Item Properties

NOTE: The following fields and descriptions apply to both the Item Properties Viewer and the Item template.

Item Name

Specifies the name of the selected item. You can use the name of the item interchangeably with its ID when entering I/O addresses in Process Database. However, item names must be unique across all servers, groups, and OPC items.

Valid Entries

Up to 30 alphanumeric characters including underscores ( _ ) and hyphens ( - ).

Item Enable Check Box

Enables the OPC Client to poll the item when you select this check box and the driver is connected to the item’s OPC server. If you clear the check box, the item is disabled and not polled.

You may want to disable one or more items in the following situations:

• You want to remove the item from the OPC server.
• You want to take the process hardware that the item is referencing off-line for servicing and you do not want to see any errors.
• You want to isolate the item for debugging.

Description

Specifies user-defined comments about the selected item. Such descriptions can be very helpful when you go back to look at old configuration or report files, or when you need to modify an existing configuration that you did not create. The more detailed and specific the information you enter, the easier it will be to identify the item at a later date.

Valid Entries

Up to 40 alphanumeric characters and symbols.

OPC Item Settings

Item ID

Specifies the fully qualified ID for this item and describes the properties of the data point that you want to read. For example, an item ID can contain addressing parameters, engineering units, and scaling properties.

Valid Entries

The format of the item ID is specific to each OPC server. Refer to your OPC server documentation for more information.

If your OPC server supports browsing, you can click the Browse Server button and select the item you want. The Power Tool updates the Item ID field with the item you select. For more information about browsing an OPC server, refer to How do I browse an OPC server?

You cannot modify this setting while the item is enabled.

Access Path

The access path is a vendor-specific method used to inform the OPC server of the path to use when retrieving data for the current item.

Example

Suppose you have two devices connected to COM1. One device is connected by radio. The other is connected using TCP/IP. In this configuration, possible access paths might be RADIO and ETHERNET.

NOTE: Not all OPC servers support access paths. If your OPC server does not use access paths, you can leave this setting blank. Consult your OPC server documentation for more information.

Item Start

Specifies the starting address of the data array. This setting is available only if the Array check box is selected.

Valid Entries

0 to 32767

Example

Item ID: Sign_Int_Array[10],L200

This item id defines a 200-element array of integers at address 10.

You cannot modify this field while the item is enabled.

NOTE: The starting address plus the array length minus 1 (start + length-1) must be less than or equal to 32767 for Process Database to be able to access all elements of the array. For example, you cannot create an array starting at 32700 with a length of 100 and have Process Database access all elements in the array. Instead the array must start at 32667 or must have a length of 67.

Item Length

Specifies the number of values stored by the data array. This setting is available only if the Array check box is selected.

Valid Entries

1 to 1000

Example

Item ID: Sign_Int_Array[0],L200

This item id defines a 200-element array of integers at address 0.

The length of the array defined in the OPC Client must match the length of the array defined in the OPC server. If the lengths of both arrays do not match, the OPC Client sets the data quality of the item to BAD.

You cannot modify this field while the item is enabled.

NOTES:

• The starting address plus the array length minus 1 (start + length-1) must be less than or equal to 32767 for Process Database to be able to access all elements of the array. For example, you cannot create an array starting at 32700 with a length of 100 and have Process Database access all elements in the array. Instead the array must start at 32667 or must have a length of 67.
• Your OPC server may not support arrays with 1000 elements. In this case, you may need to reduce the size of the data array for the item you are creating and break up the data into multiple items.

Array

When selected, the current item is configured as a data array. A data array is a set of contiguous data of the same data type. By configuring an item as a data array, you enable the OPC Client to read multiple values from an OPC server, if the server supports data arrays. Reading multiple values with a single item simplifies the driver configuration and improves driver throughput.

To configure the item to hold a single value only, clear this check box.

You cannot select or clear this check box while the item is enabled.

Requested Datatype

Specifies the item’s default data type. The driver uses this data type for the item if you do not specify a database block hardware option. When a hardware option is specified, it overrides the data type. The hardware option can be changed only when the item is disabled.

Valid Entries

Data Type	Description
Byte	Unsigned 8-bit character.
Boolean	Digital value, 0 or 1.
Double	Double-precision 64-bit floating point value.
Float	Single-precision 32-bit floating point value.
Long	Signed 32-bit integer.
Server	OPC Server specific native (canonical) data type. Consult your OPC server vendor or documentation to determine the native data type for the specified item ID.
Signed	Signed 16-bit integer.
String	ASCII string.
Unsigned	Unsigned 16-bit integer.

NOTES:

• Your OPC server may not support all data types supported by the driver. Consult your OPC server documentation to determine supported data types.
• When data array support is enabled for an item, the data type is an array of the selected data type. For example, if the selected data type is Float and data array support is enabled, the data type is an array of floats. Data arrays support boolean and numeric (integer and float) data types. Arrays of strings are not supported.

Browse Server

Opens the Browse OPC Server dialog box where you can browse an OPC server to select an item ID and access path to assign to the selected item. You can also use this dialog box to auto-create iFIX process database tags.

Client Settings

Disable Outputs

Prevents output from the OPC Client to the selected item when you select this check box.

You may want to disable outputs:

• To prevent control outputs that may be hazardous to someone performing maintenance or repair on the process control hardware.
• To prevent erroneous writes to the item.
• To isolate a datablock for debugging.

Latch Data

Controls what an operator sees in a link when a communication error occurs.

When you...	The operator sees...
Select the check box	The last good value in the link.
Clear the check box	A series of question marks (?????)

In iFIX applications, the link’s current alarm status changes always displays COMM to indicate a communication problem.

NOTES:

• FIX 6.15 does not support latched data. However, you can add support for latched data by downloading the SAC Software Improvement Module (SIM) from GE’s web site.
• Analog Register and Digital Register blocks do not support latched data. Consequently, we do not recommend using these blocks with the Latch Data option.

Enable Block Writes

When selected, all outstanding writes for the current item are sent to the process hardware.

When the driver sends its outstanding writes for a data array, it also sends any unmodified values in the array using the last known value.

Exception Deadband

Specifies the maximum acceptable data fluctuation in an exception-based iFIX database block. Entering a deadband value prevents the database block’s current value from changing when there is only a slight fluctuation in data.

NOTE: The exception dead band is used only for synchronous I/O.

Valid Entries

Any positive number for analog items. For digital items, set the deadband to 0.

Example

Suppose the current value of an item is 50 and you set a deadband of 20, SAC updates the exception-based database block when an incoming value is less than or equal to 30 or greater than or equal to 70.

To create an exception-based iFIX database block:

1. Start iFIX Process Database.
2. From the Blocks menu, choose Add.
3. Select the type of block you want to create.
4. Enter E in the Scan Time field.

Access Time

Specifies how long the OPC Client keeps an item active in the OPC server when your process control software no longer requests data from that item.

Whenever your process control software requests data from an item, the OPC Client resets the access time for that item and the item remains active in the OPC server. After data requests stop for the item and the access time expires, the OPC Client sets the item to inactive in the OPC server. When the item is inactive, the OPC server stops polling the process hardware for that data. Consequently, if the item has an asynchronous watchdog enabled, the watchdog also stops when the access time expires.

The actual implementation for setting an item to inactive is OPC server specific.

Valid Entries

Accepts the time format: days:hours:minutes:seconds, up to a maximum of 6:23:59:59

Example

To specify an access time of...	Enter...
1 second	1
1 minute	1:00
1 hour and 30 minutes	1:30:00
2 days	2:00:00:00

NOTE: You can force the OPC Client to never deactivate an item by entering DISABLED in this setting.

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