cellular communications for scad a applications

8/3/2019 Cellular Communications for Scad a Applications

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Managers o water/waste-

water acilities need tocollect accurate inor-

mation rom remote assets such aspumps, tanks and booster stations.raditionally, this inormation is

collected manually by collectingthe chart recordings. Tis mightbe done monthly, weekly or daily,depending on available stang.

While manual collectiono this data is the norm, plants

want to move to an automatedprocess using a central stationor all monitoring and control,

which can reduce or eliminatethe need or manual data collec-tion. Tis type o system is called a

SCADA (Supervisory Control andData Acquisition) system. Teseadvanced networking SCADA sys-tems can provide all the inorma-tion rom remote assets at a singlelocation, improving the accuracy and timeliness o the operation.

A SCADA system requires a network with a secure com-munication path. Many dierent technologies—includingdial-up, DSL, leased line and private radio—can provide thiscommunications link. In water applications, networks mustoten reach areas where phone lines or traditional wiring does

not exist. Conduits can be trenched and wire can be laid, butthis is oten cost-prohibitive. Radio can provide access to theseremote locations without the need or wires. When it comesto radio, there are a variety o options available. Tis articleexamines the use o cellular technology in SCADA applica-tions, how it can be implemented, the dierent networkingoptions available and security.

Cellular Communications

for SCADA Applications

Ia shap, Phonix Conac

Effective and secure cellular communications

for remote data acquisition.

Cellular modem-to-modem text message communications can be used for autonomous tank-

level control

All About Water

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All About Water

Cellular NetworkOptionsIn the world o cellular com-munications, two network options, voice and data, are

available. Each has dierentcapabilities or SCADA appli-cations. In this article, we willocus on the Global Systemor Mobile Communication(GSM) network or voicecommunications and GeneralPacket Radio Service/Enhanced Data Rates orGSM Evolution (GPRS/EDGE) or data communica-tions, but the same principlesexist or other cellular technol-ogy segments.

Te general dierencebetween these types o net-

works is that the GSM network addresses all deviceson the network by a phonenumber. On the GPRS/EDGE network, all devices areaddressable via an IP address,making data communicationseasy.

Simple Control with the GSM Network forSCADA applicationsTe GSM network connects with the Public Standardelephone Network (PSN), allowing communications romcellular devices to land-based modems using a phone number.Tis is used or voice communication and Short MessageService (SMS), also known as text messaging.

However, in the U.S., dial-up networking, where onemodem calls another using the PSN, is not permitted overthe cellular inrastructure. Tis limits the use o the GSMnetwork or SCADA applications in the U.S. to SMS-only.Despite this limitation, the GSM network can be useul orsimple control applications in a SCADA system.

For these simple control applications, modems can use atext message to take an event—such as a door alarm, high- orlow-level tank alarm, or change in pump status—and report itto a control room or another modem or autonomous systemoperation. In modem-to-modem communications, when thesecond modem receives a command, it provides some action orstatus update. Te modems create an autonomous system thatcan control some part o an event-based process.

For example, Modem A receives a low-level alarm mes-sage rom the tank. Tis modem then sends a text message to

Modem B, which turns on the pump and lls the tank. Oncethe water reaches an adequate level, Modem A sends anothermessage to Modem B, requesting that the pump be turned o.

While this process occurs, the modems also send the text mes-sage to a second number or the control room. Tis providesreal-time updates to the control room SCADA system aboutthe actions occurring on site.

I an autonomous system is not necessary, the acility can still use text messaging. Te modem can send inorma-tion about the processes to the control room SCADA master,

which will provide the needed logic or control. It can alsosend a text message directly to the technicians who are respon-sible or the system. Te technicians can then make the neces-sary changes to the system. ext messaging can be an eective

way to monitor and control simple processes.

Advanced Networking with GPRS/EDGEfor SCADA ApplicationsFor applications that demand more than simple, event-basedmonitoring and control, the GPRS and EDGE networks oeradditional capabilities. Te GPRS and EDGE networks canconnect to a private network or to the Internet using standardnetworking protocols. Since this allows or more inormationexchange rom the remote assets, greater fexibility is availableor monitoring, controlling, or even programming over thecellular inrastructure than the GSM network allows. When

VPN tunnel to the remote modem



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using the GPRS or EDGE network or data communications,you must decide i you will leverage a private network or usethe standard public network.

Private networks oer a great deal o fexibility. Just aboutany network architecture can be realized, including host-ini-tiated communication, and all communications do not needto fow over the Internet. However, to create a private cellu-lar network, you must work with a carrier—such as A&,-Mobile, Verizon, etc.—to dene how your network shouldbe constructed. Tese private networks typically charge a one-time setup ee to create the network. Tis ee can range romhundreds to more than $2,500, depending on the type o net-

work being constructed. With this type network, you will also need to do some

network management to ensure proper network use. Privatenetworking can be ideal or larger cellular networks, butsmaller systems usually nd the public network more suitable.

Te public network does not require any special congu-

rations. Service plans are easily accessible, and generally, nosetup ees are required. However, all data communications willfow over the Internet, which heightens the chance o network security threats.

In addition, typical poll-response networks used inSCADA systems will not work over the public network with-out proper preparation. Te public network is designed ormobile-originated communications. In other words, theremote device talks, and the host receives the inormation. Inmost SCADA systems, however, the host initiates the commu-nication to the remote device. A VPN (virtual private network)can overcome both the security concerns and the remotely ini-

tiated communication issues.

Security with VPN Tunneling A VPN tunnel is one simple way to ensure the security o theEthernet trac over the Internet. o use a VPN tunnel, themodem must support VPN networks. A router that supportsVPN networking must also be at the control room.

Leveraging the VPN tunnel to secure the communicatedinormation also solves other cellular issues. As mentioned ear-lier, cellular networks typically require that the remote modeminitiate all data communications. Many industrial protocols,such as MODBUS and EtherNet/IP, however, are designed or

poll response. Te SCADA master at the control room mustinitiate the communications, not the remote modem.

By creating a VPN tunnel between the remote modemand the SCADA system, the modem will be available ondemand. Tis allows the SCADA master to do the polling. Temodem will initiate communications at startup and will keepthe tunnel up, making access o the connected devices easy.

Using this type o network in a water application meansthat a SCADA master located in a control room can poll aremote PLC, which monitors various aspects o a process, orinormation on demand, such as pump status. Tis provides a

real-time look at the water process without the need or manualinteraction. In addition, changing variables or programming ispossible in the remotely located PLC over the cellular network,eliminating the need to visit each location or a system update.

Whether the application involves simple data collection,non-critical control, or remote programming capabilities, thecellular network provides the network access necessary. I/Omodems with text message capabilities provide alarm notica-tions based on a condition or control another device. Datamodems provide data communications to remote assets.

When used with a VPN, modem technology allows users tocollect inormation, program controllers and access other criti-cal inormation, all through a single secure wireless link.

P&S

Ira Sharp is Lead Product Marketing Specialist or Phoenix Contact’s wireless products. Ira has a Bachelor o Science inElectrical Engineering rom Pennsylvania State University.He has worked or Phoenix Contact with a concentrationon wireless technology, industrial automation and process control or fve years. His active proessional memberships include: the Instrumentation, Systems, and AutomationSociety (ISA); Wireless Systems or Automation (ISA100);and Institute o Electrical and Electronic Engineers (IEEE). He can be reached at 1-800-888-7388, x3777,or [email protected].



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cellular communications for scad a applications

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