Control of Discrete Outputs of Industrial PLC Controllers

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Control of Discrete Outputs of Industrial PLC Controllers

Course project for the discipline Software and Hardware Support of Computer-Integrated Systems

This project is devoted to the development of control algorithms for discrete outputs of three industrial programmable logic controllers:

Lomikont L-110
PLC154
MIK-51

The work includes analysis of the control task, implementation of control logic for different PLC platforms, development of algorithms and wiring schemes, and comparison of controller-specific approaches.

Project Highlights

Development of discrete output control algorithms for three industrial PLC controllers
Implementation using Microl, Structured Text (ST), Function Block Diagram (FBD), CoDeSys, and Alfa
Visualization and debugging of PLC154 logic in CoDeSys
Comparative analysis of different PLC programming environments and implementation approaches

Overview

Modern automated control systems are widely used in industry to improve process efficiency, reliability and product quality.
One of the key components of such systems is the programmable logic controller (PLC).

A major function of PLCs is control of discrete outputs, which are used for relay switching, valve actuation, light indicators and other on/off devices.

This course project focuses on the development of algorithms for discrete output control based on input conditions and logical rules.

Problem Statement

The control task is based on one discrete input and two analog inputs.

Inputs

di2 — discrete input
ai1 — analog input
ai2 — analog input

Outputs

do1
do2
do3
do4

Control conditions

Mode 1

If:

ai1 > ai2 and di2 = OFF

Then outputs are activated sequentially:

do1 + do2
do3 + do4

Switching time: 3 seconds

Mode 2

If:

ai1 < ai2 and di2 = ON

Then outputs are activated sequentially:

do1 + do3
do2 + do4

Switching time: 3 seconds

Mode 0

If neither condition is satisfied:

all outputs remain OFF

Additionally, each controller mode change must be accompanied by a technological message indicating the current operating state.

Controllers Used

Lomikont L-110

Lomikont L-110 is an industrial PLC suitable for multi-channel automation tasks.
Programming is performed using the Microl language.
The project includes algorithm development, I/O resource allocation, wiring scheme and user operation instructions.

PLC154

PLC154 was implemented in CoDeSys 2.3 using two IEC 61131-3 languages:

Structured Text (ST)
Function Block Diagram (FBD)

It also includes a visualization interface for simulation and debugging.

MIK-51

MIK-51 is a compact multifunctional controller with flexible communication capabilities.
Programming is carried out using FBD in the Alfa 2.0 environment.

Lomikont L-110

For Lomikont L-110, the algorithm was implemented in Microl.
The controller operates in three independent modes and uses:

one discrete input
two analog inputs
four discrete outputs
one timer

The implementation includes:

algorithm flowchart
controller specification
wiring scheme
control logic stored in program sections
user instructions for programming through the controller panel

Files

code/lomikont_l110_control_algorithm.xlsx
docs/lomikont_L110_specification.jpg

Illustrations

PLC154

For PLC154, the task was implemented in CoDeSys using both ST and FBD.

The controller uses:

din2 : BOOL
ai1 : REAL
ai2 : REAL
out1...out4 : BOOL
timers TON and TOF
technological message string
visualization screens for monitoring and input simulation

ST Algorithm

The ST implementation uses conditional branching and timer-based switching.

PROGRAM PLC_PRG
VAR
    timer3: TOF;
    reset: BOOL;
    chas: TIME;
    text: STRING;
END_VAR

timer3(IN := NOT reset, PT := t#6s, Q => reset, ET => chas);

IF (din2 = FALSE) AND (ai1 > ai2)
THEN
    IF chas < t#3s
    THEN
        text := 'mode 1';
        out1 := TRUE; out2 := TRUE;
        out3 := FALSE; out4 := FALSE;
    ELSE
        out1 := FALSE; out2 := FALSE;
        out3 := TRUE; out4 := TRUE;
    END_IF
ELSE
    out1 := FALSE; out2 := FALSE; out3 := FALSE; out4 := FALSE;
    text := 'mode 0';
END_IF

IF (din2 = TRUE) AND (ai1 < ai2)
THEN
    text := 'mode 2';
    IF chas < t#3s
    THEN
        out1 := TRUE; out3 := TRUE;
        out2 := FALSE; out4 := FALSE;
    ELSE
        out2 := TRUE; out4 := TRUE;
        out1 := FALSE; out3 := FALSE;
    END_IF
END_IF

FBD Implementation

The same task was also implemented graphically in FBD.

Visualization

Three visualization screens were created:

main menu
inputs
outputs

These screens allow testing of controller behavior for all three modes.

Files

code/plc154_codesys_2c_Kostiv.pro
code/plc154_codesys_2fbd.pro
docs/plc154_specification.jpg

Illustrations

MIK-51

For MIK-51, the task was implemented in the Alfa 2.0 FBD editor.

The controller supports:

analog inputs
discrete inputs
discrete outputs
block-oriented logic
user display messages

The implementation is divided into two major parts:

conditional part — generation of the active mode
execution part — assignment of output combinations

The following codes were formed for operating modes:

0 — all outputs OFF
0011 (3) — first half-mode
1100 (12) — second half-mode
0101 (5) — third half-mode
1010 (10) — fourth half-mode

Files

code/mik51_control_program.fbx
docs/mik51_specification_1.jpg
docs/mik51_specification_2.jpg

Illustrations

Wiring Schemes and Technical Documentation

The repository also contains technical documentation for all three controllers, including:

specifications
wiring schemes
dimensional drawings
controller-specific supporting drawings

Dimensional drawings

drawings/npt1k_dimensions.jpg
drawings/plc154_dimensions.jpg
drawings/bpo432_dimensions.jpg

Additional documentation

controller specifications
wiring and connection diagrams
course project report