School of Control Systems and Electrical Engineering

SCHOOL OF CONTROL SYSTEMS AND ELECTRICAL ENGINEERING

Department of Electrical Services

Bachelor of Engineering in Electrical Services

Program Code: (DT010)

2010/2011

Name of Module: Industrial Automation

Name of Lecturer: Joe Teehan

Student Name: Mark McCauley

Class Group: 3E

Assignment number: 2

Assignment title: Industrial Automation

Date issued: 19/11/10

Date due for return: 15/12/10

Date returned:

DECLARATION

I hereby certify that the material, which is submitted in this assignment/project, is entirely my own work and has not been submitted for any academic assessment other than as part fulfillment of the assessment procedures for the program Bachelor of Engineering in Electrical Services(DT010).

Signature of student………………………………………...

Date…………………………………………………………

Table of Contents

DECLARATION 2

Introduction 3

Objective 4

Apparatus 4

Procedure 4

RTD (Resistance Temperature Device) 5

OPC (Object Process Control) 6

Scada (Supervisory Control and Data Acquisition) 6

Temperature Control 7

Analogue to Digital Converter 7

Digital to Analogue Converter 8

Ladder Diagram 8

Reference 11

Introduction

The assignment presented to the class was to develop a list of instructions on a program that would control a rice cooker. The task given to the class to enable the student to see what work load is required for a simple temperature control and how this basic assignment could be used in the working world. The worlds industries are turning to automated controls for all sorts of processes so the importance of the assignment is greatly highlighted.

Objective

The objective of the assignment was for the student to write up list of instructions on a computer program and have it control the temperature of the rice cooker. The assignment will also demonstrate the student’s knowledge of the following;

·  A platinum RTD

·  Calibration

·  Analog to digital Converters

·  Digital to analog Converters

·  Mathematical equations relevant to the process

·  On/off control and On/off control with dead band

·  OPC server

·  SCADA

Apparatus

·  1 Multimeter

·  Leads

·  1 x 100 Ω resistor

·  1 x 39 Ω resistor

·  PC with GX developer

·  PLC, Mitsubushi FX2N

·  HMI

·  Platinum RTD

Procedure

Before using the RTD (resistance temperature device) it must be calibrated. A step by step guide would be the best way of explaining this procedure.

First step is to check the voltage is correct. Turn the multimeter switch to 200 Vdc, Check that the plc is sending out 24 volts, this should be displayed on the screen of the multimeter. When voltage checks is complete remove leads from multimeter and connect to the RTD terminals making sure the leads are connected to the correct points.

The next step is to change the settings on the multimeter to DC milliamp range (mA) and connect the leads from multimeter to the RTD terminals marked 4-20 mA, check the reading and if it reads over 20 mA the RTD is not on which means its an open circuit. By flicking the switch a lower milliamp reading should appear which means the RTD is on. If it reads 0 mA something is wrong

In order to calibrate the circuit must be in open circuit mode. Connect the 100Ω

Into the test circuit on top of the box, the reading should be close 4mA. If below or above 4mA we use the Z terminal and a screwdriver on the transmitter to correct it to 4mA. After correct figure is achieved connect the 139Ω into the test circuit to see what the multimeter is reading. If below or above 20 mA repeat the step above and screw the S terminal this time until the multimeter reads 20 mA. Repeat the test a few times on each resistor. This setting means there is a 16mA difference between the highest and lowest.

RTD (Resistance Temperature Device)

An RTD is a temperature sensitive resistor, the resistance increases with temperature because the material resistance increases with temperature change. The Platinum RTD is being used in the assignment as it has the best accuracy and stability. Platinum is the primary choice for most industrial, commercial laboratory and other critical RTD temp measurements. It has an output of 4-20mA. The 4 mA is used because at 0 mA it is difficult to detect an error. It uses current to measure the temp, this is a better way of measurement compared to voltage as current has no loss in transmission. The cables connect the device to the transmitter through a twisted pair of cables to prevent interference from outside magnetic fields. 4mA will represent 0° Celsius and the max temp of 100° shall be represented by 20mA.

Figure 1, RTD Device

OPC (Object Process Control)

OPC software enables computer programs to connect with industrial processes. It acts as a go between of the PLC, hardware and the client’s software. Man y hardware devices can be connected under one program which is cost effective, the opc in the assignment enables scada software to communicate with the PLC.

Scada (Supervisory Control and Data Acquisition)

The term scada usually refers to a centralized which monitors and controls entire sites. Most control actions are performed automatically by RTU’s (Remote Terminal Units). The advantages of a scada system are that a technician can monitor from a remote location and also change the settings of a program from a remote location. Scada systems are used a lot in Oil and gas industries. A scada system is made of a HMI (human machine interface) which presents process data to a human operator.

Temperature Control

The first 6 lines of the program are the lines that basically control the whole temperature process. The required temperature for the rice cooker is 33°C. The program is set up to allow the temperature to rise and fall close to the mark. This deadband, its tolerance is about + - 2°C. Heating has no instant on or off, when it’s switched on it takes time before the heat dissipates and when the same when switched off. The first 2 lines have a zone compare which controls this.

Analogue to Digital Converter

An analogue to digital converter is a device that converts an input analogue voltage or current to a digital number proportional to the magnitude. The reading at 4mA is zero counts an, and 20 mA is one thousand counts, so if a room temperature is 20°C it should be at 200 counts. The A/D can read preset values or average values. For identification and type of device, write to position K0 to see if it is on A/D device. In device K0 go to address K30 and take the value in it put it into data register D4. The value taken from K30 and put in D4 is one word (K1) TOP pulses it once and does not run again. Compare data in D4 with the value 2010 and if its correct the A/D is recognized to be the location K0. Next step is to set up channel 1 to read the analogue signal of 4-20mA. The program goes to K0 of the A/D and sets up so that channel 1 reads 4-20mA. To get an accurate value of the reading measured samples must be taken. Twenty samples must be taken, this being recognized in K20. K5 gives the average of the values and then puts into D10. This completes the A/D.

Digital to Analogue Converter

A digital to Analogue Converter is a device that takes a signal in decimal form and converts to an analogue signal. A pulse is set to k1 and will activate bfm (buffer memory location) K0 and preset the channels so that Ch1 is set to voltage, channels 2, 3 are set for 4-20mA. The output data from the D/A is sent from the plc through channel 1 line with the following statement T0 K1 K1 D100 K2 and stored in D100.

Ladder Diagram

Below is the ladder diagram used for the Rice cooker

Reference

DIT class notes 2010, (Tom Woolmington & Joe Teehan)

http://en.wikipedia.org/wiki/SCADA

http://www.scadasystems.net/

http://www.opcfoundation.org/Default.aspx/01_about/01_whatis.asp

Appendix