History Data Read VI

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Updated2023-02-21
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History Data Read VI

Owning Palette: Historical Access VIs

Requires: OPC UA Toolkit

Reads history data within a time range.

Example

OPC UA server refnum in specifies the reference data value of the OPC UA server.

node ID specifies the ID of the node. The format of the node ID is ns=<namespace index>;<identifier type>=<identifier>. A node ID contains the following components:

namespace index is a base 10 number that indicates the namespace of the node ID.

If namespace index is 0, the format of the node ID can be <identifier type>=<identifier>. The namespace index for a node that you created with the OPC UA Toolkit is 2.
identifier type represents the type of the identifier and has the following values:

Value Identifier Type

i Numeric

s String

g GUID

b Opaque
identifier is a string value that represents the name of the identifier.

The format of the node ID can also be ns=<namespace index>;<identifier type>=<identifier>@<index>:<index>. For example, ns=2;s=Folder.Array@1:2. This format only applies to the array data type and allows you to read a single element or a range of elements of an array. You cannot use @ in a node name.

For backwards compatibility, node ID also accepts node paths as input for OPC UA servers. You can regard the node path as the string type identifier of the node ID. For example, a node path can be Device.folder.item.

request specifies the start time, the end time, the maximum number of values to return over the time range, and whether to return bounding values.

	start time specifies the timestamp at which this VI reads the first history data.
	end time specifies the timestamp at which this VI reads the last history data.
	num values per node specifies the maximum number of values to return over the time range. The default is 0, which specifies that this VI returns all values over the time range.
	return bounds specifies whether to return bounding values. The default is FALSE, which specifies that this VI does not return bounding values. Bounding values are values associated with the starting time and the ending time. An OPC UA client can require bounding values to determine the starting and ending values when requesting data over a time range.

error in describes error conditions that occur before this node runs. This input provides standard error in functionality.

OPC UA server refnum out returns the reference data value of the OPC UA server.

history data returns data from the history database.

	value returns the history data.
	timestamp returns the timestamp at which data is generated.
	node status specifies the status code of the node.