Industrial Process Control System

Simon HuiEngineerControl and Informatics,Industrial Centre

System components

A SIMATIC 505 controller consists of a processor in a local base together with a power supply and I/O cards. With the SIMATIC 575 controller, this is a 16 slot VME bus base together with a power supply and up to 8 total controller CPUs, the remainder of VME bus slots can be filled with I/O cards or other VME bus compatible systems. Expansion I/O bases can be added to the system by adding additional bases, power supplies, remote base controllers, and I/O cards as required. Moreover, at least one communication processor is required per SIMATIC 505 controller. This communication processor should be installed in the local base together with the controller CPU.

Data Representation

Bit: A Bit holds either a 1 or 0. Byte: A Byte consists of 8 contiguous bits. Word: A Word consists of 2 bytes. Long Word: A Long Word consists of 2

contiguous words.

Bit 1

Bit 2

Bit 3

Bit 4

Bit 5

Bit 6

Bit 7

Bit 8

Binary Number Data in a bit is binary, 0 or 1. A binary number consists of one or more

bits. A binary number consists of 4 bits can be

represented in Hexadecimal.

Hexadecimal NumbersBit 1 Bit 2 Bit 3 Bit 4 Hexadecimal

Representation

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 A

1 0 1 1 B

1 1 0 0 C

1 1 0 1 D

1 1 1 0 E

1 1 1 1 F

Controller Memory User Control Program User Data System Operation

User program Memory Ladder (L) memory stores RLL

program Special (S) memory stores loops,

analog alarms, SF programs User (U) memory stores user-

defined subroutines

Data Area Memory Variable (V) memory stores

variable data Constant (K) memory stores

constant data Global (G) and VME memory is

used for VME data transfers

System Memory RLL instruction tables: drum,

timer/counter, shift register, etc. Image registers and control relays Subroutine parameter areas Special Function Program

temporary memory Status Word memory

Some of the commonly used functions available with hard keys.

- ESC returns to the previous level of menu operation - Shift? or \ displays a List screen of valid entries for the

current prompt - Alt H accesses the Help System menus - Ctrl V invokes the V-memory - Ctrl K invokes the K-memory - Ctrl T toggles the cursor position display on/off - SPACEBAR toggles between function key menus when

a plus (+) appears to the right of the function key line, also inputs a space in text.

- Shift X, Y, C and B keys access the contact, coil and box editors.

Mode of PID Loop Operation Manual Mode Auto Mode

Manual Mode In manual mode, the loop output is

not calculated by the controller, but comes from the operator. While a loop is in manual mode, the controller still monitors the Broken transmitter, High-High, High, Low, Low-Low, and Rate-of-Change alarms. The Yellow and Orange deviation alarms are not monitored.

Auto Mode In auto mode, the controller

computes the loop output. The Special Function Program for the loop comes from either an operator interface or SF program. All alarms are monitored.

Relay Ladder Logic RLL I/O Concepts In normal operation the

controller updates outputs, reads inputs, and solves the user application program. The I/O update is shown in Fig. 3-1. The series 505 controllers have reserved memory areas for storing the value of all discrete and word I/O points. Discrete I/O values are contained in the discrete image register, which provides storage for all discrete (on/off) I/O points. Word values are stored in the word image register, which provides storage for word and analog data.

RLL concept RLL (Relay Ladder Logic) is similar

in form and interpretation to the relay diagram. Two vertical lines represent power and return rails. Connections between the rails contain circuit components that represent switches, control relays, solenoids, etc.

RLL Operations

TMR OperationThe timer times down from the value specified in the preset, P. The preset

is stored in TCP-Memory (Timer/Counter Preset Memory). The timers current is stored in TCC-Memory (Timer/Counter Current Memory).

- The Enable/Reset must be on for the timer to operate. - When the Start/Stop input is on and the Enable/Reset is on, the

timer begins to time down. - Timing begins at the preset value P and continues down to zero. - If the Start/Stop input turns off and the Enable/Reset input

remains on, the timer stops but it saves the current value, TCC. If the Start/Stop input turns on again, the timer resumes timing.

- If the Enable/Reset input turns off, the timer resets to the preset time specified in P.

The output turns on when the timer reaches zero, and it stays on until the timer resets; i.e., the Enable/Reset inputs turns off.

 If the Enable/Reset input does not receive power flow, the instruction does

not execute and the output does not turn on.

Symbol of Timer, inputs and output

A Timer in RLL

Build a chart to selectively display many I/O status at the same time in a screen

Desired Output of the System You want the system to output a step

response when you want to… Want immediately. Be no difference to what you want.

For example, you want to change the room temperature from 15 degree to 25 degree within 0 seconds (immediately).

Is it possible?

Actual Output of the System

Loop FunctionBit 1, 1 = Go to manual mode. Hex 8000

1 2 3 4

1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Bit 2, 1 = Go to auto mode. Hex 4000

1 2 3 4

0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Water heater represents a simple process system