Honeywell Uniformance R300, Руководство пользователя

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Uniformance - PHD OPC Server User Guide
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5. Using the PHD OPC Server
5.1 Overview
This section describes how an OPC client application accesses data through the PHD OPC
Server.
The client must use the OPC interfaces to read data from the PHD OPC Server cache or from
the device (in this case, the PHD Server), and to write data to the PHD Server Database.
The PHD OPC Server allows OPC client applications to access the same PHD functionality
as Uniformance clients using a combination of Data Access (DA) and Historical Data Access
(HDA) standard interfaces.
The PHD OPC Server does the following:
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Reads values from PHD for
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a single point variable
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each point variable in a list
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Writes values to PHD for
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a single point variable
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each point variable in a list
5.2 Guidelines for Accessing PHD Values
Any call to read data returns a maximum of 2000 values by default. The OPC Specification
states that a client requiring more than this will see a OPC_S_MOREDATA error condition
and should repeat the call to obtain the next block of values until the condition no longer
occurs.
The maximum number of values returned by a single call to the OPC Server can be modified
by issuing a 'PHDMAN SET DEFPHDATAVAL xxxx' command where 'xxxx' is the number
of values to return.
Groups with a high item count may cause excessive CPU usage by the PHD OPC Server.
When a client is accessing a large quantity of items, Honeywell recommends that the items be
split into multiple groups of about 250.