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When should Cellular Data Networks be considered for SCADA applications?

Use of Cellular technologies for SCADA may be considered when wide area coverage is required and the cost of alternative technologies (Private Radio Systems, Satellite, etc…) is uneconomical. Although Cellular communications are available throughout many parts of North America and many remote sites are covered by Cellular, there are still many areas where it is not available due to remoteness and lack of customer base. When considering the Cellular SCADA communications option, check with your local Cellular Provider to see if Cellular data service is available in your area. Cellular communications may be employed as the link to all remote sites or as a main link to a hub site, with private radio system used to extend out to nearby sites.

What technologies are available for SCADA communications over Cellular?

Background

In the past, there was 2 options for cellular data communications:

  • Circuit Switch Data
  • Packet Data

Currently virtually all cellular data communications used is IP based, with no circuit switched data.

Circuit Switched data is essentially dialup modem communications except that instead of a normal landline, it is performed over a cellular phone network. Cost was based on connect time. A disadvantage of Circuit Switched data connection is the delay time to establish connection. It is therefore not suitable for bursty traffic where there is frequent connection required. Because Circuit Switched data services are billed by time, it is suitable when there is infrequent connection and large data files are transferred at high speed.

Packet data is characterized by an “always on IP connection”. Packet data service is billed by Kilobyte transferred rather than by time. Since the connection is always maintained, it doesn’t have the connection delay overhead associated with circuit switched data service. Packet data service is therefore suitable for bursty traffic with small data files transferred. Packet data service is suitable for common SCADA & Telemetry applications like data collection or alarming because small amounts of data are involved and remote systems often monitor 24/7.

Other advantages of packet data is the routable IP connections and the rapid transmit time.

What are the Advantages and Disadvantages of Cellular Data Networks?</2>

Advantages of utilizing Cellular Data Networks:

There may be lower capital costs since coverage provided by the existing cellular infrastructure may reduce or altogether eliminate the need to erect large telecommunication towers.

When packet data Cellular Data is used, it enables IP host connection enabling a normal desktop PC to access the remotely connected equipment.

Disadvantage of Cellular Data network:

There may be no coverage available as well as ongoing costs, and packet-based billing may limit the amount of data that can be economically transferred.

Costs

There are monthly costs for use of the cellular data network.

Monthly Circuit Switch data cost consists of a fixed data rate charge for a certain amount of data per month, with additional data typically costing about $0.05/MB. Roaming data charges are applicable if the equipment is used outside the country.

Monthly Packet data cost is charged to the nearest Kilobyte transferred. Cellular providers have different plans (which could range from a set minimum to an “unlimited” maximum); each consisting of a minimum block of Kilobytes. If the monthly Kilobytes transferred figure is exceeded, the balance is billed as extra charges. Site costs typically range from $20-$80 per month (including the Kilobyte transfer).

Coverage

Although Cellular communications are available throughout many parts of North America and many remote sites are covered by cellular, there are remote areas where coverage is not available. Check with your cellular provider for available data services.

Types of Cellular Data Services

  • IDEN Integrated Dispatched Enhanced Network
  • GSM/CDMA
  • HSPA
  • LTE

Best use of Cellular Data Technology

Due to the pricing structure of Cellular data services, SCADA over Cellular networks is optimized for SCADA applications that require periodical data retrieval such as daily reports, or change of state reports such as Alarming. and not optimized for Data Acquisition applications that require high speed and/or large amounts of data transfer. These may be better served by private radio networks.

Cellular SCADA vs. Cellular Telemetry

There are both SCADA and Telemetry solutions over Cellular networks today. What criteria is used to select which technology is best for an application? The primary factor determining this is the quantity of I/O involved in the application. If there is just a small number of I/O between 2 sites, then Cellular Telemetry products are a better and more cost-effective solution. If there is a large number of I/O and multiple sites, then Cellular SCADA is a better solution.

Below is a diagram of how an enterprise-wide IP-based SCADA system can be implemented using Bentek System’s UNICON IP RTU/Modem for SCADA communications over the cellular infrastructure. A large enterprise may have a variety of different types of remote assets and existing communication systems. The cellular infrastructure can serve as a backbone to integrate and enable communications from SCADA Hosts in the office with remote field assets including:

  • sites with dedicated I/O
  • RTU / PLC sites with RS-232 interface
  • RTU / PLC sites with RS-485 interface
  • Licensed/ unlicensed Point-Mulipoint systems
  • mobile maintenance crew with IP-enabled cellphones

app-unicon-ip-cell

 

 

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