Reading and Writing of Items

Use

Using this function, the SAP system can read values of items from OPC Data Access servers and send values to the ODA server, which may trigger certain functions there.

Example Example

A control system has executed part of a process and transfers a position value for a transport device to the PI sheet (read from item). The process operator needs this information to be able to execute his or her part of the process at the right position. After the position value was received, the process operator confirms it by pressing a pushbutton in the PI sheet. The position value is sent back to the control system (write to item). In this way, the control system gets the confirmation that the process operator has received the correct position value.

End of the example.

See also: OPC Data Access Servers

Integration

Using SAP ODA, you can access OPC data from the following applications:

In PI sheets
In manufacturing cockpits
In the transaction Create Process Messages Automatically – CO69

For more information about how the data is accessed from the above applications, see:

Prerequisites

You have installed the SAP ODA Connector on the target host.
For more information, see Installation and Deinstallation of the SAP ODA Connector .
You have made the settings for SAP ODA in Customizing for the SAP system.
To do so, you go to Customizing for Production Planning – Process Industries and execute the activities listed under SAP ODA .

Features

When reading items synchronously, you can define in Customizing for the SAP system which values are to be sent and when they are to be sent to the SAP system:

Access type An OPC value can either be read from the buffer of the DA server or directly from the device (data source).
Buffer time An OPC value can be buffered in the DA server for a certain time before it is reported to the SAP system.

Reading Items

Together with the value, the time stamp, quality, and a descriptive text are transferred.

Time Stamp

The time stamp is set depending on the following access types at the time when the value is read:

With cache data access, the last value buffered in the OPC server and the time when the value was read are transferred. The time stamp indicates how old the value is.
With device data access, the current value and time when the value was read by process control are transferred.

Quality

The OPC standard contains quality indicators for the value read. A quality indicator comprises the following quality classes:

Quality	Substatus	Limit
Specifies if a value read is good , uncertain , or bad .	Describes a quality status in more detail. A value can, for example, be bad because a device for value reading is broken.	Provides information such as whether a value is outside the defined value range of a reading device or a sensor measurement range.

A numeric value containing a specific definition is defined for each quality class. The following quality messages are based on the OPC specification Data Access Custom Interface Specification, Version 2.02 ( http://www.opcfoundation.org and www.opceurope.org ).

Quality Messages

The SAP ODA Connector analyzes the quality values and issues a suitable information or error message depending on the quality value combination:

Q = Quality; S = Substatus; L = Limit

Q	S	L	Short Text	Long Text
0	0	-	Value is bad	The value cannot be used.
0	1	-	Server configuration error	The value cannot be used due to a server configuration error.
0	2	-	Missing data source	The value cannot be determined since no logical data source is defined at present.
0	3	-	Device failure	The value cannot be used due to a device failure.
0	4	0	Sensor failure	The value cannot be used due to a sensor failure.
0	4	1	Sensor failure	The value cannot be used due to a sensor failure (lower measurement range limit reached).
0	4	2	Sensor failure	The value cannot be used due to a sensor failure (upper measurement range limit reached).
0	4	3	Sensor failure	The value cannot be used due to a sensor failure (constant value).
0	5	-	Value is obsolete	Due to a connection problem, the value is obsolete and may therefore not be usable.
0	6	-	Value cannot be determined	Due to a connection problem, no value can be determined.
0	7	-	Value cannot be determined	The value cannot be determined since the data source is inactive or switched off.
1	0	-	Value is uncertain	The value is not accurate.
1	1	-	Value is obsolete	The value may be obsolete since the data source has not provided data for sometime.
1	4	0	Sensor not calibrated	The value is not accurate since the sensor is not calibrated correctly.
1	4	1	Value is outside value range	The value is not accurate since it is below the sensor measurement range.
1	4	2	Value is outside value range	The value is not accurate since it is above the sensor measurement range.
1	4	3	Sensor not calibrated	The value may be inaccurate since the sensor only provides constant values.
1	5	0	Value is outside value range	The value is outside the defined value range.
1	5	1	Value is outside value range	The value is below the defined value range.
1	5	2	Value is outside value range	The value is above the defined value range.
1	5	3	Value is outside value range	The value is outside the defined value range.
1	6	-	Value is uncertain	The value is not accurate since redundant data sources provide diverging values.
3	0	-	Value is good	The value is accurate.
3	6	-	Value is good	The value is accurate but was set manually.