OPC Items Format

This section describes how the Desigo CC OPC server implements the OPC DA interfaces and concepts defined in the OPC Data Access Server Custom Interface Specification.

OPC DA Interface Compatibility

The OPC server supports all the required COM interfaces described in the OPC Data Access Custom Interface Standard V 2.05 and V 3.00.

Data Point Elements of the OPC Items

  • VT_BOOL
  • VT_UI4
  • VT_R8
  • VT_BSTR
  • VT_UI1
  • VT_UI1 Array
  • VT_DATE Array
  • VT_BOOL Array
  • VT_I4 Array
  • VT_UI4 Array
  • VT_R8 Array
  • VT_BSTR Array

Each data point element has the mandatory OPC items properties associated.

OPC Standard Properties

See the following table for the OPC items mandatory properties. These are handled by the Desigo CC OPC server and allow to retrieve information typical of each specific OPC item.

ID

Description

1

Item Canonical Data Type

2

Item Value

3

Item Quality

4

Item Timestamp

6

Item Access Rights

6

Server Scan Rate (in milliseconds)

OPC Custom Properties

See the following table for the OPC custom properties recommended by the OPC Foundation. These are handled by the Desigo CC OPC server and allow for the third-party OPC clients to easily read some information typical of each specific OPC item.

 

OPC Items Custom Properties1)

ID

Name

Description

7

EU Type

Indicates the type of Engineering Units (EU) information (if any) contained in EU Info.

Possible values:
0 - No EU information available (EU Info will be VT_EMPTY).
1 - Analog - HighEU and LowEU will contain two doubles corresponding to the LOW and HI EU range values.
2 - Enumerated - EUInfo will contain a list of strings (Example: “OPEN”, “CLOSE”, “IN TRANSIT”, and so on) corresponding to sequential numeric values (0, 1, 2, and so on).

8

EU Info

In case EUType is Enumerated, EUInfo will contain a list of strings corresponding to sequential numeric values (0, 1, 2, and so on).

100

EU Units

Indicates the engineering unit of the item (if any).

NOTE: This custom property is set only if not empty.

101

Description

Contains the name of the property (default language (en-US) 0 is used).

NOTE: This custom property is always present.

102

High EU2)

Present only if EU Type is Analog, and represents the highest possible value for the item.

103

Low EU2)

Present only if EU Type is Analog, and represents the lowest possible value for the item.

5000

High Enum

Present only if EU Type is Enumerated, and represents the highest possible value for the enumerated item.

5001

Low Enum

Present only if EU Type is Enumerated, and represents the lowest possible value for the enumerated item.

 

The EU Type depends on the type of OPC item:

OPC Item Type

EU Type

GmsEnum

ENUMERATED

NOTE: In this case the EU Info property contains the texts associated to the possible values.

GmsReal, GmsInt or GmsUint

ANALOG

NOTE: In this case the High EU and Low EU contain the maximum and minimum values permitted for the DPE.

Any other data point element type

NO_INFO

 

1)

Properties from 7 to 103 are handled in line with the use recommended by the OPC Foundation. Properties 5000 and 5001 are vendor-specific properties.

2)

If the range between Low EU and High EU is equal to the range between the minimum and maximum values allowed for the item’s data type, the custom properties are not kept in memory. This means that Low EU and High EU custom properties are not saved. For example, for an item of type Int32 whose range is between Int32.MinValue and Int32.MaxValue.

Further information