0


Low cost Wireless I/O’s using PLC, HMI & ZIGBEE



Abstract— During the past decade, the industrial sector throughout the world has shifted from the classical methods of Control and Automation to the state of the art techniques. This allowed the industries to attain a higher percentage of growth and production, which consequently gave rise to reduction in costs of the products. This trend of automation is gaining popularity at a very slow pace due to huge initial costs associated with it. This problem can be addressed by promoting Wireless I/O’s interfaced to Programmable Logic Controllers using Zigbee, which might encourage the industries to take the path of modern automation.

KeywordsWireless I/O’s, PLC, HMI, ZIGBEE Automation System.
I.      Introduction

PLC’s are solid state devices using integrated circuits to control process or machines.  They  can  store instructions  like  sequencing  counting,  timing, arithmetic,  data  manipulation  and  communication [7]. A PLC is an example of a hard real time system since output results must be produced in response to input conditions within  a  bounded  time,  otherwise unintended  operation  will  result.PLC  reads  the status  of  the  external  input  devices,  e.g.  Keypad,  sensor, switch  and  pulses,  and  execute  by  the microprocessor  logic,  sequential,  timing,  counting and arithmetic operations according the status of the input  signals  as  well  as  the  pre-written  program stored in  the PLC  [8]. The generated output signals are sent to  output  devices  as  the  switch  of  a  relay electromagnetic  valve,  motor  drive,  control  of a machine or operation of a procedure for the purpose of machine automation or processing procedure.
Zigbee falls in the category of wireless domain like GSM and RF technology. Zigbee provides the wireless communication. It means Zigbee only reduces the cost and maintenance of the wires used for connections else all the process will be  same  such as Zigbee will provide a particular bit on/off  status  to  the other  side due  to which  same message  or  data  we  can  get  on  the  other  side  as  wire  provides.  Thus Zigbee replaces the connecting wires and provides a wireless communication [1].
As the wireless PLCs use modem for transmitting signals from PLC to the process here we are using Zigbee as the communication interface which is used for transmitting and receiving the signals from the PLC to3 process and vice-versa. Zigbee is a wireless technology developed as an open global standard to address the unique needs of low-cost and low-power wireless personal area networks (WPANs). The Zigbee standard takes full advantage of the IEEE 802.15.4

II.   Method of Interfacing

PLC and SCADA/HMI placed at control room and consists of PLC input and output Module and a TARANG Zigbee for receiving and transferring signal.


Figure 1 Block Diagram
TARANG Zigbee acts as transreceiver. A pair of TARANG Zigbee transmitter and receiver is used where wireless exchange of data takes place and hence two way communication is done. The application “Monitoring” takes place at the field/process site. It is placed in a remote area and consists of sensors and actuators [1].
The process controlled in the project using a PLC is a Batch process used to manufacture a chemical and the parameters to be controlled and measured is level.



Some applications require specific quantities of raw materials be combined in specific ways for particular durations to produce an intermediate or end result. A batch process performs list of actions in a sequence. It executes a series of non-interactive actions all at one time. Once a batch job begins, it continues until it is done. One example is the production of adhesives and glues, which normally require the mixing of raw materials in a heated vessel for a period of time to form a quantity of end product. Other important examples are the production of food, beverages and medicine. Batch processes are generally used to produce a relatively low to intermediate quantity of product per year (a few pounds to millions of pounds).

Benefits of Batch Process
·     A batch process can be used to automate much of the work.
·     Batch processing can save time and energy by automating repetitive tasks.
·     Batch time can be adjusted to meet quality specs
·     Slow dynamics permit real-time calculations

Batch process component-

·     Process Tank 1(for mixing the two liquids in proportion)
·     UNIT Tank 1 (containing liquid A)
·     UNIT Tank 2(containing liquid B)
·     Stirrer
·     Solenoid Valve 1
·     Solenoid Valve 2
·     Solenoid Valve 2
·     High Level Float Switches
The BATCH PROCESS setup is placed in a remote area (field/process site) and is controlled from the control room wirelessly using TARANG Zigbee where PLC, SCADA and the control panel are placed. The process is controlled through SCADA&PLC in auto mode and can also be controlled in manual mode. The process can be controlled and monitored directly from SCADA and also from the control panel.
            The main components are TARANG Zigbee and PLC which control the whole process.The TARANG is used as the source and which is used in direct mode.PLC is used to control and monitor the batch process. [1]




III.  TARANG ZigBee

TRANG modules are designed with low to medium transmit power and for high reliability wireless networks. The modules require minimal power and provide reliable delivery of data between devices. The interfaces provided with the module help to directly fit into many industrial applications. The modules operate within the ISM 2.4-2.4835 GHz frequency band with IEEE 802.15.4 baseband. [3]

IV. Role of TMFT software

TMFT Software is used to configure the TARANG Zigbee via RS -232 or USB cable. [5]

Module Programming:
Step1: Open TMFT Software
Step2: Connect the TARANG module to the Serial/USB      Port.
Step3: Choose the appropriate Port and serial parameters in terminal software& press query modem.
 
Step 4: For setting I/O pins as input and output the following steps should be followed-
Step 5: Enter the command mode with ‘+++’
Response from modem should be ok.
Step 6: Enable the desired I/O pin as input with command ATIDxx. In this example first I/O line ID0 is used. For configuring it to Digital I/O input, send command as ATID02. Response from module should be ‘OK’.
Step 7: Write these parameters to memory with ‘ATGWR’ command.
Step 8: Follow the same steps for configuring I/O pins to INPUT.
Step 9: Exit command mode with ‘ATGEX’ command.
Note: Once I/O pins are configured to input their default status Will be logic high (3.3V).
Step 10: Enable the desired I/O pin as input with command ATIDxx. In this example first I/O line ID0 is used. For configuring it to Digital I/O input, send command as ATID40. Response from module should be ‘OK’.




V.     DESIGN AND IMPLEMENTATION
The PLCs provide analog and digital series input/output that can be used to control the field devices. For the PLC to be made to control data wirelessly, a wireless interface is needed. The messages from the controller are sent to PLCs through the RF transceivers. Thus, two RF transceiver circuits have to be developed such that they are able to communicate with each other as Process Side & Control Side.
 PROCESS SIDE:
The figure 6 shows process side hardware. The components used on process side consist of three tanks, Zigbee, Solenoid valve, Float switch and relay card. The Zigbee receives the data & control the process. The circuit diagram or wiring diagram is given below