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:

DepartmentStamp

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.......................................................................................................................2Introduction................................................................................................................................3Objective....................................................................................................................................4Apparatus...................................................................................................................................4Procedure....................................................................................................................................4RTD (Resistance Temperature Device).....................................................................................5OPC (Object Process Control)...................................................................................................6Scada (Supervisory Control and Data Acquisition)...................................................................6Temperature Control..................................................................................................................7Analogue to Digital Converter...................................................................................................7Digital to Analogue Converter...................................................................................................8Ladder Diagram.........................................................................................................................8Reference..................................................................................................................................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.

ObjectiveThe 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

ProcedureBefore 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 ControlThe 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 ConverterAn 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 ConverterA 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 DiagramBelow is the ladder diagram used for the Rice cooker

ReferenceDIT 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

Sensor Transmitter A/D conversionC° Ω mA Ω mA Count0 100 4 100 4 05 101.925 4.8 101.925 4.8 50

10 103.85 5.6 103.85 5.6 10015 105.775 6.4 105.775 6.4 15020 107.7 7.2 107.7 7.2 20025 109.625 8 109.625 8 25030 111.55 8.8 111.55 8.8 30035 113.475 9.6 113.475 9.6 35040 115.4 10.4 115.4 10.4 40045 117.325 11.2 117.325 11.2 45050 119.25 12 119.25 12 50055 121.175 12.8 121.175 12.8 55060 123.1 13.6 123.1 13.6 60065 125.025 14.4 125.025 14.4 65070 126.95 15.2 126.95 15.2 70075 128.875 16 128.875 16 75080 130.8 16.8 130.8 16.8 80085 132.725 17.6 132.725 17.6 85090 134.65 18.4 134.65 18.4 90095 136.575 19.2 136.575 19.2 950

100 138.5 20 138.5 20 1000