units for the selected dimension, in the following format:

    Unit Name (Formal Symbol) - Unit System

    The fields in the Test section are labeled with the formal symbol for this unit, and the selected Reference Unit. Selecting To converts from this unit to the selected reference unit, while selecting From converts from the selected reference unit to this unit. Changing the value in one of the test fields changes the value in the other field based on this formula:

    new value = ( original value / factor ) - offset

    Change the values of Offset and Factor to define how to convert the new unit to the reference unit. You can use the Test fields to verify the results. See Example: add a catalog unit for more information.

11. Enter the Time Base of Unit. When converting rates to accumulated quantities, for example "liters/minute" to "liters", or "kilometers/hour" to "kilometers", Historian must know the time basis of the rate measurement to calculate the quantity. For units that do not measure rates, you can leave this set to the default value of "seconds". For units that do measure rates (e.g. "per minute", "per hour", etc.) be sure to select an appropriate value. The most commonly used values are listed in the drop-down list, but you can set a custom value if the provided options do not meet your needs. For example, if the rate is measured in units/week, select Custom and enter 604800, as 1 week = 604800 seconds.

12. Select OK or Apply to save your changes.

    Note: The values of the Reference Unit, To, From, and Test fields are only used for displaying the unit conversion calculations, and are not persisted to the database.