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Independent Research

by: Chelsie Beer

Independent Research BUS 499

Chelsie Beer
GPA 3.84


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This 21 page Class Notes was uploaded by Chelsie Beer on Saturday September 26, 2015. The Class Notes belongs to BUS 499 at Grand Valley State University taught by Staff in Fall. Since its upload, it has received 19 views. For similar materials see /class/214384/bus-499-grand-valley-state-university in Business at Grand Valley State University.

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Date Created: 09/26/15
497 5 NETWORKING ltTODO get AB ethemet specs for MSG instructiongt ltTODO clean up intemet materialsgt Topics Networks topology OSI model hardware and design issues Network types Devicenet CANbus Controlnet Ethernet and DH Design case Objectives To understand network types and related issues Be able to network using Devicenet Ethernet and DH 51 INTRODUCTION A computer with a single network interface can communicate with many other computers This economy and exibility has made networks the interface of choice eclipsing pointtopoint methods such as RS232 Typical advantages of networks include resource sharing and ease of communication But networks do require more knowledge and understanding Small networks are often called Local Area Networks LANs These may connect a few hun dred computers within a distance of hundreds of meters These networks are inexpensive often costing 100 or less per network node Data can be transmitted at rates of millions of bits per second Many controls system are using networks to communicate with other controllers and computers Typical applications include taking quality readings with a PLC and sending the data to a database computer distributing recipes or special orders to batch processing equipment remote monitoring of equipment Larger Wide Area Networks WANs are used for communicating over long distances between LANs These are not common in controls applications but might be needed for a very large scale pro cess An example might be an oil pipeline control system that is spread over thousands of miles 511 Topology The structure of a network is called the topology Figure 59 shows the basic network topologies The Bus and Ring topologies both share the same network wire In the Star configuration each com puter has a single wire that connects it to a central hub 498 LAN A Wire Loop Central Connection Bus Ring Star Figure 59 Network Topologies In the Ring and Bus topologies the network control is distributed between all of the computers on the network The wiring only uses a single loop or run of wire But because there is only one wire the network will slow down signi cantly as traffic increases This also requires more sophisticated net work interfaces that can determine when a computer is allowed to transmit messages It is also possible for a problem on the network wires to halt the entire network The Star topology requires more wire overall to connect each computer to an intelligent hub But the network interfaces in the computer become simpler and the network becomes more reliable Another term commonly used is that it is deterministic this means that performance can be predicted This can be important in critical applications For a factory environment the bus topology is popular The large number of wires required for a star configuration can be expensive and confusing The loop of wire required for a ring topology is also difficult to connect and it can lead to ground loop problems Figure 60 shows a tree topology that is constructed out of smaller bus networks Repeaters are used to boost the signal strength and allow the network to be larger 499 4 Repeater Figure 60 The Tree Topology 512 OSI Network Model The Open System Interconnection OSI model in Figure 61 was developed as atool to describe the various hardware and software parts found in a network system It is most useful for educational purposes and explaining the things that should happen for a successful network application The model contains seven layers with the hardware at the bottom and the software at the top The darkened a1row shows that a message originating in an application program in computer 1 must travel through all of the layers in both computers to arrive at the application in computer 2 This could be part of the pro cess of reading email 500 Layer Computer 1 Unit of Transmission COmputer 2 7 Application Message Application A 6 Presentation I Message Presentation I 5 Session Message Session I 4 Transport Message I Transport I 3 Network I Packet I Network I 2 Data Link I Frame I Data Link I 1 Physical I Bit 39 Physical l 39 Interconnecting Medium Application This is high level software on the computer Presentation Translates application requests into network operations Session This deals with multiple interactions between computers Transport Breaks up and recombines data to small packets Network Network addresses and routing added to make frame Data Link The encryption for many bits including error correction added to a frame Physical The voltage and timing for a single bit in a frame Interconnecting Medium not part of the standard The wires or transmission medium of the network Figure 61 The OSI Network Model The Physical layer describes items such as voltage levels and timing for the transmission of sin gle bits The Data Link layer deals with sending a small amount of data such as a byte and error cor rection Together these two layers would describe the serial byte shown in the previous chapter The Network layer determines how to move the message through the network If this were for an intemet connection this layer would be responsible for adding the correct network address The Transport layer will divide small amounts of data into smaller packets or recombine them into one larger piece This layer also checks for data integrity often with a checksum The Session layer will deal with issues that go beyond a single block of data In particular it will deal with resuming transmission if it is interrupted or corrupted The Session layer will often make long term connections to the remote machine The Pre sentation layer acts as an application interface so that syntax formats and codes are consistent between the two networked machines For example this might convert to in HTML files This layer also provides subroutines that the user may call to access network functions and perform functions such as encryption and compression The Application layer is where the user program resides On a computer this might be a web browser or a ladder logic program on a PLC Most products can be described with only a couple of layers Some networking products may 501 omit layers in the model 513 Networking Hardware The following is a description of most of the hardware that will be needed in the design of net works Computer or network enabled equipment Network Interface Hardware The network interface may already be built into the computer PLCsensoretc These may cost 15 to over 1000 The Media The physical network connection between network nodes lObaseT twisted pair is the most popular It is a pair of twisted copper wires terminated with an RJ 45 connector 10base2 thin wire is thin shielded coaxial cable with BNC connectors lObaseF fiber optic is costly but signal transmission and noise properties are very ood Repeaters Physical Layer These accept signals and retransmit them so that longer networks can be built HubConcentrator A central connection point that network wires will be connected to It will pass network packets to local computers or to remote networks if they are available Router Network Layer Will isolate different networks but redirect traffic to other LANs Bridges Data link layer These are intelligent devices that can convert data on one type of network to data on another type of network These can also be used to isolate two networks Gateway Application Layer A Gateway is a full computer that will direct traffic to different networks and possibly screen packets These are often used to create firewalls for security Figure 62 shows the basic OSI model equivalents for some of the networking hardware described before 7 application 6 presentation gateway 5 session 4 transport 3 network 2 data link A router bridge 39 re eater switch 1 phys1cal P V V V Figure 62 Network Devices and the OSI Model 502 Layer Computer 1 Computer 2 7 Application Application 6 Presentation I resentation 5 Session Session 4 Transport Router Transport 3 Network Network I Network 2 Data Link I ata Link I Data Link 1 Physical I Physical Physical 1 quot Interconnect1ng Medium Figure 63 The OSI Network Model with a Router 514 Control Network Issues A wide variety of networks are commercially available and each has particular strengths and weaknesses The differences arise from their basic designs One simple issue is the use of the network to deliver power to the nodes Some control networks will also supply enough power to drive some sen sors and simple devices This can eliminate separate power supplies but it can reduce the data transmis sion rates on the network The use of network taps or tees to connect to the network cable is also important Some taps or tees are simple passive electrical connections but others involve sophisticated active tees that are more costly but allow longer networks The transmission type determines the communication speed and noise immunity The simplest transmission method is baseband where voltages are switched off and on to signal bit states This method is subject to noise and must operate at lower speeds RS232 is an example of baseband trans mission Carrierband transmission uses FSK Frequency Shift Keying that will switch a signal between two frequencies to indicate atrue or false bit This technique is very similar to FM Frequency Modulation radio where the frequency of the audio wave is transmitted by changing the frequency of a carrier frequency about 100MHz This method allows higher transmission speeds with reduced noise e ects Broadband networks transmit data over more than one channel by using multiple carrier fre quencies on the same wire This is similar to sending many cable television channels over the same wire These networks can achieve very large transmission speeds and can also be used to guarantee real time network access The bus network topology only uses a single transmission wire for all nodes If all of the nodes decide to send messages simultaneously the messages would be corrupted a collision occurs There are a variety of methods for dealing with network collisions and arbitration 503 CSMN CD Collision Sense Multiple Access Collision Detection if two nodes start talking and detect a collision then they will stop wait a random time and then start again CSMN BA Collision Sense Multiple AccessBitwise Arbitration if two nodes start talking at the same time the will stop and use their node addresses to determine which one goes first MasterSlave one device one the network is the master and is the only one that may start com munication slave devices will only respond to requests from the master Token Passing A token or permission to talk is passed sequentially around a network so that only one station may talk at a time The token passing method is deterministic but it may require that a node with an urgent mes sage wait to receive the token The masterslave method will put a single machine in charge of sending and receiving This can be restrictive if multiple controllers are to exist on the same network The CSMN CD and CSMNBA methods will both allow nodes to talk when needed But as the number of collisions increase the network performance degrades quickly 52 NETWORK STANDARDS Bus types are listed below Low level busses these are low level protocols that other networks are built upon RS485 Bitbus CAN bus Lonworks Arcnet General open buses these are complete network types with fully published standards ASI Devicenet InterbusS Profibus Smart Distributed System SDS Seriplex Specialty buses these are buses that are proprietary Genius 10 Sensoplex 521 Devicenet Devicenet has become one of the most widely supported control networks It is an open stan dard so components from a variety of manufacturers can be used together in the same control system It is supported and promoted by the Open Devicenet Vendors Association ODVA see http wwwodva org This group includes members from all of the major controls manufacturers This network has been designed to be noise resistant and robust One major change for the con trol engineer is that the PLC chassis can be eliminated and the network can be connected directly to the sensors and actuators This will reduce the total amount of wiring by moving IO points closer to the application point This can also simplify the connection of complex devices such as HMIs Two way communications inputs and outputs allow diagnosis of network problems from the main controller Devicenet covers all seven layers of the OSI standard The protocol has a limited number of net work address with very small data packets But this also helps limit network traffic and ensure respon siveness The length of the network cables will limit the maximum speed of the network The basic features of are listed below terminator 504 A single bus cable that delivers data and power Up to 64 nodes on the network Data packet size of 08 bytes Lengths of 500m250m100m for speeds of 125kbps250kbps500kbps respectively Devices can be addedremoved while power is on Based on the CANbus Controller Area Network protocol for OSI levels 1 and 2 Addressing includes peertopeer multicast masterslave polling or change of state An example of a Devicenet network is shown in Figure 64 The dark black lines are the network cable Terminators are required at the ends of the network cable to reduce electrical noise In this case the PC would probably be running some sort of software based PLC program The computer would have a card that can communicate with Devicenet devices The F lexIO rack is a miniature rack that can hold various types of input and output modules Power taps or tees split the signal to small side branches In this case one of the taps connects a power supply to provide the 24Vdc supply to the net work Another two taps are used to connect a smart sensor and another F lexIO rack The Smart sensor uses power from the network and contains enough logic so that it is one node on the network The net work uses thin trunk line and thick trunk line which may limit network performance thin thin th kt k1 1c run 1ne tliu nktap t1qu power tap hue m FleXIO g rack PC g 3 drop line Smart FleXIO power sensor raCk supply Figure 64 A Devicenet Network The network cable is important for delivering power and data Figure 65 shows a basic cable with two wires for data and two wires for the power The cable is also shielded to reduce the effects of electrical noise The two basic types are thick and thin trunk line The cables may come with a variety of connections to devices bare wires unsealed screw connector sealed mini connector sealed micro connector vampire taps 505 power 24Vdc I ua La y Hrainshield Thick trunk carries up to 8A for power up to 500m Thin trunk up to 3A for power up to 100m Figure 65 Shielded Network Cable Some of the design issues for this network include Power supplies are directly connected to the network power lines Length to speed is 156m78m39m to 125Kbps250Kbps500Kbps respectively A single drop is limited to 6m Each node on the network will have its own address between 0 and 63 If a PLCS was to be connected to DeVicenet a scanner card would need to be placed in the rack The ladder logic in Figure 66 would communicate with the sensors through a scanner card in slot 3 The read and write blocks would read and write the DeVicenet input values to integer memory from N 740 to N 759 The outputs would be copied from the integer memory between N 720 to N 739 The ladder logic to process inputs and outputs would need to examine and set bits in integer memory MG9 0 EN MG91EN MG90 ReadWrite Data Table Size LocalRemote Remote Station Link ID Remote Link type Local Node Addr Processor Type Dest Addr Write N720 Remote NA 506 MSG SendRec Message Control Block MG90 MSG SendRec Message Control Block MG9l MG9l ReadWrite Data Table Size Local Remote Remote Station Link ID Remote Link type Local Node Addr Processor Type Dest Addr EN DN ER EN DN ER Note Get exact settings for these 1 Figure 66 Communicating with DeVicenet Inputs and Outputs On an Allen Bradley SoftlogiX PLC the IO will be copied into blocks of integer memory These blocks are selected by the user in setup software The ladder logic would then using integer memory for inputs and outputs as shown in Figure 67 Here the inputs are copied into N9 integer memory and the outputs are set by copying the N10 block of memory back to the outputs O N1023 507 Figure 67 Devicenet Inputs and Outputs in Software Based PLCs 522 CANbus The CANbus Controller Area Network bus standard is part of the Devicenet standard Inte grated circuits are now sold by many of the major vendors Motorola Intel etc that support some or all of the standard on a single chip This section will discuss many of the technical details of the stan dard CANbus covers the rst two layers of the OSI model The network has a bus topology and uses bit wise resolution for collisions on the network ie the lower the network identi er the higher the priority for sending A data frame is shown in Figure 68 The frame is like a long serial byte like that seen in the previous chapter The frame begins with a start bit This is then followed with a message identifrer For Devicenet this is a 5 bit address code for up to 64 nodes and a 6 bit command code The ready to receive it bit will be set by the receiving machine Note both the sender and listener share the same wire If the receiving machine does not set this bit the remainder of the message is aborted and the message is resent later While sending the first few bits the sender monitors the bits to ensure that the bits send are heard the same way If the bits do not agree then another node on the network has tried to write a message at the same time there was a collision The two devices then wait a period of time based on their identi er and then start to resend The second node will then detect the message and wait until it is done The next 6 bits indicate the number of bytes to be sent from 0 to 8 This is fol lowed by two sets of bits for CRC Cyclic Redundancy Check error checking this is a checksum of earlier bits The next bitACK slot is set by the receiving node if the data was received correctly If there was a CRC error this bit would not be set and the message would be resent The remaining bits end the transmission The end of frame bits are equivalent to stop bits There must be a delay of at least 3 bits before the next message begins 508 1 bit start of frame 11 bits identi er arbitration eld 1 bit ready to receive it 6 bits control eld contains number of data bytes 08 bytes data the information to be passed 15 bits CRC sequence 1 bit CRC delimiter 1 bit ACK slot other listeners turn this on to indicate frame received 1 bit ACK delimiter 7 bits end of frame gt 3 bits delay before next frame Figure 68 A CANbus Data Frame Because of the bitwise arbitration the address with the lowest identi er will get the highest pri ority and be able to send messages faster when there is a con ict As a result the controller is normally put at address 0 And lower priority deVices are put near the end of the address range 523 Controlnet Controlnet is complimentary to DeVicenet It is also supported by a consortium of companies httpwwwcontrolnet org and it conducts some projects in cooperation with the DeVicenet group The standard is designed for communication between controllers and permits more complex messages than DeVicenet It is not suitable for communication with indiVidual sensors and actuators or with deVices off the factory oor Controlnet is more complicated method than DeVicenet Some of the key features of this net work include Multiple controllers and 10 on one network Deterministic Data rates up to 5Mbps Multiple topologies bus star tree 509 Multiple media coax ber etc Up to 99 nodes with addresses up to 48 without a repeater Data packets up to 510 bytes Unlimited IO points Maximum length examples 1000m with coax at 5Mbps 2 nodes 250m with coax at 5Mbps 48 nodes 5000m with coax at 5Mbps with repeaters 3000m with ber at 5Mbps 30Km with ber at 5Mbps and repeaters 5 repeaters in series 48 segments in parallel Devices powered individually no network power Devices can be removed while network is active This control network is unique because it supports a realtime messaging scheme called Concur rent Time Domain Multiple Access CTDMA The network has a scheduled high priority and unscheduled low priority update When collisions are detected the system will wait a time of at least 2ms for 39 J 39 J 39 J 39 J messages will be passed sooner during a special time window messages But 524 Ethernet Ethernet has become the predominate networking format Version I was released in 1980 by a consortium of companies In the 1980s various versions of ethemet frames were released These include Version 11 and Novell Networking IEEE 8023 Most modern ethernet cards will support dif ferent types of frames The ethemet frame is shown in Figure 69 The rst six bytes are the destination address for the message If all of the bits in the bytes are set then any computer that receives the message will read it The rst three bytes of the address are speci c to the card manufacturer and the remaining bytes spec ify the remote address The address is common for all versions of ethemet The source address specifies the message sender The rst three bytes are speci c to the card manufacturer The remaining bytes include the source address This is also identical in all versions of ethemet The ethemet type identi es the frame as a Version 11 ethemet packet if the value is greater than 05DChex The other ethernet types use these to bytes to indicate the datalength The data can be between 46 to 1500 bytes in length The frame concludes with a checksum that will be used to verify that the data has been transmitted correctly When the end of the transmission is detected the last four bytes are then used to verify that the frame was received correctly 6 bytes 6 bytes 2 bytes 461500 bytes 4 bytes Figure 69 525 Pro bus 510 destination address source address ethernet type data checksum Ethernet Version 11 Frame Another control network that is popular in europe but also available world wide It is also pro moted by a consortium of companies httpwwwprof1buscom General features include A token passing between up to three masters Maximum of 126 nodes Straight bus topology Length from 9600m96Kbps with 7 repeaters to 500m12Mbps with 4 repeaters With ber optic cable lengths can be over 80Km 2 data lines and shield Power needed at each station Uses RS485 ethernet ber optics etc 2048 bits of IO per network frame 526 Sercos The SErial Realtime COmmunication System SERCOS is an open standard designed for multiaXis motion control systems The motion controller and axes can be implemented separately and then connected using the SERCOS network Many vendors offer cards that allow PLCs to act as clients andor motion controllers Deterministic with response times as small as a few nanoseconds Data rates of 2 4 8 and 16 Mbaud Documented with IEC 61491 in 1995 and 2002 Uses a fiber optic rings RS485 and buses 511 53 PROPRIETARY NETWORKS 531 Data Highway AllenBradley has developed the Data Highway 11 DH network for passing data and pro grams between PLCs and to computers This bus network allows up to 64 PLCs to be connected with a single twisted pair in a shielded cable Token passing is used to control traffic on the network Comput ers can also be connected to the DH network with a network card to download programs and monitor the PLC The network will support data rates of 576Kbps and 230 Kbps The DH basic data frame is shown in Figure 70 The frame is byte oriented The first byte is the DLE or delimiter byte which is always 10 When this byte is received the PLC will interpret the next byte as a command The SOH identi es the message as a DH message The next byte indicates the destination station each node one the network must have a unique number This is followed by the DLE and STX bytes that identify the start of the data The data follows and its length is determined by the command type this will be discussed later This is then followed by aDLE and E TX pair that mark the end of the message The last byte transmitted is a checksum to determine the correctness of the mes sage 1 byte DLE 10H gt header fields 1 byte SOH 01H 1 byte STN the destination number 1 byte DLE 10H gt start fields 1 byte STX 02H data 1 byte DLE 10H gt termination fields 1 byte ETx 03H 1 byte block check a 2s compliment checksum of the DATA and STN values Figure 70 The Basic DH Data Frame The general structure for the data is shown in Figure 71 This packet will change for di erent commands The first two bytes indicate the destination DST and source SRC for the message The next byte is the command CMD which will determine the action to be taken Sometimes the function FNC will be needed to modify the command The transaction TNS field is a unique message identi fier The two address ADDR bytes identify a target memory location The DATA fields contain the 512 information to be passed Finally the SIZE of the data eld is transmitted 1 byte DST destination node for the message 1 byte SRC the node that sent the message 1 byte CMD network command sometime FNC is required 1 byte STS message sendreceive status 2 byte TNS transaction field a unique message ID optional 1 byte FNC may be required with some CMD values optional 2 byte ADDR a memory location optional variable DATA a variable length set of data optional 1 byte SIZE size of a data eld Figure 71 Data Filed Values Examples of commands are shown in Figure 72 These focus on moving memory and status information between the PLC and remote programming software and other PLCs More details can be found in the AllenBradley DH manuals 513 CMD FNC Description 00 Protected write 01 Unprotected read 02 Protected bit write 05 Unprotected bit write 06 00 Echo 06 01 Read diagnostic counters 06 02 Set variables 06 03 Diagnostic status 06 04 Set timeout 06 05 Set NAKs 06 06 Set ENQs 06 07 Read diagnostic counters 08 Unprotected write 0F 00 Word range write 0F 01 Word range read 0F 02 Bit write 0F 11 Get edit resource 0F 17 Read bytes physical 0F 18 Write bits physical 0F 26 Readmodifywrite 0F 29 Read section size 0F 3A Set CPU mode 0F 41 Disable forces 0F 50 Download all request 0F 52 Download completed 0F 53 Upload all request 0F 55 Upload completed 0F 57 Initialize memory 0F 5E Modify PLC2 compatibility le 0F 67 typed write 0F 68 typed read 0F A2 Protected logical read 3 address fields 0F AA Protected logical write 3 addr fields Figure 72 DH Commands for a PLC5 all numbers are hexadecimal The ladder logic in Figure 73 can be used to copy data from the memory of one PLC to another Unlike other networking schemes there are no login procedures In this example the first MSG instruc tion will write the message from the local memory N 720 N 739 to the remote PLC5 node 2 into its memory from N 740 to N 759 The second MSG instruction will copy the memory from the remote PLC5 memory N 740 to N 759 to the remote PLC5 memory N 720 to N 739 This transfer will require many scans of ladder logic so the EN bits will prevent a read or write instruction from restart ing until the preVious MSG instruction is complete 514 MG90EN MSG EN Send Rec Message DN Control Block MG90 ER MG9 lEN MSG EN Send Rec Message DN Control Block MG9l ER MG90 MG9l Read Write Write Read Write Read Data Table N7 20 Data Table N7 40 Size 20 Size 20 Local Remote Local LocalRemote Local Remote Station NA Remote Station NA Link ID NA Link ID NA Remote Link type N A Remote Link type N A Local Node Addr 2 Local Node Addr 2 Processor Type PLC 5 Processor Type PLC 5 Dest Addr N740 Dest Addr N720 Figure 73 Ladder Logic for Reading and Writing to PLC Memory The DH data packets can be transmitted over other data links including ethemet and RS232 54 NETWORK COMPARISONS Table 1 Network Comparison Network topology addresses length speed packet size Bluetooth wireless 8 10 64Kbps continuous CANopen bus 127 25m1000m leps 8 bytes lOKbps ControlNet bus or star 99 250m 5Mbps 0510 bytes 1000m wire 3 30km ber 515 Table 1 Network Comparison Network topology addresses length speed packet size DeVicenet bus 64 500m 125 8 bytes 500Kbps Ethernet bus star 1024 85m coax 10 46 100m 1000Gbps 1500bytes twisted pair 400m50km ber Foundation star unlimited 100m 100Mbps lt1500 Fieldbus twisted pair bytes 2km ber Interbus bus 512 128km 5002000 0246 bytes with 400m Kbps segments Lonworks bus ring 32000 lt2km 78Kbps 228 bytes star 125Mbps Modbus bus star 250 350m 300bps 0254 bytes 384Kbps Pro bus bus star 126 1001900m 96Kbps 0244bytes ring 12Mbps Sercos rings 254 800m 216Mbps 32bits USB star 127 5m gt100Mbps 11000bytes 55 DESIGN CASES 551 DeVicenet Problem A robot will be loading parts into a box until the box reaches a prescribed weight A PLC will feed parts into a pickup xture when it is empty The PLC will tell the robot when to pick up a part and load it using DeVicenet 516 RS232 quotpickupquot pickup part PLC 7 Robot feed part part waiting box full Parts Parts Pickup BOX and Feeder Fixmre Weigh Scale Figure 74 Box Loading System Solution The following ladder logic will implement part of the control system for the system in Figure 74 Figure 75 A Box Loading System 56 SUMMARY Networks come in a variety of topologies but buses are most common on factory oors The OSI model can help when describing network related hardware and software Networks can be connected with a variety of routers bridges gateways etc DeVicenet is designed for interfacing to a few inputs and outputs Controlnet is designed for interfacing between controllers 517 Controlnet and devicenet are based on CANbus Ethernet is common and can be used for high speed communication Profibus is another control network 57 PRACTICE PROBLEMS 1 Explain why networks are important in manufacturing controls 2 We will use a PLC to control a cereal box lling machine For single runs the quantities of cereal types are controlled using timers There are 6 di erent timers that control ow and these result in different ratios of product The values for the timer presets will be downloaded from another PLC using the DH network Write the ladder logic for the PLC a We are developing ladder logic for an oven to be used in a baking facility A PLC is control ling the temperature of an oven using an analog voltage output The oven must be started with a push button and can be stopped at any time with a stop push button A recipe is used to control the times at each temperature this is written into the PLC memory by another PLC When idle the output voltage should be 0V and during heating the output voltages in sequence are 5V 75V 9V The timer preset values in sequence are in N70 N7l N72 When the oven is on a value of 1 should be stored in N73 and when the oven is off a value of 0 should be stored in N73 Draw a state diagram and write the ladder logic for this station b We are using a PLC as a master controller in a baking facility It will update recipes in remote PLCs using DH The master station is l the remote stations are 2 and 3 When an oper ator pushes one of three buttons it will change the recipes in two remote PLCs if both of the remote PLCs are idle While the remote PLCs are running they will change words in their internal memories N730 means idle and N73l means active The new recipe values will be written to the remote PLCs using DH The table below shows the values for each PLC Write the ladder logic for the master controller button A button B button C l3 l7 l4 PLC 2 690 235 745 45 75 34 76 72 56 345 234 645 PLC 3 987 12 23 345 34 456 764 456 568 87 67 8 4 A controls network is to be 1500m long Suggest three dilTerent types of networks that would meet the spec ifications 5 How many data bytes maximum could be transferred in one second with DH 6 Is the OSI model able to describe all networked systems


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