The OpcProxyExt has standard proxy extension properties such as Status and Enabled, among others (for details, see “ProxyExt properties” in the Drivers Guide). Figure 12 shows the property sheet of an Opc proxy point with its OpcProxyExt expanded.
The following properties of the Opc Proxy Ext are unique or have special importance—note that some are also available in the Add or Edit dialog in the Opc Point Manager (see Figure 10):
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Device Facets
Will contain OPC “properties” for points discovered by the Opc Point Manager.
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Id
The ID of the point on the OPC server.
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Opc Data Type
Windows variant datatype of the OPC item. In most cases, the server provides this information.
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Opc Read Time
(read only) The server timestamp of the current value.
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Opc Quality
(read only) The server-supplied status of the value, as either:
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Good
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Bad
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Uncertain
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Opc Quality Subcode
(read only) The server-supplied status subcode (numeric subcodes indicate vendor information):
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Good
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Non-specific
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Local Override
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Bad
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Non-specific
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Configuration Error
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Not Connected
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Device Failure
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Last Known Value — Comm has failed, however the last known value is available.
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Comm Failure — No last known value.
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Out of Service
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Waiting for Initial Data
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Uncertain
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Non-specific
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Last Usable Value — Whatever was writing this value has stopped doing so.
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Sensor Not Accurate
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Engineering Units Exceeded
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Sub-Normal — The value is derived from multiple sources, and has less than the required number of good sources.
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Opc Limit
(read only) One of the following:
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Not Limited — The value is free to move up or down.
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Low Limited — The value has pegged at some lower limit.
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High Limited — The value has pegged at some upper limit.
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Constant — The value is a constant and cannot move.
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Server Handle
(read only) The server handle used to refer to this item. A handle of 0 means the item has not been registered with the server.
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Tuning Policy Name
If the point is not being updated via asynchronous server callbacks, this controls the tuning policy, and thus the poll frequency at which the point is synchronously polled.