Rockwell Automation T8019 User Manual

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PD-T8019

Trusted

Process Control Algorithm

Software Package

Introduction

The system architecture of the Trusted interlock applications as is possible. The control algorithms detailed in this Product Description are primarily intended to support the limited process control capabilities required for Floating Production, Storage and Offloading (FPSO) installations. The algorithms may also be used for other process control applications as required.

Control functions require the use of floating point values. This ultimately limits the integrity that can be attributed to these functions because of the introduction of an element of “loss of precision” and the general inability to exhaustively verify floating-point capabilities.

is intended to cover as large a cross section of control and

The functions are integrated into the IEC1131 TOOLSET execution environment. This environment is “Commercial-Off-The-Shelf (COTS)” and designed to commercial standards. The overall system achieves higher levels of integrity by the use of additional on-line monitoring and internal state control.

The combination of the above factors indicate that the target integrity for the basic process control functions should be SIL1 (AK3). These functions should therefore NOT be used within elements of application programs intended for SIL3 (AK6) use.

The control algorithms are executed within the Trusted program and are divided into ‘functions’ and ‘function blocks’.

‘Functions’ are those algorithms with no internal state, or time dependent operation, i.e. they have no storage element. The functions process the defined number of parameters and return a single resultant state or value. Functions, therefore, have only a single operating mode, always performing the same operation.

The ‘function blocks’ include retentive information and may return multiple values. Function blocks will have an initial state or value for each of their outputs. The initial value may be maintained for a single or multiple application iterations, depending on the detail of the algorithms.

Controller as part of the standard application

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Issue Record

Issue

Number Date Revised by Technical CheckAuthorised by Modification

6 Oct 05 J W Clark Format

7 Dec 06 N Owens I Vince P Stock Example PID loop

8 Sep 07 N Owens I Vince P Stock Corrections

Process Control Algorithms T8019

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Table of Contents

1. Description...................................................................................................................................7

1.1. Functions .....................................................................................................................................8

1.1.1. Square Root Extraction................................................................................................................8

1.2. BCD Translation...........................................................................................................................9

1.3. Analogue Select.........................................................................................................................10

1.4. Multiple Value Averaging ...........................................................................................................10

1.5. Drum Level Control....................................................................................................................11

1.6. Mass Flow Computation ............................................................................................................11

2. Function Blocks .........................................................................................................................12

2.1. Analogue Scaling .......................................................................................................................12

2.2. Analogue Value Clamping .........................................................................................................13

2.3. Low Value Select .......................................................................................................................13

2.4. High Value Select ......................................................................................................................14

2.5. Median Value Select ..................................................................................................................14

2.6. Proportional PID Function..........................................................................................................15

2.7. Incremental PID Function ..........................................................................................................17

2.8. Deviation Alarm..........................................................................................................................19

2.9. Manual Tracking ........................................................................................................................19

2.10. Time Averaged Value ................................................................................................................20

2.11. Rate of Change Detection..........................................................................................................22

2.12. Analogue Value Slew.................................................................................................................24

3. Other Functions .........................................................................................................................25

3.1. Lead/Lag Control .......................................................................................................................25

4. Sample Application Program .....................................................................................................26

Figures

Figure 1 PID Function.............................................................................................................................16

Figure 2 IPID Function............................................................................................................................18

Figure 3 Sample Application Program ....................................................................................................26

Tables

Table 1 Error Statistics .............................................................................................................................7

Table 2 BCD Translation ..........................................................................................................................9

Table 3 Example Time Average .............................................................................................................21

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Notice

The content of this document is confidential to ICS Triplex Technology Ltd. companies and their partners. It may not be given away, lent, resold, hired out or made available to a third party for any purpose without the written consent of ICS Triplex Technology Ltd.

his document contains proprietary information that is protected by copyright. All rights are reserved.

Microsoft, Windows, Windows 95, Windows NT, Windows 2000, and Windows XP are registered trademarks of Microsoft Corporation.

The information contained in this document is subject to change without notice. The reader should, in all cases, consult ICS Triplex Technology Ltd. to determine whether any such changes have been made. From time to time, amendments to this document will be made as necessary and will be distributed by ICS Triplex Technology Ltd.

Information in this documentation set may be subject to change without notice and does not represent a commitment on the part of ICS Triplex Technology Ltd.

The contents of this document, which may also include the loan of software tools, are subject to the confidentiality and other clause(s) within the Integrator Agreement and Software License Agreement.

No part of this documentation may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying and recording, for any purpose, without the express written permission of ICS Triplex Technology Ltd.

Disclaimer

The illustrations, figures, charts, and layout examples in this manual are intended solely to illustrate the text of this manual.

The user of, and those responsible for applying this equipment, must satisfy themselves as to the acceptability of each application and use of this equipment.

This document is based on information available at the time of its publication. While efforts have been made to be accurate, the information contained herein does not purport to cover all details or variations in hardware or software, nor to provide for every possible contingency in connection with installation, operation, or maintenance. Features may be described herein which are present in all hardware or software systems. ICS Triplex Technology Ltd. assumes no obligation of notice to holders of this document with respect to changes subsequently made.

ICS Triplex Technology Ltd. makes no representation or warranty, expressed, implied, or statutory with respect to, and assumes no responsibility for the accuracy, completeness, sufficiency, or usefulness of the information contained herein. No warranties of merchantability or fitness for purpose shall apply.

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Revision and Updating Policy

All new and revised information pertinent to this document shall be issued by ICS Triplex Technology Ltd. and shall be incorporated into this document in accordance with the enclosed instructions. The change is to be recorded on the Amendment Record of this document.

Precautionary Information

WARNING

Warning notices call attention to the use of materials, processes, methods, procedures or limits which must be followed precisely to avoid personal injury or death.

CAUTION

Caution notices call attention to methods and procedures which must be followed to avoid damage to the equipment.

Notes:

Notes highlight procedures and contain information to assist the user in the understanding of the information contained in this document

Warning

RADIO FREQUENCY INTERFERENCE

Most electronic equipment is influenced by Radio Frequency Interference (RFI). Caution should be exercised with regard to the use of portable communications equipment around such equipment. Signs should be posted in the vicinity of the equipment cautioning against the use of portable communications equipment.

MAINTENANCE

Maintenance must be performed only by qualified personnel, otherwise personal injury or death, or damage to the system may be caused.

Caution

HANDLING

Under no circumstances should the module housing be removed.

Associated Documents

Product Descriptions (PD) provide product specific information.

The Safety Manual contains the recommended safety requirements for the safety system design.

The PD8082B – Toolset Suite provides specific guidance on system configuration and application generation.

The Operator and Maintenance Manual contains general guidelines on maintenance and diagnostic procedures.

For technical support email: support@icstriplex.com

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1. Description

Several of the basic control algorithms may generate error conditions at run-time as all function

arameters are variable. This may result in reversed parameters, e.g. max < min, overflow and

p underflow conditions, divide by zero errors, etc. For each function, the required output under these conditions is defined and error counters are incremented. These error counters are available to the application programmer using the error statistics function block.

The function block has a single Boolean input that is used to reset the counters. Whilst this input is true, the error counters will be reset to zero. The initial value of all error counters is zero.

eversed

RESET

ERRSTAT

Param

Overflow

Underflow

Data types are

1. RESET Boolean

2. All others Integer

Output Error condition

Reversed Pairs of function parameters are reversed, i.e. max<min.

Param A function parameter is incorrect, e.g. out of range or not

Overflow An overflow error occurred in the execution of the function.

Underflow An underflow error occurred in the execution of the function.

Zero Divide A divide by zero error occurred in the execution of the

Zero Divide

The associated function has reversed the two values in order to obtain a valid result. The count is incremented on each iteration of the function whilst the parameters are reversed.

consistent with the functions required operation. The count is incremented on each iteration of the function whilst the parameter is incorrect.

The count is incremented on each iteration of the function whilst the overflow condition occurs.

The count is incremented on each iteration of the function whilst the underflow condition occurs.

function. The count is incremented on each iteration of the function whilst the divide by zero condition occurs.

Table 1 Error Statistics

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1.1. Functions

1.1.1. Square Root Extraction

SQRTX

OUT

MAX

MIN

The Process Variable (PV) is scaled to a value 0…1 according to maximum input value (IP minimum input value (IP i.e. a value greater than maximum input will use the IP will use the IP

value. The square root of the resulting value is then taken and is returned as a

MIN

). Out of range values will result in the value being clamped to the range,

MIN

value, similarly a value below the minimum

MAX

) and

percentage.

i.e.

IPIP,IPPV,MaxMin



MINMAXMIN

100

Note: All inputs (PV, IP

If IP

MAX

< IP

, the function assumes that the values have been reversed and “swap” the values. The

MIN

OUT

and IP

IP -IP

MINMAX

) and the returned value OUT must be real.

MAX

“reversed” error counter is incremented each time the function has to swap the parameters.

If IP

MAX

= IP

, the function returns a value of zero and increments the “zero divide” error counter to

MIN

indicate that a divide by zero error would have occurred.

If PV is not a number (NaN), the function returns a value of zero and increments the “Param” error counter.

All input range parameters (IP

MIN

and IP

) must be finite, i.e. not ±infinities or NaNs. Behaviour is not

MAX

defined for any other values.

If PV is not a NaN, and an overflow or underflow condition occurs the function returns zero and increment the corresponding error counter.

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1.2. BCD Translation

IP0

IP2

IP3

The BCD translation function requires the 4-bit BCD value represented as 4 Boolean parameters (IP0, IP1, IP2, and IP3), IP0 being the least significant bit, IP3 the most significant bit. All four inputs must be defined; inputs not required for specific application must be set to FALSE. M and N are of type integer.

M specifies the value multiplier and must be a power of 10, i.e. 1, 10, 100, etc. N allows the BCD functions to be cascade, by adding the value from a previous function. A value of -1 is assumed to be the result of an up-stream conversion error and will result in all chained BCD functions generating values of -1. The returned value OUT is an integer.

BCD

OUT

NMIP3IP2,IP1,IP0,BCDOUT +×=

Invalid BCD number (see table below) are to result in OUT = -1.

IP3

IP2

IP1

IP0

OUT

(with M=1 and N=0)

0 0 0 0 0

0 0 0 1 1

0 0 1 0 2

0 0 1 1 3

0 1 0 0 4

0 1 0 1 5

0 1 1 0 6

0 1 1 1 7

1 0 0 0 8

1 0 0 1 9

1 0 1 0 -1

1 0 1 1 -1

1 1 0 0 -1

1 1 0 1 -1

1 1 1 0 -1

1 1 1 1 -1

Table 2 BCD Translation

Multiple values (M) that are not powers of 10 are to result in a value of -1. If an overflow condition occurs, the function is to return a value of -1 and increment the “Overflow”, error counter.

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