Wireless networks: Adding cellular technology to the industrial toolbox
Can cellular networks provide a practical alternative for industrial use? While it may not be your primary wireless technology, Moxa explains that in certain applications, cellular is practical and economical.
Also read: Wireless Communications for Industry , supplement to the November 2009 Control Engineering print edition, containing:
Cellular technology is one of the options available as companies look for ways to increase efficiency when working with remote sites and applications. However, many people are still unfamiliar with the technology, where to apply it, and what challenges users of it can face. This tutorial can provide an introduction and answer those questions.
Cellular technology covers two prevailing standards, GSM (global system for mobile communications) and CDMA (code division multiple access). GSM is used by such carriers in the US such as AT&T and T-Mobile, and is the predominant standard globally. CDMA is favored by carriers such as Sprint and Verizon, and is found mostly in the U.S. There are several generations within those standards that dictate the speed of the data rate you can expect. Those seeking higher bandwidth should stick with 3G networks, referred to as HSDPA/HSUPA for GSM networks, and EV-DO in CDMA networks.
One of the main challenges that users struggle with is where to use cellular vs. Wi-Fi or even traditional wired networks. There are a few key points to look for in terms of finding where to deploy cellular technologies:
• Is it difficult or expensive to pull wired networks (copper or fiber) to the location that needs network connectivity? Often times it can cost thousands of dollars to pull cable to a remote site for data that is only going to be sent on a periodic basis.
• Is there only a small amount of data that needs to be transmitted? In cellular, every byte sent has a cost associated with it. Because of this, a heavy bandwidth consumer like real-time video streaming, is not recommended over cellular due to the extremely high cost of sending so much data. On the other hand, if you have a PLC that needs to send its data every once in a while, or needs to be programmed remotely, this is a great fit for cellular.
• Is the device in a location where the network is locked down? Many system integrators who provide devices to end users need some way of getting to those devices remotely. However, many IT departments will not allow outside users into their network. In this circumstance, cellular is an ideal solution as it allows outside network access to a device that cannot provide that access through a company's own local network.
There are challenges to deploying a cellular solution that you should consider at the outset. One of the main ones is knowing exactly how to get information to or from the end device. Under most circumstances, cellular providers will generally give a SIM card a private IP address. This private IP address is firewalled behind a provider's network, thus not allowing access to that SIM card from outside the cellular network. Consequently, most users are also firewalled and are also assigned a private IP address from their IT department. Thus the challenge is to get the two sides talking to each other. There are a few ways to address this. One is to use a tunneling service which is provided by some carriers. Another option is to use a private IP software solution. This software is usually provided by the hardware manufacturer and allows both sides to connect to a server on a public address. This server will then open ports on both sides to create a virtual tunnel for the connections.
A second point is to watch the amount of data transferred through the system. Many times, it's difficult to estimate the total amount of data that will be transferred per month as there are multiple types of data being transferred. These include not only data sent by the end device, but also data transferred upon connection, establishing communications, data from keep alive packets, and others. These can all increase the amount of data that is transferred every month and consequently increase service costs.
Even with these challenges, cellular connections are a very viable and attractive alternative to traditional networking methods. With careful planning, cellular can be very cost effective, and in many instances, can save money by providing access to a device or location that may otherwise require a costly site visit. It is becoming more and more reliable, and the highly competitive nature of the business is driving faster network speeds.
Some of the more common cellular applications center on meter reading or accessing remote automation. There are huge numbers of machines or devices serving process manufacturing units that have some sort of PLC or control device running them. If that machine goes down or there is an error or unexplained behavior from that PLC, often times the machine builder has to go to the customer site and physically plug into the PLC in order to troubleshoot. This is not only time consuming, especially if the machine is located out of state or even out of the country, but also costly. To mitigate this, many machine builders are choosing to install cellular IP modems in their machines that are connected to either a spare Ethernet or serial port on their PLC or controller. When an issue arises, all they need to do is open up the software that is used to monitor or program that PLC, and use the cellular modem to log in remotely. Often the solution is simple fix that a technician can implement from afar. An illustration of this can be seen below.
Other times, cellular applications can be more imaginative. An environmental monitoring application is one example of this. In regions of the world where earthquakes are common, there is a great need to monitor and track seismic activity. Since sensors for earthquakes are often in remote locations, it's often too expensive for governments to install network wires, and a standalone solution is desired. Traditionally, these include single board computers connected to I/O devices and seismic sensors. With cellular I/O, extraneous components can be eliminated and the sensor can be directly connected into the IO device, which in turn has a cellular modem already integrated into it. Combining all the legacy devices into one saves money, and increases the reliability of the system since there are fewer potential points of failure. Using an integrated cellular modem also eliminates the need for a seismic technician to personally visit each of the sensors to take a reading, thereby increasing efficiency for that employee. An overview of this system can be seem in the below illustration.
Cellular technology can be daunting for those who are not familiar with its concepts. However, once understood, cellular becomes a practical and cutting edge technology that is a better fit for many applications than traditional networking.
--Ariana Drivdahl is industrial wireless product marketing manager for Moxa Americas .
Moxa offers a selection of cellular-based hardware. There are also products available from:
-Edited by Peter Welander, process industries editor, PWelander@cfemedia.com
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