Intek RheoVac 950A - Manual (Page 47)

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I:\OFFICE\WPMANUAL\RV950A Appendix C revB.doc Feb. 4, 2010
OPC for RheoVac Model 950
C.3.1 INTRODUCTION
The RheoVac Model 950 also incorporates an OPC Server to provide access to Process Variables (PVs)
through the OPC standard. OPC provides the functionality for accessing (reading and writing) data from
various networked devices via a standard set of interfaces. The primary intent of OPC is to provide the
interfaces for data acquisition in support of the vertical architecture (serve data from a device to a client
application on a higher level computer)
In order to access data, an OPC client application needs to specify the following:
x The name of the OPC Server
x The name of the machine hosting the OPC Server
x The vendor specific OPC Item Definition (a.k.a. OPC Tag)
C.3.2 OPC ITEM DEFINITION
For each probe attached to a RheoVac Model 950, 11 Process Variables (PVs) are available through OPC.
Three OPC tags are published for each of the 11 PVs: Label, Units, and Value. The “Label” and “Units”
tags are strings that represent the current label and units for each PV. The “Value” tag contains the actual
8-byte, double-precision float value corresponding to the PV. The OPC tags for these PVs follow a basic
path structure as follows:
x \\\\Label (string)
x \\\\Units (string)
x \\\\Value (double)
For each RheoVac Model 950, the basic path structure above must be customized according to the
following rules in order to access OPC data:
x corresponds to the Network ID for the RheoVac Model 950 (without the
“<”,“>” characters).
x is always “OPC_Intek-exe” (without the “<”,“>” characters).
x corresponds to the individual probe name (without the “<”,“>” characters).
x is one of “PV1”, “PV2”, “PV3”,… “PV11” depending on the desired PV (without the
“<”, “>” characters).
The individual PVs are listed in Table C2.5.
Table C2.5: OPC Process Variable List
Tag Name Description
PV1 RheoVac Time Stamp
PV2 Actual Volume Flow
PV3 Total Mass Flow
PV4 Water Vapor Flow
PV5 RheoVac Pressure
PV6 Water Vapor Specific Volume
PV7 Water Vapor to Air Mass Ratio
PV8 Relative Saturation
PV9 Water Vapor Partial Pressure
PV10 Air Flow In-Leak
PV11 Probe Temperature