Allen-Bradley Pyramid Integrator/Interchange

Allen-Bradley Pyramid Integrator/Interchange
Interface Documentation

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Table of Contents

Introduction 1

Interface Design Overview 2

PI Point Configuration 3

Order of Pre/Post Processing 7

Hardware Configuration 8

Software Configuration 9

Interface Operation 13

Installation 14

Appendix A 15

Data Table Specifications 16

February 1998 17

Introduction

This document describes Oil System’s AllenBradley Pyramid Integrator/INTERCHANGE Interface to the Plant Information (PI) System. The Interface runs with Allen Bradley's DTL or INTERCHANGE software. To run with DTL, PINet is installed on the MicroVAX Information Processor contained in the Pyramid Integrator chassis and the Interface runs from this PINet node. With INTERCHANGE, the Allen-Bradley software and the Interface are both installed on a remote VAX or Alpha AXP. This machine may be either a PI home or PINet node. Details of the hardware and software requirements are covered in Hardware and Software Configuration sections.

The Interface has access to data in the modules in the Pyramid Integrator chassis and through PLC2, PLC3, PLC5 and PLC5/250 processors on a Data Highway or Data Highway Plus Link. In addition, the Interface can obtain data directly from Ethernet PLCs. To access data, the user defines a group of tags known as data tables. The Interface collectively scans these data tables either at a user defined rate or based on events of a specified tag. In addition, the Interface allows for output of data tables based on events.

To operate the Interface effectively, the user must be familiar with Allen-Bradley’s DTL or INTERCHANGE software. In particular, the user must know how to specify which data in the PLC the Interface will be accessing. In addition, the user should possess the appropriate DTL or INTERCHANGE documentation set.

After this introduction, this document contains a brief design overview followed by the details of creating points to be scanned by this Interface. Subsequent sections provide an overview of the hardware and software configurations while instructions for operation and installation are contained at the end.

The following table summarizes the features of this interface:

Interface Design Overview

The Pyramid Integrator Interface consists of a single executable program and a number of utility files for the interface startup and shutdown. The Interface must be installed on a VAX/Alpha AXP with the DTL or INTERCHANGE (Interchange Runtime Software part no. 9351-VSRT) software already installed before installation of the Interface can be successful. Only one copy of this interface can run on a single VAX/AlphaAXP. However, a PI System can support multiple Pyramid Integrators, each running its own interface.

Interface Point List

At startup, the Pyramid Integrator Interface scans the PI Point Database for all associated PI points and builds a point list. This list is composed of all unique Data Table (DT) Definitions and all points associated with each Data Table. The Interface performs bounds checking on all important point attributes, and each Data Table Definition is passed to the Data Table Library for verification. Not all of the parameters in the Data Table Definition string can be verified before communication with the Pyramid Integrator is attempted. Therefore, specifying invalid remote PLCs can introduce errors that are not well defined.

The Interface signs up for point updates and updates (approximately every minute) its point list: adding, changing, or deleting points as necessary. Large changes to the point database can result in a short break in scanning while the interface reconfigures its tag list. For example, adding one hundred tags to the interface suspends scanning for approximately 10 seconds for a system running a MicroVAX 2000.

Input and Output

The Pyramid Integrator Interface supports both data input and data output with any module residing on the Pyramid Integrator chassis or between PLC2, PLC3, PLC5, or PLC5/250 processors on a Data Highway or Data Highway Plus Link. In addition, the Interface supports bi-directional access to Ethernet PLCs. All data transactions take place in the form of Data Table transfers. A Data Table (DT) is defined by the DT's starting address, the number of elements in the DT, and additional routing information that specifies routing to the remote hardware.
Input Data Tables may be associated with multiple points, improving communications efficiency and overall throughput. For output data points, a unique output Data Table must be defined for each point. To improve performance, output data are only sent based on events of a trigger tag.
PINet Node Note: Events for output data are derived from the snapshot on the PINet Node. Thus, outputs based on an output tag (self referenced), as opposed to a separate source tag, should originate from programs running on the PINet Node, as they will not be propagated from the PI Home Node.

Time Stamps

Data scanned by the Pyramid Integrator Interface are put into the snapshot using the VAX/Alpha AXP System Time corresponding to the time the data are received. Time Stamps are not used in conjunction with output data.

PI Point Configuration

A PI Point or Tag corresponds to a single parameter in a programmable controller. For example, a counter, a set point, a process variable, and the high and low control limits would each serve as a separate point in the PI System Database. Each of these points must be defined and configured individually using either the Point Create/Edit or PIDIFF utilities. The following describes the PI point configuration for use with the Pyramid Integrator Interface. For more information regarding point configuration, see the Data Archive (DA) section of the PI System Manuals.

Point Source

All points defined in the PI Point Database for use with the Pyramid Integrator Interface must share a common point source. The point source may be any single character or symbol, for example P. The point source must be defined in the point source library before point configuration; see Software Configuration.

Point Type

The interface supports all three PI point types, real R, integer I, and digital D.
Note that a PI integer is a 15-bit integer with a possible range of 0 to 32,767. If a value is collected by the Interface is outside of this range, a real point type should be used. Otherwise, the value will be flagged as "Over Range".

Location 1

The first location parameter specifies the Pyramid Integrator Interface Number. That is, each Pyramid Integrator System requires a unique interface to the PI System, identified by any arbitrarily chosen integer number from 1 to 256.

Location 2

The second location parameter specifies the data type on the foreign device. The following table lists the different supported data types.

Location 3

The third location parameter specifies the offset location of this point's data in a data table. The offset location is specified as an integer number of bytes with the first byte in a data table having an offset location of 0. By default, output data has an offset of zero (0).

Note: Most AllenBradley hardware uses word or two byte registers whereas the offset specified in location parameter 3 must correspond to the offset in bytes (not registers) of the desired data from the starting address. For example, a floating point or long word register will contribute to a four byte offset while a word register contributes to a two byte offset.

Location 4

The fourth location parameter is used to specify a bit mask for interpretation of scanned (read) data only. The bit mask should only be used with word register data and for PI integer, I, or PI digital, D, tags. A zero in location parameter is the default for NO bit mask. To define a bit mask, the starting and ending bit positions are specified. Bits are ordered from 0 (the low end bit) to 15 (the high end bit). The following formula is used to calculate location parameter 4:

ending bit position + ( 100 * starting bit position ) + 10000 = location parameter 4

For example, if we wanted to look at just the first bit in the scanned word, we would specify a location parameter of 10000:
0 + ( 100 * 0 ) + 10000 = 10000
If bits 4 through 7 correspond to the states of a control loop, we would access them by specifying a bit mask in location parameter 4 equal to 10407:
7 + ( 100 * 4 ) + 10000 = 10407

Location 5

Location parameter 5 is interpreted as a flag bit field. Currently only bit position number 1 is being interpreted.

The scaling flag indicates whether the interface will execute a linear transformation on the incoming data. The transformation uses the zero, span and the conversion factor in conjunction with the incoming data, to generate the value to send to the snapshot.
Value(snapshot) = ( Value(input) * span / conversion ) + zero

Scaling may only be applied to input (scanned) tags of point type R. If no scaling is specified then the conversion factor acts as it used to, (i.e., as a direct multiplier of the incoming value), with real R and integer I tags. (Neither scaling nor conversion factors apply to digital D tags.)

Extended Descriptor

The extended descriptor specifies the following Data Table and scanning information:

Data Table Number
Data Definition String
Scan Rate or Trigger Tag
Source Tag (optional)

A semicolon separates each of the above four fields within the extended descriptor.

The Interface reads and writes data in the form of a Data Table. Every Data Table has an associated data definition string and a scan rate or trigger tag. Every tag in a given Data Table must have the same Data Table Number and scan rate or trigger tag.

A basic extended descriptor has one of the following formats:

data_table_number;data_definition_string;scan_rate
or
data_table_number;data_definition_string;t=trigger

In addition, a source tag may be specified for output tags using the following format:

data_table_number;data_definition_string;t=trigger;s=source

The Data Table number may be any integer from 1 to 999 and may be arranged in any manner.

The data definition string has the following format:

address,elements,VAX/AlphaAXP_data_type,access_type,port_id,station_id,proc_id,ni_id

with each parameter as described in the following table:

If there is a discrepancy between definition strings for a data table number, then the first definition encountered will be used, and a warning message will be logged for each tag with an inconsistent data table definition.