For remote monitoring and alarm systems, cellular technology can offer the perfect balance of cost effectiveness and simplicity when establishing a connection to a control center. These basic tips can help you determine how cellular technology might be incorporated into your own remote monitoring project, whether you are establishing the monitoring system for a new site or upgrading the monitoring system for an existing site:
When to go cellular
In the field of industrial automation, remote monitoring and alarm systems are used to keep site administrators informed on things such as equipment health, usage levels, environmental conditions, and unauthorized intrusion. The remote data collection devices are typically connected to a management or control center over RS-485 or Ethernet, depending on factors such as distance and the type of management system used. In many cases, the RS-485 or Ethernet connection can be replaced or augmented with cellular technology.
Here are just some of the benefits of using cellular communication to monitor your remote site:
- You do not need to string
cable over long distances.
- You can connect to your remote site from any location and any number of locations at your discretion.
- You have new options for connecting to your remote site, such as by cell phone or PDA.
- The cellular provider has already invested in the communication infrastructure, saving you the trouble and the cost.
- It is often a far easier and more cost effective way to monitor a greater number of sites and locations.
Administrators can consider incorporating cellular technology into their monitoring system in any of the following situations:
- Isolated or very remote site
- New site not tied to existing infrastructure
- Difficulty adapting existing infrastructure for current needs
- No existing connection to central control center
- Require ability to connect to/from different locations
- Moderate or low bandwidth requirements (most simple monitoring)
- Wish to avoid laying wires
- Modem or IP-based access to remote site
- Strict space limitations
- Require high scalability
There are some situations where it might not make sense to incorporate cellular technology:
- Require millisecond response time
- High bandwidth requirements (i.e., video data)
- Poor cellular reception/service
- Robust communication infrastructure already in place
The key components
The control component of a remote monitoring and alarm system can take several different forms. You can use cellular communication technology with any of these control components, but the implementation and available options will differ.
 An on-site PLC connects to the various sensors and devices. Typically, the on-site PLC processes and store monitoring information and communicates it over RS-485 to the monitoring center. It also activates alarms or LEDs as needed. Since PLCs are highly specialized high performance devices, they are generally expensive and use proprietary technology. Adding Ethernet or cellular communication functions will typically involve the purchase of an expensive, proprietary module.
 An embedded computer is similar to a PLC in that it connects to the various sensors and devices, processes and stores data, and communicates that data to a central management center. Embedded computers offer a lighter, more general computing platform that is much easier to develop for. As with PLCs, cellular modules may be available. It may also be possible to attach a cellular modem through a serial port.
 A "dumb" I/O module connects to the various sensors and devices and does not provide any native control or management ability. Instead, it responds passively to polling requests from a PLC, PC, or embedded computer. This type of module will need to be connected to an embedded computer or PLC with cellular functions.
 An "intelligent" I/O module is built with native control logic that allows it to poll attached sensors and devices itself. It can then selectively report that data to PCs or embedded computers, using minimal bandwidth. An intelligent I/O module can be a space-saving, cost-effective alternative for simpler monitoring and control systems, and is especially suited for bandwidth-sensitive cellular applications. Cellular functions may be built in, or it may be connected to a cellular router or an embedded computer with cellular functions.
Establishing the cellular connection
When it comes to data communication, there are several options available with cellular technology.
If your control component at the remote site communicates over a serial interface, you can install a cellular modem (or cellular module with modem functions) on-site. At the monitoring center, you will need to communicate with the remote site using a regular serial modem. This approach has several disadvantages worth noting:
- Cumbersome configuration and application development for modem communication
- Low bandwidth and low speed transmission
- Potentially high recurring costs due to per-minute cellular charges
A cellular IP modem (or cellular IP module) is another option that connects to the on-site PLC or embedded computer over a serial line. 2G cellular technology allows the monitoring center to connect to the device over the Internet using an IP address. This approach offers several advantages over using regular cellular modems:
- Separate modem not required at monitoring center
- Remote PLC or embedded computer can be treated as a network device or as a physically attached serial device
- Potentially lower recurring costs due to per-data-packet cellular charges
For remote monitoring equipment that relies on Ethernet for communication, a cellular connection can be established through a cellular router. A cellular router combined with an intelligent I/O module can be a lightweight and cost-effective alternative to using PLCs.
Another option would be to connect to an embedded computer that has a cellular module, especially if you require additional computing power or additional options for device connections. In this situation, the monitoring center would not directly connect to the monitoring equipment—the embedded computer would act as an intermediary between the monitoring equipment and the monitoring center.
Creating the complete system
Railway equipment monitoring offers an ideal candidate for using cellular technology for remote monitoring. Scattered widely along the railroad tracks are numerous unmanned sites housing critical equipment. These unmanned sites need to be regularly monitored, and site administrators need to know immediately of any abnormal events or circumstances.
Sensors and alarm devices can be attached to a smart I/O module that is programmed to activate local alarms if necessary. The I/O module can be connected to a cellular router that transparently connects it to an IP network, or to an embedded computer that has a cellular module.
You can use either of these approaches across hundreds of remote sites at low cost and with minimal development time. These approaches are also easily adapted and expanded for different situations, without requiring comprehensive changes to your software or management systems.
In summary
Site administrators may deal with hundreds of unmanned sites that require basic monitoring and a simple way to connect to a remote management center. For this type of low-bandwidth monitoring application, a cellular approach may be the ideal solution. You can achieve a high degree of flexibility, scalability, and cost-effectiveness by combining cellular technology with a flexible, easily-configured control components such as an intelligent I/O module and/or an embedded computer. Be sure to consider these and other options when setting up your remote monitoring and alarm system.
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